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Planetary News: Mars Exploration Rovers (2005)

Mars Exploration Rover Update

Opportunity Discovers Iron Meteorite as Spirit Finds Peace

While the Huygens probe that landed on Titan last week made history and grabbed the global spotlight, the Mars Exploration Rovers trekked onward, making a little history of their own.

At Meridiani Planum, Opportunity discovered that one of her targets -- a pitted rock the size of a basketball -- is actually an iron meteorite -- making this the first meteorite of any type ever identified on another planet. "This really came as a surprise, Steve Squyres of Cornell University, principal investigator for the science instruments on the rovers, said in an interview with the Planetary Society yesterday. "I do everything I can to have us be prepared for every reasonable eventuality, but stumbling across an iron meteorite is not something I saw coming." But from now on, as the rover continues her journey southward toward her next major target, a circular feature the MER team calls Vostok, she'll be stopping to inspect a few more targets that might be similar to see if there are more meteorites out on the Meridiani plains.

Meanwhile, at Gusev Crater, Spirit got stuck for a few days during her climb up the Cumberland Ridge in the Columbia Hills. The going has been tough. The soil is sandy and the rover has been slipping backward, sometimes as much 100%. During one slide, she picked up a rock that locked up one of her wheels, which left her, basically, stuck in one place for five sols.

If it seems that Spirit cannot quite catch up with her twin in terms of accomplishments -- if it seems she is forever struggling with something as Opportunity revels in the limelight with some new find or feat -- hold on. "The exciting rover these days is Spirit not Opportunity," Squyres declared yesterday. Since the team managed to maneuver lose the rock, the rover has been making good progress toward Larry's Lookout, a flattened waypoint area on the route up Husband Hill. Along the way, she found Peace, which as Squyres told it, was the most unusual rock seen on the mission so far. Spirit will be at one with Peace this weekend, examining it up close with her suite of investigative tools.

Both rovers are reported to be in "excellent health," although both Spirit and Opportunity have suffered from bouts of low power. It's the time of year when dust storms begin to kick up, whipping sand up into the sky. Storms have already hit both Meridiani Planum and Gusev Crater, and there is another one currently underway at the Gusev site.

"We're not expecting major dust storms right now, but this is the time of year when local dust storms are common in many parts of the equatorial regions of Mars, including both of our landing sites, and we're starting to see them," Squyres said. These storms can impact the rovers' output. "[They] increase the opacity of the atmosphere and that makes the sky cloudier and that means we get less Sun on the solar panels which means we have less solar power, so we have to deal with temporarily reduced solar power while one of the storms is going on," he explained. "We knew this was going to happen to us if we lasted this long -- we've just got to deal with it."

The Spirit operations team is now closely monitoring orbital images for dust storms so they can get a sense for how they have to adapt their science investigations. "When these things happen, we have to tactically adjust our plans to do less with the rover each day, because we have less power, and then we wait for the storm to blow over and then we go back to normal," said Squyres.

Spirit from Gusev Crater

With one eye on the weather, Spirit has slowly been continuing her journey up the Cumberland Ridge in the Columbia Hills, but progress has been tediously slow. The rover has been encountering many rock obstacles and patches of soft sand that are causing her to either slip or dig in. Basically, she's been in roughly the same spot for the past 30 sols.

Just before her first birthday, January 3, Spirit got stuck in place by a potato-shaped rock that was locking up her right rear wheel. "We do have software on board which monitors for just that condition, a high-current condition and it just stopped any further driving from happening after that," explained JPL's Rick Welch, Spirit mission manager. It took engineers five days to maneuver the rover in such a way that she could dump the little rock - something the team confirmed by comparing before and after images that the rover took with her rear hazard-avoidance camera.

Spirit then continued on her way and made it to a new target -- a rock called Champagne. The rover spent a couple of days there taking a detailed look at it using her full suite of investigative instruments. Since the rock in the wheel episode, however, the engineers have been extra careful to really watch the slippage as she goes. If the wheels slip too much, engineers stop the drive to avoid the possibility of picking up another rock as the rover spins and digs with her wheels.

