The Rosetta spacecraft orbiting around the comet 67P/Churyumov-Gerasimenko (67P) has recorded strange data in ultraviolet readings from the icy body. This announcement comes at the same time as NASA announced a proposed plan to crash the orbiter into the comet near the site where the Philae lander came to rest after an unsuccessful touchdown.
Comets can be thought of as dirty snowballs, in many respects. As they approach the sun, comets warm up, releasing carbon dioxide (CO2) and water through jets within their bodies. As these molecules rise, they are usually split apart by the action of photons of ultraviolet light from our parent star.
Atoms of hydrogen (from water), oxygen (from water and carbon dioxide) and carbon from CO2 each emit and absorb photons at specific frequencies. These can be measured from Earth, but not in the detail seen by Rosetta, currently circling the comet.
Researchers examining the phenomenon believed that photons of electromagnetic energy were driving the changes on 67P. But the Alice ultraviolet spectrograph onboard the Rosetta observatory found that nearly all of the observed molecular breakdowns surrounding the comet were actually driven by electrons.
"First, an ultraviolet photon from the sun hits a water molecule in the comet's coma and ionizes it, knocking out an energetic electron. This electron then hits another water molecule in the coma, breaking it apart into two hydrogen atoms and one oxygen, and energizing them in the process. These atoms then emit ultraviolet light that is detected at characteristic wavelengths by Alice," the European Space Agency (ESA) reported.
Astronomers could now utilize Alice to trace the jets of water and CO2 emissions down to their sources on the surface of the comet. This study could help researchers better understand the nature of cometary formation and development.
In recent years, astronomers have started to change their ideas about the process by which comets eject material to space. Researchers once thought emissions were largely homogeneous around the surface of the icy body (apart from thermal differences). Now, astronomers realize most of the material lost from comets comes from jets on the icy bodies.
Rosetta, launched in 2004, is nearing the end of its operational life. Mission planners are currently deciding what to do at the end of the spacecraft's lifetime. The vehicle will be out of fuel in September 2016, and the mission cannot continue past this time. One idea is to purposely crash Rosetta onto the surface of the comet, near the final resting spot of the Philae lander. Mission planners believe there is a chance that the spacecraft could land softly on the surface of the comet, although no one is holding out hopes the vehicle would survive the encounter.
Analysis of the Alice data and what it tells us about the atmospheres of comets was published in the journal Astronomy and Astrophysics.
