Mars Meteorites, Martian Rocks Have Same Origin

The rear of the stone from the Tissint Martian meteorite is almost completely covered with a glossy black fusion crust.

CREDIT: Image © Natural History Museum, London

Scientists are a step closer to reconciling a mystery on Mars, a cosmic oddity centered on Martian rocks and pieces of the Red Planet discovered on Earth.

The composition of meteorites long suspected to come from Mars have confounded scientists for a long time.

Planetary scientists know that rocks sampled from the Martian surface are high in nickel, yet the Martian meteorites (known as the SNC meteorites) happen to have significantly less nickel than those other sampled rocks.

Bernard Wood

Now, a new study unveiled today (June 19) may help explain why the rocks are chemically different yet still hail from the same planet.

"The Spirit rover in the Gusev crater found nickel concentrations five times as high in the crater than in the meteorites," Bernard Wood, a geologist at the University of Oxford and lead author of the study, said.

A study published in November 2012 that analyzed Martian meteorites found that Earth and the Red Planet share similar formation histories.

CREDIT: NASA

Wood and his team found that oxygen is a key element that could explain the chemical components of these rocks.

The older rocks sampled by the Spirit rover (in operation on Mars until 2010) formed under more oxygen-rich conditions, while the young meteorites were crafted in a low-oxygen environment, according to Wood's model.

Hap McSween

"[In Wood's model] the upper mantle of Mars was more oxidized than the lower mantel, so when you partially melt the upper mantle, you get these ancient rock compositions and when you partially melt the less oxidized lower mantel, you get the Martian meteorite compositions," said Hap McSween, a planetary geologist at the University of Tennessee who is unaffiliated with the study.

When the volcanic liquids that produced the SNC meteorites were formed under low-oxygen conditions in Mars' interior, sulfides remained behind as the liquids rose, leaving nickel trapped in the deep interior.

The volcanic rocks were therefore low in nickel, Wood said.

The surface rocks, found in the Gusev crater, were formed in a high-oxygen environment in Mars' interior where the sulfides — together with their nickel — dissolved in the volcanic liquid.

The rocks are therefore nickel-rich.

This piece of hardened lava came from Mars. 

After being knocked off the Martian surface by an asteroid or comet, it drifted in space for millions of years, until it reached Earth and fell to the ground as a meteorite.

CREDIT: AMNH/D. Finnin

The rocks in the Gusev crater formed more than 3.7 billion years ago while the SNC meteorites date back 118 million to 1.3 billion years, Wood said. This plays into the theories scientists have about Mars' past.

"It's still consistent with one idea of Mars, which is that it's sort of wet and warm … and the atmosphere was oxidized very early on, that's certainly an idea that's been kicking around for a long time," Wood told reporters.

Wood applied his knowledge of Earth's geological processes to understand what might be happening on Mars.

"On Earth, we know that we cycle oxygen rich rocks into the Earth's interior through plate tectonics, through so-called subduction," Wood said.

"The oxidized surface materials are pushed down into the interior and so we argue that’s a plausible explanation for Mars."

Although that explanation could account for why the older but oxygen-rich rocks were found in the upper mantle while the oxygen-poor rocks came from a deeper part of Mars' interior, McSween doesn't think there is necessarily evidence to support a tectonic past on Mars.

"Although there are some suggestions that Mars might have had plate tectonics at some point, there really is no evidence for it, but this is at least a suggestion that something presumably cycled oxidized materials from the surface back into the upper mantle and maybe that's in the cards here," McSween told reporters.

MARS: Spirit rover stuck in sandtrap - new instructions prepared

Part of a mosaic of images from the Spirit rover, taken on Sol 1925 (June 2, 2009), that helped engineers assess the rover's state and plan Spirit's extraction from the soft soil at the site called "Troy."


The images were taken by Spirit's microscopic imager instrument, mounted on the end of the robotic arm. Image Credit: NASA/JPL-Caltech/Cornell/USGS.

Driving commands are being prepared to instruct Spirit to attempt to drive forward. These are the first driving commands since Spirit became embedded in a Martian sandtrap approximately six months ago. These commands will be transmitted to Spirit at 1 a.m. PST (4 a.m. EST) Tuesday, Nov. 17.

