Spider-Like Crater On Mercury

[SoulSplat]

By SETH BORENSTEIN, AP Science Writer
Wed Jan 30, 11:11 PM ET
LINK TO STORY: http://news.yahoo.com/s/ap/20080131/ap_on_sc/mercury_messenger
LINK TO IMAGE: http://d.yimg.com/us.yimg.com/p/ap/20080131/capt.nyol92301310005.mercury_messenger_nyol923.jpg?x=400&y=269&sig=xmzPVfJqmWZFT1kCX0JeAQ--


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 birthmark 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 wrinkle-like 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 couple 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 an infant 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, who is part of the science team.

Prockter guessed that it could be remnants of a volcano. Other scientists think the leg-like features could be the same ridges seen all over Mercury.

First seen in the 1970s, the ridges now seen more widely provide evidence that Mercury is contracting, the scientists said.

Scientists had theorized that as the core of Mercury cools, it contracts and the whole planet shrinks. That was even a 19th Century theory for why Earth had mountains, but one that later proven wrong, Solomon said. But with Mercury that seems to be the case. As the planet shrinks, a bit of crust is pushed over another, forming what Prockter calls "wrinkle ridges."

Besides having what looks like the leftovers from volcanoes, Mercury has at least one crater that seems to be filled with what would be that planet's version of lava, Prockter said.

NASA launched the $446 million Messenger on its nearly 5 billion-mile mission in 2004. It will fly by Mercury two more times, this October and September 2009, before settling into orbit around in 2011. Messenger will take pictures, measure the planet's tenuous atmosphere, hills and valleys and unusual magnetic field — Mercury is the only solar system planet other than Earth to have a magnetosphere.

Quirky Mercury is one of the bigger question marks in the solar system, probed not nearly as much as Mars, Jupiter, Venus or Saturn.

Strom, a retired University of Arizona scientist who worked on Mariner 10, said that as he awaited Messenger's flyby earlier this month, "I couldn't sleep at all. I was like a kid on Christmas Eve."

Only he had to wait 30 years for his presents. It was worth it, he said: "What I saw was astounding to me."

[SoulSplat]

Probe detects "spider" crater on Mercury
By Will Dunham
Wed Jan 30, 4:28 PM ET
LINK TO STORY: http://news.yahoo.com/s/nm/20080130/sc_nm/space_mercury_dc


WASHINGTON (Reuters) - A NASA probe that shot past Mercury this month detected a puzzling geological feature that scientists on Wednesday labeled "The Spider" and found evidence of past volcanic activity on the closest planet to the sun.
 
The U.S. space agency's car-sized MESSENGER spacecraft on January 14 flew past Mercury, whose diameter is just a third the size of Earth's, and its seven scientific instruments gathered new information about the little understood planet.

Data collected by MESSENGER showed that a massive impact crater on its surface is larger than previously thought. The probe is due to fly by again this October and in September 2009 before beginning a yearlong orbit of the planet in 2011.

While Mercury looks superficially like Earth's moon with a cratered, rocky surface, scientists said the new findings show they are quite different.

"We were continually surprised. It was not the planet we expected. It was not the moon," said Sean Solomon of Carnegie Institution of Washington, the mission's lead investigator. "It's a very dynamic planet with an awful lot going on."

Mercury is a mystery in many ways and its proximity to the sun has made it difficult to observe from Earth.

Mercury has been visited by a spacecraft only twice before, in 1974 and 1975 when NASA's Mariner 10 flew past it three times and mapped about 45 percent of its surface. The latest fly-by covered another 30 percent of the surface.

"The Spider" was the most striking feature described by the scientists. It is made up of more than 100 narrow, flat-floored troughs radiating from a central point, much as petals from a daisy or the legs of a spider.

"A REAL MYSTERY"

"The Spider" has a crater 25 miles wide near its center, but it is unclear whether this is related to the feature's original formation and scientists aren't sure what to make of it.

"It's a real mystery," said Louise Prockter of Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, who works on the mission.

"The Spider" is in the middle of Mercury's Caloris basin, one of the solar system's biggest impact craters, formed more than 3.8 billion years ago when a large space rock hit.

Based on the probe's new observations, the diameter of the Caloris basin is now thought to be 960 miles, larger than a previous estimate based on Mariner 10's data. The basin's interior looks like it was volcanically resurfaced by magma from deep within Mercury's crust or mantle.

Prockter said Mariner 10 data provided some evidence of volcanism, but it was not universally accepted. Based on the new observations, Prockter added, "there's very little doubt, I think, in the minds of most of us from the geology team that there has been widespread volcanism on Mercury's surface."

MESSENGER stands for Mercury Surface, Space Environment, Geochemistry and Ranging. It was launched in 2004 and flew past Venus twice and Earth once en route to Mercury.

MESSENGER also collected data on Mercury's magnetic field, its tenuous atmosphere and its topography.

Mercury's surface is a mix of craters caused by bygone impacts with space rocks, plains and long, winding cliffs. The spacecraft saw basins as deep as 1.7 miles and peaks jutting out as high as 3 miles above the surface.

With Pluto classified as a dwarf planet, Mercury is the solar system's smallest planet, with a diameter of 3,032 miles , only a bit larger than Earth's moon.

(Editing by Chris Wilson)