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Philae probe location 'a problem'

Philae, the European spacecraft that made an historic descent to a comet, is resting at an angle in the shadow of a crater wall more than half-a-mile from its planned landing site, scientists believe.

One of its three legs appears to be suspended in space while the other two have made contact with the ground.

Scientists are frantically trying to establish precisely where the probe ended up on comet 67P/Churyumov-Gerasimenko, a 2.5 mile rugged lump of ice and dust more than 300 million miles from Earth.

As the news emerged today it became clear how narrowly the landing mission averted disaster.

After being released from its Rosetta mothership, Philae descended as planned to a relatively flat area on the smaller of one of the comet's two lobes.

But two harpoons that were supposed to anchor the craft to the surface failed to deploy and the probe bounced a kilometre (0.6 miles) into space, remaining suspended above the comet for nearly two hours.

Drawn by the comet's ultra-low gravity, it slowly fell again and bounced a second time before finally coming to rest - apparently to one side of a large crater.

The craft is partly in the shadow of a cliff-like wall, which could seriously hamper its ability to generate electricity from its solar panels.

By using one of Philae's instruments to transmit radio signals through the comet, scientists were able to obtain a rough idea of its location.

They believe it to be about a kilometre away from the original landing site.

Speaking at ESA's mission control centre in Darmstadt, Germany, lander scientist Professor Jean-Pierre Bibring, said: "We are below a cliff.

"Don't ask me how many metres, but very close by.

"Because of that we are in a sort of a shadow permanently, and that is a problem ...

"We're almost vertical; one foot probably is in open space and two feet are on the surface."

Pointing to a large image of the comet, Philae lander manager Dr Stephan Ulamec added: "It could be that we are somewhere in the rim of this crater, which could explain this bizarre orientation."

The scientists revealed that the probe could theoretically "hop" to a better position by moving its landing gear.

But this was unlikely to be attempted because of the amount of power it would drain.

The comet presented a major headache for mission planners because it is strewn with deep pits, craters, boulders - some the size of houses - and towering cliffs and peaks.

For Philae to survive after missing its chosen landing site by such a wide margin is nothing short of a miracle.

Despite the rollercoaster landing, the probe is maintaining radio contact with Rosetta and many of its instruments are already working.

It remains to be seen whether scientists will risk using Philae's drill, which is designed to bore out samples to a depth of 23 centimetres (nine inches).

Without the probe being firmly tethered to the ground, drilling could destabilise it in the low gravity.

The lack of sunlight to recharge the craft's batteries is one of the biggest problems the scientists now face.

Koen Geuts, technical manager at the lander control centre in Cologne, said: "The lander is relying on solar energy to operate over an extended period of time. We see that we're getting less solar power than we planned for the nominal landing site. This, of course, has an impact on our energy budget."

Philae was designed to operate for two-and-a-half days on primary battery power before switching to a solar energy phase lasting three months or more.

Yesterday's landing followed an epic 10-year journey that took Rosetta and Philae four billion miles across space.

It has been hailed as one of the greatest scientific achievements of all time, and compared to landing a fly on a speeding bullet.

Philae has a suite of 10 scientific instruments including Ptolemy, a British-led device for analysing the chemical composition of samples.

Open University engineer Ross Burgon, a member of the UK team in Darmstadt, said: " Ptolemy is already operating and sending back data. There are two ways it can accept samples, either from a pipe open to the atmosphere and also from the ovens which heat up the drill samples.

"There will be dust kicked up from the surface, and also subliming from the surface due to heat from the sun."

Scientists now believe much of the surface of the comet to be covered in soft fluffy material with a harder layer underneath.

On its first touchdown, Philae sank nearly two inches before bouncing away.

Early images from the probe's cameras show rock-like formations, but they are not thought to be as solid as rocks on Earth.

The comet has a similar density to plywood. Dropped into an ocean, it would float.

As Philae begins to study the comet, Rosetta will manoeuvre from its post-separation path back into orbit.

Next year, as the comet grows more active, Rosetta will step further back and fly unbound "orbits", making brief fly-bys to within five miles of the surface.

The comet will reach its closest point to the sun on August 13 next year at a distance of about 115 million miles, roughly between the orbits of Earth and Mars.

UK scientists are involved in 10 of the 21 experiments Rosetta will carry out during its mission.

British engineers have also made major contributions to the mission's electrical, software and imaging systems.

Scientists hope the mission will shed new light on the origins of the solar system, the Earth, and even life.

Comets bombarding the early Earth are thought to have imported large amounts of water, as well as complex organic compounds.

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