Satellite orbiting Mars imaged descending Phoenix
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: May 26, 2008
Still basking in the elation of a successful Mars landing, engineers with the Phoenix program unveiled a dramatic photo today showing the spacecraft descending to the martian surface under its parachute Sunday. The black-and-white photo, shot by NASA's Mars Reconnaissance Orbiter spacecraft as it sailed overhead, shows the inflated parachute and the backshell supporting Phoenix dangling below, somewhere between 10,000 and 1,000 feet above the surface.
Phoenix was designed to send its own pictures and data back to Earth using UHF radio relay links with the Mars Reconnaissance Orbiter and NASA's Mars Odyssey. Additional pictures showing the terrain around the lander are expected to be downlinked every afternoon, helping scientists build up a high-resolution 360-degree panorama around the landing site.
The north polar landing site was chosen because it is flat and generally free of large boulders and other topographic features that might cause problems for Phoenix's touchdown. More important from a science perspective, the Mars Odyssey spacecraft has detected what scientists believe is a layer of water ice a few inches below the surface of Mars' extreme northern and southern latitudes. Pictures from NASA Mars orbiters and now from Phoenix show repeating polygonal patterns in the surrounding terrain that are indicative of an "active" surface.
"As the ice gets cold, it tends to contract a little bit and it'll form very narrow cracks and then the sand falls into those cracks, so now you see a little depression on the surface where the sand has fallen into a crack," Smith said. "And then in the sun, when the ice tries to expand back to where it was, the crack's filled with sand, it can't do that, and it tends to buckle a little bit. So you see these mounded structures."
Similar patterns are found in cold regions on Earth.
"As we look over this landing site, we see a very flat, kind of barren landscape," Smith said. "But you have to realize in the winter, this is encased in carbon dioxide ice, which might be several feet deep, it's a completely different landscape in the winter. And so it's gone through these cycles of winter, summer, winter, summer, and while it goes through those cycles, the polar tilt is changing, so the climate changes.
"One thing we've found about polar regions on the Earth is it's a good record keeper of climate change. So we wonder if perhaps on Mars we'll find clues as to what the climate has been like in the past by studying various signatures under the surface. Our mission is all about digging. So we're not roving over the surface, we're digging into the surface and that's where the science discoveries are likely to be made. So the pictures may look a little bleak, but the science can be absolutely fascinating.
"The other thing we've learned about polar regions on Earth is that there's a long record of organic materials preserved in the ice, just as you preserve organics in the freezer in your kitchen," Smith said. "That's the place where you can go back a million, two million years and bring signatures of organisms back for analysis, that's where they are. ... So we're wondering on Mars is there any indication that organic materials are preserved in this ice? And probably, the organic materials would come from asteroids and comets that have hit the surface of Mars over the last many eons. If it's preserved there, I think that changes the way that we're going to be exploring Mars, we're going to be going where ice is accessible."
Phoenix is equipped with a 7.7-foot-long robot arm capable of digging trenches up to 20 inches deep. A scoop and an ice rasp will be used to collect soil and ice chips for microscopic analysis by a suite of sophisticated instruments capable of detecting organic compounds and characterizing how the soil might have been affected by water in the past. The instruments also will sniff out whether organic compounds are, in fact, preserved in the sub-surface ice.
If all goes well, engineers will unlimber the lander's robot arm Tuesday, after its joints reach the proper temperature. Digging operations are not expected to begin for another week or so, after the Phoenix camera photographs the entire area reachable by the arm to give scientists a chance to prioritize possible target sites.
Scientists are hopeful a depression marking a possible sub-surface ice crack will be within reach of the arm to help them determine exactly what sort of mechanism might be responsible. In some cases, liquid water is required, in others it is not.
"Our priority is to first see the entire martian scene around the lander to give us a sense of place as to where we are and try and put these few polygons we've been able to see up close into perspective with the rest of the site around us and also to understand the rock distributions," Smith said.
Examining the handful of pictures already sent back from Phoenix, scientists noted that "some of the rock patterns don't line up with the polygons, it's like they're remnants, perhaps, of a more ancient surface," Smith said. "That's one thing our science team is considering.
"As far as knowing what's under the rocks, I'm anxious to find out. ... When you look at some of those troughs, you actually see what looks like freshly dug depressions in the center of them. And this is just like the active surfaces we see in the arctic regions on Earth. It implies we have an active surface, in other words, the ice is still there and expanding and contracting with the seasons."
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