Astronomy Picture of the Day |
APOD: 2008 November 3 - A Spectacular Rayed Crater on Mercury
Explanation:
Why does Mercury have so many rayed craters?
No one is sure.
The robotic
MESSENGER spacecraft that is taking unprecedented images as it swoops past the innermost planet has provided dramatic confirmation that
Mercury has more
rayed craters than
Earth's Moon.
Pictured
above,
a particularly spectacular rayed crater spanning approximately 80 kilometers was imaged by
MESSENGER
during last month's flyby from about 20,000 kilometers up.
The rays prevalence is a mystery because
space weathering
effects such as dust accumulation and
solar wind attenuation should be greater on Mercury than on the Moon.
Hypothesized solutions currently include the
optical properties of Mercurian dust,
and that Mercury's high mass and proximity to the Sun cause more
violent impacts, thus typically raising more light material.
MESSENGER will buzz past Mercury again next year before entering orbit in 2011.
APOD: 2008 October 8 - Mercury as Revealed by MESSENGER
Explanation:
The planet Mercury has been known since history has been recorded, but parts of the Solar System's innermost planet have never been seen like this before.
Two days ago the robotic
MESSENGER spacecraft buzzed past
Mercury
for the second time and imaged terrain mapped previously only by
comparatively crude radar.
The above image was recorded as
MESSENGER looked back 90 minutes after passing,
from an altitude of about 27,000 kilometers.
Visible in the
above image, among many other newly imaged features,
are unusually long
rays that appear to run like
meridians of
longitude
out from a young crater near the northern limb.
MESSENGER is scheduled to fly past
Mercury
once more before firing its thrusters to enter orbit in 2011.
APOD: 2008 July 10 - Enhanced Color Caloris
Explanation:
The sprawling Caloris basin
on Mercury
is one of the solar system's largest impact basins.
Created during the early history of the solar system by the impact of
a large asteroid-sized body, the basin spans about 1,500 kilometers
and is seen in yellowish hues in
this enhanced
color mosaic.
The image data is from the January 14th
flyby of the
MESSENGER spacecraft,
captured with the
MDIS
instrument.
Orange splotches around the basin's perimeter are now thought to be
volcanic vents,
new evidence
that Mercury's smooth plains are indeed lava flows.
Other discoveries at Mercury
by NASA's MESSENGER mission include
evidence that Mercury, like planet Earth, has a global
magnetic field
generated by a
dynamo
process in its large core,
and that Mercury's surface has
contracted significantly as its core cooled.
APOD: 2008 March 19 - Mercury in Accentuated Color
Explanation:
The colors of Mercury are subtle but beautiful.
At first glance, our
Solar System's
innermost planet appears simply
black and white,
but images that include
infrared
colors normally beyond human vision accentuate a world of detail.
One such image, shown above, was acquired by the robotic
MESSENGER spacecraft
that swung by Mercury in mid-January.
Here, most generally, the hot world itself acquires a slightly more brown hue.
Many craters that appear on top of other craters -- and so surely have formed more recently -- appear here as bright with bright rays that include a slightly blue tint, indicating that soil upended during the impact was light in color.
A few craters, such as some in the huge
Caloris Basin impact feature visible on the upper right, appear unexpectedly to be ringed with a dark material, the nature of which is being researched.
MESSENGER continues to glide through the inner Solar System and will pass
Mercury
again this October and next September, before entering orbit around the desolate world in 2011.
APOD: 2008 February 4 - A Spider Shaped Crater on Mercury
Explanation:
Why does this crater on Mercury look like a spider?
When the robotic
MESSENGER spacecraft
glided by the planet Mercury
last month, it was able to image portions of the Sun's closest planet that had never been seen before.
When imaging the center of Mercury's extremely large
Caloris Basin,
MESSENGER found a crater, pictured above, with a set of unusual
rays emanating out from its center.
A crater with such troughs has never been seen before anywhere in
our Solar System.
