Comet orbiter poised to deliver as lander sleeps

As the first probe ever to be stationed on a comet hibernates, attention is turning to the Rosetta orbiter that’s still buzzing around the space rock, just a few miles from its surface.

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

“Of course the lander is exciting,” she said in a telephone 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 Earth telescopes in August, Rosetta will still be there, she said. It will pass as close as 6 kilometers (3.7 miles) from the comet’s surface, or lower than an airplane’s cruising altitude of about 30,000 feet (5.7 miles).

Philae bounced out of its intended, sunny landing site 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, Altwegg said.

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 rock 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, too, said Joel Parker, a director at the Southwest Research Institute in Boulder, Colorado, who’s 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. Scientists said that comets may provide ready-made ingredients for life, such as water and complex molecules.

Planets probably began their existence in a hot, 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’s 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 Earth-bound life, Parker said. Close analysis has also found glycine, one of the amino acids that make up protein, and bases, which are needed to make DNA, in space rocks.

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 rock pieces were obtained, suggesting that the comet was a tougher nut to crack 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.

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 it’s rich in deuterium, a heavy form of hydrogen, one of the two elements that make up water, he said. 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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