by Rod Pyle
The images of Victoria Crater provided another benefit—to assist MER mission planners in their guidance of Opportunity into Victoria Crater. These were all examples of multiple Mars missions working together, something never before accomplished on such a scale. And not only did they provide data from different perspectives; these multiple machines were actually able to help each other. Mars exploration was becoming a team sport.
There is one more area of discovery to be attributed to MRO: the observation of “real-time” or near-real-time events. One such occurrence was an avalanche seen by HIRISE in February 2008. A sloping hillside in Mars's northern regions had a huge dust cloud billowing from the base of the slope, clearly demonstrating a huge movement of material to the base of the incline—an avalanche. The camera was actually targeting a dune field nearby as a part of its regular survey of carbon dioxide frost. The avalanche was a serendipitous capture, only noticed later when a mission scientist was reviewing the images. It may have been caused by water ice being exposed, suddenly sublimating, or evaporating, and undermining the soil.
Another new feature was spotted via a comparison of images taken by MRO and Mars Odyssey. Again, it was a team effort. MRO's wide-angle context camera had snapped an image in 2008 in which a small black dot was spotted. No big deal. But when compared to an image from Mars Odyssey from 2006, there was no such spot. Excited researchers aimed MRO's HIRISE camera at the same place and found a small, otherwise insignificant crater about eighteen feet across. The hole itself was not what was spotted by MRO—it was darker material exposed by the shock of the impact, which blew the overlying, lighter surface away. They had spotted a brand-new crater. While not hugely significant, it was a fun moment…and there is always room in science for some fun.
The Mars Reconnaissance Orbiter has, to date, returned more data than all the missions launched past the moon. It is a huge amount of scientific material, and it has been estimated that if just the HIRISE images were shown consecutively for ten seconds each, it would take over four years to view them. So make sure you are well-stocked for snacks.
And MRO isn't done yet. Stay tuned.
From his home near the foothills of Southern California, Richard Zurek can look toward JPL and see the object of his study, some forty years since he began to study it: the air. When not enjoying the view, he hikes the local mountains. But his consuming interest is, of course, Mars. And he has been a part of seeing Mars as it has never been seen before, through the high-fidelity eyes of the Mars Reconnaissance Orbiter. His inspiration to study Mars would sound familiar to many of his compatriots at JPL…the flight of Mariner 4.
“I was in high school at the time, the Mariner 4 flyby. Now, as recently just a year or two before Mariner 4 was launched, you [could] still read papers on the dark areas, what did they represent, was it vegetation, what was this planet like? And at [that] time they overestimated the amount of atmosphere that it had…. [They estimated] the atmosphere to be ten times thicker than it really was.
“Mariner 4 was the first to see that this thing was about 1 percent of the Earth surface pressure…. [T]hen [there was] the challenge of orbiting a spacecraft around the planet; Mariner 9 succeeded in doing that, becoming the first earthly object to orbit a planet other than the Earth itself. So first we have Mariner 4 and say, ‘maybe there's nothing here,’ then the flybys for 6 and 7 and the controversy on whether or not they detected chlorophyll, and it turned out to be another weak indication of carbon dioxide, so arguments about Mars—what is it like, what it's not—continued.”1
Mars was proving to be more adept at hiding its secrets than anyone would have guessed, especially after the dramatic results of Mariner 4. Mars transformed from a planet populated (in the minds of some) by an advanced civilization of water-hoarding civil engineers to a dry desert wasteland overnight. But then the follow-up flights made it clear that things were not so simple. The highlight of this may have been when Mariner 9 arrived at Mars, only to see a huge planet-girdling dust storm. But sticking out of that storm were the peaks of three huge volcanoes on the Tharsis Bulge. Mars was revealing its past slowly, making us work for it.
“This happened to us a couple times, certainly with Mariners 4, 6, and 7, and then Mariner 9 changed the idea again, both in the sense of ‘yes, there were mountains, and there were vast channels on the planet,’ and ‘yes, the atmosphere was thin, but it was vigorous enough to be able to sustain regional dust storms into a global haze that could blanket the entire planet,’ and so Mars sort of came alive again.”
