Since landing on 67P/Churyumov-Gerasimenko last August, the Rosetta spacecraft has been studying the comet closely. The European Space Agency's (ESA) probe has now discovered an unexpected process at work, which is causing molecules of carbon dioxide and water to rapidly spew from the comet's surface.
There are 11 instruments aboard the Rosetta for observing and studying the comet. One of these instruments is NASA's Alice spectrograph, which has the purpose of examining the chemical composition of the comet's atmosphere using far-ultraviolet wavelengths.
At these wavelengths, the instrument allows mission scientists to identify highly abundant elements like nitrogen, carbon, oxygen and hydrogen. By splitting the light produced by the comet into different colors, Alice is able to identify the chemical composition of its atmosphere.
Using Alice's detections from Rosetta's first four months on the comet, mission scientists have analyzed carbon dioxide gas and water plumes coming off the surface as triggered by the sun's warmth. They looked at emissions produced by oxygen and hydrogen atoms, which are a result of carbon dissociating from carbon dioxide molecules and water molecules breaking close to the nucleus of the comet.
The molecules appear to split via a two-step process, explained Paul Feldman, an astronomy and physics professor from the Johns Hopkins University lead author of the study. Analyzing relative intensities observed in atomic emissions allowed the team to ascertain that "parent" molecules are breaking up because of electrons being produced by the comet's nucleus.
By comparison, space observatories on or in Earth's orbit are only able to spot atomic components of comets after parent molecules have been disintegrated by sunlight, many hundreds of miles away from the comet's nucleus.
The Alice spectrograph aboard the Rosetta space probe is one of two "Alices" currently in space. The other ultraviolet spectrograph is being used by New Horizons. Rosetta-Alice is operated by the Southwest Research Institute as part of a contract with NASA's Jet Propulsion Laboratory.
Alice is in place to help mission scientists study the comet's surface and atmosphere, providing insight into the formation and evolution of comets. It also permits scientists to closely observe the nature of comet activity. Understanding the comet's surface and atmosphere will hopefully shed light on the role of the comet's nucleus in changes within the comet's tail and atmosphere, in addition to comet interaction with solar wind.
This study was published in the journal Astronomy and Astrophysics.