Despite the recent increase in opacity from the first local dust storm, Spirit's energy level, happily, faired well. The rover had adequate energy -- with a safe margin -- to continue normal operations, and during the past week has logged a number of very successful drives. "In the past week, we completed two shorter drives for a total of about 20 meters and both went pretty well, reported JPL's Rick Welch, Spirit mission manager. "We were down below a 15% slip, which in climbing the 15-20-degree slope here is pretty good. It indicates we're on pretty solid footing."

The rover has also found Peace. "We were making pretty good headway towards the lookout and then saw this thing and went -- 'Whoa!'" Squyres said. "I don't know what it is yet but it's fascinating." At the moment though, Spirit is hunkering down for the second local wind storm that's raising the dust at Gusev.

"Dust storms are more common this time of year, but the real dust storm season is still a couple months from actually starting and that's when the more regional and global storms happen - the things we're seeing now are small, local dust storms," Welch noted. Even so, he added: "This is the worst we've see since we landed."

Atmospheric scientists describe the differing opacity levels using a numbering system, where 1 is okay, but much past that and things go from hazy to downright dark. "When we first arrived, the atmospheric opacity was just under 1 and Wednesday our number was 1.3. After landing we were below .5 for a long time and then in the past month it started to go up, averaging .8, and then we saw this rapid rise up to 1.3 in the last couple of sols."

Although there is no major concern about Spirit's well-being, this is new territory. "We have not been on the surface with solar powered rovers in dust storms," Welch pointed out. "Our last experience with dust storms was Viking 25 years ago and those [landers] were nuclear-powered so it didn't have the same effect."

Given the storm and resultant rise in the atmospheric opacity and reduction in solar energy, Spirit will likely stay put at Peace for the next five or six sols. From the way Squyres tells it, they've got no reason to rush this investigation. "There's nothing I can tell you now for sure, but we got some microscopic images down of [Peace] that are just bizarre looking," he said yesterday. "It's very finely-layered and very coarse-grained rock and really doesn't look like anything we've seen at the Gusev site before. The only thing it even looks remotely similar to is Pot of Gold. But it's layered. It's a very strange-looking rock."

Spirit was commanded to use her rock abrasion tool (RAT) on Peace today and will follow up through the weekend with long integrations with her Mössbauer spectrometer and alpha particle x-ray spectrometer. "Now that we're not in Mars time anymore we do long, extended plans on the weekends, so we'll likely leave the rover here investigating the rock and doing long integrations through the weekend and probably won't be moving again until next Wednesday," said Welch.

Currently, Spirit is approximately about 164 feet [50 meters] from Larry's Lookout, a flattened waypoint up the Cumberland Ridge, on a route that leads to the top of Husband Hill. The rover's goal is still to reach the summit of Husband Hill. At this point, she has climbed about half way up to the highest point of the Columbia Hills, which are about 100 meters in elevation.

Opportunity from Meridiani Planum

No matter what the competition may -- or may not -- be between the two rovers, there is no denying that Opportunity keeps sending home scientific 'gems' from Meridiani Planum. For the last couple of weeks, this robot field geologist has been examining the wreckage of the heat shield she jettisoned on entry nearly one year ago. It's the first time a robot has been able to report on her own landing wreckage. And Opportunity even managed to get some microscopic images of one of the fractured edges of the debris.

Once rover completed her study of the debris, she turned her attention to a pitted rock the size of a basketball that was just about 20 feet [6 meters] to the north of the main heat shield piece. "Ever since the start of the mission, we've seen lots of little rocks on the plains - rocks we have been calling cobbles -- and we've never really gone and looked at one -- it's been on our to-do list for a long time and we figured we'd get around to it sooner or later -- and we figured they would probably be little pieces of basalt," explained Squyres. But Heat Shield Rock, as this target was dubbed, had another story to tell.

