March 21, 2017
Rosetta scientists have made the first compelling link between an outburst of dust and gas and the collapse of a prominent cliff, which also exposed the pristine, icy interior of the comet.
Sudden and short-lived outbursts were observed frequently during Rosetta’s two-year mission at Comet 67P/Churyumov–Gerasimenko. Although their exact trigger has been much debated, the outbursts seem to point back to the collapse of weak, eroded surfaces, with the sudden exposure and heating of volatile material likely playing a role.
In a study published today in Nature Astronomy, scientists make the first definitive link between an outburst and a crumbling cliff face, which is helping us to understand the driving forces behind such events.
The first close images of the comet taken in September 2014 revealed a 70 m-long, 1 m-wide fracture on the prominent cliff-edge subsequently named Aswan, in the Seth region of the comet, on its large lobe.
Over the course of the following year as the comet drew ever closer to the Sun along its orbit, the rate at which its buried ices turned to vapour and dragged dust out into space increased along the way. Sporadic and brief, high-speed releases of dust and gas punctuated this background activity with outbursts.
One such outburst was captured by Rosetta’s navigation camera on 10 July 2015, which could be traced back to a portion of the comet’s surface that encompassed the Seth region.
The next time the Aswan cliff was observed, five days later, a bright and sharp edge was spotted where the previously identified fracture had been, along with many new metre-sized boulders at the foot of the 134 m-high cliff.
“The last time we saw the fracture intact was on 4 July, and in the absence of any other outburst events recorded in the following ten-day period, this is the most compelling evidence that we have that the observed outburst was directly linked to the collapse of the cliff,” says Maurizio Pajola, the study leader.
The event also provided a unique opportunity to study how the pristine water-ice otherwise buried tens of metres inside the comet evolved as the exposed material turned to vapour over the following months.
Image Credit: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0; ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA