Landing on a Comet

European space scientists made history when they landed a probe onto the surface of a comet, but not everything went to plan.
18 November 2014

Interview with 

Professor Andrew Coates, University College London


An image sent back to earth from the Philae lander.


European space scientists have made history.  As part of a mission called Image from PhilaeRosetta, they have landed a washing machine-sized probe called Philae on the surface of a comet, over 300 million miles away. This needed precision equivalent to firing a bullet from London and hitting the head of a nail in New Delhi.

But not everything has gone to plan. Philae didn't land in the spot it was supposed to and now, it might not get enough lights to charge up its solar panels.  UCL space scientist Andrew Coates developed one of the instruments on the Rosetta Orbiter and spoke to Chris Smith. 

Andrew -  Well, what happened with the lander was, it landed first of all, almost in the right place, in fact within 10 meters of the expected point.  But unfortunately, there are a couple of systems which were supposed to happen, which didn't, one of the things where the thruster which was supposed to hold on to the comet, the other thing was harpoons, which were supposed to anchor it to the comet. And those didn't work. What happened was it bounced off to a completely different location.  In fact, the location that it bounced off to haven't quite been found yet.  But within the last few minutes, it's been shown that there was a photograph after the bounce which shows the direction of travel.  So, that will help to narrow down where it actually did.  But when it got to the surface, it landed unfortunately very near to an ice cliff on the comet and also, surrounded by boulders, in a place where sunlight actually was very limited.  So, that meant that there was a limited battery life. So the comet rotates every 12 hours and the place where it landed is about 1 ½ hours of sunlight. To add to that it was actually on its side.  So, it was trying to do the experiment on the surface and it successfully did do all the experiments in the first experiment block, 100%.  So actually, I think that's pretty impressive to get that data back to Earth before the batteries run out.

Chris -  What experiments has it done, Andrew?

Andrew -  Well, what it has been able to do is obviously take images.  There's images of the location, there's panoramic images.  Basically, all of the experiments on board were exercised in some way, including a drill that was extend to try and drill at the surface and get the pristine material from the cometary nucleus, into the laboratory to do some tests and so, all of that was successfully done.  So, drilling was done.  It's not quite sure exactly whether we caught a pristine sample yet.  It certainly was able to sample the vicinity and also to do some measurement of the physical structure of the surface and those sorts of things.

Chris -  Some of the big broadsheets are saying today and yesterday that there could be data now loitering on the probe which can't be returned but which could be very, very important.  Is that because it's just out of power and can't transmit the data back?

Andrew -  Well actually, 100% of the data was in fact transmitted back from the first experiment sequence.  So, the next step is to try and charge up the batteries and do some more experiments.  I mean, it was a huge success really to get all the data back on on Friday night which possibly could be off the orbiter, so there is not one bit of information left on the lander that could in principle be sent back.  So actually, it's a huge success to have gotten all that data back.  But the next step is to try and charge the batteries and this will probably take days or weeks, possibly months even.  So, to put in perspective, the comet is traveling around the sun and it gets closer to the sun over the next few months up until august next year.  And so, every moment, the amount of sunlight is increasing.  So, although the power available per day or the sunlight available per day is relatively limited, the amount of power will actually be increased.  In addition to that, it was possible to actually move the probe a little bit on the surface to mean that there's more solar panels now which are facing the sun than there were before.  And so again, that is a good possibility for being able to power it up in the future. But in the meantime, I think 100% success rate in getting the data back from the first few hours is actually very, very impressive and putting combination with experiments on the orbiter where we're involved, this means that this was a fantastically successful mission which is still going to be sending us back data over the next few months. 

Chris -  What do we hope to still learn or what have we learned so far?  Why is this important?

Andrew -  With the orbiter, there's a number of experiments on board.  There's 11 experiments on board the orbiter and 10 on the lander.  Comets are very important because they're very old members of our Solar System.  We're taking in fact 4.6 billion years.  So, they're the building blocks really of the planet.  So, formed in the region between Uranus and Neptune where it's cold enough for water ice to be in a solid state.  And so comets, they're building blocks really of the outer Solar System.  So, they were made there and then kicked out to sort of storage regions.  One of them is the Kuiper Belt which is in the plane of the planets.  The other one is Oort cloud which is a sort of spherical cloud of comets, a quarter of the way to our nearest star.  So, they've been in cosmic deep freeze effectively from the beginning of the Solar System.  So every time one of these comets comes into the inner Solar System, there is the possibility to look back really about time, 4.6 billion years ago.


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