ASTRONOMY
Exploding cavities on distant comets
When cavities in comets explode, they hurl gas and dust into space.
Comet 67P/Churyumov-Gerasimenko, observed by the Rosetta space probe, hurling dust and gas into space. | Photo: ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA
Explosions in the underground cavities of comets are now providing the first-ever insights into the hidden inner workings of these clusters of ice, dust and rock formed billions of years ago at the outer edge of the Solar System. “They are time capsules. Inside, they harbour material from the beginnings of the Solar System that could tell us more about how it emerged and developed”, says Daniel Müller of Space Research & Planetary Sciences at the University of Bern.
However, the interior of comets remains largely hidden from us when we study them with our telescopes and space probes. We’re only able to analyse their surface, tail and so-called coma – a kind of mini-atmosphere around the comet’s nucleus. But explosions on a comet’s surface could offer information about its interior. “We’ve already observed such explosions on some comets”, says Müller. “But so far, our data have been too inaccurate for us to understand what actually happens during an eruption”.
The Rosetta Mission to Comet 67P/Churyumov-Gerasimenko offered a unique opportunity to study the explosive surface of a comet from close up. When this space probe accompanied the comet in question during the latter’s closest approach to the Sun back in 2015, its cameras recorded roughly 30 eruptions, and it was even able to capture some of them with its mass spectrometers. “This enabled us to measure the change in the gas composition of the comet’s coma during an eruption”.
These eruptions were sometimes caused by evaporating ice. But carbon dioxide was also often involved. “It’s possible that the high pressure caused by such eruptions might burst cavities in the comet and hurl material into space”, says Müller. Scientists calculated that the cavities on 67P could be up to 500,000 cubic metres in size – about one-fifth as big as the Pyramid of Cheops. “Comets are thus rather like lumps of Emmental cheese”, says Müller. But it remains unclear just how these cavities were formed. “It could have something to do with the frequent, severe fluctuations in temperature that occur beneath the surface of a comet”. Researchers are hoping that further insights will be gained both from experiments in the lab and from ESA’s Comet Interceptor Mission that is due to launch in 2029.
