NASA probe aims to unlock Mercury's secrets (Update)

Mar 30, 2011 by Jean-Louis Santini
This WAC image showing a never-before-imaged area of Mercury’s surface was taken from an altitude of 450 km (280 miles) above the planet during the spacecraft’s first orbit with the camera in operation. The area is covered in secondary craters made by an impact outside of the field of view. Some of the secondary craters are oriented in chain-like formations. This image was taken during MESSENGER’s closest approach to the sunlit portion of the surface during this orbit, just before crossing over the terminator. The oblique illumination by the Sun causes the long shadows and accentuates topography. The highly elliptical orbit of MESSENGER brings the spacecraft down to a periapsis (MESSENGER’s closest approach to Mercury) altitude of 200 km (125 miles) and out to an apoapsis (MESSENGER’s farthest distance from Mercury) altitude of 15,000 km (9300 miles). Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

NASA scientists pored Wednesday over stunning new images of Mercury as their MESSENGER probe began a year-long mission to map the surface of the solar system's least-understood planet.

After a 4.9-billion-mile (7.9-billion-kilometer) journey that took six-and-a-half years, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft finally entered the planet's orbit on March 17.

MESSENGER could unlock the secrets of a planet where temperatures reach a mind-boggling 800 degrees Fahrenheit (427 degrees Celsius) during the day but plummet to minus 150 degrees (minus 100 degrees Celsius) at night.

Despite its relative proximity to the Earth, Mercury has been little explored because it is the closest planet to the Sun and therefore subject to enormous gravitational pulls and massively high levels of radiation.

The first image, released on Tuesday, showed a dark crater called Debussy, while the lower part revealed a portion of Mercury near its south pole that has never before been photographed by a spacecraft.

MESSENGER, the first spacecraft ever placed in Mercury's orbit, captured 363 more images over six hours, 224 of which had been transmitted back to eager NASA scientists by Wednesday afternoon.

"Mercury has many mysteries, and now we will be able to get the close-up information that will unlock these secrets," said James Head, a geological sciences professor who is part of the MESSENGER team.

"In the coming year, we will be making discoveries every day, answering old questions and revealing new mysteries that we can't even suspect today.

"On Earth, we don't understand how plate tectonics started several billion years ago. Mercury may hold the answer," Head said.

"We also want to know that if the material in the permanently shadowed craters on Mercury is water ice, how does it get there in this hellishly hot environment? Could this be a record of the history of water in the solar system?"

The wide-angle camera (WAC) is not a typical color camera. It can image in 11 colors, ranging from 430 to 1020 nm wavelength (visible through near-infrared). It does this with a filter wheel: the 11 narrow-band filters (plus one clear filter) are mounted onto a wheel that can be rotated to allow the camera to capture an image through each filter. In this image the 1000 nm, 750 nm, and 430 nm filters are displayed in red, green, and blue, respectively. Several craters appear to have excavated compositionally distinct low-reflectance (brown-blue in this color scheme) material, and the bright rays of Hokusai crater to the north cross the image. During MESSENGER’s orbital operations, we will typically use just eight of the WAC's filters. This decision was made to reduce the amount of data that must be stored on the spacecraft’s solid-state recorder before the information can be downlinked. It’s also quicker than cycling through all 11 filters - the spacecraft is moving rapidly over the surface, and there isn't much time to image the same spot on the surface 11 times over before moving to the next area of interest. The sets of color images will help us learn about the variation in composition from place to place on the planet. For example, some minerals such as olivine and pyroxene often absorb more light at longer wavelengths than at shorter ones, so we’ll be looking for their signatures in the reflectance spectra derived from each eight-color set. WAC images will be used in coordination with the Mercury Atmospheric and Surface Composition Spectrometer (MASCS), a hyperspectral instrument that provides reflectance information at many more wavelengths, but only for one spot on the surface at a time. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Mariner 10, an earlier probe that made three passes of Mercury in 1974 and 1975 mapped out about 45 percent of the surface of the planet. NASA hopes now to be able to complete that work.

MESSENGER will begin continuous mapping on April 4, orbiting the planet every 12 hours at a minimum altitude of 124 miles (200 kilometers).

Scientists believe enormous volcanic eruptions produced many of Mercury's expansive plains, which are littered with meteor craters, and say its strong magnetic field appears to be generated by a molten iron core.

MESSENGER, a 1,067-pound (485-kilogram) robotic probe, was launched in August 2004, making one flyby of Earth, two of Venus and three of Mercury before entering its new orbit.

"The entire MESSENGER team is thrilled that spacecraft and instrument checkout has been proceeding according to plan," said mission spokesman Sean Solomon of the Carnegie Institution for Science in Washington.

"The first images from orbit and the first measurements from MESSENGER's other payload instruments are only the opening trickle of the flood of new information that we can expect over the coming year. The orbital exploration of the solar system's innermost planet has begun."

Named after the Roman messenger god, hence the name of the NASA probe, Mercury is heavily cratered and similar in appearance to the Moon. It is the smallest of the eight planets and orbits the Sun every 87.969 Earth days.

