Listening In: Lander to Record Mars Sounds
Delivered for the Mars Surveyor 2001 Lander, the Mars Descent Imager (MARDI) was designed to produce images of the geology around the landing site during landing.

NASA scientists hope to hear what it sounds like on the surface of Mars for the first time when they attempt to switch on the Phoenix Mars Lander?s microphone in the next week or two, mission leaders announced on Monday.

"This is definitely a first," said Phoenix principal investigator Peter Smith, of the University of Arizona, Tucson.

Phoenix's microphone is a part of the Mars Descent Imager system that was included on the underside of the lander to take downward-looking images during the three minutes of descent before the spacecraft touched down on the planet's surface. The MARDI on Phoenix was originally designed for the Mars Surveyor 2001 Lander missions, which were eventually canceled. The system is also similar to the one aboard 1999's ill-fated Mars Polar Lander.

The plan to use the imager and microphone on May 25 (when Phoenix landed) were scrapped when tests showed that using the system would create an unacceptable risk to a safe landing for Phoenix.

Phoenix did safely land at its appointed side in the Martian arctic, where it has been digging up samples of dirt and subsurface water ice and analyzing them with its instruments to assess the planet's past potential habitability.

Though the original plan to use Phoenix's mike during landing was scrapped, mission scientists didn't rule out using it later during the mission.

"We'd always hoped to turn it on," Smith said.

The team needed NASA's approval for funding to turn on the microphone, and now they've gotten the go-ahead, Smith said.

They can't flip the switch right away ? there are still a few checks that need to be done, and Phoenix's software needs to be changed a bit, Smith told

"We're just kind of cranking it up," he said.

Martian sounds

Once all the preparations are ready, the team plans to try to turn the microphone on while the lander is digging or using the rasp on the end of its robotic arm scoop, "just to make sure we hear something," Smith said. "You at least want to know if there's a chance of noise being created."

Phoenix scientists aren't sure just what, or how much, they'll hear. For one thing, Phoenix's mike is "not a professional microphone," Smith said (he likened it to the microphones used on a standard cell phone).

For another, sound waves don't travel as far on Mars as they do on Earth because Mars' atmosphere is thinner. It would be similar to listening to sound at an altitude of about 100,000 feet (30,500 meters) above Earth's surface, Smith said.

If the team can hear Phoenix's operations, they'll then turn the microphone on while Phoenix is quiet and just see what they can hear. What that might be, Smith isn't certain.

Potential images

In addition to potentially hearing Martian sounds, the Descent Imager system will take a picture once it's switched on, Smith said.

One potential photographic subject is the Holy Cow ice feature directly underneath the lander. The ice was exposed when Phoenix's thrusters pushed away the dirt lying on top of it during landing. The feature was first imaged by Phoenix's robotic arm camera.

The imager might also catch a glimpse of some so-called "barnacles" attached to Phoenix's legs. Smith describes these as "bright dots on the legs" that are pieces of the Martian surface that were splashed onto the legs by the thrusters during landing.

Some of the dots have grown and some have moved around over the course of the mission, which is now entering its fifth month on the Martian surface. Mission scientists aren't sure why the dots have such unusual behavior.

"It's one of those wonderful Martian mysteries," Smith said.

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