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Last Updated: Monday, 8 March, 2004, 15:54 GMT
Beagle descent possibly too fast
Beagle 2 descent (European Space Agency)
A heat shield was designed to protect Beagle during descent
The Beagle 2 lander could have crashed into Mars because the atmosphere on the planet was less dense than expected.

Mission scientists told a London meeting the probe may simply have been going too fast for its parachute and airbags to bring about a soft landing.

The Royal Society conference also heard photographic evidence had found four bright spots, dubbed the "string of pearls", on the surface of the planet.

Scientists are studying the images to see if they show the lander's remains.

They want to know if the spots are the probe's airbags and chute or are merely an artefact of the imaging process.

The Beagle team, led by Professor Colin Pillinger, told the society the latter was probably the case.

Reduced density

Readings of the Martian atmosphere taken on the day Beagle 2 was due to land were obtained by the Mars Express orbiter, using its Spicam Ultraviolet and Infrared Atmospheric Spectrometer.

"The Spicam data shows that there was considerably reduced atmospheric density at 30-40km above the surface," said Beagle 2 mission manager Dr Mark Sims.

"We now need to find out where (on Mars) that measurement was taken. If that was true of the Beagle 2 landing site we might have ended up with a situation where we didn't turn the radar altimeter on."

This radar altimeter was supposed to prompt Beagle to deploy its airbags once it reached 200m above the surface. But if Beagle was travelling too fast, they might not have deployed.

The data shows that there was considerably reduced atmospheric density at 30-40km above the surface
Dr Mark Sims, Beagle 2 mission manager
Without airbags to cushion the landing, Beagle 2 would simply have crashed into the Martian dust.

However the Spicam data from Mars Express is contradicted by readings from Nasa's Mars Odyssey spacecraft, which did not show greatly lowered atmospheric density on Mars.

Dr Sims said that if Beagle's chute deployed properly it would have been travelling towards the surface at 16m/s. A failure involving the parachutes higher in the atmosphere might have meant Beagle approached Mars at up to 6km/s.

Dr Sims said turbulence high in the atmosphere could also have caused the craft problems as it approached the surface.

High velocity

Beagle 2 was targeted to land in a large lowland basin called Isidis Planitia at 0254 GMT on 25 December.

It was designed to look for past or present life.

No signal has ever been detected from the craft to indicate it got down safely, and all attempts to locate the probe with Mars obiters and radio telescopes on Earth have failed.

The idea that Beagle may have had too high a velocity as it approached the surface of Mars is not a huge surprise.

The US space agency also reported a less dense atmosphere than expected on the entry of its first rover, Spirit.

This was explained by the dust storm activity on the planet at the time which acted to warm the atmosphere.

The Nasa vehicle managed to get down safely thanks to its chute, retro-rockets and robust airbag system.

Even so, the entry parameters for the second rover, Opportunity, were changed as a result. This was deemed particularly important because Opportunity was aimed at a higher altitude target.

The meeting was also told that an unidentified object could be seen in the image taken immediately after Beagle was ejected from its mothership, Mars Express, five days prior to the landing attempt.

Scientists said this needed further investigation.

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