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Second Mars Landing Promises to Explore ASU Findings

On Saturday, January 24, at 10:05pm Arizona time, the Opportunity Rover, the second of NASA’s twin Mars Exploration Rovers (MER), landed on a very interesting part of Mars known as Meridiani Planum. A crowd of about 500 onlookers cheered as NASA executed a flawless landing in what turned out to be a small, shallow crater in an exotic gray plain, with weathered rock outcroppings. Arizona State University scientists watched it all unfold with anxiety, anticipation, jubilation and a great deal of personal and professional interest.

Meridiani Planum is literally on the opposite side of Mars from Gusev Crater, where the first rover, Spirit is currently picking its way across a flat, ochre-colored, dust and rock covered landscape. Opportunity, ASU scientists hope, is about to explore a landscape that is significantly different, especially when you look at it in infrared light.

Meridiani Planum is a plain in the middle of Mars’ Terra Meridiani region, an area of Mars that has long intrigued planetary geologists - particularly Philip Christensen, Regents’ Professor and Korrick Professor of Geological Sciences, and Principal Investigator for four Mars instruments that are either currently orbiting Mars or on the rovers. Meridiani, Christensen frequently notes, is a “layered” area, where erosion has exposed the martian rock and a number of clearly distinct geological layers.

One of Christensen’s instruments, the Thermal Emission Imaging System (THEMIS) on the Mars Odyssey orbiter, has taken infrared and visible light images of the Meridiani area that show several clear layers of rock with distinctly different thermal characteristics. The distinct differences in temperature of these layers implies strongly that they are different in mineral or structural composition.

The finding that the layers are different in turn implies that there were differences in the local martian environment at the times these layers were formed. In the way geologists look at things, exposed layers of different kinds of rock are chapters in the history of the planet (and perhaps of the planet’s climate) made visible.

With its varying rock formations, Meridiani is an exciting landscape for geologists to study, like the Grand Canyon here on Earth. However, this is only a small part of the reason the site was selected for a visit by the Opportunity Rover.

The clincher came when Christensen’s other Mars-orbiting instrument, the Thermal Emission Spectrometer (TES) on Mars Global Surveyor, detected a clear signal of the mineral hematite in one of Meridiani’s layers. Hematite, a gray mineral mainly composed of iron, generally only forms in the presence of liquid water, so the implication is that Meridiani’s Hematite Formation was once associated with water in some way.

The Meridiani Hematite Formation turned out to be the largest patch of that mineral yet found on the surface of the planet, and so, after much scientific discussion, the Meridiani area was selected to be the second MER landing site. Meridiani Planum was specifically selected because it is a good landing area right in the middle of the Meridiani Hematite Formation.

The minerals at Meridiani Planum are almost certainly remnants of a place in Mars’ past where there once was water, but the question remains with regard to what kind of water. Here, theories vary widely, with some scientists arguing that the hematite could have been formed by a subsurface hydrothermal system, by an above- or below-ground lake, or by volcanic activity causing a deposit of iron-rich ash. Christensen argues convincingly, however, that the hematite signature detected by TES does not match the signature of a mineral that developed from volcanic deposits and thus must have been left by liquid water.

In an article that Christensen has recently submitted for publication, he argues further that other evidence seen by THEMIS points to the conclusion that the Meridiani Hematite Formation was once the site of an ancient martian lake. He shows that the Hematite layer is thin, which is consistent with it being deposited by a lake, and that it appears to have flowed in and around the older channels and craters in the area. If the hematite had been deposited by dust or air-born volcanic ash, it would be spread evenly across all features in the landscape. The fact that the layer only occurs in the lowest areas points to it being deposited by standing water which would have pooled in those places.

If Christensen’s lake hypothesis turns out to be true, the Opportunity mission may prove to be even more exciting in the search for signs of ancient life on Mars than the Spirit mission. Gusev Crater, Spirit’s landing site, is also believed to be an ancient martian lake site, but we know from the information that has already come back from the first rover that much of the lakebed is buried under layers of martian dust, volcanic rock and rocks ejected from meteor craters. TES’s finding of hematite at Meridiani strongly implies that the Meridiani lakebed – if that is what it is – has largely been scoured clean by erosion and lies at the surface for all to see.

What will Opportunity see when it turns on Christensen’s Mini-TES and other instruments? What is the chemistry of the gray surface and the dark red subsoil? What geological secrets lie in the blocky formation that pokes out of the dirt a few yards beyond the lander? And what strange new landscape lies beyond the gentle slope of the crater walls? No one really knows anything yet, but ASU scientists are already fairly sure that this grayer Mars will be even more revealing than the Red Planet that we have previously seen. The next few weeks and months will tell.

For more information, contact James Hathaway, 480-965-6375 or


The Opportunity Landing Site at Meridiani Planum. The oval is the expected landing area. This image was taken by the THEMIS instrument on the Mars Odyssey spacecraft from orbit, and shows the area during daytime in infrared wavelengths of light.

Photo Credit: NASA/JPL/ASU

Read More:

• Mars Student Imaging Project (MSIP)
• MSIP Curriculum Overview
• Mars Education Program
• Thermal Emission Imaging System (THEMIS)
• Jet Propulsion Laboratory
• 2001 Mars Odyssey
• ASU’s Department of Geological Sciences
• Chain Reaction Magazine
• ASU Research Magazine

News Releases:
• ASU Mars Research on National Stage
• ASU Mars discovery links melting snow to gullies
• Photography for Public Use: First MSIP Photo news release
• Odyssey thermal data reveals a changing Mars
• ASU findings could dash hopes for past oceans on Mars
• Opportunity launch presents anticipation for ASU, NASA
•  Students Begin Exploring Mars with NASA’s Mars Odyssey
• Students to Release First Mars Image, Science Findings from Next Generation

• Scientists, children eager for deeper look at Red Planet
• Watch Global Warming Happen in Real Time – on Mars



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