Galileo Webchat April 10,1997

Steve Collins Galileo Attitude Control: . . . . Thu, Apr 10, 4:02PM PDT (-0700 GMT)
Spiff: On galileo, each change of attitude requires us to update the onboard "star set". Unlike Cassini and more modern spacecraft, Galileo attitude determination uses only 2 to 6 stars and we have to pic the ones that are in the slice of sky that the star sensor sweeps out. We were able to restore attitude accuracy over the weekend (before the encounter!) by changing one of the stars in our "star set" to one in a different part of the sky. (WHEW!)

espaŅol: . . . . Thu, Apr 10, 3:57PM PDT (-0700 GMT)
Exacto, alguien pregunta por ahi si es cierto que el hielo de Europa es de agua (H2O), esta esto comprobado? tiene algun otro componente detectado a parte del agua?

Edward Hirst: . . . . Thu, Apr 10, 4:04PM PDT (-0700 GMT)
espanol: Se sabe que el hielo de Europa es de agua por los calculos que se han hecho de la densidad de Europa. Es possible calcular la densidad de Europa por medio de medidas que se han hecho de la gravedad alrededor de Europa. Se especula que el hielo esta mezclado con una variedad de elementos - organicos y otros, pero no se ha comprobado la existencia.

Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 4:00PM PDT (-0700 GMT)
Spiff: There are 3 OTMs per orbit: usually 3 days before and after an encounter and at apojove. The pre-encounter OTMs are typically a few tenths to a meter per sec. The post-encounter OTMs vary from a meter per sec or less up to several meters per sec. At one time, we thought they might be as large as 10 m/s. The apojove OTMs are generally small: meter per sec or less, with a few exceptions - i. e. , the apojove OTMs that have detrministic comoponents.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 3:59PM PDT (-0700 GMT)
Aso De Pacaro: neutrinos should still pass through Jupiter. Keep in mind that they pass through the Sun, which is much more massive than Juptier

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 4:04PM PDT (-0700 GMT)
Hi Vincent de Jager, Sublimation probably does occur on all of these icy satellites, but Europa's surface is definately less cratered than that of Ganymede and Callisto (which are darker and should sublimate faster).

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 4:09PM PDT (-0700 GMT)
Hi Muichkine, I meant the dynamics are more similar to ice sheets (i.e., brittle failure in a thin shell) than to glaciers (ductile flow).

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 4:07PM PDT (-0700 GMT)
Hi Buggs, Europa's surface is COLD (-150 C) so there could be no liquid water there. We think there is liquid below the surface due to tidal heating.

,HR>
Aso De Pacaro: . . . . Thu, Apr 10, 4:00PM PDT (-0700 GMT)
How do we KNOW that neutrinos pass through the sun? How can we detect neutrinos that come from the sun and neutrinos that come from behind it?

Steve Collins Galileo Attitude Control: . . . . Thu, Apr 10, 4:04PM PDT (-0700 GMT)
Spiff: All our thrusters are still working and we still do regular thruster flushes every few weeks.

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 4:12PM PDT (-0700 GMT)
Spiff, I can concur that we do thruster flushes every few weeks. The ground radio receiving system is so sensitive that it is affected by the *unmodeled* doppler caused by the flushing of the Z-axis thrusters! The change in the spacecraft generated S-band downlink frequency caused by each pair of Z-thrusters is 0.25 Hz. That's 0.25 Hz out of a total of 2,295,000,000 Hz. Recent thruster flushes have knocked the downlink receiver out of lock momentarily. The NAV folks are trying to model the timing of the flushes better, a work very much in progress.

espaŅol: . . . . Thu, Apr 10, 4:03PM PDT (-0700 GMT)
Si no por un cable, por radio desde el interior del agujero hasta la antena anclada en la superficie...

espaŅol: . . . . Thu, Apr 10, 4:05PM PDT (-0700 GMT)
Edward: que opinas? seria posible?

Edward Hirst: . . . . Thu, Apr 10, 4:14PM PDT (-0700 GMT)
espanol: perdon por el atrazo.. las ideas de las sondas para la superficie de Europa son excellentes y effectivamente algunas de las ideas que se estan estudiando.

espaŅol: . . . . Thu, Apr 10, 4:18PM PDT (-0700 GMT)
Edward: ok, si me necesitais estoy dispuesto a unirme al equipo de diseŅo de la Nasa :-)

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:04PM PDT (-0700 GMT)
faciovi: Sulfur compounds in Jupiter's atmosphere give it that red color.

Edward Hirst: . . . . Thu, Apr 10, 4:11PM PDT (-0700 GMT)
faciovi: Los colores en la atmosfera de Jupiter son evidencia de los procesos quimicos que estan occuriendo. Algunos cientificos creen que el color rojo es debido a la precencia de fosforo, otros creen que es debido a la precencia de compuestos organicos.

moebius: . . . . Thu, Apr 10, 4:01PM PDT (-0700 GMT)
james or duane, is it known what is on the inside of europa? i mean, under the layer of liquid water...

Duane Bindschadler, Magnetometer & Dust Detector, Planetary Scientist: . . . . Thu, Apr 10, 4:05PM PDT (-0700 GMT)
moebius: There is probably both rocky material (silicates) and metallic iron (possibly with some sulfur mixed in) in the interior of Europa. Both of these would have to transport at least some heat. But whether they do so by conduction, or convection, or by melting and being transported as magma, we don't know yet.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:06PM PDT (-0700 GMT)
moebius: metallic hydrogen is hydrogen that's ionized: it's essentially protons (hydrogen nuclei) floating in a sea of electrons. It's highly conductive, hence its name. Normal hydrogen, with neutral charge, doesn't conduct.

Steve Collins Galileo Attitude Control: . . . . Thu, Apr 10, 4:07PM PDT (-0700 GMT)
SPiff: on Galileo, we actually send the Ra and Dec of each star we want up to the spacecraft in the star set. We don't have a "full sky" catalog like Cassini et al. The darned computer's too small!

Stuart Stephens, Ultraviolet Spectrometer Team, JPL: . . . . Thu, Apr 10, 4:09PM PDT (-0700 GMT)
Duane, Kent suggested your name for driving the van home tonight! anonymous: I believe ozone has been positively identified on Gaynemede, and I confess I should know for sure since I believe UVS has seen it in our Ganymede data.

espaŅol: . . . . Thu, Apr 10, 4:09PM PDT (-0700 GMT)
faciovi: la Galileo no regresara a la Tierra, no puede, ademas no tendria ningun sentido.

Rebecca Westbrook, Galileo Outreach: . . . . Thu, Apr 10, 4:11PM PDT (-0700 GMT)
facoivi, Galileo no regresa a la tierra sino permanecera a Jupiter. (No hablo espanol...)

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:08PM PDT (-0700 GMT)
ToddSaintPe': one theory I've heard is that the wildly different types of terrain adjacent to each other indicates that there was a hot spot under one region, but not the other. I don't understand why there is such a sharply divergent line between the two regions. I suspect the satellites people are puzzled, too.

jph of md: . . . . Thu, Apr 10, 4:09PM PDT (-0700 GMT)
Dear sally; that's not exactly what I had in mind. if "down" was essentially the same as "up" why would one of the tails of Hale Bopp appear to be above the other? Why wouldn't they both fan equally in the same direction?

Stuart Stephens, Ultraviolet Spectrometer Team, JPL: . . . . Thu, Apr 10, 4:17PM PDT (-0700 GMT)
about ozone on Ganymede: HST (Hubble Space Telescope) observed ozone absorption at 2600 Angstroms in 1996 (KS Noll et al., Science). It is thought that the combination of molecular oxygen (O2) and ozone (O3) that is observed is in some combined form that is not actually a gas atmosphere, but rather represents molecules trapped in near-surface ice. This would be what causes the absorptions. The Ultraviolet Spectrometer (UVS) on Galileo confirms these observations at similar wavelengths.

espaŅol: . . . . Thu, Apr 10, 4:11PM PDT (-0700 GMT)
Muichkine: quizas cristalizaciŪn por la diferencia de temperaturas?

Muichkine from Spain: . . . . Thu, Apr 10, 4:13PM PDT (-0700 GMT)
EspaŅol: No lo se... Pero como se explica que las estructuras lineales que aparecen presenten relieve sobre el casquete... parecen flujos de algo no colisiones entre placas de hielo...

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 4:18PM PDT (-0700 GMT)
Spiff, you asked about our bit error rate, as compared with Voyager. No, they're not the same, at least not any more. Voyager and Galileo (up to the time of the use of the new on-board 'Phase 2' software last year) required a bit error rate no worse than 1/200. The error rate is a function of the received signal power. Galileo Phase 2 has a formal error rate requirement of 1 part in 10 million. We translated this to mean the loss of about one frame of telemetry data in the rest of the prime mission. Alas, we lose more than 1 frame per day, but not because of bit error rate issues. Thruster flushes, for example, as I wrote before.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:09PM PDT (-0700 GMT)
Kirk Sorensen: only on GEM, nothing else.

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 4:14PM PDT (-0700 GMT)
Hi Tim, We think it is likely that Europa is rotating nonsynchronously (turning slowly when viewed from Jupiter, unlike Earth's Moon, which always faces the same way). This is based on the reorientation of fractures/ ridges on its surface. If we learn that the interior is locked to Jupiter, then it would require that the crust is decoupled from the core.

Steve Collins Galileo Attitude Control: . . . . Thu, Apr 10, 4:12PM PDT (-0700 GMT)
Silvio: The attitude control processor has about 128k of ram and is a 286 class processor (but with built in floating point) The CDS is really a bunch of small integer processor modules with some ram (don't know how much...) on each. Tal? You out there?

