Buttoning up the Mars Orbiter Camera science investigation
Posted by Emily Lakdawalla
15-01-2010 16:21 CST
The science team for Mars Orbiter Camera, or "MOC" (pronounced "mock") has just published a paper that attempts to summarize an investigation that spanned more than two decades. MOC's first image of Mars was taken on July 2, 1997, while Mars Global Surveyor was still more than 17 million kilometers from Mars orbit insertion; the final image was taken on October 17, 2006 as part of MOC's routine weather monitoring, a few weeks before contact was lost with the orbiter, on November 3, 2006. Between those two dates were nearly ten Earth years, and, more importantly, more than four Mars years, of nearly continuous observations, including 62,571 images from MOC's wide-angle camera and 97,097 from the narrow-angle camera. The wide-angle camera covered all of Mars nearly every day of the mission, while the narrow-angle camera provided high-resolution shots covering 5.45% of the planet's surface.
Apparently the MOC team is working on a ginormous tome of a "MOC Final Report" that will "take several more years to complete"(!). This paper, "An overview of the 1985-2006 Mars Orbiter Camera science investigation," is intended as a sort of executive summary of what that final report will be. As such, it contains most of the information that will be of most interest to anybody who's reading this blog entry, and I definitely recommend you download and read it. Because of its overview nature it's not too technical, and it contains lots of interesting anecdotes.
For example, I didn't realize that, when it was originally selected as part of the Mars Observer payload in 1986, the MOC was considered the "last on, first off" instrument -- in other words, if it was found necessary to remove a science instrument from Observer (for cost, mass, or other reasons), it would be the first to go. At least, it was last on, first off until 1988, when it incorporated the Mars Balloon Relay, provided by the French space agency CNES, which "would relay data from balloons planned to be deployed at Mars by France and Russia on a USSR mission to launch in 1992." Because of this bit of international cooperation, MOC became a "launch-critical payload element." Following the loss of Mars Observer, when a new MOC was built for Mars Global Surveyor, it retained the Mars Balloon Relay as the just plain Mars Relay, which wound up relaying data not from Mars balloons but instead from two rovers -- a total of 7680 Megabits of rover data came through the Mars Relay on MOC. Because it used the MOC image buffer, relaying rover data resulted in a halt of MOC science; the same is not true when Odyssey relays rover data.
Here's another section that readers of this blog should find especially interesting:
Starting in August 2003, the MOC team began soliciting broad public and science community suggestions for MOC narrow angle camera targets through an interface available on the Internet. The MOC Public Targeting Program resulted in a total of 4,636 requests, 1,086 of which were satisfied by acquisition of one or more narrow angle images (and, usually, a red wide angle context frame) by the time of the abrupt end of the MGS mission. About a quarter of the public requests came from members of the Mars scientific community, but this resource was generally underutilized by Mars scientists. A little more than half of the requests came from a single individual, a member of the general public. Some of the science community requests resulted in publications....One member of the public who [participated in the target request effort expressed his experience in a letter to The Planetary Society's The Planetary Report, saying, "For two years, I made suggestions and received many pictures back from Mars. It was one of the most exciting ventures I've ever attempted. It was like a football fan being able to run a few plays in the Super Bowl."
Another interesting tidbit: The MOC on Mars Observer acquired a total of four images of Mars on approach: two through the narrow-angle camera, and one each through the red and blue wide angle cameras (the last two show Mars as only one pixel). The article states that "The PDS elected not to receive this data." That seems like a loaded sentence but I can't interpret the subtext. Here's one of the two narrow-angle camera images of Mars from Mars Observer; the whole Mars Observer imaging data set, all four pictures, is available here, part of the supplemental data provided with the article.
There's a highly detailed mission timeline that describes various things that affected the MOC experiment, both negatively, like problems with the spacecraft and weather events on Mars, and positively, like when they developed new techniques that permitted them to capture images off-nadir and with extra-high resolution.
The timing of the final images is kind of interesting. The last images taken by MOC were on October 17, just before the spacecraft went into solar conjunction. In fact, the very last images were very strongly affected by the spacecraft being so close to the Sun in Earth's sky. They were taken and relayed normally by the spacecraft, but it was difficult for the DSN antennae to receive the signal and the data as received on the ground is really really cruddy. I dug in to the PDS to retrieve the very last image of Mars taken by Mars Orbiter Camera, and it was this one; I checked with Ken Edgett and confirmed that yes, this is how the image appears to him, too. This is what happens when you try to transmit data too close to the Sun!
As garbled as it looks, there is a tiny bit of "sense" in the image, a small area of cratered terrain near the top. Ken tells me this is in southern Terra Sirenum near the Copernicus basin.
The paper goes on to detail the ways in which MOC changed our view of Mars -- that is, its successful science. It can basically be summed up as saying that MOC transformed the view of Mars, formed from Viking data, as, essentially, the Moon with a brief but long-past period of water activity that slightly modified Mars' uppermost surface, to a Mars that has had a much longer, more dynamic, and more complex history of somewhat Earth-like sedimentary geology, with some of these sedimentary processes continuing down to the present day. Yet Mars is still not Earth; the sedimentary geology changed Mars' surface at a rate much lower than it operates on Earth, such that impact cratering, volcanism, and sedimentary processes all have somewhat similar importance in terms of how they shaped Mars' surface.
On top of the geology, MOC provided a resource for continuous monitoring of Mars' weather over four Mars years, and what they learned is pretty cool. I don't read many publications about Mars weather because, to be totally honest, reading about atmospheric stuff makes me yawn violently. But there were several statements in the weather section that made me sit up and take interest. For instance, they presented a fascinating set of observations where they saw the same storm appear at the same time (calendrically speaking) in the same place on Mars for four Mars years straight. Also, they drew a careful distinction between planet-encircling dust clouds (which do exist) and "global dust storms" (which don't). The distinction has to do with the violence of local weather. Local dust storms with dust-raising winds can loft dust to where it gets transported around the whole globe; but the whole globe is not experiencing dust-raising winds in those global dust events.
All in all, a fascinating -- and relatively easy -- read; go check it out for yourself!