What isn't clear is the relation of the crater to the radial troughs.
Perhaps the crater created the
radial rays, or perhaps the two features appear only by a chance superposition --
the topic is sure to be one of future research.
MESSENGER is scheduled to fly past Mercury twice more before
firing its thrusters to
enter orbit in 2011.
APOD: 2008 January 26 - Crescent Mercury in Color
Explanation:
Hard to spot against the
twilight glow near planet Earth's horizon,
a crescent Mercury was imaged close up by the
MESSENGER
spacecraft early last week.
Colors in this
remarkable picture were
created using data
recorded through infrared, red, and violet filters.
The combination enhances color differences otherwise not visible to
the eye across the innermost planet's
cratered surface.
In this view,
light
bluish material seems to surround
relatively new craters,
contrasting with the mostly
drab, brown terrain.
Mercury itself is 4,880 kilometers in diameter.
The full resolution image shows features as small as 10 kilometers
across.
APOD: 2008 January 21 - Mercury's Horizon from MESSENGER
Explanation:
What would it look like to fly past Mercury?
Just such an adventure was experienced last week by the MESSENGER spacecraft during its
first flyby of the strange
moon-like world nearest the Sun.
Pictured above is the limb of
Mercury
seen by MESSENGER
upon approach, from about 1 1/2
Earth diameters away.
Visible on the hot and barren planet are many
craters, many appeared to be more shallow than similarly sized craters on the Moon.
The comparatively high
gravity of
Mercury helps
flatten
tall structures like high crater walls.
MESSENGER
was able to take over 1,000 images of Mercury which will be beamed back to
Earth for
planetary geologists
to study.
The robotic MESSENGER spacecraft is
scheduled to fly past Mercury twice more before firing its thrusters
to enter orbit in 2011.
APOD: 2008 January 16 - MESSENGER Passes Mercury
Explanation:
Two days ago, the MESSENGER spacecraft became only the
second spacecraft in human history to swoop past Mercury.
The last spacecraft to visit the Sun's closest planet was
Mariner 10 over
35 years ago.
Mariner 10 was not able to
photograph Mercury's entire
surface, and the
images it did send back raised many questions.
Therefore, much about
planet Mercury
remains unknown.
This week's flyby of
MESSENGER
was only the first of three flybys.
Over the next few years MESSENGER will swing past twice more and finally enter Mercury's orbit in 2011.
MESSENGER is currently moving too fast to enter orbit around Mercury now.
The above image was taken two days ago during MESSENGER's flyby and shows part of Mercury's surface that has
never been imaged
in detail before.
Many more detailed images of Mercury
are expected to be sent back over the next few days.
The data acquired by
MESSENGER
will hopefully help scientists
better understand how Mercury's surface was formed, and why it is so dense.
APOD: 2008 January 12 - Mercury Chases the Sunset
Explanation:
This colorful view of the western sky at sunset features
last Wednesday's slender crescent Moon.
Of course, when the Moon is in its
crescent phase it can
never be far from the Sun in the sky.
Also always close to the Sun in Earth's sky
is innermost
planet
Mercury, seen here below and right of center
against the bright orange glow along the horizon.
Mercury is usually
difficult
to glimpse because
of overwhelming sunlight, but increasingly better views of
the small planet after sunset will be possible as
it wanders farther
east of the Sun in the coming days.
On January 14th, NASA's MESSENGER
spacecraft will have a
good view
too, as it makes
its first Mercury flyby.
APOD: 2004 September 12 - Mercury: A Cratered Inferno
Explanation:
Mercury's surface looks similar to our Moon's.
Each is heavily
cratered and made of rock.
Mercury's diameter is about 4800 km, while the
Moon's is slightly less at about 3500 km
(compared with about 12,700 km for the
Earth).
But
Mercury is unique in many ways.
Mercury is the closest planet to the
Sun,
orbiting at about 1/3 the radius of the
Earth's orbit.
