Mercury is an odd little planet, tiny but incredibly dense, relatively close by but hard to study via telescope. The MESSENGER probe‘s latest findings, 57 papers presented two days ago at conference, bring new weirdness to our understanding of the planet closest to the Sun.
Take, for instance, the new revelations about Mercury’s core. We always knew that Mercury had a proportionally larger core than Earth does; geologists thought that it might make up a whopping 42% of the planet’s volume, in comparison to Earth’s 17%. The newest estimate, though, blows that out of the water: We now think the number is 85%. To boot, there appears to be an extremely dense layer more than a hundred miles thick encasing the core, perhaps a shell of iron sulfide. That makes the mantle and crust—to use the memorable analogy of a planetary scientist interviewed by Wired—like a mere orange peel on a giant orange of metal.
Another memorable finding: the largest crater on Mercury, Caloris Basin, isn’t actually much of a basin. It seems that the crater’s center gradually rose at some point in the not-too-distant past until it was higher than its edges. This has geologists revising their impressions that Mercury stopped being geologically active 4.5 billion years ago to something more like 2 billion years ago.
Image courtesy of Case Western Reserve University
Hello again, Mercury. This week in a trio of papers Science, the scientists behind the Messenger probe released their findings from the craft’s third and final flyby of the planet closest to the sun, which it executed last September. Mercury, they’ve shown once again, is full of surprises—and they’ll get the chance to explore them when Messenger returns and finally enters Mercury’s orbit in March 2011.
Scientists have now mapped 98 percent of the planet by combining the new observations with the first two flybys in January and October 2008, plus the Mariner 10 mission in the ’70s, [said Brett Denevi, coauthor of one of the papers]. The latest flyby filled in a 360-mile-wide gap that had never been imaged before.
“It wasn’t a huge amount of real estate, but there was a lot of really interesting stuff there,” Denevi said. The most exciting features include a 180-mile-wide basin filled with hardened lava, and a crooked bowl surrounded by glass and magma that may be the largest volcanic vent ever identified on Mercury. Together, these features suggest that Mercury had active volcanoes later in its history than scientists had suspected [Wired.com].
The first image above shows a smooth basin dubbed Rachmaninoff, which is one of the smoothest regions seen on Mercury—so smooth that it must have formed from volcanic material in the last billion years or so. The yellowish part in the upper right of this false color image is that volcanic vent.
When NASA’s Messenger space probe swung past Mercury on September 29, it snapped this picture of the innermost planet’s barren and strange landscape. The $446 million probe’s third flyby brought it within 142 miles (228 km) of Mercury’s surface to cover more uncharted terrain, leaving 98 percent of the planet now mapped [SPACE.com].
The images taken and the data recorded during the flyby are the last that will be acquired until Messenger finally slips into orbit around Mercury in 2011. The probe has now completed about three-quarters of its swooping 4.9-billion-mile journey that will eventually bring it into orbit.
Researcher Brett Denevi explains that this enhanced color shot shows a bright area surrounding an irregular depression, with steep sides and an odd shape, “all of which are hallmarks of something like a volcanic vent,” Denevi said [SPACE.com]. The double-ring basin in the center of the photo measures about 180 miles in diameter. It appears to be a relatively young impact crater–researchers believe it formed about 1 billion years ago–and the smooth stuff on the crater floor may be even younger volcanic material.
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Today in the innermost region of our solar system, NASA’s Messenger space probe will swoop past Mercury for the third and final time. The maneuver will give scientists a close look at the dense, iron-rich, oddball planet, and will also alter the probe’s trajectory and prepare it to begin orbiting Mercury in March 2011.
As Messenger travels within 142 miles of Mercury at 12,000 miles per hour, the spacecraft’s camera will swivel to stare at a succession of craters and other geological features…. One target will be an old 90-mile-wide crater. Another will be young 13-mile crater and a splash of light-colored soil surrounding it. A third crater of interest has materials of unusual color perhaps produced by violent volcanic eruptions [The New York Times]. When this third flyby is complete, 95 percent of the planet will have been mapped in high resolution.
When the Messenger spacecraft swooped low past the planet Mercury on October 6 2008, it gathered up a wealth of data that will have planetary scientists puzzling for years. As researchers sort through findings regarding Mercury’s volcanic past, meteor impacts, and the effect of the solar wind on the innermost planet’s magnetosphere, one broad conclusion stands out: Mercury isn’t just a boring chunk of rock. Marilyn Lindstrom, a NASA program scientist, said the Messenger findings show that Mercury is “just an amazingly dynamic planet, both in the past and in the present” [Baltimore Sun].
Superficially, Mercury looks a lot like the moon: small, grayish-brown and pockmarked with craters. Some scientists assumed that Mercury’s surface formed the same way the moon’s did, with lighter rocks rising to the surface of a magma ocean and congealing into a brittle crust early on. But the new observations reveal that 40 percent of the surface was formed by volcanoes. “Up until before Messenger’s arrival, we weren’t even sure that volcanism existed on Mercury” [Wired], says researcher Brett Denevi. The presence of titanium oxide also suggests that the planet was hot enough in its first 100 million years to be covered in magma oceans.
On October 6, NASA’s Messenger space probe swooped down to within 125 miles of the surface of Mercury, and the just-released images from that flyby are shaking up astronomers’ ideas about the planet’s geologic history. The remarkable pictures reveal a vast patch of lava, indicating that the planet was shaped by a long age of volcanic eruptions. Astronomers used to dismiss Mercury, the planet closest to the sun, as mere “dead rock,” little more than a target for cosmic collisions that shaped it, said MIT planetary scientist Maria Zuber. “Now, it’s looking a lot more interesting,” said Zuber [AP].
Messenger’s cameras spotted a crater of about 60 miles in diameter that was not as deep as other nearby craters, and determined that it had been filled in with a huge amount of solidified lava. To get an idea of how much, Zuber explains, you could imagine the entire Baltimore-Washington region covered with a layer of solidified lava about 12 times the height of the Washington monument. “So it’s a great, great deal of vulcanism,” she says. “That’s an awful lot of volcanic material in one place for such a little planet” [NPR News]. Researchers think the eruption happened between 3.8 and 4 billion years ago.
Yesterday, the Messenger space probe swooped down and flew 124 miles from the surface of the innermost planet, Mercury, furiously snapping more than 1,200 pictures of a side of the planet that has never before been seen by a spacecraft. Today, after the NASA probe turned its antenna back towards Earth, it began sending home remarkable photos of Mercury’s pockmarked surface.
The second Mercury flyby of Oct. 6 comes after a first flyby on Jan. 14, which looked at a different side of the planet. “When these data have been digested and compared, we will have a global perspective of Mercury for the first time,” said [astronomer] Sean Solomon…. Launched in August 2004, MESSENGER – short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging – is the first spacecraft in 33 years to greet Mercury up close since NASA’s earlier Mariner 10 mission of the 1970s [SPACE.com].