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Astrophysics

Mónica G. Salomone

Madrid

The last farewell to the ‘Rosetta’ spacecraft

There are made expressions, created by someone clever and then repeated a thousand times, appearing over and over again in the texts that disseminate a scientific fact.

16 November 2009

Mónica Salomone, Madrid

There are made expressions, created by someone clever and then repeated a thousand times, appearing over and over again in the texts that disseminate a scientific fact. A classic: the comets, those bodies whose orbit takes them through the solar system to approach them at a certain moment to the sun, will help us understand the history of the Solar System (how it was formed and from which materials).

ESA/C.Carreau

The concept is used so much that even the European Space Agency (ESA) has baptized the mission that will study a comet with the name of 'Rosetta'. In fact, it is the first one to include the landing of a small probe into one of these travelling bodies to accompany it on its journey towards the sun. And 'Rosetta' of course, makes reference to the Rosetta stone that helped to decipher the ancient Egyptian hieroglyphs. In this case, the mystery to unravel is the one of the origin of our cosmic neighbourhood. But why do the comets have the key to this question?

I confess here, that when I finally knew it, I sensed the thrill of personal finding that scientists describe so much, of course, at a small and modest scale. But there was also a prick of discomfort. Why do we fall into the trap of lack of time and space in the released articles? Anyone can disagree with this self-criticism but here it goes: in fact, we almost always recourse to the already expressed concepts to hide the internal big hole that comes from not having made the right question, not having thought a bit more, to be able to identify what we do not know. The point in which science and journalism meet (or one of them) is precisely that one: the ability to make good questions.

But this incursion into the ‘metajournalism’ of science subjects is only an infiltrated thought. What I wanted to do here is to say goodbye to the spacecraft 'Rosetta'! Right: Readers engaged in their daily work, stressed workers, public transport travellers who are late, you all should know that last 13th of November, at 8:45 in the morning, the European spacecraft 'Rosetta' approached the Earth for the third and last time before entering the depths of space towards her meeting with the 67P/Churyumov-Gerasimenko comet in about four years time. Does this fact change our life? Clearly not. But isn't it wonderful that the trajectory of a spacecraft launched more than five years ago can be defined with such precision? Gravity is a powerful law. In our Solar System's pool game it would be enough to know the exact position and speed of each body to trace its trajectory in the future.

At its closest approach to Earth, 'Rosetta' flew over the south of the island of Java, in Indonesia, at a speed of 13.34 kilometres per second regarding the surface, and at a height of 2,481 kilometres. In the operation centre of the spacecraft, the European Space Operation Centre from ESA, in Darmstadt (Germany), nothing special happened at that key moment. Neither applauses nor hugs from the engineers. Everything had been planned to the millimetre weeks before and the communications with the spacecraft (via the deep space antenna from the ESA in New Norcia (Australia) indicated a perfect development. At 9.05, another antenna in Maspalomas (Gran Canaria, Spain) was confirming the flyby.

‘Rosetta’ with this operation got a gravitational boost of 3.6 kilometres per second. It is the fourth impulse it receives of this kind; after two others with the Earth and one with Mars. Now it still has 2,600 million kilometres to go to reach its objective and it will mainly do so in a state of hibernation. In July 2010, when passing through the asteroid belt between Mars and Jupiter, it will be woken up to observe the asteroid 21 Lutetium. Once at its final destination, ‘Rosetta’ will enter into the 67P/Churyumov-Gerasimenko orbit and will release a landing module of 100 kilos weight, equipped with nine scientific instruments that will stick to the icy nucleus of the comet. During the following two years, the space device with 11 instruments on board and its landing module will study the comet on its journey towards the sun.

And after all that, I haven't said why the comets are so important to understand the origin of the Solar System. The ESA explains: “Being the most primitive objects of the system, its chemical composition hasn't changed much since its formation and therefore it preserves a register of the composition of the early Solar System". Ok, but what does it mean that they are the most primitive objects?

Here is the answer I so much liked at the time. The comets are formed of iced volatile material, what demonstrates that they have maintained themselves at large distances from the sun and at low temperatures. That also means that things haven´t happened to them as they have with the terrestrial planets, who have been victims of all kinds of impacts that have made them melt and solidify on several occasions, with the subsequent chemical transformations. No. The comets have been maintained in a fridge preserving their chemical composition just as it was 4,600 million years ago, when the planets did not exist and only a vast cloud of asteroids and comets orbited around the newborn sun. One could say that they are, almost, like a small piece of original nebula.

So, knowing this doesn't change daily life, but it is beautiful. Or not?

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