Rosetta goes beyond the limits

The ESA probe Rosetta with the instrument Alice, notes that are generated “plumes” issued by the coma, not due to photons, at least not directly, but to the electrons. It’s an unexpected result, impossible with the space telescopes and impossible to be seen from Earth.
Not lacking in surprises in store for the ESA’s Rosetta. Illustrated in a study that will appear in Astronomy and Astrophysics team spectrograph Alice, the contribution of NASA’s mission, it detected an unexpected process that causes the rapid dissolution of water molecules and carbon dioxide escaping from the surface of the comet.


Credit: NASA/ESA/ATG Medialab

The instrument Alice analyzes provided by NASA, examined the chemical composition of the comet at wavelengths in the far ultraviolet, which identifies some of the most abundant elements in the universe as hydrogen, oxygen, carbon and nitrogen.
For this study, the team focused on the nature of the “plume” of water and carbon dioxide produced by the Sun’s heat and which are emitted from the surface of the comet. In doing so they have discovered how the molecules of water and carbon dioxide seem to “break” into two phases.
In the first phase, it’s about a photon emitted by the Sun hitting a molecule of water in the comet’s coma. The electron ousted hits another water molecule that is divided into two atoms of hydrogen and one of oxygen, producing energy and emitting ultraviolet light which is detected at characteristic wavelengths for Alice.
Similarly is the impact of an electron with a molecule of carbon dioxide.
“The analysis of the relative intensities observed atomic emission allows us to determine that we are looking directly molecules” founding “that are broken at about 1 km from the comet’s nucleus, where they are produced,” explains says Paul Feldman, professor of physics and astronomy at the Johns Hopkins University in Baltimore and lead author of the research.
“The discovery is quite unexpected,” says the Principal Investigator Alan Stern of Alice, “shows us the value of going to closely observe comets, since this discovery simply would not be feasible from Earth or Earth orbit with any observatory existing or soon expected. It’s important because it is transforming our understanding of comets. ”
The team of Alice compares the process that occurs for the comet to that relative to the plumes detected on Jupiter’s icy moon, Europa, except for the electrons of the comet is produced by solar photons, while the electrons in Europe come from the magnetosphere of Jupiter.
The results of Alice are supported by data obtained from other instruments of Rosetta, in particular MIRO, ROSINA and VIRTIS, which are able to study the abundance of the various constituents the crown and their variation over time, and the tools of detection of particles such as RPC-ies.
“These initial results from Alice show how important are the studies of a comet at different wavelengths and with different techniques in order to explore the various aspects of the comet,” says Matt Taylor from ESA.
“We are actively looking at the comet as it evolves approaching the Sun, in August we will reach perihelion and see plumes increasingly active and we can also study the effects of the interaction of the comet with the solar wind.”

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