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Kirsten Magasdi reports for BBC News
"It's hoped the lander can beam back pictures and sounds "
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Tuesday, 30 November, 1999, 16:39 GMT
Polar lander ready for Mars

The spacecraft will land in the Martian spring The spacecraft will land in the Martian spring

By BBC News Online Science Editor Dr David Whitehouse

The Mars Polar Lander spacecraft will soon make the first-ever landing near a Martian pole, following an 11-month, 220-million-kilometre trip.

After its sister ship, Mars Climate Orbiter, was destroyed while attempting to go into orbit around the Red Planet, Nasa scientists will be sparing no effort on this mission.

But if all goes well on Friday, we will once again gaze across a new panorama on a distant world. It will be only the fourth time a US spacecraft has touched down on Mars.

The polar frosts are expected to have thawed The polar frosts are expected to have thawed
Its goal is to land in one of the strangest landscapes ever discovered, the so-called polar-layered terrain.

Until a few weeks ago, the region was covered with hard carbon dioxide frost. Now, as the temperature rises, slightly, the ice vaporises unveiling a dust-strewn undulating terrain that will no doubt contain many surprises.

Seen from the cameras of the Mars Global Surveyor, currently in orbit around Mars, the region appears as alternating bands of colour that seem to contain differing mixtures of dust and ice.

Like the growth rings of trees, these layered geological bands may reveal the secrets of past climate change on Mars. They may tell us if Mars experienced catastrophic, episodic or gradual changes.

Soft landing

The exact landing site co-ordinates were selected in August 1999, using images and altimeter data from Mars Global Surveyor.

Like the Mars Pathfinder spacecraft that landed on Mars in July 1997, Polar Lander will dive directly into the Martian atmosphere, using a heat-shield and a parachute to slow it down.

But unlike Mars Pathfinder, the smaller Polar Lander will not use airbags, but will rely on an onboard computer and retro-rockets to land softly on the layered terrain.

On its way down, after the heat shield is jettisoned, a camera will take pictures of the landing site. These will be recorded onboard and transmitted to Earth after landing.

The probes will smash into the ground The probes will smash into the ground
About 10 minutes before touchdown, two microprobes will be released. Once free, the projectiles will collect atmospheric data before smashing into the Martian surface at about 640 kilometres per hour (400 miles per hour).

Much of the microprobes will be destroyed but some parts of them have been designed to survive. A tiny instrument will draw a small soil sample into a chamber, heat it and use a miniature laser to look for signs of vaporised water ice. Water would be crucial to the success of any future manned mission to Mars.

Digging and listening

Fifty-five kilometres (35 miles) away from the microprobe impact sites, Mars Polar Lander will settle into the circumpolar dust deposits. Its first task is to take a look around.

In the coming days, it will dig a trench using a two metre (6.5-foot) robotic arm.

X marks the polar spot X marks the polar spot
Also onboard the lander is a light detection and ranging (lidar) experiment provided by Russia's Space Research Institute. It will detect the altitude of atmospheric dust hazes and ice clouds above the lander.

Inside the craft is a small microphone, provided by the Planetary Society that will record the sounds of wind gusts, blowing dust and mechanical operations onboard the spacecraft itself.

Mars Polar Lander is expected to operate on the surface for 60 to 90 Martian days through the planet's forthcoming southern summer (a Martian day is 24 hours, 37 minutes).

The mission will continue until the spacecraft can no longer protect itself from the cold and dark of lengthening nights and the return of the Martian polar frosts.

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See also:
30 Nov 99 |  Sci/Tech
Martian mysteries under microscope
11 Nov 99 |  Sci/Tech
Orbiter loss blamed on 'silly mistakes'
06 Oct 99 |  Sci/Tech
Evening clouds on a Martian volcano
10 Nov 99 |  Sci/Tech
Scientist fights Mars setback
27 Aug 99 |  Sci/Tech
Life on Mars - new claims
03 Sep 99 |  Sci/Tech
Mars Lander set for soft touchdown

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