The Rosetta mission's lander is now on the surface of comet 67P/Churyumov-Gerasimenko, although there are some concerns about it.
In a briefing late Wednesday, Stephan Ulamec, head of the lander operation for the European Space Agency, said Philae may have made two landings on the comet. Meanwhile, mission manager Paolo Ferri said they lost their radio link earlier than planned, although he said that's not concerning.
Despite some overnight nervousness at mission control in Darmstadt, Germany, Nov. 12 is now an historic day in space exploration after the first landing ever on a comet.
The ESA's Rosetta mission to 67P, which is four kilometres in diameter, already ranks as "completely revolutionary for comet science," says comet expert Karl Battams.
"Their mission is already an extraordinary thing and it will only get even more extraordinary if the lander's a success," Battams says in an interview with CBC News.
He is an astrophysicist and and computational scientist at the space science division of the U.S. Naval Research Laboratory. This week Battams is in Darmstadt observing at mission control.
Back in the U.S. he has led the NASA-funded Sungrazer comets project since 2003, which has discovered over 2,500 comets.
When it comes to studying comets, Battams says, "We've only looked at it and sniffed it from a distance, we've never gone up to it and actually touched it and been able to merge our remote sensing observations with the actual physical results we get from doing experiments on a comet."
First image from the surface of Comet 67P/Churyumov-Gerasimenko from the Rosetta million’s lander Philae Photograph: ESA/Rosetta/Philae/CIVA/Photograph: ESA/Rosetta/Philae/CIVA
What's inside a comet
Philae has radar sounding devices inside its landing feet that, along with infrared and spectral analysis are supposed to reveal what's inside a comet. That has Battams excited, since we don't know the actual structure of comets or how they're made up.
"Are there layers or pockets of certain materials floating around, or is it really just a huge, completely random rubble pile of solar system junk that's been mushed together and frozen in outer space?" he said.
The lander can also take samples from below the surface of the comet and this will be material that has not been exposed to solar radiation and then analyzed in the lander. Battams says he'll be "fascinated to find out what stuff they start seeing when they bake that raw comet material."
Some new discoveries from the Rosetta Mission are being presented this week at the American Astronomical Society meeting in Tucson, Ariz.
Jay Melosh, who worked on three NASA comet missions, was there. He told CBC News this mission offers much more opportunity to learn about comets and the solar system.
Those missions, including the Deep Impact mission that cratered comet Tempel 1 in 2005, were just rapid fly-bys, he says. Melosh is a professor of Earth, atmospheric and planetary sciences at Purdue University in Indiana, and the asteroid 'Melosh' is named in his honour.
Not only does the Rosetta mission have a lander on the comet surface, it will also follow P67 as it plunges towards the sun. As it gets closer, the comet gets very active. P67 will reach its closest point to the sun in August 2015 before it heads back to the outer solar system.
It's going to be quite a ride, Melosh says.
How well the landing system will work has been a topic of discussion at the Tucson meeting, and earlier. Since the mission began a decade ago, Melosh says much has been learned about comets and their surfaces.
Cometary material very weak
"They seemed to be composed of very dark, very dry powder that's finer than talcum powder and very weak, and that was not anticipated before the launch," he explains.
He compares that cometary material to a finely made soufflé, which will rise many centimetres. If it rises too high, it will collapse.
"If you made a soufflé of this comet stuff, it would rise about one millimetre and then collapse under its own weight in earth gravity, so there's absolutely nothing in our experience that's as weak as this stuff," Melosh says.
The question is then, how well will the anchoring system work in that extremely weak powdery material?
The ESA is learning more about that today.
67P very, very black
Melosh says scientists have "already learned from Rosetta the comet is very, very dark, black as coal, blacker than almost anything you'd seen."
That means it's reflectivity is also very low, like it was intended to absorb all light. That blackness comes from organic material, a kind of tar, he says, "that may actually form some of the precursors for life on earth."
Melosh wants to learn more about that substance, as comets are a "pristine sample" of the building materials for the planets.
The Rosetta mission has also already discovered that on P67 water dominates over carbon dioxide in composition. From the Hartley 2 mission in 2010 — Melosh worked on it — we learned that comet's composition is the other way around.
There's much hope that the mission will help shed light on the origin of life. Scientists already know that comets have the necessary ingredients water, amino acids, and carbon molecules. And comets bombarded Earth in the solar system's early days.
So did comets contribute the basic ingredients for life on earth? Battams says by phone from Germany that the only way we're going to learn more about that, "is to get real up close and get our hands dirty with a comet and dig around and look at the properties of the materials there, and the different molecules and isotopes and compare it to earth and see which models seem more plausible."
But he cautions, don't expect the Rosetta mission to answer that question definitively.
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