Sizing Up Near-Earth Asteroids

author
by Amy Mainzer
Scientist and Engineer

Asteroids. The word conjures images of pitted rocks zooming through space, the cratered surfaces of planets and moons, and for some, memories of a primitive video game. Just how hazardous are these nearest neighbors of ours? We think that one contributed to the extinction of the dinosaurs, giving rise to the age of mammals. How likely is this to happen again?

The Wide-field Infrared Explorer (WISE) mission, an infrared telescope launching in about a year, will observe hundreds of near-Earth asteroids, offering unique insights into this question. The risk posed by hazardous asteroids is critically dependent on how many there are of different sizes. We know that there are more small asteroids than large ones, but how many more, and what are they made of?

Asteroids reflect sunlight (about half of which is the visible light that humans see), but the sun also warms them up, making them glow brightly in infrared light. The problem with observing asteroids in visible light alone is that it is difficult to distinguish between asteroids that are small and highly reflective, or large and dark. Both types of objects, when seen as distant points of light, can appear equally bright in visible light. However, by using infrared light to observe asteroids, we obtain a much more accurate measurement of their size. This is because the infrared light given off by most asteroids doesn’t depend strongly on reflectivity.

asteroid
This image of near-Earth asteroid 433 Eros reveals that its ancient surface has been scarred by numerous collisions with other small objects. Image credit: NASA/JPL/JHUAPL

WISE will give us a much more accurate understanding of how many near-Earth asteroids there are of different sizes, allowing astronomers to better assess the hazard posed by asteroids. The danger posed by a near-Earth asteroid depends not only on its size, but also on its composition. An asteroid made of dense metals is more dangerous than one of the same size made mostly of less dense silicates. By combining infrared and visible measurements, we can determine how reflective the asteroids are, which gives us some indication of their composition.

 

 

 

This entry was posted on Wednesday, November 12th, 2008 at 3:14 pm and is filed under Earth, Solar System. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

    17 Responses to “Sizing Up Near-Earth Asteroids”

  1. Peter Says:
    November 13th, 2008 at 9:58 pm

    Seeing as how Jupiter was struck by a comet a few years ago, are there any plans to track objects which might be on collision courses with other bodies in the solar system besides earth?

    Mainzer says

    There is a program in place at JPL to look for impacts on other planets in our solar system as well as Earth. The JPL near-Earth object observation program (neo.jpl.nasa.gov) predicted a possible impact on Mars on January 30, 2008, although subsequent observations ruled out the possibility a couple of weeks before that date. The JPL near-Earth Object office tracks possible impacts on all the planets in our solar system, although somewhat less precisely than it tracks potential Earth impactors.

  2. mary anne smit Says:
    November 15th, 2008 at 11:58 pm

    when will info be available from april/may 1999 of night sky of large rock object /asteroidal ? is there info on rocky objects that do not fill the critera of a “typical asteroid or small bodies object. attention to Amy Mainzer thank you .

  3. Bill Wright Says:
    November 25th, 2008 at 7:31 pm

    Hi Amy,

    As I watch the History’s specials on different matters of the cosmos - questions for you “scientists” at JPL come to mind. Where is the scientific method employed in your organizations work? If I am remembering my scientific method properly, it is a method to eliminate subjectivity as much as possible. Matters such as replication and testability of hypothesis are important parts? Are there alternate universes that you are using as a second and third rep? Have things that do not have the ability to be ran through the scientific process become objective of late? In my focus of science it is necessary for publication that the work be able to be reproduced by anyone utilizing the same methods.

    I dont mean to sound off - but it seems to me if we are going to solve some of our own earthly problems - it might be useful to utilize some of your talents/knowledge here on earth - things such as energy, resource use and sustainability. Then all of us could collectively explore the various unknows of the tomorrow and universe.

    It is sad to me that our time is spent on things we cannot control rather than on things we can - where is the history’s channel public outreach toward our current problems? And where is the distinction between science and an adventure.

    I welcome your thoughts and becoming educated on how astronomy is a scientific discipline.

    Dallas

  4. Derek Says:
    November 30th, 2008 at 8:26 pm

    Amy,
    How do scientist see the asteroid that is supposed to come very near to the Earth in or around the year 2022. It must be so very very far away at this point, the mathmatic’s and the ability to even see this asteroid are astounding. How is this done?

    Thanks, Derek

    Mainzer says

    Good question, Derek. It turns out that most asteroids aren’t found when they’re that far away. The Earth and the asteroid are both always going around the sun like they’re on a racetrack, with the Earth lapping the asteroid since it’s usually on the inside track. So you can imagine that we usually see them at one close approach, allowing us to predict when the next close approach will be. Astronomers generally find new asteroids by taking a series of snapshots of a particular part of the sky, then looking for things that move between the frames. Stars move very slowly if at all, and more distant objects like galaxies do not appear to move at all, whereas the motion of asteroids stands out. Once we identify all the asteroid candidates in each snapshot, we have to make sure it’s the same asteroid that we’re seeing from frame to frame - sometimes there are more than one in a frame. We can figure this out by using what we know about the laws of gravity and orbital dynamics to calculate possible orbits for the detections. Once this is done, we have a tentative knowledge of the orbit, which allows us to make predictions about where the object should be in the future. We can improve our knowledge of an asteroid’s orbit by making more observations of it. This is why JPL’s Near-Earth Object tracking system is constantly updating impact predictions as new observations are fed in.

  5. Jon Hutto Says:
    December 1st, 2008 at 7:17 am

    Well I guess I don’t need the meteor portion of my car insurance policy!

