CHASING COMETS

THESE ENIGMATIC, ICY TRAVELLERS MAY HOLD THE SECRET TO LIFE ON EARTH. THAT’S WHY SCIENTISTS ARE DESIGNING A MISSION THAT WILL PAY A VISIT TO A COMET TO TAKE A CLOSER LOOK…

- DR STUART CLARK

We’ve come a long way since thinking that comets were ghostly apparitions in the sky that foretold disaster and disease. Now we understand that these mysterious celestial objects are time capsules to an earlier era in the history of the Solar System. They can tell us about the days when the planets were forming. Comets can also reveal some of the chemical constituents that would have been present on the early Earth and so could have contributed to the origin of life.

It’s therefore no surprise that the various space agencies around the world are keen to explore comets with spacecraft. Currently under development is Comet Interceptor, which is due for launch in 2028 and will allow us to inspect these icy bodies in greater detail. But it’s by no means the first mission to visit a comet.

In 1986, Europe, the USSR and Japan launched missions to fly past Halley’s Comet. Of these, the spacecraft that drew the closest was the Giotto mission, from the European Space Agency (ESA). It gave us the first image of a comet’s icy nucleus and showed that gas was shooting into space from jets on the surface.

ESA’s more recent comet mission, Rosetta, rendezvoused with the comet 67P/Churyumov Gerasimenko, and followed it for two years between 2014 and 2016. It revealed unprecedented information about how a comet behaves as it draws close to the Sun, and then heads into deep space again. One thing became very clear. “There are a lot of evolutionary processes taking place on the surface layers of a comet. The surface actually changed as we were watching with Rosetta,” says Dr Colin Snodgrass, an astronomer from the University of Edinburgh who was part of the Rosetta team.