Area Beneath Phoenix Lander Is Changing

[/caption]
The bright, hard surface feature beneath the Phoenix Mars Lander has visibly changed from when it was first imaged shortly after the lander touched down on the Red Planet. Scientists believe the area, called “Snow Queen” could possibly be ice. Thruster exhaust blew away surface soil covering Snow Queen as Phoenix landed, exposing a hard layer with several smooth, rounded cavities. Phoenix’s Robotic Arm Camera (RAC) took its first close-up image of the area under the lander on May 31, the sixth sol of the mission. Now, more than 60 days since landing, cracks as long as 10 centimeters, or about four inches, have appeared in Snow Queen. A seven-millimeter (less than one-third inch) pebble or clod not seen there before has popped up on the surface, and some smooth texture has subtly roughened. These changes have been occurring slowly. “Images taken since landing showed these fractures didn’t form in the first 20 sols of the mission,” Phoenix co-investigator Mike Mellon of the University of Colorado, Boulder, said. “We might expect to see additional changes in the next 20 sols.”

Mellon said long-term monitoring of Snow Queen and other icy soil cleared by Phoenix landing and trenching operations is unprecedented for science. It’s the first chance to see visible changes in Martian ice at a place where temperatures are cold enough that the ice doesn’t immediately sublimate, or vaporize, away. Phoenix scientists discovered that centimeter-sized chunks of ice scraped up in the Dodo-Goldilocks trench lasted several days before vanishing.

“I’ve made a list of hypotheses about what could be forming cracks in Snow Queen, and there are difficulties with all of them,” Mellon said.

One possibility is that temperature changes over many sols, or Martian days, have expanded and contracted the surface enough to create stress cracks. It would take a fairly rapid temperature change to form fractures like this in ice, Mellon said.

Another possibility is the exposed layer has undergone a phase change that has caused it to shrink. An example of a phase change could be a hydrated salt losing its water after days of surface exposure, causing the hard layer to shrink and crack. “I don’t think that’s the best explanation because dehydration of salt would first form a thin rind and finer cracks,” Mellon said.

“Another possibility is that these fractures were already there, and they appeared because ice sublimed off the surface and revealed them,” he said.

As for the small pebble that popped up on Snow Queen after 21 sols — it might be a piece that broke free from the original surface or it might be a piece that fell down from somewhere else. “We have to study the shadows a little more to understand what’s happening,” Mellon said.

Meanwhile, scientists and engineers for the mission are studying the icy soil on Mars, examining how it interacts with the scoop on the lander’s robotic arm, trying different techniques to deliver a sample to the TEGA or Thermal and Evolved Gas Analyzer instrument.

“It has really been a science experiment just learning how to interact with the icy soil on Mars — how it reacts with the scoop, its stickiness, whether it’s better to have it in the shade or the sunlight,” said Phoenix Principal Investigator Peter Smith of the University of Arizona.

Last weekend, the team tried two different methods to pick up and deliver a sample of icy soil to one of the ovens in TEGA. In both cases, most of the sample stuck inside the lander’s scoop, with only a small amount of soil getting into the oven. All the data received from the lander – both images and other data — indicated that not enough soil had been funneled into the oven to prompt the oven to close and begins its analysis.

The team plans to keep gaining experience in handling the icy soil while continuing with other Phoenix studies of the soil and the atmosphere.

Smith said, “While we continue with determining the best way to get an icy sample, we intend to proceed with analyzing dry samples that we already know how to deliver. We are going to move forward with a dry soil sample.”

Original News Source: Phoenix News site