Kirk Sorensen, Utah State University: . . . . Thu, Apr 10, 4:09PM PDT (-0700 GMT)
Lou: I'm glad you're back.

Io amo Io!: . . . . Thu, Apr 10, 4:09PM PDT (-0700 GMT)
Duane Bindschadler: If Ganymede has this great, big magnetic field, why wouldn't Io? It certainly has all sorts of energy input in the form of gravitational deformation, and its overall composition surely must include iron, nickel, and/or other conductors.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:12PM PDT (-0700 GMT)
Io amo Io!: There may be a magnetic field around Io: it hasn't been definitively detected yet. This is something of a controversy right now, and is one of the reasons why the magnetometer team wants to do another Io flyby.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:14PM PDT (-0700 GMT)
Jim Lukash: this was exactly one of the points made at the press conference yesterday: it's certainly possible that there is an enrichment of organic material under Europa's crust.

Jim Lukash: . . . . Thu, Apr 10, 4:17PM PDT (-0700 GMT)
Thanks Jo (Jo Pitesky, Galileo Outreach:) I was unable to see all of the conference (Some of us work for a living). I wanted to thank the whole team of folks for taking the time to do this with the general public.(Heck, even those of us who work in the space industry learn about current events from this).

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 4:19PM PDT (-0700 GMT)
Hi B., About the double ridges: we don't know how long they take to form, but we can make some back-of-the-envelope calculations assuming that the tidal strain is taken up by a few discrete fractures, and that some fixed fraction of their volume reaches the surface during each flexing cycle. It appears possible to build ridges on a short time scale ( a few tens of thousands of years) but, as with all geophysical modelling, the answer depends on your assumptions.

Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 4:14PM PDT (-0700 GMT)
Spiff: We take into account solar pressure, velocity impulses from both thruster flushing activities and unbalanced spacecraft turns. Solar pressure is very important for the larger orbits.

Kirk Sorensen, Utah State University: . . . . Thu, Apr 10, 4:12PM PDT (-0700 GMT)
Lou: That would be great. How long does that take?

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:18PM PDT (-0700 GMT)
Byran in Kansas: GEM will use new plans for observing Io, not a repeat of '95 (though the science goals are the same).

Stuart Stephens, Ultraviolet Spectrometer Team, JPL: . . . . Thu, Apr 10, 4:40PM PDT (-0700 GMT)
Andre' (I think) asked about Callisto's interior some time ago.... I believe the Radio Science team was able to get useful constraints on the degree to which Callisto's core is separated from its mantle/crust, from C3 Callisto-flyby data. But I'm forgetting the result.... Was it that Callisto appeared to have very little density variation (i.e., like a sphere that has the same density throughout)? Anyone else remember? I think they didn't expect to learn much from that encounter because it wasn't that close to the satellite, but I think they did get something (we may learn more after the C9 and C10 Callisto encounters).

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:17PM PDT (-0700 GMT)
Todd, I suspect that the hot spot causes the ice to break up, so that would be the indication of the hot spot. OTOH, the bumps that are noted (the circular areas) could also be signatures of hot spots. I know this sounds contradictory, which just shows that all of the science analysis is just beginning.

espaŅol: . . . . Thu, Apr 10, 4:14PM PDT (-0700 GMT)
Repito la idea del lander: el vehiculo se posa sobre la superficie y desplega una antena que queda anclada al hielo. Luego la sonda se hunde en la capa por calor, y por medio de un cable unido a la antena o por radiotransmision se comunican los datos para ser enviados a la Tierra. Quizas sea ridicula la idea...

espaŅol: . . . . Thu, Apr 10, 4:20PM PDT (-0700 GMT)
waiting...

Edward Hirst: . . . . Thu, Apr 10, 4:21PM PDT (-0700 GMT)
espanol: No es ridicula la idea. Es muy buena, lo que hay que considerar es que hay que transportar todo ese equipo de la tierra hasta la superficie de Europa... incluyendo todo el cable. Si la capa de hielo de Europa es muchos kilometros de profunda, te imaginas cuanto cable hay que llevar, y cuanto pesara? Un transmisor en la sonda y otro en el lander no requiere tanto cable, pero en ese caso se trata de poder transmitir atravez del hielo o se corre el riesgo que el hueco se cierre detras de la sonda.... que piensas?

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:20PM PDT (-0700 GMT)
Io amo Io!: I don't think the data was unreliable, just inconclusive. Duane has gone home, so I don't know if the problem was spatial or temporal (time) resolution.

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 4:24PM PDT (-0700 GMT)
You're really up on our communications system, Spiff. No, we don't generally transmit a carrier now. The receiving system restores the carrier from the data sidebands, to allow demodulation to proceed. Thus, the ground system has a carrier tracking loop in operation, even though we don't transmit a carrier. We learned in preparing for the 1995 solar conjunction (radio path passing close to the limb of the sun), that we would do better against the solar plasma effects if we transmitted a carrier. There is always something new to learn, something new to try in spacecraft communications!

Steve Collins Galileo Attitude Control: . . . . Thu, Apr 10, 4:18PM PDT (-0700 GMT)
Silvio: Sorry I think I left the wrong impression. We use a custom processor NOT a 286. The performance is something like a 286 running at a few megahertz.

espaŅol: . . . . Thu, Apr 10, 4:22PM PDT (-0700 GMT)
Silvio: y encima correra con Windows 3.1 !!! :-D

Silvio U. Zanzi (Italy): . . . . Thu, Apr 10, 4:26PM PDT (-0700 GMT)
EspaŅol - Windows non puedes funcionar sobre um 286! ;-)<=BR CLEAR left>

espaŅol: . . . . Thu, Apr 10, 4:29PM PDT (-0700 GMT)
Silvio: me equivoque, pero si con Windows 3.0 ...

Kirk Sorensen, Utah State University: . . . . Thu, Apr 10, 4:18PM PDT (-0700 GMT)
Lou: You send a message to query@jpl.nasa.gov with the person's name as the text of the message.

van Gogh: . . . . Thu, Apr 10, 4:18PM PDT (-0700 GMT)
Any estimates on what kind of ocean pressures any possible living organism would have to endure?

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:23PM PDT (-0700 GMT)
van Gogh: no specific idea on the pressure, but keep in mind that there is sea life down in the trenches of Earth's Pacific basin. So high pressure is not enough to rule out life.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:22PM PDT (-0700 GMT)
Todd SaintPe': we have chains of islands here following hotspots because of plate tectonics. But Europa doesn't have moving crustal plates, so the hot spot would not change location. Compare to the gigantic volcanoes on Mars, which are huge because the vent doesn't move around, allowing Olympus Mons to build up.

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 4:23PM PDT (-0700 GMT)
Hi Robert Sterling, Mike Carr noted that a layer of ice three feet thick would form IMMEDIATELY when liquid water reaches the surface (did you see Total Recall? :-). After that, it would freeze by thermal conduction, rapidly at first and more slowly later on.

< Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 4:28PM PDT (-0700 GMT)
Spiff: The current PM (90% confidence) to the end of the prime mission is ~50 kg (that includes the 20 kg bookkept as Project Manager Reserves). The PM to the end of GEM (the second of two Io encounters) is ~9 kg. I believe the probability of completing GEM (from a propellant point of view) is >95%.

HR>
Io amo Io!: . . . . Thu, Apr 10, 4:20PM PDT (-0700 GMT)
All this talk about Ganymedean ozone has got me wondering: What are the opinions of the folks at NASA and JPL regarding the Antarctic "ozone hole"? Is there a consensus opinion? It seems to me that the very best, brightest scientists are continually surprised at incoming data and find themselves remodelling like mad when (for example) a magnetic field is detected around Ganymede. Given a hugely complex system like the Earth's atmosphere, and the fact that we've only been observing a part of it (ozone) for less than 20 years, doesn't it seem rather ridiculous to run around shouting "The sky is falling!" when there's a variation in ozone levels? Or is this too far off-base for this chat? If so, I withdraw the question.

Stuart Stephens, Ultraviolet Spectrometer Team, JPL: . . . . Thu, Apr 10, 4:25PM PDT (-0700 GMT)
Io amo Io: I'm inclined to agree with you. There are other (e.g., solar) influences that may affect global climate, and data for longer time-frames can help tell us which influences are the most important.

Jim Lukash: . . . . Thu, Apr 10, 4:30PM PDT (-0700 GMT)
I do not wish to abuse this privilege, but I'll politely repeat my question once more. What is the current "End of Mission" scenario/date?

Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 4:32PM PDT (-0700 GMT)
Jim: The end-of-mission date for the prime mission is 12/7/97.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:33PM PDT (-0700 GMT)
Jim Lukash, end of mission is now end of GEM, which will be in Dec of 1999, assuming the spacecraft is still functioning. Eventually, the s/c will 1) crash into Jupiter (most likely), 2) crash onto one of the satellites, or (least likely) 3) be flung out into interplanetary space.

Nancy Vandermey, Seq-Sys: . . . . Thu, Apr 10, 4:34PM PDT (-0700 GMT)
Jim - re: end of mission: GEM has 8 Europa encounters, then 4 Calisto encounters to lower the perijove, then 1-2 Io encounters, at which time Galileo will either be fried from radiation, out of power, or out of nav fuel. Plus, it will be December 1999, and our sequence computers can't handle the year 2000. (Seriously!)

Edward Hirst: . . . . Thu, Apr 10, 4:34PM PDT (-0700 GMT)
Jim Lukash: The Galileo prime mission will end in December of this year. NASA has approved a 2 yr follow-on mission called the Galileo Europa Mission... it will end 7 December 1999.

Edward Hirst: . . . . Thu, Apr 10, 4:24PM PDT (-0700 GMT)
espanol: lo de la n~... no se, la verdad es que no me preocupo mucho por la n~ o por tildes... pero, se me ha dicho que es aceptable usar n~...

espaŅol: . . . . Thu, Apr 10, 4:25PM PDT (-0700 GMT)
Edward: Mmmmm... a ver si se me ocurre algo...

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:24PM PDT (-0700 GMT)
KenKong, Europa's density is about 3 g/cc

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 4:24PM PDT (-0700 GMT)
Hi KenKong, Europa's density is abou 3 g/cm?3.

Rebecca Westbrook, Galileo Outreach: . . . . Thu, Apr 10, 4:27PM PDT (-0700 GMT)
aLiEn: What kind of class are you doing extra credit for?

anonymous: . . . . Thu, Apr 10, 4:30PM PDT (-0700 GMT)
Rebecca: well, im 13, so im in junior high, for a science class

aLiEn: . . . . Thu, Apr 10, 4:30PM PDT (-0700 GMT)
sorry, that was me rebbeca, forgot to put my name :o)

Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 4:23PM PDT (-0700 GMT)
Kirk: Thanks.

Steve Collins Galileo Attitude Control: . . . . Thu, Apr 10, 4:24PM PDT (-0700 GMT)
Silvio: Even in the asteroid belt, there's lots of room between things. That's why they call it "space"...

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:26PM PDT (-0700 GMT)
Silvio: Lou may have more to say about this, but most of the asteroid belt is empty space, not like something out of the scene in Star Wars where the Millenium Falcon flies into the remains of an exploded planet. Galileo had two flybys of asteroids, and we actually had to *detour* to get near them. There is some danger, but it's not as great as it would seem.

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 4:30PM PDT (-0700 GMT)
Silvio U, the questions left over from being 8 years old are the best. The answer to how Galileo got through the asteroid belt safely is that there is a lot more empty space than there are particles. I remember sitting in a Galileo review in the mid-80s in which your very question was asked. Someone came up with an answer that the chances of Galileo being damaged was about one part in a million. (They could have made up that number for all I know, just being a radio guy.)

Silvio U. Zanzi (Italy): . . . . Thu, Apr 10, 4:30PM PDT (-0700 GMT)
Jo Pitesky and Steve Collins - Ok but I always tought that inside the asteroid belt there is a high probability to hit very small fragment, not easily detectable on Earth ground observations. I always tought wrong! Thank you for your explanation!

Stuart Stephens, Ultraviolet Spectrometer Team, JPL: . . . . Thu, Apr 10, 4:35PM PDT (-0700 GMT)
About end-of-GEM scenarios: I don't think they're talking about going into Jupiter's atmosphere or crashing onto one of the moons or anything like that. I think they want to try to use it as fully as possible before the money runs out. E.g., the philosophy is to "use the tape recorder until it breaks" (although obviously they take great pains to be very careful in doing so!). Maybe they'll run out of fuel first, maybe the central computer will fail, etc. (I don't think power degrades before other limits come into play). Anyone else have thoughts...?

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:27PM PDT (-0700 GMT)
Spiff, are you asking about updates to the ephemerides?

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:30PM PDT (-0700 GMT)
Mick B: It's pretty much a 10 that there WAS, at some point, liquid water under the surface. But none can answer with any assurance yet if there is liquid water there right now.

JK (SSI Imaging Team): . . . . Thu, Apr 10, 4:30PM PDT (-0700 GMT)
Mick B - Based upon all the movement we see on Europa's surface, it appears VERY likely that the water underneath it's icy shell is liquid. It is still not proven, of course, and there is still talk that some of the traction for movement could be caused by ice under very high pressures with some sort of solid state convection going on. However, the opinion at the press conference was that only a liquid ocean is going to cause the type of uplifted blocks we've seen.

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 4:31PM PDT (-0700 GMT)
Hi Mick B, I'd give it a 9! There is a possibility that convection in warm (but solid) ice could produce Europa's surface features, but at the moment, I couldn't tell you how. The main elements of the ice berg observations are rotation, translation (sideways motion) and tilting. These are easy to accomplish if they're floating in a fluid, difficult otherwise. Based on their heights (and minimum widths), we guess the ice bergs were 1 - 2 km thick at the time they were formed.

espaŅol: . . . . Thu, Apr 10, 4:28PM PDT (-0700 GMT)
Aso: los teclados en Spain llevan la - a la derecha de la L.

Muichkine from Spain: . . . . Thu, Apr 10, 4:28PM PDT (-0700 GMT)
With the keyboard spanish configuration of course!

Aso De Pacaro: . . . . Thu, Apr 10, 4:29PM PDT (-0700 GMT)
Muichkine from Spain: you must show me. Reference?

Muichkine from Spain: . . . . Thu, Apr 10, 4:32PM PDT (-0700 GMT)
De Pacaro: Es una opciŪn de comfiguraciŪn...

JK (SSI Imaging Team): . . . . Thu, Apr 10, 4:35PM PDT (-0700 GMT)
Tim - Europa definitely has one of the youngest surfaces in our solar system. There are simply very very few craters on its surface. Something has gone on very recently to flood the surface of Europa and destroy any past impacts that have hit its surface. Clark gave an estimate at yesterday's press conference of 1 million years old for the ice flow regions shown. Even if he's off by a factor of 10 or 100, 100 million years is still very young compared to the fact that the moon has been here for 4500 million years.

Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 4:28PM PDT (-0700 GMT)
Kirk: I think I missed an earlier question. Can you repeat it?

Kirk Sorensen, Utah State University: . . . . Thu, Apr 10, 4:31PM PDT (-0700 GMT)
Lou: I'm surprised that it is so hard to get software. On the COSMIC page, it says that NASA is under mandate to release its software to the public in a timely manner....

Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 4:34PM PDT (-0700 GMT)
Kirk: I know about COSMIC. There was quite an effort a few years ago here to define a s/w release policy. Prior to that, there was no policy. The current JPL pilicy may conflict with what COSMIC says. I'm really not an expert in this area.

Jim Lukash: . . . . Thu, Apr 10, 4:33PM PDT (-0700 GMT)
Dear Kirk Sorensen, Utah State University: Let me try to answer, based upon my experience in the industry(I'm Not JPL). . . . Kindly realize trajectory software has many uses, some of which are not exactly peaceful. I am sure gulf war veterans are happy the software is not readily available.

Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 4:43PM PDT (-0700 GMT)
Spiff: Because of perturbations caused by errors in the last flyby (Io 25), the trajectory is predictable only in a statistical sense and only reliably for one or two orbits. It's a highly nonlinear, chaotic system

Tim: . . . . Thu, Apr 10, 4:30PM PDT (-0700 GMT)
I am 17

Aso De Pacaro: . . . . Thu, Apr 10, 4:30PM PDT (-0700 GMT)
Looks like Silvio from Italy is the youngest. He says he is 8.

Silvio U. Zanzi (Italy): . . . . Thu, Apr 10, 4:34PM PDT (-0700 GMT)
Aso De Pacaro - I'm sorry for my english. I (tried) to say that the asteroid question was generated when I was 8 years old. Now I'm pretty older... :-)

Aso De Pacaro: . . . . Thu, Apr 10, 4:32PM PDT (-0700 GMT)
Of course, my age is PI, but I won't tell you what calendar I go by.

aLiEn: . . . . Thu, Apr 10, 4:34PM PDT (-0700 GMT)
steve: im 13

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:33PM PDT (-0700 GMT)
aLiEn, ask away.

aLiEn: . . . . Thu, Apr 10, 4:35PM PDT (-0700 GMT)
Mr Jo: um..well.. what exaclty are you trying to do?

espaŅol: . . . . Thu, Apr 10, 4:35PM PDT (-0700 GMT)
pensando...

Edward Hirst: . . . . Thu, Apr 10, 4:36PM PDT (-0700 GMT)
espanol: Solo mandale el mensaje a 'askgalileo@jpl.nasa.gov' y los encargados me la haran llegar.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:35PM PDT (-0700 GMT)
RAC, the decision to concentrate GEM on Europa was made long ago: it's long been considered the most interesting moon in the system. Io is also of great interest, but having to deal with the radiation field is a major technical problem.

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 4:37PM PDT (-0700 GMT)
Hi RAC, GEM was decided upon last year, long before the latest images became available. There were some interesting alternatives discussed.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:36PM PDT (-0700 GMT)
Thanks, Lou.

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 4:54PM PDT (-0700 GMT)
Spiff, you asked what (besides modeled and unmodeled velocity changes) affects the doppler. That's the only thing, if you include acceleration and rate of change of acceleration in your definition of velocity. The thruster flushes, for example, impart a small change in the spacecraft's velocity. Perhaps I wasn't clear before about the "unmodeled" doppler. The thrust level, for example, is known very well. It's just that the modeled time of a thruster firing (transmitted to the stations as a prediction) did not agree within less than one second of the actual thrusting time. The new receivers require that degree of accuracy because of the very narrow carrier tracking loop and the impulsive nature velocity change caused by thrusting. The whole field of radio science and quite a bit of navigation depends on observing changes in the radio signals, such as doppler. "One man's noise is another man's data" is a famous radio science saying. As a radio link operator, I'd like a! In absolutely steady signal. That would be very boring to a radio scientist. 8-)

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:39PM PDT (-0700 GMT)
RAC: That would be some controlled descent: the probe needed an aeroshell to protect against the heat of entry, and a parachute to slow down. The orbiter just isn't built to handle conditions like that.

Tim: . . . . Thu, Apr 10, 4:39PM PDT (-0700 GMT)
RAC: I like your idea!

Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 4:40PM PDT (-0700 GMT)
RAC: If the spacecraft is unusable in a science gathering sense at the end of GEM, then it is probably also uncontrollable, because we would need functioneing onboard computers to perform propulsive maneuvers.

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 4:45PM PDT (-0700 GMT)
RAC, what they turned off on Pioneer 10 was the last of the science instruments, and allocating ground stations to track the spacecraft. I understand that the spacecraft's radio transmitter is still operative, at least for a while. A press release from NASA Ames Center (operator of Pioneer) said the spacecraft would still be "tracked" in the process of training mission operators for their lunar mission (Clementine?) I agree with you that it's up to us to figure out and sell science-valuable end-of-mission activities.

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 4:41PM PDT (-0700 GMT)
Hi Marc, Even if Europa were lifeless it is important in understanding our own world - after all, it is a rocky planet with a layer of water and ice on its surface - sound familiar?

JK (SSI Imaging Team): . . . . Thu, Apr 10, 4:41PM PDT (-0700 GMT)
Marc - One of the main differences between Mars and Europa is that mars used to have liquid water 3.5 billion years ago, most of it is now either gone or frozen. The neat thing about Europa is that the water is most probably liquid beneath it's ice shell, providing an environment for life to exist today.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:43PM PDT (-0700 GMT)
Marc: One of the things that solar system research gives us (besides fantastic pictures) is a view of how changing conditions on Earth will influence the Earth's evolution. Europa is the only place in the solar system where we think there may yet be liquid water; on Mars, it's frozen. We're looking for information on how to preserve our own home, not just on how to colonize. Finally, quoting from yesterday's press conference, to the first order, the hunt for life on Mars will be a fossil hunt. To first order, the hunt for life on Europa will be for actual life.

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 4:45PM PDT (-0700 GMT)
Hi Todd St. Pe' Europa orbits Jupiter every 3.6 days - the length of a "day" on Europa. The regions near the equator get more sun than the polar regions, just like on Earth. As far as life is concerned, there are better energy sources from geological activity, fueled by tides.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:46PM PDT (-0700 GMT)
Todd: Europa (like Jupiter) only gets about 1/25th as much sunlight as does the Earth. The heat source that would make any type of life possible would come from tidal heating of Europa's interior by Jupiter.

Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 4:47PM PDT (-0700 GMT)
Tim: It's actually very difficult to alter the trajectory to produce a Jupiter impact. It's necessary to remove a great deal of energy from the orbit, and the satellites (gravity-assist) can only do so much. The rest has to be done with a combination of solar perturbations and spacecraft propulsion (and there won't be much propellant left at the end of GEM).

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:48PM PDT (-0700 GMT)
Tim: we won't shut off the spacecraft, but we will probably be unable to commmunicate with it after some point (all the radiation damage will probably kill it off). We may not even be able to get back all of the data from the second Io encounter (or even get the second encounter at all).

Tim: . . . . Thu, Apr 10, 4:49PM PDT (-0700 GMT)
Thank you for clearing that up:) I didn't know that.

espaŅol: . . . . Thu, Apr 10, 4:46PM PDT (-0700 GMT)
esperando...

JK (SSI Imaging Team): . . . . Thu, Apr 10, 4:50PM PDT (-0700 GMT)
Keith - I think it is premature to say that we have found life on Europa. We have found evidence that points very strongly to liquid water below it's surface. The main things you need for life are liquid water, organics, and an energy source. Europa very well may have all three - providing the proper environment.

Nancy Vandermey, Seq-Sys: . . . . Thu, Apr 10, 4:47PM PDT (-0700 GMT)
Many computers worldwide will have problems with the year 2000, because they won't be able to distinguish it from 1900 - many year-based calulations are done on the last two digits only

Stuart Stephens, Ultraviolet Spectrometer Team, JPL: . . . . Thu, Apr 10, 4:50PM PDT (-0700 GMT)
about GEM in 1999: I have to confess I don't know why we're limited beyond the end of 1999, but I've heard the same thing that Nancy Vandermey reported, that the computers can't currently handle it (something about going from 97..98..99.. to ..00.. in the data references that the computers use). You'd think there would be a way around it. I'm sure NASA doesn't want us to worry too much about it right now because they are wanting us to concentrate on the funded GEM mission. There's no money beyond end of 1999.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:51PM PDT (-0700 GMT)
Another comment on the year 2000 and Galileo's computers: keep in mind that the mission was supposed to end at the end of this year (and that we were supposed to launch in 1986, not 1989, and get to Jupiter much faster than 6 years). The year 2000 was not on people's minds.

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 4:50PM PDT (-0700 GMT)
Hi B., There are clearly ice thickness variations on Europa. Our first pictures were of the polar reaches of the trailing hemisphere, and looked quite different from the equatorial regions imaged in the last two orbits.

Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 4:50PM PDT (-0700 GMT)
Bryan: In the current GEM reference tour, there is a Ganymede non-targeted encounter on orbit 12 at 14K and there is another one on orbit 16 at 145K.

Todd St. Pe' teacher, Houston, Tx.: . . . . Thu, Apr 10, 4:52PM PDT (-0700 GMT)
Marc, In order to make an educated decision about where to direct our big lever, we should scout around first. Europa may well be a better target for that lever than Mars. I do agree however that we need to pull out the big lever soon... Grand goals can inspire even the most penny pinching congressperson.

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 4:54PM PDT (-0700 GMT)
Hi Marc, Perhaps you are right... but human presence in space is costly and requires commitment. Robots are inexpensive, can be sent anywhere, and don't risk life. Why not have both?

Steve Collins Galileo Attitude Control: . . . . Thu, Apr 10, 4:57PM PDT (-0700 GMT)
Todd: Futurist and Visionary scientist Freeman Dyson gave a talk here recently and made the point that we should consider applying the "big lever" where it is easiest rather than to the place most likely to harbor life. In other words: look where the light is. I'm not sure I agree with this philosophy, but Mars seems currently much easier to reach.

KenKong: . . . . Thu, Apr 10, 4:50PM PDT (-0700 GMT)
This site has been slow. Do I need a mirror or is it just AOL?

Andre': . . . . Thu, Apr 10, 4:50PM PDT (-0700 GMT)
Leslie: I think access has been faster this time when compared to the chat on October 30 of last year.

anonymous: . . . . Thu, Apr 10, 4:51PM PDT (-0700 GMT)
Leslie : I can not compare the access speed with recent Chats but my access (Europe) was very fast. Thanks for that !

Spiff: . . . . Thu, Apr 10, 4:51PM PDT (-0700 GMT)
Sorry anonymous was me...

Vincent de Jager, the Netherlands: . . . . Thu, Apr 10, 4:53PM PDT (-0700 GMT)
Leslie, Galileo Outreach: Acces from here is very good!

Silvio U. Zanzi (Italy): . . . . Thu, Apr 10, 4:54PM PDT (-0700 GMT)
Leslie, Access here is very good.

Ljubo: . . . . Thu, Apr 10, 4:53PM PDT (-0700 GMT)
Leslie: I haven't noticed the difference.

espaŅol: . . . . Thu, Apr 10, 4:50PM PDT (-0700 GMT)
Edward: que opinas? que es una locura?

Antonio from Europa: . . . . Thu, Apr 10, 4:51PM PDT (-0700 GMT)
EspaŅol: En ese sentido es mejor el RADAR... y ya hay experiencias al respecto en antartida...

espaŅol: . . . . Thu, Apr 10, 4:51PM PDT (-0700 GMT)
Edward: espero tu respuesta antes de irme a dormir, aqui ya es tarde...

Edward Hirst: . . . . Thu, Apr 10, 4:52PM PDT (-0700 GMT)
espanol: Interesante idea... que haces para que los ecos de las senales no te causen mucha interferencia? En Galileo, yo trabajo en la oficina de planificacion (Mission Planning) en donde establecemos los planes a "alto-nivel".

espaŅol: . . . . Thu, Apr 10, 4:52PM PDT (-0700 GMT)
Antonio: si, pero se trata de transmitir datos a traves del hielo...

Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 4:53PM PDT (-0700 GMT)
Ron: I don't know the distance from Europa today (it's probably a million km or more). We return to Europa for the last close flyby of the prime mission on 11/6/97. The altitude of that flyby is 2300 km.

JK (SSI Imaging Team): . . . . Thu, Apr 10, 4:53PM PDT (-0700 GMT)
Ron - Jupiter and Europa are next to each other about 400 million miles from Earth. Galileo completes an orbit around Jupiter (and thereby gets very close to its moons) about once every 1-2 months.

espaŅol: . . . . Thu, Apr 10, 5:00PM PDT (-0700 GMT)
Antonio: estoy en Valencia,EspaŅa. Se trata de que una sonda se hunda en la capa de hielo para analizar quimicamente lo que hay debajo in-situ y transmitir los datos hasta la antena de la superficie... y sin cables!

Antonio from Europa: . . . . Thu, Apr 10, 5:01PM PDT (-0700 GMT)
Ya, Ya... Ya lo estaba siguiendo... Yo estoy en Barcelona y trabajo en remote sensing...

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 4:58PM PDT (-0700 GMT)
Jeff Adolph, at this very moment we are receiving 80 bits/second, using an array of stations in Australia. One of the stations is 70 meters in diameter, two are 34m, and a fourth one is 64m. That fourth one is at Parkes, Australia, and ordinarily is used for radio astronomy. Galileo made an arrangement to use it to track our low gain antenna signal. We "bought" about 25% increase in array capability by doing so.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:59PM PDT (-0700 GMT)
Kirk, Lou signed off--you'll have to email him.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:55PM PDT (-0700 GMT)
Tim, Jupiter's magnetic field bends somewhat when there's a powerful flare, but the flare itself will not penetrate.

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 5:00PM PDT (-0700 GMT)
Hi Tim, Both Jupiter's magnetic field and Europa's ice would prevent charged particles from reaching down into Europa's interior... as has already been pointed out, this makes Europa's subsurface a potentially cozy environment in which to nurture life (we always assumed that a magnetic field or thick atmosphere would be needed to shield the surface of a planet capable of supporting life...).

Edward Hirst: . . . . Thu, Apr 10, 4:56PM PDT (-0700 GMT)
Antonio: No se. Pero me imagino que se podrian hacer una variedad de pruebas aqui en la tierra antes de manadar algo hasta Europa y resulte que no funcione...

Todd Barber, Propulsion: . . . . Thu, Apr 10, 5:01PM PDT (-0700 GMT)
And yes, we do use all the thrusters in the flush utility. Some are not used for any other purpose (for example, the S1B and S2B thrusters, the back-up spin-down and spin-up thrusters). But we have to keep them all fresh, because a failure on the primary would cause us to have to use the secondary.

Stuart Stephens, Ultraviolet Spectrometer Team, JPL: . . . . Thu, Apr 10, 5:13PM PDT (-0700 GMT)
Tom: PPR = Photo-Polarimeter Radiometer. It acts as a photometer (amount of light in infrared wavelengths), a polarimeter (discerning the polarization of the light), and a radiometer (amount of light at larger infrared wavelengths, where the radiation is mainly due to heat). I've been told by members of that team that if you can say Photo-Polarimeter Radiometer three times fast you can be on their team!

Leslie, Galileo Outreach: . . . . Thu, Apr 10, 5:14PM PDT (-0700 GMT)
PPR stands for Photopolarimeter/Radiometer. This instrument can measure the temperatures of the surfaces of the satellites, determine the type of grains on their surfaces (smooth or rough), and measure the temperature of Jupiter's atmosphere at different heights below the cloud tops.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 4:57PM PDT (-0700 GMT)
Kelvin, we've found all kinds of amazing ice structures: bumps, ridges that look like triple bands, blocks of ice turned every which way. The satellite seems to resemble a ball of twine at first glance. Look at button for the latest released images.

JK (SSI Imaging Team): . . . . Thu, Apr 10, 5:03PM PDT (-0700 GMT)
Spiff - The exposure intervals the camera can handle are between 4 milliseconds and 51,200 milliseconds (.05 seconds). However, getting this data to the taperecorder and doing other processes on the space- craft can take between 2 seconds and 60 seconds. The amount of plat- form slewing depends on how close we are to the surface being imaged. spacecraft can take between

JK (SSI Imaging Team): . . . . Thu, Apr 10, 5:05PM PDT (-0700 GMT)
Spiff - slight correction, 51000 milliseconds is 51 seconds. Call me crazy! Thinking in microseconds again.

Todd Barber, Propulsion: . . . . Thu, Apr 10, 4:59PM PDT (-0700 GMT)
James in Irvine, yes propulsion is required--quite frequently! Each orbit we allow for a maneuver just before the flyby, just after the flyby, and at apojove. Since many of our orbits are quite short, we may do a maneuver every 2-3 weeks on average! Most of these maneuvers are required, primarily because we don't know the exact positions of the Jovian satellites or Galileo.

Edward Hirst: . . . . Thu, Apr 10, 4:58PM PDT (-0700 GMT)
Antonio: Seria mas dificil no? Se tendria que lograr aterrizar varias 'estaciones' en un lugar localizado y luego lograr que se puedan comunicar, no?

Kirk Sorensen, Utah State University: . . . . Thu, Apr 10, 4:57PM PDT (-0700 GMT)
That would be available to someone like me, I forgot to add....

Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 4:59PM PDT (-0700 GMT)
Kirk: I know that Vickie Coverstone-Carroll at U. of Illinois (Urbana) is currently working under contract with JPL to develop low-thrust trajectory optimzation software. It might be easier to get this type of software from a university.

Kirk Sorensen, Utah State University: . . . . Thu, Apr 10, 4:59PM PDT (-0700 GMT)
Dang, all the good ones get away...... **sorrow**

Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 5:01PM PDT (-0700 GMT)
Kirk: There may also be trajectory optimization s/w packages available from the commercial sector (for a price), but none come to mind immediately. You could ask Dennis about that also.

Edward Hirst: . . . . Thu, Apr 10, 5:03PM PDT (-0700 GMT)
Antonio: Ahh.. Ya le entendi! Gracias por la explicacion. Claro que si se podria hacer. Te sabes que tan sensitivos son eso sistema? Se requere movimientos grandes o se puede detectar movimientos mas pequenos? La importancia seria en poder los satelites en orbita un tiempo suficiente para poder capturar buena informacion... ademas de saber que tan seguido se tendria que mandar la informacion a la tierra....

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:03PM PDT (-0700 GMT)
Marc: the scientist in me cringes when I see the factual errors in some of the reports. My husband, who is far more pragmatic, reminds me that publicity, however inaccurate, should be looked on as a good thing.

Lou D'Amario, Galileo Navigation Team: . . . . Thu, Apr 10, 5:02PM PDT (-0700 GMT)
flyonwall: We plan to fly by Europa at 200 km altitude on orbit 12 (12/16/97). That will be closer than any previous flyby (of any satellite).

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:04PM PDT (-0700 GMT)
anonymous: the GEM trajectory data and flyby dates will be online in the next couple of months.

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 5:07PM PDT (-0700 GMT)
Tustin James, no, the moon (earth's satellite) doesn't need to be in line of sight to receive the signal from Galileo. In fact, we don't want anything in the line of sight. Galileo Navigation sends me a memo each year defining periods when the moon will be in line of sight. We try to avoid transmitting science data during those times. We also account for when other things, such as the hills east and west of the 70-meter antenna at Canberra, Australia, are close to the line of sight. Our receiving system has a sensitivity (defined in terms of noise temperature) of about 13 Kelvins. When Galileo's radio signal passes close enough to the moon that the antenna "sees" the moon, the temperature goes up to 120 Kelvins. This is a 10:1 degradation in capability. The hills are about 270 Kelvins. Forget about communicating near the hills.

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 5:05PM PDT (-0700 GMT)
Hi Tim, Radar should be able to penetrate the ice on Europa and directly detect water under the surface. It's used routinely in mapping bedrock under the Antarctic ice sheet, and has even detected liquid water there in the form of subglacial Lake Vostok.

Bryan in Kansas: . . . . Thu, Apr 10, 5:05PM PDT (-0700 GMT)
Hello Todd! I wish I was still living in Wichita. Topeka is the biggest and most boring small town this side of Cleveland, Ohio.

Todd Barber, Propulsion: . . . . Thu, Apr 10, 5:06PM PDT (-0700 GMT)
Bryan, I miss Wichita, too. I'm sure you've been to Cosmosphere--they showed Galileo getting into orbit there, live! My parents came up and watched it, got interviewed by the news and paper, etc. It was pretty cool!

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 5:11PM PDT (-0700 GMT)
Bryan in Kansas -- Topeka boring? Maybe that's why our good friends moved to Boise, Idaho.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:08PM PDT (-0700 GMT)
keith: We get lots of email from people complaining that they can't find out anything about Galileo except through our web page, and asking why the news media doesn't have more coverage of the mission. Most people don't have web access, have no idea about what Galileo sends back: so yes, I like seeing lots of coverage.

keith: . . . . Thu, Apr 10, 5:14PM PDT (-0700 GMT)
Jo - yes, ok. I guess this isn't really the place for a discussion of the coverage of science in the media.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:10PM PDT (-0700 GMT)
Jennifer: if you look at the europa images (on our home page: click on the thumbnail images to see the larger browse images), it's pretty clear that there are broken patterns: rather like an asphalt highway that has been broken up by an earthquake (not that there are earthquakes on Europa). Look at button to see what I'm referring to.

Jennifer at University of Arizona: . . . . Thu, Apr 10, 5:12PM PDT (-0700 GMT)
Jo: Thanks, that makes alot of sense!

Edward Hirst: . . . . Thu, Apr 10, 5:08PM PDT (-0700 GMT)
espanol: Mucho gusto! Gracias por participar.

espaŅol: . . . . Thu, Apr 10, 5:09PM PDT (-0700 GMT)
Edward: no se te paso ninguna pregunta. Solo me queda despedirme. Hasta pronto y que la Galileo tenga un gran exito, de hecho ya lo tiene.

Todd Barber, Propulsion: . . . . Thu, Apr 10, 5:12PM PDT (-0700 GMT)
Tustin James, it's too bad Lou just left. You'd be surprised how inaccurate our knowledge of the position of Jupiter's moons was, esp. before the Galileo flybys. We actually don't even know the "exact" period of the planets. There is always some residual error. For example, just a few days back at our last Ganymede flyby, the best we could do was fly within 7 km of our target altitude. This slight error meant a post-flyby correction maneuver. As the tour progresses, we are gradually fine-tuning the orbits of the Jovian satellites more and more. But we have exquisite control in propulsion--we could probably do sub-km maneuvers no problem, if we knew our solution accurately enough and that was whatwas required.

Tustin James: . . . . Thu, Apr 10, 5:16PM PDT (-0700 GMT)
Todd Barber -- Wow - I didn't know that. When I was at JPL a month or two ago, to see the Cassinni, I remember seeing an illustration of the orbits that it was going to make around Saturn. I assumed that with Newtonian mechanics, the exact orbits could be determined. Thanks for the info!

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:12PM PDT (-0700 GMT)
Andre', there will be observations of Jupiter's aurora, a global equatorial hydrogen map, among others.

Todd Barber, Propulsion: . . . . Thu, Apr 10, 5:13PM PDT (-0700 GMT)
Bryan in Kansas, wow! So you are quite familiar w/ the Cosmosphere. I've only been once, but I was very impressed. I will definitely return now that the Apollo 13 hardware is there.

Steve Collins Galileo Attitude Control: . . . . Thu, Apr 10, 5:14PM PDT (-0700 GMT)
Bryan: My mother grew up in Hutchinson as well.

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 5:14PM PDT (-0700 GMT)
Hi Vincent, Radar penetration depth depends on wavelength, the temperature of the ice (which affects absorption) and the voids/cavities which scatter the signal. With one proposed system (not too different from terrestrial ice penetrating radars) we could see down about 50 km.

Edward Hirst: . . . . Thu, Apr 10, 5:15PM PDT (-0700 GMT)
Antonio: Aqui estoy. Gracias por la informacion. Pero la sonda Magellan si pudo hacer mapas de la superficie de Venus, no?

Paul Geissler, Galileo SSI: . . . . Thu, Apr 10, 5:11PM PDT (-0700 GMT)
Hi Todd St. Pe' Question for you... why do you think the chances of sentience would be small for a hypothetical Europan life form?

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:16PM PDT (-0700 GMT)
FireMeal, even without the high gain antenna, we can return about 70% of the science objectives, even though we are getting nowhere near 70% of the total amount of data. How can we do this, you ask? By cutting out science goals that need a lot of imaging i.e. atmosphere dynamics (movies of the atmosphere, essentially). And yes, we are hitting our objectives.

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 5:22PM PDT (-0700 GMT)
Fire Meal, the issue of how much science we would have gotten with the high gain antenna vs. how much we actually are getting is very interesting. I myself would like to see what other Galileans here think. Of course, in terms of raw data rate, we are getting back less than 1/800th. That from a simple division between the original highest data rate of 134,400 bits/second and the highest one we can use now (160 bits/second). However, I remember hearing an estimate that the S-band mission (or low-gain antenna mission) would provide about 70% of the science *value* of the original mission. Other numbers, anyone?

Stuart Stephens, Ultraviolet Spectrometer Team, JPL: . . . . Thu, Apr 10, 5:27PM PDT (-0700 GMT)
Tom, I believe, asked about the NIMS image that showed a Galileo IR version of a region that looked like an "X", compared to a Voyager visual picture of the same region. My first thought, too, was that there was a (dark) spot in the recent Galileo NIMS image that wasn't in the Voyager image, but I suspect it has to do with the different wavelengths. It's an obvious question, though.... Does anyone know the answer?

JK (SSI Imaging Team): . . . . Thu, Apr 10, 5:18PM PDT (-0700 GMT)
Lynx - good question. I don't thing anyone knows for sure what is forming the ridges on Europa. The main force driving most of the activity are tidal forces. Ridges also look different - some have one band, some triple bands, some multiple bands. This might be a clue as to how they're forming - especially if we're seeing ridges at different stages of development.

Vincent de Jager, the Netherlands: . . . . Thu, Apr 10, 5:19PM PDT (-0700 GMT)
in Enschede

Antonio from Europa: . . . . Thu, Apr 10, 5:19PM PDT (-0700 GMT)
Edward: Gracias por todo! Aqui en Barcelona ya estamos after-hours y maŅana hay que trabajar!

Edward Hirst: . . . . Thu, Apr 10, 5:23PM PDT (-0700 GMT)
Antonio: Sabes si es la misma tecnologia que usaron con el transbordador espacial y un radar SAR? Seria de desenar una sonda espacial que se podria llevar un SAR hasta Europa. Creo que he oido de una version del radar SAR que se uso en con el transbordador que estan tratando de poner in orbita alrededor de la tierra... sin usar el transbordador espacial! Has oido algo? Creo que se llama Lite-SAR.

Carlos: . . . . Thu, Apr 10, 5:24PM PDT (-0700 GMT)
Antonio: No dignifiques las estupideces de Stupi con tus respuestas. Es triste ver que alguna gente necesita recurrir a estas cosas para llamar la atencion... Te deseo buenas noches.

Edward Hirst: . . . . Thu, Apr 10, 5:25PM PDT (-0700 GMT)
Antonio: Ha sido un placer, a pesar de los comentarios.... :D

Stuart Stephens, Ultraviolet Spectrometer Team, JPL: . . . . Thu, Apr 10, 5:25PM PDT (-0700 GMT)
Antonio, gracias for tuning in. I didn't follow all that you said, but I agree with your last message.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:18PM PDT (-0700 GMT)
Carlos, GEM is a go!

Carlos: . . . . Thu, Apr 10, 5:20PM PDT (-0700 GMT)
Really? Yeahoooooo! I can't wait for the closer look at Europa and the long-awaited flyby on Io!!

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:19PM PDT (-0700 GMT)
Todd, we do this once every few months. Check on our home page (or subscribe to our email list) to find out when the next one will be.

Steve Collins Galileo Attitude Control: . . . . Thu, Apr 10, 5:19PM PDT (-0700 GMT)
Alien: Go ahead

Leslie, Galileo Outreach: . . . . Thu, Apr 10, 5:20PM PDT (-0700 GMT)
Hi aLiEn, go ahead with your question.

Leslie, Galileo Outreach: . . . . Thu, Apr 10, 5:21PM PDT (-0700 GMT)
Levendis, one of Clarke's representatives has requested we send him our Europa photos! We'll be awaiting his reaction!

Levendis: . . . . Thu, Apr 10, 5:22PM PDT (-0700 GMT)
Thanks for the response Leslie...I can't wait.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:21PM PDT (-0700 GMT)
Jennifer, GEM stands for Galileo Europa Mission. It's our extended mission, and will last for two years, focusing on Europa and (at the end, when the radiation damage doesn't kill off the entire mission) Io.

Jennifer at University of Arizona: . . . . Thu, Apr 10, 5:23PM PDT (-0700 GMT)
Jo: Cool! A flyby of Io would certainly be very exciting! I wish I had more time to keep up with science news. But being a college student and all. I'm lucky if I have enought time to sleep!!

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:26PM PDT (-0700 GMT)
aLiEn, we've discovered that there may be another place in the solar system where there is liquid water...which implies that there is the possibility of life existing somewhere other than on Earth. We've found that there are magnetic fields around Jupiter's moons, which means that we don't entirely understand how magnetic fields arise, and which means we need to learn more about our own magnetic field (which affects the operation of e.g. electronics equipment). We've learned how wind patterns work on a planet that turns much faster than ours, which tells us something about how Earth's weather patterns work. That's a few things.

Steve Collins Galileo Attitude Control: . . . . Thu, Apr 10, 5:27PM PDT (-0700 GMT)
Well, most of Galileo's science discoveries will just make us smarter and help us understand Jupiter and the solar system better.

aLiEn: . . . . Thu, Apr 10, 5:31PM PDT (-0700 GMT)
Mr. Jo: Thank you, wow really??? electronics? a planet can effect electronics? wow!!! kewl!!! When will this whole thing be over? Is there a chance there is life on that moon??? (aliens, like me :o))

lynx: . . . . Thu, Apr 10, 5:21PM PDT (-0700 GMT)
S, I meant gravitational forces and plate tectonics (movement of the crust on Europa, in the form of plates, like earth's)

JK (SSI Imaging Team): . . . . Thu, Apr 10, 5:31PM PDT (-0700 GMT)
lynx - again, ridge formation is still not very well understood. I wish I could give you an answer. Any thoughts?

JK (SSI Imaging Team): . . . . Thu, Apr 10, 5:26PM PDT (-0700 GMT)
Petrus - What was shown in the press conference yesterday were images of giant ice rafts that appear to have at one time floated through a liquid slush on Europa's surface. This strongly supports the presence of liquid oceans beneath this icy shell. We haven't found any life, of course, just an environment that may be well suited for it.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:29PM PDT (-0700 GMT)
Petrus: you need three things for life as we know it: water, an energy source, and organic material. Europa has an energy source from tidal heating by Jupiter. It could gather organic material from comets hitting its surface (we've seen comets hit Jupiter lately). The big question was, did/does Europa have liquid water under its surface? And now we see ice "rafts": icebergs that have been tilted and displaced. Wind didn't do that. They didn't slide down a slope (Europa is remarkably flat, overall). Only remaining possiblity is water underneath.

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 5:32PM PDT (-0700 GMT)
Bryan in Kansas, we continually change the data rate. This is so that the actual data rate is as close to what the received radio link can support, without dropping below. For example, right now we are receiving 80 bits/second over the array of Australian stations. Earlier today, when these stations were joined by the 70-meter station in Goldstone, Calif., the rate was 120 bits/second. In a little less than two hours, the spacecraft is sequenced to send 60 b/s as the pointing angle of the Australian stations drops closer to the horizon. A little less than an hour after that, Galileo goes to 40 b/s, then to 20 b/s at the lowest "elevation angle". Then the tracking is taken over by the station in Madrid, and the sequenced rate starts to rise: 32 b/s, then 40 b/s, and so forth. We won't be able to receive the highest rate, 160 b/s until April 19. Why? The communications range between Galileo and the Earth is decreasing at this time, and 160 bps capability comes in on th! e Goldstone/Australian array on the 19th.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:30PM PDT (-0700 GMT)
Andre' yes, those are compression artifacts. These depend on the compression scheme used to send data back to Earth, and not on the brightness contrast.

< HR>
Katie Berryhill: . . . . Thu, Apr 10, 5:26PM PDT (-0700 GMT)
Hi. I just finished taking NASA/Ames first Internet course on Telerobotics. What are the possibilities for sending a robot to search the Europan "sea"?

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:31PM PDT (-0700 GMT)
FireMeal: any atmospheric movies will have to await a different mission: Galileo can't do that.

Leslie, Galileo Outreach: . . . . Thu, Apr 10, 5:30PM PDT (-0700 GMT)
Rob, our representative from yesterday's press conference just left, but I can tell you that the last time an ocean was discovered was over 400 years ago, on earth! Of course, we are claiming we see evidence for a "young" ocean, which on a geologic time scale is 1,000,000 years or less.

Stuart Stephens, Ultraviolet Spectrometer Team, JPL: . . . . Thu, Apr 10, 5:38PM PDT (-0700 GMT)
someone (Andre'?) asked about whether Galileo's flyby of Gaspra and Ida showed signs of magnetic fields around those asteroids: I think the answer is given in the following excerpt from a paper I dug up (I don't have a stack of these, I've been checking on-line!): "The most notable results from the spacecraft's magnetometer are the detection of magnetic field deflections in the vicinity of the two asteroids, Gaspra and Ida, that the spacecraft has flown by. The signatures are not the result of a direct sensing of an internal asteroid field. The asteroid disrupts the solar wind flow by emitting low-frequency waves and these form the signature that the spacecraft detects. The size of the disrupted region set up by Gaspra has led the Galileo magnetometer team to propose that the asteroid may have a substantial dipole moment, a result that raises substantial questions about how and where the object cooled."

Vincent de Jager, the Netherlands: . . . . Thu, Apr 10, 5:31PM PDT (-0700 GMT)
hoogerheide...ehh nee... ik ben student chemische technologie aan de universiteit twente, en ik ben verder niet bij het project betrokken.. (ps vul iets in bij de handler.. een naam is wel makkelijk)

Leslie, Galileo Outreach: . . . . Thu, Apr 10, 5:33PM PDT (-0700 GMT)
Messier, we believe under Europa's surface is or has been liquid water. It won't be PURE water, as it has some of the dark surface contaniments in it. These are likely from the meteorites which have bombarded Europa overtime, and do contain the building blocks for life.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:34PM PDT (-0700 GMT)
Messier: we don't know yet if what is there right now is H20 water or H20 ice...but yes, we're sure it's H20. Spectroscopic data from the surface shows that the surface is covered with water ice, and gravitational studies (which give us density and mass distribution) show that the interior is mostly H20

Messier: . . . . Thu, Apr 10, 5:36PM PDT (-0700 GMT)
Thanks Leslie, I was happy to see that you answered me, the news doesn't seem to speak about "Astronomical Issues" professionally like scientist do. Thanks again!

Messier: . . . . Thu, Apr 10, 5:36PM PDT (-0700 GMT)
and thanks you to Jo.

Edward Hirst: . . . . Thu, Apr 10, 5:30PM PDT (-0700 GMT)
Antonio: See ya!

Stupid: . . . . Thu, Apr 10, 5:32PM PDT (-0700 GMT)
ok I understand now

Leslie, Galileo Outreach: . . . . Thu, Apr 10, 5:37PM PDT (-0700 GMT)
Rob, Miranda is a moon of Uranus, so its way too far away to see with Galileo. We are studying the 4 Galilean (discovered by Galileo) moons up close and personal (Io, Europa, Ganymede, and Callisto), and will look at some of the minor moons as well, including Amalthea, Thebe, Adrastea, Metis, Elara, and Himalia.

Carlos: . . . . Thu, Apr 10, 5:33PM PDT (-0700 GMT)
My question again.... Does Io's volcanic activity affect Europa's underground "bodies of water" in any way?

Duane Bindschadler, Magnetometer/Dust Detector: . . . . Thu, Apr 10, 5:35PM PDT (-0700 GMT)
Carlos: Io's volcanic activity doesn't *directly* affect anything that might be under the surface of Europa. Is that what you wanted to know?

JK (SSI Imaging Team): . . . . Thu, Apr 10, 5:36PM PDT (-0700 GMT)
Carlos - While not an io expert, I believe that most of the gases erupted from Io's volcanoes are either trapped in Jupiter's magnetic field (knowns as the Io Torus) or fall back down to Io's surface. Thus there is probably not a connection between Io's volcanoes and Europa's oceans. Tidal forces from Jupiter is the main force influencing both of these moons, though.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:36PM PDT (-0700 GMT)
Petrus: Yes, water does not always mean life. But we now have a place in the solar system where the three building blocks for life could coexist. The possibility (and that's all it is right now) of life is what is so exciting, since those conditions don't seem to exist anywhere else in the solar system.

Duane Bindschadler, Magnetometer/Dust Detector: . . . . Thu, Apr 10, 5:36PM PDT (-0700 GMT)
Katie: There are impact craters on Europa. Just not very many compared to Ganymede or Callisto.

Duane Bindschadler, Magnetometer/Dust Detector: . . . . Thu, Apr 10, 5:37PM PDT (-0700 GMT)
Stuart: yes, he gave me the fudge. If it weren't for that, you'd never have been forgiven smile.

Stuart Stephens, Ultraviolet Spectrometer Team, JPL: . . . . Thu, Apr 10, 5:46PM PDT (- 0700 GMT)
Andre', about UVS observations of aurora on Jupiter: Both the Ultraviolet Spectrometer (UVS, which operates from about 1100 to 4400 Angstroms, and is located on the point-able scan platform part of Galileo) and Extreme Ultraviolet Spectrometer (EUV, from about 500 to 1300 Angstroms, on the rotating part of the spacecraft, so that its field-of-view is limited) have observed Jupiter's aurora. I think results are along the lines of: altitudes (300-1800 km above a reference pressure in Jupiter's atmosphere), electron energies (10-50 kilo-electron-Volts) and abundances, and variability. Also, they've obtained spectral information that nicely complements the visual images that Hubble Space Telescope has taken at the same time.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:39PM PDT (-0700 GMT)
Mairead: we haven't seen volcanoes yet on Europa, but we see evidence that there could be geysers there (all of the thick lines that look like triple bands might be formed by material geysering up). Do we think there's life? We think it's possible. We don't know yet, and I don't think we'll know for a long time (probably not until you're an adult and working, yourself). But I certainly hope so!

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 5:46PM PDT (-0700 GMT)
Hi, Mairead, no one knows yet if there is life on Europa. Some of what Galileo saw makes us think there could be. Just that thought has made people think of what other kind of spacecraft we could send to Europa. Would you be interested in coming to JPL in 15 or 20 years to help? I'll be an old man by then, but I'd love reading about Mairead's project in the newspaper. Er, on the Internet.

BlacKLighT: . . . . Thu, Apr 10, 5:38PM PDT (-0700 GMT)
(sorry , I meant uniform composition)

Duane Bindschadler, Magnetometer/Dust Detector: . . . . Thu, Apr 10, 5:40PM PDT (-0700 GMT)
BlacKLighT: The "rafts" were always solid. The idea that's been suggested is that the terrain around them was once liquid - or slushy, anyway. It seems likely to me that any water/slush layer that there might be under Europa would be very non-uniform. In fact, it's possible that it might only occur in certain parts of Europa and/or only at certain times.

Leslie, Galileo Outreach: . . . . Thu, Apr 10, 5:45PM PDT (-0700 GMT)
Petrus, Callisto is not very much like Europa. It IS covered with ice, but it is "dirty" (has other stuff mixed in with it, probably from the meteorites that have hit it). There are MANY craters on Callisto, unlike Europa. This means Callisto's surface isn't getting changed by much else besides meteorite impacts. We also think that the inside of Callisto is alike throughout, probably mixed rock and ice. Europa probably has a layered structure inside, but we're still analyzing the data to tell that for sure.

Duane Bindschadler, Magnetometer/Dust Detector: . . . . Thu, Apr 10, 5:47PM PDT (-0700 GMT)
Icelander and Katie: Whew! you guys have just run smack up against the limits of my knowledge of cratering flux rates in the outer solar system. The important thing is that knowledge of the cratering rate is probably what limits our ability to find the ages of surfaces in the Jovian system at this point. Icelander, Jupiter certainly acts as a focus for (especially) cometary impactors. But whether the rate of impact there is much higher -- and just how much higher, I don't know.

aLiEn: . . . . Thu, Apr 10, 5:40PM PDT (-0700 GMT)
can anyone answer a question that i am always interesed in?????? do you think there is life anywhere near us???

Edward Hirst: . . . . Thu, Apr 10, 5:40PM PDT (-0700 GMT)
aLiEn: Given the stunning discoveries of the past year (Mars, Europa), I would certainly not dismiss the possibility.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:46PM PDT (-0700 GMT)
aLiEn: well, my officemate is here, so I know there's life near me :-) Seriously, the nearest life would be on Mars or on Europa, and they are both pretty far away. If there is/was any life on them, it's unlikely that it's anything that you could talk to or keep as a pet. Is there life in other star systems (which is REALLY far away)? We dont' know.

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 5:50PM PDT (-0700 GMT)
Mr. Honig, we gave up in 1993 trying to get the high gain antenna to open. Nothing that we'd tried seemed to budge it. The project decided to focus or concentrate its efforts on making the best possible mission using the antenna we did have. I miss that high gain antenna, but I have to admit my telecommunications life has been a lot more interesting and challenging without it.

Leslie, Galileo Outreach: . . . . Thu, Apr 10, 5:57PM PDT (-0700 GMT)
Mr Honig, in fact, we probably couldn't use the high gain antenna now if it did open. We reprogrammed the computer on board Galileo to get the best use out of the low gain antenna, and ignore the high gain!

JK (SSI Imaging Team): . . . . Thu, Apr 10, 5:47PM PDT (-0700 GMT)
Lynx - thanks for your reply. There are a lot more ridges on Europa than there are craters. One thought for how they are formed is that ice plates smash into each other and build up ridges at these boundaries. Another is that cracks in the ice lead to geysers that spout up water and build up ridges. Everything I have heard so far is very hypothetical still. The jury is definitely still out.