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User comments : 14

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El_Nose
2.1 / 5 (8) Mar 30, 2011
was anyone suprised by this??? why is this news to anyone -- i know why it made it on the science web site -- but the fact someone got paid to write this paper ---

hate hate hate hate ----
"If you have hate in your heart let it out"
~! Dave Chapell Show

Im not trying to hate but really -- were u surpised Mecury has a lot of craters --- now if it was smooth i would have been like wow - really
apex01
not rated yet Mar 30, 2011
I wonder what the mineral content of the moon is like? With all the asteroids it catches, there has to be a lot of iron and rare minerals on the surface.
Shootist
3 / 5 (4) Mar 30, 2011
First Mercury images in orbit show lots of
buried
craters


Fixed

Bigblumpkin36
3 / 5 (2) Mar 30, 2011
Looks like the lead singer of metalica's face
an_p
1 / 5 (1) Mar 30, 2011
First Mercury images in orbit show lots of
buried
craters


Fixed



+1 on that
omatumr
4.5 / 5 (2) Mar 30, 2011
Thanks for the interesting story. Two comments:

1. If craters are produced when material falling toward the gravitational center of the solar system - the Sun - encounters a planet on the journey, perhaps it is not surprising that the closer a planet is to the Sun the more craters will be created on its surface.

2. Of course the other variable is the length of time a crater will survive on the surface before being destroyed by geologic activity.

With kind regards,
Oliver K. Manuel

antialias
4 / 5 (2) Mar 31, 2011
perhaps it is not surprising that the closer a planet is to the Sun the more craters will be created on its surface.

Perhaps it is not surprising that smaller boides (with less or no atmosphere and less or no erosion proscesses going on) will display more craters per square kilometer than others. This has little to do with 'proximity to the sun'.

Once stuff gets into orbits in a solar system very little of that starts falling towards the sun unless stuff collides and the angular velocity changes (and most of that doesn't fall into the sun but just goes into slightly lower or a bit more eccentric orbits).
Callmewhatuwant
not rated yet Mar 31, 2011
Thanks for sharing.....Mercury is unique by itself....ofcourse it's indeed a wonderful thing to look up at the stars...it has a much more inspiring and out-of-the-world experience..and know more abt the stuff out there...and comparing the way the Laws of Physics have treated the earth's siblings....
barakn
1 / 5 (1) Mar 31, 2011
perhaps it is not surprising that the closer a planet is to the Sun the more craters will be created on its surface. -omatumr

... This has little to do with 'proximity to the sun'. -antialias

It has everything to do with proximity. The orbits of most solar system objects are quasi-elliptical, and it is well known that such objects are moving fastest at perihelion (closest to the sun) and slowest at aphelion (furthest). Mercury's proximity to the sun means it is more likely to encounter perihelion objects moving fast, and a faster object makes a bigger crater. The bigger the crater, the more likely we are to see it and count it as a crater.
antialias
not rated yet Mar 31, 2011
The issue he had was about 'more' craters - not 'larger' craters. According to your logic we should see markedly more craters on Mercury than on the Moon.

At first glance looking at the Moon
fluidforms.eu/moon-bowl/img/content/MOON/550/Moon_surface_craters.jpg

and at Mercury
mercurypicgall.co.cc/pictures/car/images/7/i2-6.jpg

they don't seem qualitatively different to me.

Mercury also has about twice the gravity of the moon, which means that the ejecta from impacts don't travel as far - so craters on Mercury should actually be _less_ visible than on the moon for similar impact energies.

omatumr
4 / 5 (1) Mar 31, 2011
The issue he had was about 'more' craters - not 'larger' craters. According to your logic we should see markedly more craters on Mercury than on the Moon.

Mercury also has about twice the gravity of the moon, which means that the ejecta from impacts don't travel as far - so craters on Mercury should actually be _less_ visible than on the moon for similar impact energies.


Greater gravity would also "pull in" more passing meteors.

And, " Of course the other variable is the length of time a crater will survive on the surface before being destroyed by geologic activity."
barakn
1 / 5 (1) Mar 31, 2011
Antialias - You overlooked the statistical argument in the last sentence of my previous post. There are a lot more craters that are smaller than we can see than there are craters that we can see. The extra speed an object has near the bottom of the sun's gravity well might make the difference between creating a crater that's too small to see and one that's just barely visible. Thus the speed effect should increase the number of VISIBLE craters. Also, gravity's effect on "ejecta heaval distance" has a much smaller effect on crater size than you suggest, and you seem to be ignoring the fact that falling into a bigger gravity well speeds up an object more, causing a bigger impact energy and thus a bigger crater. The image of the Moon you posted happens to be of the heavily-cratered and very old lunar highlands. Lunar maria are much smoother than this or your Mercury photo. The Mercury photo is fairly typical of the entire planet (or at least the part we've seen so far).
barakn
1 / 5 (1) Mar 31, 2011
There are some other more subtle effects at play. The stronger gravity means the Mercurian craters have less vertical relief, augmented by lava infill and perhaps by rock of a stronger consistency. Also, because the radius of curvature is roughly similar between your two photos but Mercury is larger than the Moon, the Mercury photo is taken from a higher altitude, and thus we are doing an apples-and-oranges comparison of craters of different scales. The fact that we see a large number of central peaks in the Mercury craters confirms this, as they only tend to occur in larger craters. The Mercury photo is also of lower quality, perhaps even a photo of a tv image, and the loss of resolution may be hiding smaller craters.
antialias
not rated yet Mar 31, 2011
Also, gravity's effect on "ejecta heaval distance"


Double the gravity gives you half the travel distance for a projectile of same mass and same initial velocity. So a crater from an object of the same mass/velocity will cover four times as much area on the moon than it will on mercury.

Speed is not significantly different due to the different gravities since these asteroids travel on average at 70km/second. That's very little time they spend in the gravity field of the Moon (or Mercury) in which they could be significantly accelerated.

Speed ratio of Earth to Mercury is about 30/48 - so the impact speed of an object is roughly 50% higher for Mercury...that still leaves craters (for the same mass of impacting object) of only half the size (by area) as on the moon.