I was just sent a press-release e-mail giving some of the details of the MRO mission now that it has completed its primary 2-year science phase. First, the good news: it has been approved for another 2-year phase for science operations. This is great as the orbiter has only sent back about 73 TB of data—yes, terabytes. As in, more data all previous Mars missions combined. One terabyte is 1,099,511,627,776 bytes (2⁴⁰) or the equivalent of about 132,000 introductory physics textbooks—you know, those 9"×10" jobs that are a couple inches thick. So MRO's data would fill nearly 10 million such tomes.

To quote from the release: "Since moving into position 186 miles above Mars' surface in October 2006, the orbiter also has conducted 10,000 targeted observation sequences of high-priority areas. It has imaged nearly 40 percent of the planet at a resolution that can reveal house-sized objects in detail, with one percent in enough detail to see desk-sized features. This survey has covered almost 60 percent of Mars in mineral mapping bands at stadium-size resolution. The orbiter also assembled nearly 700 daily global weather maps, dozens of atmospheric temperature profiles, and hundreds of radar profiles of the subsurface and the interior of the polar caps."

This has been a very successful mission and all I can say is congratulations to all those scientists and engineers who pulled it off. I'm looking forward to another 73 TB of data!

Last Saturday I was listening to WHYY's broadcast of Studio 360 which is a great show covering the gamut of the arts. And on this particular day there was a nice piece on the rovers' PANCAM instruments—the two-eyed cameras on the "head" of Spirit and Opportunity. I have to admit that I get so buried in the science aspects of imaging that I don't always step back to just admire the view; there really is a majesty in these images. The best part is that, since the cameras are mounted at about human-eye-level, the views are very close to what you would see if you were standing there yourself.

Fortunately, we have Jim Bell in charge of the project and he sees both the science and the art. He's even published two books collecting and discussing some of the best images from the missions. Postcards From Mars that tells the story of sending the rovers and their first views, and Mars 3-D that is a collection of the stereo-images, complete with built-in red/blue glasses. Jim was interviewed for the Studio 360 piece which you can hear, and download, from their web site.

In other rover news, the next one to go, the Mars Science Laboratory has been delayed. It was intended to be launched in December 2009 but various technical difficulties have cropped up and now it is being scheduled for the next launch window in 2011. Of course, this means a tightening of the budget for other Mars missions, and a possible push-back of other 2011 probes, but as of yet nobody knows to what extent. It also means there will be no US Mars mission for the 2009 window.

One of the instruments on the Mars Reconnaissance Orbiter that seems to have not garnered a lot of press is the Shallow Subsurface Radar or SHARAD. I guess that's because it doesn't return a lot of pretty pictures although the radar information it does return can be put into picture form.

SHARAD sends out a high-frequency pulse of radio waves that penetrate the surface. What happens to those waves (if they return, how they return, and how they are modified) is a complex function of what they bump into on the way down. In this way, the SHARAD team intended to look for subsurface ice layers—layers deeper than the Mars Odyssey Gamma Ray Spectrometer (GRS) could measure.

One of their prime target were these lobate debris aprons in the mid-latitudes (e.g. 35–65°). They had been first photographed by Viking orbiters and they were curious in that they appeared to have smoothed out features that one would expect of flows that were lubricated by water or ice mixed in them as opposed to just being massed of rock and boulder that had slumped.

Well, word from the SHARAD team is that in these regions, they get far more radar return than if there was just rock. The measurements they make imply a very thick layer of ice below a "thin" layer of debris (if the debris were removed, the ice would begin sublimating). Not only that, but the extent of the ice goes on for miles.

So what are buried glaciers doing so far south? It turns out that the axial tilt of Mars, currently about 25° (very similar to Earths 23.5°) wobbles significantly. The technical term for this motion is nutation and it is tied very closely to climate change.

On Earth this polar wobble is fairly small, about 2.4° but it, combined with other orbital variations, leads to a cycle of ice ages on an about 100,000 year period. Since Mars doesn't have the stabilizing effects of a large moon (due to a physics property known as conservation of angular momentum—why spinning top is harder to knock over than one that isn't) its axial tilt can swing wildly from about 15° to 35° which, combined with its significantly more elliptical orbit, can lead to great swings in climate.

Based on models and an understanding of climate at a general level, back when Mars had a much larger tilt it could have supported vast areas of glaciers down to low latitudes. If these then get covered up by dirt and debris, they could survive that way now that the axial tilt is much less. So these results appear to confirm models of early Martian climate.

I'll resume some discussion of the DPS presentations shorty; I'm currently at a workshop on Mars Atmospheric Modeling which is really interesting and I'll share some of what I'm learning here. It's amazing how much "we" really do know and understand about the physics of climate!

In the mean time, I thought I'd let everyone know that the Mars Phoenix mission had officially ended.

Since it is at such a high latitude, as autumn progresses the days get shorter and the Sun gets lower in the southern sky, just as it does for folks in northern Canada, Scandinavia, and northern Asia here on Earth. This means less sunlight to charge the batteries and thus less overall power to keep the craft operating. The engineers had begun a program of systematically shutting down heaters and instruments in order to keep it running as long as possible. But on 2 November, they lost contact with it and as of yesterday, with no further contact, they declared the mission over.

I'll have more on the incredible science that has been done—which I learned about at the DPS meeting—soon. I've got to get some breakfast and then head off to conference sessions.

We've known for a long time now that there is water on Mars. Well, more specifically, we've known there is water vapor in the atmosphere and water ices at the poles and in the clouds. In the late 70's the Viking 2 lander confirmed surface frosts existed. The big question about water is not whether on not its there, but whether or not liquid water existed and if so, how long.

As science and technology progressed scientists been able to confirm various minerals on Mars that, at least on Earth, usually form in the presence of liquid water. We call these hydrated minerals and many of them start out as other minerals but then get chemically altered by water. Typically, the water breaks up into H⁺ (hydrogen) and OH^- (hydroxyl) with the latter bonding to the mineral. Other times, the entire water molecule gets stuck into the mineral. One important class of these is the phyllosilicates.

Silicates are minerals that are derived from the SiO₄ tetrahedral molecule—it's sort of like methane but with silicon and oxygen instead of carbon and hydrogen. This makes sense if you look at a periodic table; silicon is in the same column as carbon which means it behaves similarly in general chemistry—this fact is what leads to sci-fi writers talking about "silicon-based life". You can stick these triangular pyramids together into a huge single crystal where each Si shares all of its O's with another Si, so you have Si + 4 "half" O's or SiO₂ which is quartz. You can also connect them into pairs or chains or double chains or sheets or even rings. The sheet form is the phyllosilicate group that contains things like mica and clays.

So one of the DPS talks by Eldar Noe Dobrea, now at the Jet Propulsion Laboratory, discussed his study of an outcrop of phyllosilicates in the highlands around Mawrth Vallis. Using new high resolution images and spectra from the Mars Reconnaissance Orbiter he hypothesizes that different types of phyllosilicates weren't put there over different times, but rather that the layering suggests a primary layer of iron and magnesium phyllosilicates was put down and the the upper level interacted with liquid water leaching out some elements and leaving behind aluminum phyllosilicates. Eventually, this was covered up by some other rock and then parts of this layer eroded away by the wind "sandblasting" some parts of this top layer.

A second talk on hydrated minerals by James Wray was about trying to infer formation times and conditions of sulfate minerals. Sulfates tend to form out of the salts left behind when water containing them evaporates—more evidence of liquid water on Mars. However, in this case his work seems to indicate that all these sulfates formed during the earliest geologic period on Mars, called the Noachian Epoch which ended about 3.5 billion years ago.