Gullies in wall of Hale Crater. Credit: NASA/MRO

Here's a quick status on the active ones:

Mars Reconnaissance Orbiter: The most recent arrival at Mars (2006), MRO's 5-year mission (hmmm—sound vaguely familiar?) is to study the history of water and climate on Mars, as well as to serve as a telecommunications relay for other spacecraft. Armed with a suite of powerful instruments to study the atmosphere, surface, and subsurface of Mars—including a camera, HiRISE, that can almost read the license plates on Martian automobiles—MRO has to date sent back more data than all other Mars missions combined. It's not been a glitchless flight, however: in 2009, MRO's computer reset itself four times for unknown reasons; the last reset, in August, was followed by a 4-month operational hiatus as Earth-side controllers performed some careful programming updates to help guard against effects of any future resets. MRO resumed operation in December.

Mars Odyssey 2001: NASA's 2001 Odyssey is still going fine after nine years—although the computer glitchiness out around Mars seems to be catching: Odyssey's computer put itself into a safe mode last November 2009 in response to a memory error. This was corrected and Odyssey has resumed doing science. Among Odyssey's major discoveries was the detection of huge expanses of water ice just under the surface of polar lowlands, and the surveying of deposits of water-related minerals in various locations around the planet.

Mars Express: Arriving at Mars in 2004, Mars Express became the European Space Agency's first mission to another planet, which was recently extended to 2012. Though the Beagle 2 lander component of the mission fell to Mars and was never heard from again, the Mars Express orbiter has sent back years of captivating images and important data, including the confirmation of methane in Mars' atmosphere (whose source is in all likelihood subsurface, and the origin of which—organic or inorganic processes—is being debated).

Mars Exploration Rover Opportunity: After six years of crawling around Meridiani Planum discovering chemical and geological evidence for past water on Mars, Opportunity is now on a long march to a large impact crater, which it will reach (if it can keep on running) in about two years. Currently, the rover has stopped to RAT out chemical and geological information from a rock called Marquette Island—the RAT is its rock abrasion tool, or rock grinder. Still going….

Mars Exploration Rover Spirit: Also still alive after six years—almost 25 times longer than it was planned to run—Spirit has been stuck in a sand bog for the last six months. With a couple of wheels on the fritz, Earth-side operators have been confounded in trying to free the robot—but Spirit has continued to make scientific measurements anyway…and in fact made a significant discovery in the course of trying to get unstuck.

Phoenix lander: Although it's been in the deep dark freeze of a Martian winter since November 2008, the Phoenix lander has an outside chance of survival. Now that light is returning to Phoenix's landing site, NASA is listening for the robot's radio signal, in case the return of solar power means that Phoenix will rise from the frost and live again! So far, no such signal….

Next up: The Mars Science Laboratory rover, "Curiosity."

NASA/Mars Reconnaissance Orbiter; Fans of dark dust on Mars'
southern ice cap, apparently blasted from beneath the ice
by thawing carbon dioxide."

At least, that's what happens at the polar ice cap on the planet Mars. I'd sure love to be there to see it, even if there are no flowers in bloom. Still, there seems to be plenty of "blossoming" going on….

NASA's Mars Reconnaissance Orbiter—the spacecraft with that high powered camera that could spot a beach ball on Mars' surface—has captured images of the aftermath of some of Mars' springtime polar action. Appearing as dark fan-shaped bursts strewn across the thinning springtime polar ice, these features are explained as plumes of Martian dust that have settled after being blasted into the air by releases of gas pressure from under the surface of the ice.

To describe what's going on, let me paint a picture of the Martian polar region as it emerges from the deep freeze of winter into spring.

Mars' year is almost twice as long as Earth's—and so too are its seasons. Winter at the southern pole of Mars lasts almost six months. In that time, the normally freezing temperatures on the Red Planet plummet to as low as -225 degrees Fahrenheit at the pole. During this time, Mars' permanent water ice cap acquires a layer of frozen carbon dioxide (dry ice) on top, formed from carbon dioxide freezing directly out of the atmosphere.

This seasonal dry ice cap also forms around the edges of the water ice cap, covering adjacent ice-free surfaces as well. The carbon dioxide ice cap may grow to as much as a meter thick.

Then, as spring approaches and the ice cap gradually comes out of the dark and receives more and more sunlight, it begins to warm up (though don't get the impression that it is ever "warm" anywhere on Mars' surface! Air temperatures recorded by the Viking landers in Mars' more temperate latitudes was barely ever higher than 1 degree Fahrenheit). Spring Equinox in Mars' southern hemisphere was on December 26th.

As the layer of solid carbon dioxide heats up, its ices turn to gas, both at the top of the layer and beneath it as well. The gases forming underneath build up pressure, which seeks a path to escape. Evidently the pressurized carbon dioxide gas can actually carve channels in the Martian soils under the ice as it flows—said channels have been seen in the past after the seasonal ice cap dissipates entirely.

When the gases find a weak point in the ice, they can erupt upward, bursting into the air, sometimes carrying dust with it. The dust rockets skyward and is blown by prevailing winds, settling out on the ice in great dark fans—which is what Mars Reconnaissance Orbiter has shown us.

Ah, to be on Mars in springtime….