Second Opportunity, Safe on Mars
Two For Two
Opportunity Lands on Mars
|In Pasadena, Califormia, project engineers, Rob Manning and Wayne Lee, from JPL look on with California governor (center) and the former Vice President Al Gore (back right)
Credit: NASA TV/JPL
Opportunity mission engineers reported at 9:06 pm PST Saturday night that the spacecraft had landed successfully on the Martian surface.
|Principal investigator, Dr. Steve Squyres, Cornell University, describes the Meridiani landing site and plans for exploration of the flat, basaltic plain. Squyres speculated on Sunday morning that the Opportunity rover may actually be in a shallow crater or depression, if the layered mound in front of the rover is a remnant of the crater rim.
Squyres first addressed the rover’s location, some 20 to 25 kilometers downrange from the spot scientists initially targeted.
"The place that we thought we were heading, which was a little bit long [past the original target], was very bland looking. We’ve overshot that by a significant amount and I think we may be into some fairly interesting stuff, in terms of geologic variety, different kinds of materials present [that are close enough for the rover to reach]".
First "we’ve got to figure out exactly where we are. There may not be a whole lot of landmarks on the horizon in a place like this. It’s going to be an interesting challenge to figure out where we are and then decide which direction to go, but we’ve got time".
"The hematite concentration actually increases toward the east [the direction in which Opportunity is believed to have traveled past the original target]. So we should be deeper into the hematite where we came down than we would have been otherwise".
"We were contemplating a TCM [trajectory correction maneuver, or course correction] that would have nudged us back to the very center of the ellipse. If you look at the hematite region, there are some areas that are more geologically varied than others. There’s this hematite-bearing unit, and then there’s something else beneath. And the something else beneath it pokes up in some places but not in others".Credit: NASA/JPL
Opportunity descended through the martian atmosphere, then bounced and rolled to a stop exactly according to plan. Three weeks earlier, Opportunity’s twin sister, Spirit, also landed flawlessly.
Unlike Spirit, however, Opportunity came to rest on its side. Although the preferred landing orientation is right-side-up – Spirit landed this way – the rovers were designed to accommodate landing on any of their four sides.
While former Vice President Al Gore and California Governor, Arnold Schwartzenegger, looked on from the Jet Propulsion Center’s mission control room, flight controllers celebrated the passage of the Opportunity rover through its critical entry, descent and landing phase.
Local time on Mars was about one-thirty in the afternoon.
Simple tones received in the moments following this approximately six minute phase between entry and landing showed the lander in a no-fault condition.
The lander struck the surface of Mars at approximately two to three G’s (or earth-equivalent gravitational acceleration units). The landing site is the highest altitude (from the outer atmosphere to the surface) ever attempted by NASA, and approximately a mile higher (4500 feet) than the Spirit site inside a crater and potentially ancient lake bed.
Because it lands inside a protective shell shaped like a tetrahedron (or pyramid), it stands a one-in-four chance of landing on its base-petal. This was the case for both Pathfinder and Spirit, but Opportunity arrived on its side. This state is referred to as "side-down".
|Image from Opportunity of surrounding surface at Meridiani.
By sequencing the order in which this tetrahedral shell opens, like a flower petal, the unfolding called ‘reverse robotic origami’ eventually will right the lander to its nominal base-petal down configuration to drive off later in the mission. First events to happen then after retraction of the airbags is the opening of the rover’s solar panels, which allow the batteries to recharge.
Near real-time engineering data was collected using a constellation of orbital relay stations, which concluded their support for the landing phase with a sign-off, "Welcome to Mars, Again."
The landing site, called Meridiani Planum, is a flat plain, without hills. The region is expected to be a good engineering landing site becaues the rock coverage is less than eight percent, which makes both landing and driving feasible. Meridiani is of scientific interest mainly because it is one of two areas on Mars with unusually high concentrations of an aqueous iron-containing mineral called hematite.
Opportunity’s landing site is on the opposite side of the planet from Spirit.
Meridiani Planum was chosen as the landing site for Opportunity because the hematite was detected there in large quanities. Hematite is an iron oxide that, on Earth, typically forms in the presence of water. The mineral was detected by the Thermal Emission Spectrometer (TES) onboard NASA’s Mars Global Surveyor (MGS) orbiter.
More than one process could have formed this hematite. It might have formed as the result of hydrothermal activity in association with volcanism, in hot water. Or it might have formed as sediment carried by water flowing across the martian surface.
The instruments carried on Opportunity will enable scientists to determine which process was responsible for the hematite at Meridian Planum, and thus to learn about the history of water on Mars.
The question scientists hope to answer, says Ray Arvidson is, "Has water been on the surface for a long period of time in the past, as lakes and rain systems and rivers, or has most of the [water-related] action been on the inside, a frozen surface but [hot] water circulating in the interior?" Arvidson is the deputy principal investigator for Spirit and Opportunity.
The science team will look for several clues to help unlock the landing site’s secrets. One important clue will be what other minerals are present.
|A wrapped panoramic image of Opportunity, as if taken from above the rover. At the top is visible the layered mounds, which principal investigator Steve Squyres spontaneously declared at first sight to be good candidates for early science driving. The same mound is shown in the top banner.
Squyres said: "Where we targeted the original center of the ellipse was a place where there was a lot of this poking up stuff. It looked like we were going to land a little bit long [past the desired spot], which would have taken us into a place that was much more uniform – it’s just the hematite-bearing stuff without a lot of the other stuff".
"As it is, we overshot that too and are back into [yet another] region that looks like it’s got more of the variety. So where we ended up and where we originally put the center of the ellipse may both be equally good".
Phil Christensen, the payload element lead for Opportunity’s Mini-TES instrument puts it this way: "The hematite itself is not particularly interesting. We know it’s there; we’ve mapped it. So what? I argue that it’s a beacon that says, water was here, okay? And so now if you’re looking for the most interesting places to go land, there’s a beacon that says, hey, there was mineral evidence of water here, go there. And you look in detail and see what else is there."
One such mineral has already been detected in Meridiani Planum. Oddly, it was detected by two of the earliest missions ever flown to Mars, Mariner 6 and 7. These spacecraft, which flew past Mars in 1969, carried infrared spectrometers, instruments similar to TES and Mini-TES.
Wendy Calvin, a member of the MER science team, recently examined the data recorded by the Mariner spacecraft and found the signature of a water-bearing mineral other than hematite. She was unable to identify it, however.
It’s not a typical silicate or carbonate, says Calvin. If it were, TES would have been able to detect it. Calvin believes it is probably a type of clay known as ferrous silicate.
Ferrous silicates are clays that, on Earth, "were formed before there was a lot of oxygen in the atmosphere," says Calvin. "They’ve got lots and lots of iron in them."
This is consistent with what is known about Mars’s atmosphere. "Mars doesn’t have a lot of oxygen in the atmosphere – never did. Early Earth didn’t," either, says Calvin.
According to Christensen, Opportunity’s Mini-TES instrument should be able to identify Calvin’s mystery mineral. This will help scientists determine how Meridiani Planum’s hematite formed.