Inspired by JPL's missions of Mars exploration, Zurek decided to aim for the stars: “I went to the University of Washington, and mathematics graduate school, but I was pretty certain as I soon as I got there that I didn't want to be a theoretical mathematician. I chose the University of Washington because I knew they had a department of atmosphere and science that took people with math and physics backgrounds. I had that, [so I] transferred into that department, and it just happened that they had a new professor. This new professor had an interest similar to what I'd had as a kid, so I was fortunate. Not only was he a new professor at the school, he had an unfilled assistant role that he needed to fill, and so I walked in and I was a good match.
“When you get to a mission like MRO, which came along after the great discoveries of Mariner 9 and the Viking orbiters and landers, things kind of build up incrementally. But [the results were] profound, and I think a couple of the things really impressed me. The ground is so oddly patterned. There were polygons, and fractures; it just looked like a surface that has had many places that were once wet and had since dried out. It's like looking at mudflats, only the scales are bigger than that, and I think that tells us two things. First, there's been these drying out episodes, that there's still ice in the surface of the planet, and the other one is of course the composition measurements that have indicated that you have these areas where these minerals are present. When you put that whole picture together, what you see is that what you're looking [at] is an ancient surface that's been covered up.
“With the ancient surface, we were looking at a lot of water interaction in it, because it altered the composition of the surface; actually changed the material into sulfates, and carbonates. Seeing [this] early history, and trying to figure out just how widespread it was is interesting. [However] the fact [that] there are different minerals indicating different kinds of watery environments, some of them more acidic than others, to me, once again increases the potential that Mars might have developed life somewhere.”
Every mission has its highs and lows. MRO was no exception, and coming on the heels of the twin failures of Mars Climate Orbiter and Mars Polar Lander, the stakes were still high, even years later: “Just getting into [Martian] orbit, getting safely into low-altitude orbit, was a high point. Scientifically, seeing these constant changes of Mars climate from an ancient period [when] water was active, there must have been water surging through the ground, and in salt lakes, to form these mineral deposits that we see today. And then you have the more recent climate change…in the polar caps, and the buried ice deposits. It's all very interesting. Of course, as an atmospheric scientist, dust storms are still a big question. Why do some storms get huge, [involving a] large fraction of the atmosphere, and at other times we only have [a small one] out of three Mars years?” These and other questions were nagging Zurek when the MRO entered its science orbit, bringing its revolutionary imaging capability to Mars.
“That's what resolution does for you. When you're looking at a lower resolution, you don't see the variations that are there; they are fuzzed out by the inability to resolve. [At] the scale in which we're now seeing the planet, the colors [can be] stretched so we can see the variations. We do that because it tells us different things, the bluer materials are often the sand-covered things, the white-zoned areas are often things that get altered by being in contact with water.”
The resulting images are truly magical and have a beauty all their own. MRO br
ought a new dimension to the visuals coming back from the Red Planet: “The principal investigator of the high-res camera says that one of his prized moments was when he was here at JPL, and he was looking for an office. Someone told to him to go to the end of the hall where the abstract painting was, and to turn left. So he walked down the hall, and the abstract art turned out to be his camera's picture on the wall. The beauty of seeing these different elements at high resolutions and seeing that landscape…shows that they've done a great job.”
But MRO's job went beyond basic science. It was pressed into service as a relay for the Mars Exploration Rovers, and also to help identify landing areas for the upcoming Mars Science Laboratory (MSL).
“Today they announced the landing site for MSL, it's going to be Gale Crater, which was one of the four finalists. I took great pleasure in that, because our MRO team provided the basic data by which precise selections were made, both [in] terms of the engineering safety and also in terms what interesting things are in these places.
