Rosetta data points to comet landslide as cause of dramatic outburst
ESA's Rosetta spacecraft has observed adramatic increase in activity from the comet67P/Churyumov-Gerasimenko, seemingly brought on by a landslide. Thenew data will help scientists to further characterize the activitythat continues to shape 67P to this day.
Whilst the Rosetta spacecraft and herPhilae payload have done an admirable job in probing the secrets ofthe comet 67P since their arrival in August 2014, our understandingas to the nature of these wandering oddities is yet relativelyjuvenile.
One of the key issues faced byscientists hoping to observe and learn from comet activity is theunpredictable nature of 67P. We are aware that, as the travellermakes its closest approach to the Sun, known as perihelion, heatfrom our star causes a massive increase in outgassing activity. This knowledgeallowed mission controllers to send Rosetta into a moredistant orbit in the months before and after perihelionin order to protect the probe.
However,perihelion is now long gone, and 67P is racing back into the colddepths of our solar system. Now, for Rosetta to catch sight of one ofthe comet's unpredictable and dramatic bursts of activity, luck isthe key factor. If the probe were to capture such an event, it wouldhave to occur with Rosetta in the right place, at the right time,with her instruments actively observing the comet.
Ataround 9:40 GMT on the 19th of February, Rosetta got lucky. 67P let forth a deluge of activityfrom the Atum region, located on the comet's large lobe, and nine ofthe probe's instruments were in a position to document the entireevent. In the two hours following the initial detection, the proberecorded elements of comet activity sometimes reaching a factor of100 times the intensity prior to the outburst.
During the event, Rosetta was orbitingat a distance of 35 km (21.7 miles)from the comet, and was able toharvest the most comprehensive data set detailing the characteristicsof an outburst from 67P to date. These measurements were taken by awide range of instruments, including the probe's gas and plasmaanalysers, the OSIRIS wide-angle camera, and the GIADA dust impactinstrument.
Atthe height of the activity, GIADA was struck by 200 particles, wherenormally the instrument would collect 3 – 10 over the course of afull Earth day. The probe also recorded a 30 ºCincrease in the temperature of thesurrounding gas, alongside a brightening of the coma.
Aswould be expected following such a period of activity, Rosettarecorded a significant increase in the quantity of gas and plasmapresent in the comet's coma following the event. The sheer amount ofmaterial escaping the surface of 67P had the effect of scattering thelight from distant stellar bodies, which interfered with the probe'sstar trackers.
Star trackersare navigational instruments mounted at a 90-degree angle on the sideof the spacecraft. The interference experienced by the nav toolshelped Rosetta scientists to create a 3D model of the outburst, andto track its evolution.
An analysis of the data, paired withthe fact that the dust cone was very broad in nature, suggests thatthe unexpected activity resulted from a landslide on the surface of67P rather than a release of fresh material from deep within thecomet.
The Rosetta team believe that thesurface shift, which took place on a steep hill, was created bythermal pressures brought about as the Atum region transitioned intoa period of sunlight. The resultant landslide uncovered shallowdeposits of water ice, which, in the direct glare of the Sun's light,were immediately transformed into gas. Dust was then carried alongwith the escaping gas, and subsequently recorded and captured byRosetta's instruments.