Brief but powerful blasts of material from Comet 67P/Churyumov–Gerasimenko as it neared the sun are reported in the Monthly Notices of the Royal Astronomical Society.
In the three months around the comet’s closest approach to the sun in August last year, Rosetta’s cameras captured 34 outbursts.
These are different to the usual jets and flows streaming from the comet. The comet’s general activity sees material flying off for long periods.
But these bursts are only spotted in single images, meaning they must only last five to 30 minutes and blast 60 – 260 tonnes of material during that time.
Rosetta’s snapped three types: long, narrow jets, others with a broad, wide base and some that appear to be a complex hybrid of the two.
They could well be different timepoints in the evolution of one type of jet – as they only appear in single images, scientists don’t know if they were captured at the start, middle or end of their life.
So what’s triggering them? Again, scientists aren’t sure, but just over half of the blasts occurred in regions corresponding to early morning, as the sun began warming up the surface after many hours in darkness.
This rapid warming is thought to fracture the surface and expose volatiles which vapourise into these powerful streams.
Other events which took place in the afternoon could be a result of heat making its way into pockets of volatile material buried beneath the surface. These then explode.
Sometimes the bursts take place in darkness. These may be due to cliff collapse, where fresh material is exposed, leading to an outburst.
“Studying the comet over a long period of time has given us the chance to look into the difference between ‘normal’ activity and short-lived outbursts, and how these outbursts may be triggered,” says Matt Taylor, Rosetta project scientist.
“Studying how these phenomena vary as the comet progresses along its orbit around the sun give us new insight into how comets evolve during their lifetimes.”