“So, we expect a lot more in MRO. It has enough fuel to go for another decade. [The spacecraft is] working so beautifully, sending so much data back, we're looking forward to continuing for hopefully nine more years. Things are looking pretty good at the moment.”
Here's to another decade of Mars Reconnaissance Orbiter, and the secrets that it will reveal.
On sol 159, the indefatigable rover Spirit reached its first stop at the Columbia Hills. It had been dawdling, pursuing its scientific endeavors, at Lahonten Crater since sol 118, driving around the rim of the two-hundred-foot depression. Then the long drive to the hills began.
At the base of the hills, it spent a full twenty-three sols studying a feature known as Hank's Hollow, and in particular an odd-looking rock named Pot of Gold (there was no lack of imagination within the MER team). Lo and behold, there be hematite in these hills—Spirit was catching up with the discoveries of its precocious twin, Opportunity. The rock was described as looking “as if somebody took a potato and stuck toothpicks in it, then put jelly beans on the ends of the toothpicks”; a colorful way to describe the oddly shaped, softball-sized rock. The process of formation was thought to be water based, especially because hematite is usually found in the presence of water. But there are chemical processes that could result in such a feature, so it was studied exhaustively.
After investigating with its “sniffer,” the rover repositioned itself (which took several sols, due to the slippery and treacherous nature of the surrounding soil) and ground away at another side of the rock with the RAT. Whatever formed this rock took a long time and was not a mild process. It was harshly eroded and knobby, and the nodules on the rock appeared to be cousins to the “blueberries” found by Opportunity, half a planet away.
Spirit left Pot of Gold to investigate more strange-looking rocks nearby. Dubbed Cobra Heads, these rocks, as did Pot of Gold, appeared to have come down from higher up in the Columbia Hills. The Cobra Heads were probably the cores of more normal-looking rocks that were left behind when the softer surrounding layers wore away to leave the harder interior behind, silently hissing at Spirit.
At this point, while still very capable, Spirit's spirit was being dampened by some problems. The mechanical arm was suffering from a bit of dysfunction in one of the motorized joints. The radio was having issues, making the reception of commands sent from Earth difficult. And the front right wheel was draining far more electrical current than the other five, and this drain was increasing. It was an indication that the gearing that drove that wheel was failing, probably due to sand, dust, and grit having crept inside. To make matters worse, the season was advancing and Spirit was receiving less sunlight on its solar panels every day.
Still, the rover continued its labors, taking a northerly course along the base of the hills, investigating as many rocks as it could along the way. Then, on sol 239, the rover powered down for solar conjunction, when Mars is on the far side of the sun from the Earth and out of communication with JPL.
When we last left Opportunity, it was embarking upon the long and lonely journey to Endurance Crater. On April 30, 2004, the mammoth feature loomed into view. About 430 feet across, Endurance Crater is named after the ship captained by Sir Ernest Shackleton on his epic voyage to Antarctica. It was a fitting name for a landmark so prominent in Opportunity's life.
The rover paused at the lip of the crater, taking its time to survey the sixty-foot-deep interior. As with most impact craters, Endurance ripped through the surface of the planet, exposing the strata below. Finding a suitable point of entry, Opportunity, shaking its metal arm in the Great Galactic Ghoul's odious face, took the plunge and began the risky descent into the crater. The point of entry was named Karatepe (“Black Hill” in Turkish), and the rover took a tentative drive inside the crater rim, then stopped and backed out, just to make sure that it could. It was a bit like watching Neil Armstrong on that July night in 1969, coming down the ladder of the Lunar Module, then before setting foot on the moon, hoisting himself back up the rungs just to be sure that he could.
Nobody wanted Endurance Crater to be the final resting place of Opportunity, though everyone involved knew that it might be. As it turned out, the rover spent the next six months driving around Endurance Crater. The first stop was a patch of exposed bedrock strata. Opportunity got up close and personal with the outcrop and sampled each layer of the strata as carefully as possible. It noted that both the texture and the chemistry of the rocks varied with depth, with the lower layers being the oldest, just as on Earth. And both magnesium and sulfur declined in abundance as the rover's sniffer went from the upper (younger) to the lower (older) rocks, once again confirming the presence of (and alteration by) water in the past.