    Being more able to determine danger from no danger will really be of a big help to the people tracking near earth objects. Sounds like a fun project. Need some help? :)

    Mainzer says

    Hi, Jon -
    No, you definitely don’t need asteroid insurance! Just to be clear, WISE will not find all the potentially hazardous objects out there - far from it. However, it will observe a statistically significant fraction of the population down to small sizes. This will give us a better understanding of how many asteroids we should expect expect to find.

  6. Magnus in Sweden Says:
    December 5th, 2008 at 8:14 am

    The universe is so amazing! I’m deeply impressed with the efforts done to explore the unknown. Maybe one day, asteroids will be mined for minerals, water and other valueable material (in space, water IS expensive) when man starts to go beyond the solar systems limits. Now is really a fascinating period of time to live in.

    It’s interesting how the science and literature (science fiction) seems to have a close relationship and inspire each other. Ones vision (e.g. Carl Sagan) can turn into reality by inspiring (NASA) scientists.

    Amy, keep up the good work! I’ve seen you in a couple of episodes of “The Universe” on the History Channel and really hope to see more of you in the future!

    /Magnus

  7. John K Says:
    December 10th, 2008 at 3:54 pm

    amy, I saw your demonstration with the yellow and blue paints. I thought it was a good analogy but its still hard to imaginge that the 2 would be close enough to mix together to form green at the second bang. John K in Phoenix

  8. Patricio Says:
    December 10th, 2008 at 7:41 pm

    Cheers from CHILE Amy. You know we got here one of the most clearest skies … so I really like your presentations in The Universe (by Discovery Channel in Chile). BEST REGARDS

    Mainzer says

    Chile is indeed one of the most amazing places on Earth for astronomy! And it is a beautiful country.

  9. Andre Garcia Says:
    December 11th, 2008 at 9:05 am

    Dear Dr.Amy Mainzer,

    It was a great surprise to see new faces on scientific world (I saw you on History Channel serie “The Universe”) , mainly women, which are getting more and more good positions in the scientifc world.

    Two questions: 1-how do the effect of friction and tide effect (earth against the asteroid) could deteriorate the impact of a possible asteroid ? 2- I believe that several nuclear devices (it would need millions of Giga Joules for small 1 km diameter granite asteroid) won’t be enough to evaporate these introdures rather to deviate would be smarter. Am I correct?

    Best regards.

    Andre Garcia
    Brazil

    Mainzer says

    Hi, Andre -
    How close an asteroid has to get to Earth before its shape is affected by Earth’s gravity is an interesting question. Some speculate that when the asteroid Apophis makes its close approach to Earth in 2029, the asteroid could undergo some amount of plastic deformation as a result of Earth’s gravitational pull.

  10. Luis Delgado Says:
    December 11th, 2008 at 2:27 pm

    Hi Amy:

    My concern is about how behaviors affect perceptions of life, in that sense I would like to ask: How would you think that the reactions of ordinary people if you look at an apocalyptic asteroid? And what think is the best way of alerting the world population?

    Tks

    Luis

  11. Carl Hoffman Says:
    December 22nd, 2008 at 1:36 pm

    Hi Amy,
    I was glad to find your blog! I really enjoy you on The Universe along with the chinese physicist fellow.Both of you amaze and enthrall me with your dialog and pure openess.I hope to see you guys again,soon…Carl

  12. johnny Says:
    January 5th, 2009 at 2:05 pm

    “By seeing what’s behind the dust, Spitzer has shown us star and planet formation is a very active process in our galaxy,” Churchwell said.

    from an 04 jpl press release, in the const. centaurus, a planet rich environment in the star forming region, is this a possible target for the wise mission and what kind of surprises await us?

  13. Ely Says:
    January 12th, 2009 at 11:10 pm

    Hi Amy,

    Asteroids is very amazing object in the outer space of the universe, floating around the outer space. but, it is very dangerous object. it can destroy planets and moons even human being life and animal life. so i suggest to continue study hard this object. Godspeed! Ely From Mindanao,
    Philippines

  14. Scott S Says:
    January 16th, 2009 at 7:51 pm

    Hi Amy,
    Great job on The Universe episode about meteors and asteroids that recently aired. My question is: Are you still refining the path of Apophis, and what is the likelihood of it impacting the earth in either 2029 or 2036? I recently heard that there’s a zero chance, but prior, I read that the chances were about 1 in 45,000 for 2036, which is a bit scary. Can you shed some more light on this one? And will WISE track Apophis, and if so, is there a website that we can keep up to date on WISE, including other near-Earth threat-tracking? Thanks for your time.

    Scott

  15. johnny Says:
    January 22nd, 2009 at 10:17 pm

    are “shooting stars” a potential hazard as well, what can wise do to determine if these earth sized meteors flying through space have the potential to cause catastophic occasions to “worlds” in their path?

  16. George Says:
    January 28th, 2009 at 2:53 am

    Amy, your job sounds fun!

    Good luck with the project..my question has to do with evaluating the composition of these asteroids. Can we detect water? How about some of the more rare metals? Seems to me that you guys have a good oportunity to educate the public and politicians on what these things are made of and propose some future science missions as well as the eventual mining of these asteroids.

    It’d be nice to see these things as a good source of rare metals and H2o instead of being afraid of them.

  17. Lars Hansson Says:
    January 28th, 2009 at 4:40 am

    Hi Amy,

    Regarding the movement of a newly found asteroid, how do you determine its movement in the third dimension from a series of two dimensional snapshots?

    Best regards,
    Lars

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