Rosetta: Data provides more surprises

Composition of the comet is even more complex than expected

A crack in the comet: At the neck of 67P / Churyumov-Gerasimenko a long crack extends for about 500 meters. Top left: A view of the Hapi region. Bottom left: This image shows the crack in the Hapi region and beyond. Right: The rift extends to the Anuket region. © ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA
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News from Rosetta: The spacecraft provides astronomers from around the world with groundbreaking data on the comet 67P / Churyumov-Gerasimenko. Its different landscapes are visible in previously unimaginable detail and also its gas envelope holds surprises ready. The science magazine "Science" dedicates Rosetta and the findings gained a special with seven articles.

The arrival of the spacecraft Rosetta at comet 67P / Churyumov-Gerasimenko, in short "Chury", and the landing of the landing unit Philae are among the scientific highlights of the past year. For the researchers involved, however, these spectacular events were just the beginning. While Philae is now in hibernation, Rosetta continues to orbit the core of the comet and provides highly interesting data. In a special issue of the magazine "Science", seven scientific articles deal with the findings.

A crack on the neck

With Rosetta's two OSIRIS cameras, astronomers have now captured enormously detailed images of the visible areas of the comet's surface. The discovered landscapes could hardly be more different: Smooth areas alternate with rugged and furrowed or those covered by a possibly meter-thick layer of dust. A total of 19 different regions have been identified by the researchers, who named them after Egyptian deities.

The comet consists of two parts, a "head" and a "body, " which makes it look like a rubber duck. The OSIRIS data shows that Chury loses a lot of gas and dust, especially in the "neck area", as he approaches the sun. In this area also runs a roughly 500-meter-long crack through the surface, according to the researchers suggesting mechanical stress. The scientists are now speculating whether the cometary nucleus consists of two collided parts, or instead of a large chunk, which, however, especially around the center shrinks "like an apple that you eat around the case."

A total of 19 morphologically distinct regions have been identified by researchers from the OSIRIS team on the surface of comet 67P / Churyumov-Gerasimenko and named after Egyptian deities. ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA

For the first time, scientists also determined the density of a cometary nucleus. Chury is therefore surprisingly porous: its density is comparable to that of cork. "We assume that the comet consists of ice and dust, materials that both have a significantly higher density, " explains Holger Sierks from the Max Planck Institute for Solar System Research. "The measured value suggests that the comet has a porosity of 70 to 80 percent. We currently see it as a kind of loose accumulation of ice and dust particles with many, many gaps between them. "Display

Surprisingly changeable gas bubbles

The effluent gas is mostly water. However, there are also considerable amounts of carbon monoxide and carbon dioxide. The composition of the gas bubble around the comet is anything but consistent and constant: Instead, it fluctuates very much, to the great surprise of the researchers: "When I saw this behavior for the first time, I thought something Things are going wrong, "says Myrtha H ssig of the Southwest Research Institute in San Antonio.

But the data agreed and now suggests much more complex connections between the comet and its gas well than previously thought. The temporal change may reflect a kind of day and night change, or the comet surface may be even more patchy than expected.

In addition, a relatively dense dust layer probably also isolates the icy core underneath. "This might explain why 67P and other comets that penetrate into the inner solar system are so durable and many orbits are exposed to the sun, " said Paul Hartogh of the Max Planck Institute f Sonnenr Solar System Research in G ttingen.

Dark Comet Core: This is how the Earth, Moon and Chury appear under the same lighting conditions (sizes not to scale). © ESA / Rosetta / MPS for OSIRIS MPS / UPD / LAM / IAA / RSSD / INTA / Team

Twice as black as coal

Despite the abundance of details, almost half of the comet is still in the dark: Only his "north side" is visible to Rosetta, his "South Pole" points away from the sun. In addition, Chury appears extremely dark, reflecting only about six percent of the incoming light. By comparison, the earth reflects 31 percent, the moon at least twelve percent. "Comets are almost twice as black as coal, with a thick layer of dust that covers the surface, " says Dennis Bodewits of the University of Maryland.

The activity of the comet will continue to increase as it travels around the sun. The astronomers are curious to see how Chury will develop. From the data already obtained and the future observations, they hope to find out how the comet came about. Since comets are considered well-preserved remains from the early days of the solar system, this could also provide clues to its genesis. (Science, 2015; Special Issue: Catching a Comet)

(Southwest Research Institute / University of Maryland / MPI for Solar System Research, 23.01.2015 - AKR)