Unmanned lander ‘Philae’ to touch down on distant comet

Like moving an object from one bullet to another, says mission manager; Suggested 25 years ago by TAU scientist, colleagues.

By JUDY SIEGEL-ITZKOVICH
THE ‘PHILAE’ robotic lander approaches the surface of a comet (Illustrative) (photo credit: Wikimedia Commons)
THE ‘PHILAE’ robotic lander approaches the surface of a comet (Illustrative)
(photo credit: Wikimedia Commons)
The European Space Agency’s Rosetta spacecraft’s Philae robotic lander – about the size of a washing machine – is due to land on the Churyumov- Gerasimenko comet on Wednesday.
A quarter of a century ago, a Tel Aviv University astrophysicist was part of an international group that suggested the idea of a soft landing of a robotic probe on the surface of a comet.
Prof. Akiva Bar-Nun of TAU’s earth sciences department, who was part of the group then, has eagerly waited to see the lander’s touchdown. It has legs to soften the impact, a thruster to bring it down and a harpoon to anchor it to the comet’s surface.
Rosetta’s mission manager, Dutch astrophysicist Dr. Fred Jansen, said that Earth is as much as 500 million kilometers away from the comet. His team members “won’t know if Philae has set down successfully on the icy surface until they receive a signal at around 6 p.m. Wednesday. If all goes well, it’ll be an awesome achievement – the equivalent of transferring an object from one speeding bullet to another,” he was quoted as saying.
Both the comet and Rosetta are flying through space at 60,000 km. per hour.
Bar-Nun said the idea for the lander was to check the strength of the ice and what it is made of. The comet was created at a temperature of -250 degrees centigrade at the edge of our solar system. The team believes now that it was less likely that comets brought water and organic material to the Earth, a theory that previously was popular.
Until now, the presence of nitrogen was the biggest discovery, said the TAU professor.
“It was an explosive discovery because until now we did not find nitrogen on comets.
Now we expect to find noble gases [six chemical elements that are odorless and colorless with very low chemical reactivity] including argon, krypton and neon. As the comet and lander get closer to the sun, it warms up and becomes more active, making it possible for us to discover elements at very low concentrations,” said Bar-Nun.
“Until now, all spacecraft passed comets, but none ever landed on [one]. Twenty-five years ago, we thought of landing on a comet, drilling into the surface and bringing material back to Earth. The problem is that we didn’t know what mechanical strength the surface had. Engineers told us first to measure the comet. As comets have very little gravitational pull, something has to hold the surface by force.
We think the ice is not very dense but is like snow that fell and remains quite soft,” he said.
His research has been supported for the last four years by the Science, Technology and Space Ministry’s Israel Space Agency.
Bar-Nun invites the interested public to visit their TAU lab on Wednesday between 2 p.m.
and 5 p.m. to view the devices with which they create examples of comet ice and research them.
The landing site has been given an official name, Agilkia, selected based on a public essay competition. The name is in keeping with Rosetta’s Egyptian theme. The mission itself was named Rosetta after a stone slab inscribed with a decree issued in 196 BCE on behalf of Egyptian King Ptolemy V. The name Agilkia refers to an island on the Nile River; ancient buildings were relocated there after the island Philae flooded.
If all goes well, Philae will transmit the first images ever taken from a comet’s surface.
It will also take samples of the surface to study their composition and broadcast how the comet changes as it travels closer to the sun day by day.
Philae can remain “alive” for only about 60 hours, but the Rosetta spacecraft will remain in orbit until July 2015. Rosetta was launched in March 2004 and spent 957 days in “hibernation,” as it flew through the darkness of space.
Comets not only are beautiful cosmic objects, but they also hold vital clues about the history of our solar system, of which they are regarded as primitive building blocks literally frozen in time. Astrophysicists believe they may have played a role in “seeding” Earth with water and, possibly, the basic ingredients for life.
The Rosetta was “awakened” 11 months ago to prepare for its August arrival in orbit around the Churyumov-Gerasimenko comet. Since then, cameras have sent stunning images of the parts of the comet that are illuminated.
These features include steep ravines, sharp cliffs and numerous boulders.