Category: Mars

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Spacecraft orbiting Mars have found only weak magnetic fields present in various regions of the Red Planet. These fields are probably remnants of an earlier global field that has since disappeared. But how and why did the global field vanish? Recent studies have proposed that giant asteroids slamming into Mars may have wiped out the planetary magnetic field. But scientists are still trying to determine if the magnetic field was suddenly blasted out of existence or if it slowly withered away.

Mars early magnetic field was likely driven by a dynamo formed from the convection of material in the core as molten iron rises, cools and sinks, much like the Earth core works today. In a new study, Robert Lillis and Michael Manga, from the University of California, Berkeley along with James Roberts of John Hopkins University Applied Physics lab suggest that energy released by massive collisions upset the heat flow in Mars’ iron core that produced the magnetic field.

Magnetic analysis of the Martian surface indicates that when Mars was just 500 million years old, its global magnetic field disappeared. Without this shield, streams of ionizing particles spewing from the sun strip away a planet’s atmosphere, vaporizing any water on the surface, and killing any life that may have emerged, or perhaps, forcing it underground.

A massive asteroid collision would have warmed Mars’s mantle, disrupting core convection. That’s because the cooling action of the mantle draws heat from the core, keeping it churning. Without that flow, core convection grinds to a halt.

This theory fits with the observation that only the oldest impact craters on Mars are magnetized. Newer impact regions like Hellas basin are show no traces of magnetism, and must have been formed when the magnetic field of Mars had ceased to exist.

Last year Lillis and Manga linked age estimates of impact basins with magnetic field strength to show that the previously established date of heavy bombardment, about 3.9 billion years ago, corresponds to the death of Mars’s dynamo.

Now, Lillis, Manga, and Roberts have modeled the effects of heat produced by impacts. When they added the heat release from the biggest asteroids to models of mantle convection, they found that the mantle became a heating blanket rather than an ice pack. The extra heat was enough to stop core convection, the team reports in the current issue of the Journal of Geophysical Research – Planets.

Mars was hit by at least five particularly large asteroids during the bombardment. “Any one of the super-giant impacts could have shut off [the dynamo],” says Roberts. Earth likely suffered the same onslaught, but at twice the radius of Mars, it probably had a strong enough dynamo to withstand or recover from huge impacts.

But according to an article in ScienceNow, some scientists are not convinced the collisions released enough energy to influence the dynamo, which may have stopped working on its own. “The dynamo does not need to have an external influence to stop functioning,” said David Stevenson, a planetary scientist at the California Institute of Technology, adding that without enough core convection, “it may simply die of its own accord.”

Source: ScienceNow

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It’s been a worrying month for the health of Mars Expedition Rover Spirit. Two weeks ago, the embattled robot failed to wake up after three successive communication sessions, and then over the Easter weekend (April 12th and 13th), mission HQ noticed the rover had rebooted its systems at least twice during use of the high-gain antenna. The same thing happened on April 18th. In addition to this, Spirit has been suffering bouts of what seems to be an ‘electronic amnesia’, where the onboard computers have failed to record data onto their flash memory.

Today however, it would appear Spirit is still operational after over two weeks of remaining planted in the same position. It managed to enact commands sent from NASA to start driving once more, trundling 1.7 metres over the Martian regolith. She hasn’t given up the good fight quite yet…

Since when have electronics on Earth ever lasted more than five years? I always seem to hit a two-year wall with my laptops when something nasty happens to the hardrive and/or motherboard (usually a day or two after the warranty runs out). But when we talk about the computers on board the Mars Expedition Rovers (MER), these electronics aren’t in the snug safety of my office; they are on the surface of an alien planet, dealing with extremes in temperature, high energy particles and copious amounts of dust. What’s more, the rovers were only designed to operate for a few months and yet they are still going strong, five years later. It’s the NASA mission that just keeps on giving.

I think this is what makes the MER mission so impressive for me. Not only are Spirit and Opportunity still operational, they are operating 20 times longer than their designated lifetime and they are notching up a very healthy odometer count. Their cumulative distance travelled is not measured in metres, or kilometres; it’s measured in tens of kilometres. They are giving us an unprecedented insight to the Martian surface, information that will shape our understanding of planetary science for generations to come.

But like any planetary mission, times can be tough, and both rovers have been tested to their engineered limits. Unfortunately, Spirit has been hit by a few more setbacks than Opportunity, but NASA has been able to find workarounds for each problem. The Mars Science Laboratory has a lot to live up to, I wonder if the MER mission will still be operational when the MSL finally touches down? Perhaps the next generation rover will have a robotic welcoming party!

The most recent issue for Spirit has been the flash memory problem. Flash memory helps the rovers store data even when they are powered down, but when the little rover forgets to actually store the data on the flash memory, something is obviously awry. In an attempt to make sure the rover can still take commands and to see if the computer problems persist, NASA ordered Spirit to travel 1.7 metres toward a target 150 metres away. All seems to be going well so far.

“We expect we will see more of the amnesia events, and we want to learn more about them when we do,” said JPL’s Sharon Laubach, chief of the rover sequencing team, which develops and checks each day’s set of commands.

“We decided not to wait until finishing the investigations before trying to drive again. Given Spirit’s limited power and the desire to make progress toward destinations to the south, there would be risks associated with not driving.”

Hopefully keeping the rover mobile will help NASA troubleshoot the recent computer problems, but so far, she’s still rolling over the Martian dirt…

Source: Physorg

…and yes, the picture is in focus.

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This strange image was captured by the High Resolution Imaging Science Experiment (HiRISE) camera on board NASA’s Mars Reconnaissance Orbiter (MRO) on April 11th. At first it looked like a classic example of my early camera days without a tripod; most of the photos I took were blurry or out of focus (due to my less-than-perfect eyesight). So when I first saw this picture of the summit of one of the huge Martian ex-shield volcanoes, Pavonis Mons, I assumed it was a mistake; HiRISE either had the shakes or it had developed myopia.

Actually, this image is in focus, HiRISE is working perfectly. It’s the Martian surface that’s blurry…

Pavonis Mons is one of the Martian “Big Three” ancient volcanoes situated on the Tharsis bulge. Second only to Olympus Mons (the biggest volcano in the Solar System, standing at a mighty 27 km above the Martian surface), Pavonis Mons certainly isn’t small. It reaches 16 km into the Martian skies where the air is so tenuous, it barely reaches a pressure of 130 Pa (compared with the 600 Pa mean surface pressure of Mars), that’s 0.1% the average sea-level pressure on Earth.

When you have an atmosphere so thin at such high altitudes, there are consequences. In the case of this HiRISE image, the issue is that the summit of Pavonis Mons becomes rather blurred.

During major dust storms on the planet, huge quantities of dust can be deposited at the tops of these tall volcanoes, covering them in a thick layer. When the wind blows, it lacks the muscle of the thicker atmosphere found 16km below, so less dust is picked up and transported away. Although small ripples in the dust can be seen (highlighting the fact that there is a weak wind blowing up there), it doesn’t carve definite shapes into the regolith. Instead, it leaves a thick layer of fluffy, smooth dust to collect. When images are taken from space, it has a blurry appearance.

In case you don’t believe me, look at this high resolution version of the image above, zooming into the top right-hand corner where you’ll see a small, recent (and in-focus) impact crater. Also, look at the focused ripples in the dust on the lighter northern edge of the volcano.

Source: HiRISE