Rosetta - Landing on a Comet
Tuesday 21st August, 2018
Our speaker was Dr Andrew Morse from the Open University's Planetary and Space Sciences Research Institute, and his lecture was entitled "Rosetta — Landing on a Comet". Dr Morse introduced himself by saying that he had studied meteorites for his doctorate at the Open University and was fortunate to have had as his supervisor the late Prof Collin Pillinger. Prof Pillinger became well known for his leadership of the ill-fated Beagle 2 mission to Mars. This small lander made it all the way to the Martian surface but, sadly, failed to operate as part of its mechanism that resembled a petal did not unfurl correctly, meaning it could not communicate with any of the orbiting spacecraft.
Dr Morse began his talk by saying that to understand how the Solar System formed you needed to firstly analyse what it was made of. He gave the analogy of when he bakes a lemon drizzle cake in his kitchen there are often remnants of the ingredients left around on the work surfaces. Similarly, the debris left from our Solar System's formation is still around today in the form of asteroids, comets or meteorites.
He then explained that the problem with analysing material from meteorites is that you have to wait for one to fall to Earth and it can be contaminated with other material as it passes through the Earth's atmosphere before finally crashes into the surface. Also, a meteorite may just burn up in the atmosphere or be lost as it enters heavy vegetation or the ocean. A comet's constituents can be studied by looking at its tail but it only produces such a tail when it nears the heat of the Sun and this means that only certain elements are emitted and not the whole range of material the comet is made up of.
The ideal situation is to actually go and visit a comet or asteroid as it orbits the Sun and the Rosetta spacecraft with its small Philae landing craft successfully achieved this goal . In this way pristine material can be studied and there are even upcoming missions where a sealed sample of an asteroid will be collected and returned to Earth.
Dr Morse continued by saying that there were problems when the Philae lander tried landing on the actual surface of comet 67P/Churuyumov-Germasimenko. Instead of settling level on the comet's surface it had actually bounced twice before coming to a halt, wedged in a crevice at the edge of a large crater. Luckily, the onboard instrument he had been involved with called "Ptolemy" had been able to sample some of the material kicked up when the lander had collided with the surface. Analysis of the sample showed the presence of organic compounds, carbon dioxide and water, plus other unusual substances not seen before on a comet. Philae was also able to use its small hammer on the surface and found it had a strong hard crust with the consistency of concrete underneath a 10-20 cm layer of dust that was more like candy floss.
Dr Morse ended his talk by saying that he thinks that it would be better if future landers could be more autonomous and control their own landings, as instant communication is not possible out to the far reaches of the Solar System.
This article was written for the club news column of the Stratford Herald. The actual lecture explained the subject at a deeper level.