• Bloomberg


As the first probe ever to be stationed on a comet hibernates, attention is turning to the Rosetta orbiter, which is still buzzing around the space snowball.

The Philae lander’s batteries lasted about 60 hours before running out. Rosetta is expected to observe comet 67P/Churyumov-Gerasimenko for more than a year and perhaps even into 2016, said Kathrin Altwegg, an experimental physicist from the University of Bern who is working on orbiter experiments.

“Of course, the lander is exciting,” she said in an interview. “The science from the orbiter is probably more extensive and ultimately more valuable, because you have more time and better instruments.”

Unlike the lander, which is fixed in one spot, Rosetta will observe the comet from all angles for months to come, Altwegg said. When the comet is visible to telescopes in August, Rosetta will still be there, she said. It will pass as close as 6 kilometers (19,700 feet) from the comet’s surface, lower than an airplane’s cruising altitude of about 30,000 feet (9.1 km).

Philae bounced out of its intended sunny landing site on Nov. 12 after its anchoring harpoons failed to fire. European Space Agency scientists expect the lander to get a solar energy boost and wake up as it approaches the sun.

Lander experiments

Before running out of power, the lander performed a number of experiments aimed at understanding the comet and its structure. One involved sending a radio signal through the comet to the orbiter. Researchers are studying the transmission to see what it can tell about how comets form and how they break up.

“Knowing the inner structure of the comet is the most exciting aspect of the mission,” said Essam Heggy, a planetary scientist at NASA’s Jet Propulsion Laboratory at the California Institute of Technology in Pasadena. “It’s like medical imaging.”

The experiment may also provide clues as to how planets develop, said Joel Parker, a director at the Southwest Research Institute in Boulder, Colorado, who is a member of the Rosetta science team. Both the orbiter and the lander were designed to study the comet for clues to the origins of the solar system and life on Earth. Comets may hold ready-made ingredients for life, such as water and complex molecules.

Comet origins

Planets began their existence in a molten state that would have been inhospitable to water and complex molecules, Parker said. Comets have their origin deep in space, which may have served as a “cold storage” reservoir for these substances, he said.

Complex molecules can occur in mirror-image forms, called chirals. Most of those on Earth occur in what scientists think of as a left-handed form, but it is possible that the comet may have a preference for right-handed versions, said Mark Hofstadter, also a planetary scientist at JPL.

The orbiter can also distinguish among various versions of elements, called isotopes, that are in the comet, Hofstadter said.

“By looking at the details of abundances in the comet and comparing them to Earth, we can get an idea of not only what temperatures and conditions were when the comet was formed, we can get an idea of whether comets provided these molecules to Earth,” he said.

Multiple missions and experiments have shown that comets and asteroids harbor organic molecules, which contain carbon, an element in all forms of life on Earth, Parker said. Close analysis of space rocks has also found glycine, one of the amino acids that make up protein, and bases, which are needed to make DNA and RNA.

Tough nut

Before going dark, Philae attempted to drill into the surface of the comet and sweep up some crumbs for analysis. While the drill deployed, no pieces were obtained, suggesting that the comet was harder than anticipated.

The orbiter can still answer some questions that the lander left hanging. As the comet approaches the sun at the rate of about a kilometer per second, more ices on and beneath its surface will heat and turn directly into gas. The reaction with the sun is almost like a laboratory experiment itself, and Rosetta is equipped with a sensor, called a mass spectrometer, that can see what these gases and the comet contain, Altwegg said.

Puzzling questions

One of the most puzzling questions that scientists have about life on Earth has to do with the original source of water, Parker said. The orbiter can analyze gases released by ice on the comet to determine whether its water is rich in deuterium, a heavy form of hydrogen, which with oxygen forms water. A match in the mix of heavy water may show whether comets could have borne water to Earth, he said.

Scientists are anxiously awaiting the data from the orbiter to answer such questions, Parker said.

“The lander did an amazing job,” he said. “A lot of people think that’s the end of Rosetta, and they’re going to be surprised a few weeks from now when we’ll have fantastic new pictures and observations.”

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