An interview with Mark McCaughrean, the ESA scientific consultant.
– This year’s November the Rosetta space probe is supposed to make the first comet surface landing in history. How is that even possible?
– It’s not an easy task, but it is possible. Rosseta is going to approach the comet from the front side, so that it doesn’t get into the comet’s tail, which is full of dust. Once it’s close enough, it will drop its lander – Philae. This device will land on the surface and attach to it.
– It took Rosetta almost ten years to even reach the comet. I assume its task is to do some vital research, which would be impossible to conduct otherwise.
– Correct. Comets are enormous lumps of ice, but their exterior is much different. It is covered with a black crust, which was created by Sun’s activity. Sometimes we can see something leaking through this crust, but in order to examine it, we need to land on its surface and drill into its interior. That’s our goal. The lander is equipped with a 25 centimeter drill, with which it is going to break through the outer layer, collect samples and examine them.
– It’s fairly obvious, what’s inside: ice, that is, frozen water.
– That’s the whole point. One of the questions such comet landing is going to help us to answer is: where did water on Earth come from. When it was still forming itself, it was far too hot for water to last on its surface. It is more than likely, that it appeared on Earth much earlier. Scientists have been speculating for quite some time, that water might come from comets, which are in fact huge ice blocks. The Rosetta probe is going to prove this theory either right or wrong. It will show us, whether the water on Earth is the same as inside the comets.
– And what could determine one sample of water different from another?
– Deuterium. Water contains regular hydrogen, but there’s also deuterium, a heavier hydrogen isotope. Its concentration in the oceans is stable. The research we’ve made thus far remotely proved that the amount of deuterium on comets varies. Only one comet, Hartley 2, had a pattern similar to that on Earth.
– So the Solar System can have comets with various amount of deuterium?
– Exactly. The ones we’d examined before came from the Oort cloud, which is located in the outskirts of the Solar System. Hartley 2 is from the Kuiper Belt, which is a much closer to the Sun. The Churyumov-Gerasimenko comet, which will also be examined by Rosetta comes from this region as well. If we will find an appropriate amount of deuterium in these, we might assume, that the water on Earth came from the Kuiper Belt.
– Apart from deuterium, what else is Rosetta going to examine?
– We’re going to look for organic compounds, the matter of living organisms. If we succeed, it will also prove, that life forms came to Earth thanks to comets.
– This sounds a lot like archaeology or paleontology. Only you’re reaching much deeper into the past.
– You could say so. We’re something like space archaeologists.
– But you do something more than just explore the past?
– Of course. For instance the Gaia observatory is supposed to monitor asteroids, which could be hazardous to Earth. Ones that could collide with the Earth one day.
– We’re hearing a lot of stories about those planetoids causing cataclysms here on Earth, yet not a single one managed to hit us so far. Perhaps the risk is overrated?
– There’s always the risk, although minor. Chances that within the next 10 years an asteroid of a couple hundred meters in a diameter would hit the Earth is zero. But if we take a longer time period like 10 000 or 100 000 years, chances get bigger. In case of such a collision millions of people would die.
– And if Gaia would find such a asteroid, could we do anything to prevent the collision with the Earth?
– As for now - no. But we hope we might find a remedy one day. It’s up to politicians, whether they take the risk seriously. However, asteroids observation is but one of Gaia’s tasks. Its main objective is to create a thorough map of the Milky Way.
– Why do we need such a map? Maps are made to travel, and it’s improbable that we will visit far reaches of our Galaxy anytime soon.
– It won’t be just a mere map. Gaia will not only chart over a billion stars, but also their velocity and movement directions. And it will be incredibly precise. All this data will be uploaded to supercomputers, thus creating a model of the Milky Way. We will be able to rewind this model, just like a VHS tape, and see the origins of our galaxy.
– So it will enable time travel!
– Yes, and all thanks to observation of remote galaxies.
– Have you got any bets on what you’ll see once you rewind this ‘tape’?
– Actually, when we watch the stars, we don’t see them as they are now, but what they looked like in the past, billions of years ago, as it took a lot of time, before their light reached Earth. We know for sure, that once there were more galaxies, but they were smaller than today. Hence, we assume, that the Milky Way came to be as a result of smaller star clusters joining together.
– So it was a space cataclysm?
– No. When galaxies fuse, there are no explosions or other such phenomena. Stars don’t collide. It is „peaceful” method of fusing, which enables us to trace the past of the Galaxy. If stars collided, then such a ‘time travel’ would be a much more difficult affair.
– So by rewinding the tape, we might be able to see smaller galaxies, which made our Milky Way?
– I believe we will be able to see smaller parts of it, which fused together. These will be star clusters which go on similar trajectories.
– How many such ‘pieces’ were there?
– I don’t know. A couple hundred, I think.
– So we will be able to say: This is the cluster our Sun came from . It’s again not unlike archaeology.
– Indeed. Recently I had a chance of talking to a British journalist, famous for his harsh and controversial demeanor. When I told him about my job, he just exclaimed: „It’s archaeology all over again! Boring!” But I think archaeology is a very interesting subject, and our activities at ESA are even more interesting.
– It’s hard to disagree: after all, you are space archaeologists, who perform comet landings!
Interview by Łukasz Kaniewski.
date of publication: 30.04.2014
Prof. Mark McCaughrean – he works for the European Space Agency, where he is the Senior Science Advisor in the Directorate of Science and Robotic Exploration, responsible for communicating the scientific results from ESA’s astronomy, heliophysics, planetary, and fundamental physics missions. Following his PhD in astronomy from the University of Edinburgh in 1988, he has worked in the UK, the US, Germany, and the Netherlands. His personal research involves observational studies of the formation of stars and their planetary systems using state-of-the-art ground- and space-based telescopes. He is an Interdisciplinary Scientist on the Science Working Group for the NASA/ESA/CSA James Webb Space Telescope.