Duane Bindschadler, Magnetometer/Dust Detector: . . . . Thu, Apr 10, 5:52PM PDT (-0700 GMT)
Carlos: Io and Europa interact gravitationally. Because they have resonant orbital periods (the time it takes Io to go 'round Jupiter and the same for Europa make an integer ration), they create tides in addition to the tides Jupiter raises on both of them. Even though they're solid, this is a measureable effect. So they both help heat each other up. I'm not sure how large the effect is, though.

Carlos: . . . . Thu, Apr 10, 5:53PM PDT (-0700 GMT)
Thanks again Duane... Do you know anything about the Pluto Express?

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:48PM PDT (-0700 GMT)
(?): The safety/contamination question is one of the many issues that has to be thought about before a sample return mission. People at NASA also are thinking about this issue for any mars sample return mission.

Duane Bindschadler, Magnetometer/Dust Detector: . . . . Thu, Apr 10, 5:54PM PDT (-0700 GMT)
BlacKLighT: There is a distinct possibility that some parts of the interior of Europa are warm enough to cause convection. Particularly in the outer ice/water layer. The images showing ice flows and ice volcanism on the surface are evidence of that.

MRHonig: . . . . Thu, Apr 10, 5:47PM PDT (-0700 GMT)
Stupid: The reason for saying "H2O Ice" is simple...Not all ice is water...Just like not all liquid is water.

Duane Bindschadler, Magnetometer/Dust Detector: . . . . Thu, Apr 10, 5:56PM PDT (-0700 GMT)
Carlos: Only a little bit. And what I know is over a year old, which means it's probably wrong. When they're first being developed and before there is a lot of funding, these missions undergo many changes. But if you have a specific question, I'll try (or maybe someone else will know).

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:55PM PDT (-0700 GMT)
mpeach: the probe sent back about an hour's worth of data, and the results are available on the probe home page at button The probe itself vaporized 10 hours after the end of the mission, and is now part of Jupiter.

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 5:59PM PDT (-0700 GMT)
Gualala SBMer Matthew -- hi, and welcome! I hadn't heard about people thinking there might be oxygen in Europa's water (other than as part of H20 molecules). I would think if there is oxygen suspended there, it would stay there even if the ice layer was broken. You'd have to think of some effect that would force the oxygen out, same as when a gas is suspended in water on earth.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:58PM PDT (-0700 GMT)
Tim: now is not the time to become a member of the Galileo team, because the mission is winding down :-) But to work at JPL, you get a college degree in science or engineering or math or computers (though we also have people here who were medieval studies and rhetoric majors!). Then you apply. It's a great place to work.

Stuart Stephens, Ultraviolet Spectrometer Team, JPL: . . . . Thu, Apr 10, 5:59PM PDT (-0700 GMT)
Tim: I got to be an assistant science coordinator on my instrument team partly by design, partly by good fortune. I received my PhD in Planetary Science, and wasn't sure whether I wanted to (i) teach, (ii) continue research (which is what you do to get a PhD!), or (iii) work on a spaceflight project like the ones they do at JPL, or some combination of the above. A friend of mine told me about an opening on an instrument team on Galileo, which I applied for since I was looking at JPL opportunities anyway (I got my degree at Caltech, which runs JPL, and I did some of my thesis work on-lab). It turns out I got hired on a different instrument team than the one I interviewed with first, but I'm very glad to be "on-board." I joined less than a month before Galileo arrived at Jupiter (12/7/95), and feel fortunate in that respect to be involved in such an exciting enterprise!

Duane Bindschadler, Magnetometer/Dust Detector: . . . . Thu, Apr 10, 6:00PM PDT (-0700 GMT)
lynx: the images we've seen definitely show that water "lava" flowed in places on Europa's surface. Since we know the interior of Europa is likely to be warmer than the exterior, that's the most likely place for the "lava" to have come from. It's certainly been that way elsewhere in the solar system.

John Keller (SSI Imaging Team): . . . . Thu, Apr 10, 5:58PM PDT (-0700 GMT)
Rob - The Torus is a phenomenon related to Jupiter's magnetic field. Tidal forces are related to Jupiter's gravitational field. Yes, Europa is affected by tidal forces from Jupiter.

Duane Bindschadler, Magnetometer/Dust Detector: . . . . Thu, Apr 10, 6:00PM PDT (-0700 GMT)
Icelander: I think Cassini will provide some important data on that -- especially if it can find some young terrain on any of the Saturnian satellites. We don't really expect any, except for Titan. But that's a whole 'nother story.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 5:59PM PDT (-0700 GMT)
anonymous, we don't use telescopes. We have various types of cameras (that look at different wavelengths of light: visible, near infrared, ultraviolet), and instruments that measure magnetic fields, plasma, dust, and other particles. We get enhanced resolution because we are so close to Jupiter.

aLiEn: . . . . Thu, Apr 10, 6:01PM PDT (-0700 GMT)
thank you Mr Jo, that anonymous was me :o)

BlacKLighT: . . . . Thu, Apr 10, 5:59PM PDT (-0700 GMT)
(adding to my question) shouldnt the atmosphere escape in the space?

Duane Bindschadler, Magnetometer/Dust Detector: . . . . Thu, Apr 10, 6:07PM PDT (-0700 GMT)
BlacKLighT: Yes, any atmosphere escapes to space pretty rapidly. That's exciting because it means something on the surface is replenishing it. But the atmosphere is very tenuous

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 6:00PM PDT (-0700 GMT)
Mairead: I first toured JPL when I was 11 years old, at which point I told my father "this is where I want to work when I grow up." And here I am!

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 6:03PM PDT (-0700 GMT)
Mairead, I'm sure there are others here hoping to see you join us. You must be in about the second or third grade now. What are you most interested in? I hope you ask everyone questions about how things in nature work or why things are the way they are.

Mairead's Dad: . . . . Thu, Apr 10, 6:04PM PDT (-0700 GMT)
Jo, Jim: Thanks for helping science real to my daughter.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 6:01PM PDT (-0700 GMT)
Jay, the oceanographer quoted was giving his personal opinion. It was followed by a big round of good-humored laughter, because it was clear that he was expressing a preference, and not a carefully weighed scientific opinion.

Duane Bindschadler, Magnetometer/Dust Detector: . . . . Thu, Apr 10, 6:03PM PDT (- 0700 GMT)
Jay in NJ: to understand the quote, you'd need to listen to most of what John Delany said. By the way, he's not a NASA spokesperson. Essentially, he was asked what he believed -- in the religious sense. He very badly *wants* there to be life there, but he also knows that we don't know enough to be sure one way or the other. The idea, then, is to pose the question and to see if we can answer it.

Duane Bindschadler, Magnetometer/Dust Detector: . . . . Thu, Apr 10, 6:09PM PDT (-0700 GMT)
Carlos: sorry to take so long. Man, is this a busy room! Pluto Express is not approved yet. They're still trying to get the funding to fly a mission.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 6:03PM PDT (-0700 GMT)
Tim: there will be TONS of programs for you to work on by the time you finish college. New missions are starting up all the time, and other missions (e.g. Cassini) that are now on drawing boards or about to launch will be actual flight projects in a few years. Don't feel that you are missing out on the "good stuff"!

Jim Taylor, Galileo radio: . . . . Thu, Apr 10, 6:10PM PDT (-0700 GMT)
Gualala Matthew... You're on the right track. That's what I was trying to write, that maybe there is dissolved oxygen in the water. Can any Galileans or others on this Chat answer Matthew, about whether this dissolved oxygen might come out if the surface ice cracked?

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 6:05PM PDT (-0700 GMT)
aLiEn: you can find lots of Galileo information at our web site at www.jpl.nasa.gov/galileo here's the button: button

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 6:07PM PDT (-0700 GMT)
RiceBerg: All the other proposed Jupiter missions are very much on the drawing board, but include: an ice sample return mission, a driller mission to sample Europa's (possible) subsurface ocean, a balloon to drift in Jupiter's atmosphere, and an Io observer. These are all highly tentative, and almost certainly all will not fly (at least not in our lifetimes).

Leslie, Galileo Outreach: . . . . Thu, Apr 10, 6:07PM PDT (-0700 GMT)
lynx, GEM will look at Europa's surface, atmosphere, and interior for the first 13 months, then focus on Jupiter's atmosphere for a few months as we work our orbit down to meet close up with Io at the end of 1999.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 6:10PM PDT (-0700 GMT)
IntelKernel=Junk: we use everything to process the data: people work on various unix boxes (sun workstations are very popular), vax mainframes, whatever. Lots of Macs, too. It's a mix of programs and hardward.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 6:10PM PDT (-0700 GMT)
Icelander: since Europa's craters look very much like meteor-formed craters seen everywhere else, the odds are that they are formed by meteors.

Leslie, Galileo Outreach: . . . . Thu, Apr 10, 6:14PM PDT (-0700 GMT)
BlacKLighT, that's a great question! Earth's atmosphere is still around in its present form largely due to the presence of life that converts oxygen into carbon dioxide, and the other way around. The ocean provides a continuous reservoir of water to the atmosphere. Perhaps heating one day when the sun starts to age will drive this away. On Europa, it would take a very long time to lose molecules from the surface. Right now, this primarily happened by bombardment from very small charged particles (this is called sputtering, right Stuart?). The ocean underneath would be very well protected from this.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 6:12PM PDT (-0700 GMT)
lynx: We'd like both types of samples: the surface ice sample could be returned to Earth for analysis, and an in-situ driller down to the ocean (if it is liquid) could look for organic material.

Jo Pitesky, Galileo Outreach: . . . . Thu, Apr 10, 6:14PM PDT (-0700 GMT)
Pirate Bob: we really don't know what, if anything, we'd find! Maybe nothing. Maybe single cells. Maybe something as complex as the tube worms found in the deep trenches of the Pacific Ocean. All of these are possiblities.

Return to Project Galileo Homepage