As Mercury slowly rotates, its surface temperature
varies from an unbearably cold -180 degrees
Celsius to an unbearably hot 400 degrees
Celsius.
The place nearest the
Sun in
Mercury's
orbit changes slightly each orbit - a fact used by
Albert Einstein
to help verify the correctness of his then
newly discovered theory of gravity:
General Relativity.
The above picture was taken by the only spacecraft ever to pass
Mercury:
Mariner 10 in 1974.
A new mission, Messenger,
launched for Mercury last month
and is scheduled to enter orbit around the Solar System's
innermost planet in in 2011.
APOD: 2004 August 14 - Messenger Launch
Explanation:
Streaking
into the early morning sky on August 3rd, a
Delta II rocket launches NASA's
Messenger
spacecraft on an interplanetary voyage to
Mercury.
Scheduled to become the first probe to orbit Mercury, Messenger
will begin by
looping through the inner Solar System in a
series of close flybys of planet Earth and Venus.
The flybys are designed as trajectory changing
gravity
assist encounters to ultimately achieve the goal of orbiting
Mercury in 2011.
Prior to entering orbit, Messenger will also flyby Mercury
in 2008 and 2009 as the first spacecraft to visit
the Solar System's innermost planet since
Mariner 10 in the
mid 1970s.
This dramatic view
of the Messenger launch was recorded from
a pier in Jetty Park at the north end of Cocoa Beach
about 2.5 miles from the
Cape
Canaveral launch site.
So what's that erratic blue streak on the right?
It's the reflection from a camera
blurred in the time exposure.
APOD: 2000 December 16 - Degas Ray Crater on Mercury
Explanation:
Like the Earth's Moon,
Mercury is scarred with craters
testifying to an intense bombardment during the
early history of
the Solar System.
In 1974,
the
Mariner 10 spacecraft
surveyed this innermost planet up close,
producing the only detailed images of its tortured surface.
In the above mosaic the bright rays
emanating from the 45 kilometer wide
Degas crater almost appear to be painted on.
The rays consist of light colored material blasted out during the
crater's formation.
Craters older than Degas are covered by the
ray material while younger craters are seen
superimposed on the rays.
Mercury's gravity and density
are about twice
that of Earth's Moon
so such bright
ray
craters on the lunar surface tend to be much larger.
NASA plans to launch MESSENGER
to the least explored terrestrial planet
in 2004.
APOD: August 23, 1998 - Vega
Explanation:
Vega is a bright blue star 25 light years away. Vega is the brightest star in the Summer Triangle, a group of stars easily visible
summer evenings in the northern hemisphere. The name
Vega derives from Arabic origins, and means "stone eagle."
4,000 years ago, however, Vega was known by some as "Ma'at" -
one example of ancient human astronomical knowledge and language.
14,000 years ago,
Vega, not Polaris, was the
north star. Vega is the fifth brightest star in the night sky, and has a diameter
almost three times that of our Sun.
Life
bearing planets, rich in liquid water,
could possibly exist around Vega. The
above picture,
taken in January 1997, finds Vega, the
Summer Triangle, and
Comet Hale-Bopp high above
Victoria,
British Columbia, Canada.
APOD: July 15, 1997 - Vega
Explanation:
Vega is a bright blue star 25 light years away. Vega is the brightest star in the Summer Triangle, a group of stars easily visible
summer evenings in the northern hemisphere. The name
Vega derives from Arabic origins, and means "stone eagle."
4,000 years ago, however, Vega was known by some as "Ma'at" -
one example of ancient human
astronomical knowledge and language. 14,000 years ago, Vega, not
Polaris, was the
north star. Vega is the fifth brightest star in the night sky, and has a diameter
almost three times that of our Sun.
Life
bearing planets, rich in liquid water,
could possibly exist around Vega. The
above picture,
taken in January, finds Vega, the
Summer Triangle, and
Comet Hale-Bopp high above
Victoria,
British Columbia, Canada.