The European Space Agency’s Rosetta spacecraft has been witnessing growing activity from comet67P/Churyumov-Gerasimenko as it approaches perihelion (its closest point to the sun during its orbit). On July 29, while the spacecraft orbited at a distance of 116 miles (186 kilometers) from the comet, it observed the most dramatic outburst to date. Early science results collected during the outburst came from several instruments aboard Rosetta, including the Double Focusing Mass Spectrometer (DFMS), which uses NASA-built electronics. The DFMS is part of the spacecraft’s spectrometer for Ion and Neutral Analysis (ROSINA) instrument.


When the outburst occurred, the spectrometer recorded dramatic changes in the composition of outpouring gases from the comet when compared to measurements made two days earlier. As a result of the outburst, the amount of carbon dioxide increased by a factor of two, methane by four, and hydrogen sulphide by seven, while the amount of water stayed almost constant. There were also hints of heavy organic material that might have been dust.


Kathrin Altwegg, principal investigator for the ROSINA instrument from the University of Bern in Switzerland noted that although the outburst my have been freed from beneath the comet’s surface, it is too early to say for sure that this is the case.


A sequence of images taken by Rosetta’s scientific camera OSIRIS shows the sudden onset of a well-defined, jet-like feature emerging from the side of the comet. The jet, the brightest seen to date, was first recorded in an image taken at 6:24 a.m. PDT (9:24 a.m. EDT, 13:24 GMT) on July 29, but not in an image taken 18 minutes earlier. The jet then faded significantly in an image captured 18 minutes later. The OSIRIS camera team estimates the material in the jet was traveling at 33 feet per second (10 meters per second), at least.


On Thursday, August 13, the comet and Rosetta will be 116 million miles (186 million kilometers) from the sun – the closest to the sun they will be in their 6.5-year orbit. In recent months, the increasing solar energy has been warming the comet’s frozen ices, turning them to gas, which pours out into space, dragging dust along with it. The period around perihelion is scientifically very important, as the intensity of the sunlight increases and parts of the comet previously cast in years of darkness are flooded with sunlight. The comet’s general activity is expected to peak in the weeks following perihelion.


Comets are time capsules containing primitive material left over from the epoch when the sun and its planets formed. Rosetta is the first spacecraft to witness at close proximity how a comet changes as it is subjected to the increasing intensity of the sun’s radiation. Observations are helping scientists learn more about the origin and evolution of our solar system and the role comets may have played in seeding Earth with water, and perhaps even life.


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