Moving on, more “blueberries” were seen in the rocks and scattered about the crater itself. Soon the same solar conjunction that idled Spirit forced Opportunity to cease operations for two weeks as the two rovers waited out the silence from Earth.
As Mars moved back within range of the ground controllers, Opportunity moved to a rock unlike anything seen in the Meridiani Planum area. Dubbed Wopmay (after a semifamous Canadian bush pilot), its lumpy, serrated surface promised more signs of alteration by water. More “blueberries” were found here as well, and the sightings of these was becoming almost boring…almost. Again, signs of a watery past.
About this time you might well be wondering just how much evidence of water in Mars's past a planetary scientist might need. It's a good question. But with such an arid planet meeting virtually every spacecraft sent there, and the promise of life, past or present, dangling on this finding, there could be no such thing as too much evidence. Not yet anyway.
Tellingly, the investigation of this rock corresponded with the publication in a scientific journal of the results of the MER missions' efforts to find evidence of a watery past on Mars. The paper included the efforts of 122 authors and was confidently published in Science, perhaps the most important journal appropriate for this kind of news. This made it official: there has been large amounts of water on the Red Planet, and the evidence would just keep piling up. Besides the “blueberries” and various chemical residues, there were cavities, the oddly named vugs, in many of the rocks investigated that were indicative of crystals that had been dissolved over time by water as the rocks lay immersed. This finding, wondrous in the extreme, told of not just large amounts of H2O, but also that it had existed as a liquid on the surface of the planet for a long time in the past. And this indicated a thicker, warmer atmosphere way back when.
If there was a downside, it was that this water would have been salty and acidic and not overly friendly to life. But life finds a way, as it has in so many hostile environments on our own planet, so this was far from a deal breaker.
Returning to Spirit and its numbing slog across the Gusev region, the rover had found something interesting (well, it was all interesting, but this was a major find). The mineral in question was goethite, kin to the jarosite found earli
er by Opportunity, and it was another sure indicator of water sometime in the past. The beauty of this mineral is that, unlike hematite, which usually forms in a watery environment, goethite forms only within such an environment. Anyone sweating out the declarations in the Science article could take a deep, relieved breath.
Making spirits brighter, to coin a phrase, the worrisome friction buildup in the front right wheel was diminishing. Nobody could be sure why without a mechanic's house call to Mars, but the fact that controllers had been “babying” that wheel may have helped. All they knew for sure was that it was drawing less current, and that was a good sign of mechanical health.
Spirit now ascended a formation known as Husband Hill (named after the NASA astronaut who died in the shuttle Columbia's demise) in an effort to ascertain how high the water might have once stood. The hope was that it was not merely an underground store but might have pooled on the surface for some length of time, as it appeared to have done at the Opportunity site. Confirmation was the name of the game.
Then Opportunity, never content to allow Spirit to bask in the limelight for long, found something wonderful.
Ascending out of Endurance Crater, the rover had spied its own heat shield from its fiery descent onto Mars. Scientists wanted to examine the structure to see how it had been affected by its hot journey through the Martian atmosphere, and the results were interesting, if not remarkable. Nearby was an interesting rock, dubbed, appropriately enough, Heat Shield Rock. As the rover neared this stone, it began to look eerily familiar to some on the ground, and very unlike the others they had been investigating. Soon, it was confirmed. Opportunity had found the very first meteor found on another planet. Where it came from (besides space) and when it arrived would remain a mystery, but finding it was excitement enough. And it was an iron-rich meteorite, not the more common “stoney”-type. Of course, meteorites are found on Earth, so the rock itself was not the real news. What it would reveal about the area on which it sat was the interesting part. It could help to answer the question about whether or not Meridiani Planum was gradually eroding away as so much of Mars is, or if it was still being built up in geological terms.