"We went [to the area] to study the heat shield of course and we actually spent a couple of days studying the heat shield before we even realized there was a rock there," Squyres elaborated. "We said, 'Yeah alright, we ought to check this out.' We looked at it in more detail with the panorama camera (Pan Cam) and realized that this is a very strange object. It had this very bizarre pitted texture. And then when we looked at it with the mini thermal emission spectrometer (mini-TES), the only thing that made sense was that it was made of metal. To mini-TES, it looks like the Martian sky, because it's reflecting the sky which is what metal does in the infrared, and so that gave us a hint it's metal and then we said, 'We've really got to check this out.'"

So, Opportunity drove close enough to Heat Shield Rock to use her Mössbauer and alpha particle X-ray spectrometers. As it turned out, the 'rock' is mostly made of iron and nickel according to readings from spectrometers - and that indicated it was actually a meteorite. The meteorite identification was confirmed last weekend. "I never thought we would get to use our instruments on a rock from someplace other than Mars," Squyres mused. "Think about where an iron meteorite comes from: a destroyed planet or planetesimal that was big enough to differentiate into a metallic core and a rocky mantle."

Rover-team scientists are wondering now whether some of those cobbles they've been seeing here and there on the Meridiani plains are also meteorites. "We've been seeing lots of cobbles out on the plains, and this raises the possibility that some of them may in fact be meteorites," Squyres said. "Mars should be hit by a lot more rocky meteorites than iron meteorites," he added. Opportunity's find does have some impact the MER team's science agenda. "It does raise the possibility that meteorites may be significantly more common than we thought -- and we had this on our to-do list anyway -- and so this sort of bumps that task up higher in priority," Squyres said.

The key is not what scientists will be able to learn about meteorites -- "we have lots of meteorites on Earth," Squyres pointed out -- but what the meteorites can tell them about Meridiani Planum. "If we only find one it may be that we just got lucky. It's very hard to extrapolate much from a sample of one. But if we do find that meteorites are common out on the plains then that would be a hint that this in fact is a surface that's being stripped," he said.

"If you've got meteorites accumulating -- which they will over time -- and sand is blowing in and burying things, you shouldn't see very many meteorites. But if you see a lot of meteorites lying around, that may be a hint that even though these things come in and hit and maybe get buried and maybe form craters, eventually the craters that they form and the sand that buried them gets stripped away, and what you get left is the meteorite sitting there," Squyres explained. "So if we see a significant number of these and we get a sense that they are pretty common out on the plains, we may be able to turn that in to some conclusions about the efficiency with which material has been eroded from the plains over time."

To date, Opportunity has driven a total of 1.3 miles [2.10 kilometers] and the rover is likely to pick up her pace in coming sols. The dust storm that descended on Meridiani a little more than a week ago has slowly receded, allowing ever-increasing solar exposure. The opacity of the atmosphere above Opportunity has averaged 0.75 with a slight downward (clearing) trend over the past week. To conserve energy, the rover had been going into the DeepSleep mode every night, but with power improving, the team is planning to resume using some early-morning Mars Odyssey communication passes to reduce a backlog of unsent telemetry. "Right now the situation at the Opportunity site is very good -- the dust capacity there is quite low," Squyres reported yesterday.

The dust from these local storms, interestingly, does not cause a problem for the rovers in terms of build-up on their lenses or solar arrays. That noted, a small amount of dust appears to have accumulated on Opportunity's rear-hazard-identification camera since the rover entered the area of her heat-shield debris. It is causing a slight "mottling" in the images produced with that camera, as JPL's Jim Erickson, rover mission manager, described it, although the effect is barely noticeable on the images. It would almost not be worth mentioning, except that neither rover has really accumulated any dust on their camera lenses, making this the first, and considering both rovers have been on the planet about one year, that is worth noting.

In coming sols, Opportunity will continue her journey southward along the Meridiani plains, to an area called Etched Terrain, "hop-scotching from crater to crater," as Squyres put it. The next target is Vostok -- a circular feature that is crater-like in appearance but is unusual. But from now on, she'll be giving those cobbles a second look.

Log back on regularly for the continued adventures of Spirit and Opportunity.