WASHINGTON — The first pictures from the unseen side of Mercury reveal the wrinkles of a shrinking, aging planet with scars from volcanic eruptions and a mark shaped like a spider.
Some of the 1,213 photos taken by NASA’s Messenger probe and unveiled Wednesday help support the case that ancient volcanoes dot Mercury and that it is shrinking as it gets older, forming wrinklelike ridges. But other images are surprising and puzzling.
The spidery shape captured in a photo is “unlike anything we’ve seen anywhere in the solar system,” said mission chief scientist Sean Solomon of the Carnegie Institution of Washington. The image shows what looks like a large crater with faint lines radiating out from it.
Mercury, the closest planet to the sun, has often been compared to Earth’s dull black-and-white moon. But the new photos, which reveal parts of Mercury never seen, show the tiny planet is more colorful and once had volcanic activity.
With the help of NASA high-tech enhancement, Messenger photos showed baby blues and dark reds.
“It has very subtle red and blue areas,” said instrument scientist Louise Prockter of Johns Hopkins University, which runs the Messenger mission for NASA. “Mercury doesn’t look like the moon.”
The last time a NASA spacecraft went to Mercury was Mariner 10 in 1975. It took pictures of just 45 percent of the planet.
Messenger, which will do a few more flybys of the planet before going into a long-term orbit, already has taken pictures of another 30 percent of Mercury, Prockter said. The rest will be seen eventually.
Planetary scientist Robert Strom, who was part of both the Mariner 10 and Messenger teams, said, “This is a whole new planet we’re looking at.”
And Prockter noted “there are some features we haven’t been able to explain yet.”
Example No. 1 is what scientists are calling “the spider.” It is in the middle of a basin formed billions of years ago when space junk bombarded Mercury.
Mariner had only seen part of the crater. When Messenger took a look with sharper cameras and a better angle, it photographed this odd central plateau jutting up, about half a mile high with dozens of tiny ridges radiating out.
It is as if “something is pushed up,” said MIT planetary scientist Maria Zuber.
Prockter guessed that it could be remnants of a volcano. Other scientists think the leglike features could be the same ridges seen all over Mercury.