Rosetta Spacecraft Watches Comet 'Wake Up' as it Hurtles Toward the Sun

Do you remember Comet 67P Churyumov-Gersimenko? It's the comet that made headlines after a spacecraft landed on it. Now, the comet is "waking up." The RPC-ICA instrument onboard Rosetta spacecraft, currently orbiting the comet, has been watching the comet form a magnetosphere as it moves closer to the sun.

As the comet becomes warmer, volatile substances, mainly water, evaporate from the surface and form an atmosphere around the comet. The sun's untraviolet radiation and collisions with the solar wind ionizes some of the comet's atmosphere. Then, the newly formed ions are affected by the solar wind electric and magnetic fields and can be accelerated to high speeds.

When the comets gets close enough to the sun, its atmosphere becomes so dense and ionized that it becomes electrically conductive. When this happens, the atmosphere starts to resist the solar wind and the magnetosphere is born. Currently, Rosetta is watching this amazing birth.

"It was an unambiguous signature of the comet, a clear detection of ions from the comet's atmosphere," said Hans Nilsson, one of the researchers, in a news release. "Rosetta is a unique space mission. Previous spacecraft that have studied comets have rushed past them at a great distance and at speeds of tends of kilometers per hour."

Yet Rosetta is currently orbiting the comet at a distance of just a few tends of kilometers at low speed. This allowed scientists to get a closer glimpse at what comets are like and how they react when approaching the sun.

"For the first time, we can see what happens before the comet atmosphere resists the solar wind," said Nilsson. "We discovered that the comet atmosphere affects the solar wind more than we thought it would at this early stage. We are also surprised how much structure we see in our data-the comet atmosphere appears to be very unevenly distributed around the nucleus."

The findings are published in the journal Science.

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