The rover will be instructed to drive straight ahead (north) in two steps. Each step will be a commanded wheel motion of about 2.5 meters (8.2 feet). At the conclusion of the commanded motion, the rover will collect a three-frame Microscopic Imager mosaic of the rover underbelly.

Spirit will also collect Pancam images of the middle wheels, pre-drive and post-drive visual odometry (Visodom), Navcam images, and supporting front and rear Hazcam images.

The rover will drive with the robotic arm (Instrument Deployment Device) already deployed in the "fishing stow" position, like Opportunity, so it can take Microscopic Imager images without having to stow and un-stow the arm before and after each drive.

The team expects to spend all day Tuesday analyzing the drive results before the next drive attempt, possibly on Wednesday, Nov. 18. It is expected, at least initially, that little actual motion of the rover will be observed.

The attempt to extract Spirit from the Martian sandtrap is expected to take weeks or months, if it is at all possible. The next status update will be issued Tuesday, Nov. 17.

NASA: Attempt to Free Sand-Trapped Mars Rover

PASADENA, Calif. -- NASA will begin transmitting commands to its Mars exploration rover Spirit on Monday as part of an escape plan to free the venerable robot from its Martian sand trap.

Spirit has been lodged at a site scientists call "Troy" since April 23. Researchers expect the extraction process to be long and the outcome uncertain based on tests here on Earth this spring that simulated conditions at the Martian site.

"This is going to be a lengthy process, and there's a high probability attempts to free Spirit will not be successful," said Doug McCuistion, director of the Mars Exploration Program at NASA Headquarters in Washington. "After the first few weeks of attempts, we're not likely to know whether Spirit will be able to free itself."

Spirit has six wheels for roving the Red Planet. The first commands will tell the rover to rotate its five working wheels forward approximately six turns. Engineers anticipate severe wheel slippage, with barely perceptible forward progress in this initial attempt. Since 2006, Spirit's right-front wheel has been inoperable, possibly because of wear and tear on a motor as a result of the rover's longevity.

Spirit will return data the next day from its first drive attempt. The results will be assessed before engineers develop and send commands for a second attempt. Using results from previous commands, engineers plan to continue escape efforts until early 2010.

"Mobility on Mars is challenging, and whatever the outcome, lessons from the work to free Spirit will enhance our knowledge about how to analyze Martian terrain and drive future Mars rovers," McCuistion said. "Spirit has provided outstanding scientific discoveries and shown us astounding vistas during its long life on Mars, which is more than 22 times longer than its designed life."

In the spring, Spirit was driving backward and dragging the inoperable right front wheel. While driving in April, the rover's other wheels broke through a crust on the surface that was covering a bright-toned, slippery sand underneath. After a few drive attempts to get Spirit out in the subsequent days, it began sinking deeper in the sand trap. Driving was suspended to allow time for tests and reviews of possible escape strategies.

"The investigations of the rover embedding and our preparations to resume driving have been extensive and thorough," said John Callas, project manager for Spirit and Opportunity at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "We've used two different test rovers here on Earth in conditions designed to simulate as best as possible Spirit's predicament. However, Earth-based tests cannot exactly replicate the conditions at Troy."

Data show Spirit is straddling the edge of a 26-foot-wide crater that had been filled long ago with sulfate-bearing sands produced in a hot water or steam environment. The deposits in the crater formed distinct layers with different compositions and tints, and they are capped by a crusty soil. It is that soil that Spirit's wheels broke through. The buried crater lies mainly to Spirit's left. Engineers have plotted an escape route from Troy that heads up a mild slope away from the crater.

"We'll start by steering the wheels straight and driving, though we may have to steer the wheels to the right to counter any downhill slip to the left," said Ashley Stroupe, a JPL rover driver and Spirit extraction testing coordinator. "Straight-ahead driving is intended to get the rover's center of gravity past a rock that lies underneath Spirit. Gaining horizontal distance without losing too much vertical clearance will be a key to success. The right front wheel's inability to rotate greatly increases the challenge."