Goodbye Philae!

We say goodbye to the lander that bounced its way to fame across the surface of comet 67P.
02 February 2016

Interview with 

Andrew Coates, UCL Mullard Space Science Laboratory, and Ian Wright, The Open University


Philae Landing


Philae is the lander that shot to fame when it landed, not once, but, in fact, three times as it bounced across the surface of comet 67P.  It's part of a mission that was Philae landingdecades in the making and also a YouTube sensation thanks to "that" reaction from team-member Monica Grady when it landed.

Philae, and the Rosetta probe that delivered it, are both now nearing the ends of their operational lives. Connie Olbach has been looking over what the first mission ever to land on - and analyse - a comet has achieved, beginning with mission scientist, Andrew Coates...

Andrew - What's happening now is that the comet, the spacecraft Rosetta and Philae, the lander, which is still on the surface of the comet, these are all getting further away from the sun, further and further with every second as we speak, of course.  As we get towards the end of January, then the temperature in the lander is getting lower.  There's a particular temperature limit of -51 degrees centigrade where it gets too cold for the batteries, and too cold for the electronics to work, so we give up hope really after the end of January

Connie - A sad thought for those of us who have become attached to the little lander.  But all is not lost, Rosetta is still in good shape and will keep orbiting until September.  For now though, let's say our goodbyes - Philae lander this is your life...  Let's start by delving back into our archives.  This is Ian Wright, a scientist working on the Rosetta mission.

Ian - Rosetta was born as a comet nucleus sample return mission.  So this was not merely going to go to a comet; it was going to drill down 3 metres into the surface, collect the core and bring it back to Earth undisturbed.  It turned out that this was technologically quite challenging and beyond the financial means of the world space agencies, because this was going to have to be a joint venture.  So eventually, in the early 90s, that  idea was sort of knocked on the head, at which point ESA decided to go it alone and do this one way mission.  And then all of a sudden there was absolutely no chance of doing that so the question was, well, if you can't bring the sample to the instrument, can you take the instrument to the sample and that's ultimately what we had to do.

Connie - Rosetta launched back in 2004.  It was then a good ten year wait for it to reach the comet 67P.  This was the site of the first ever soft landing of a probe onto a comet, and the scene of the celebration made news around the world.

"How audacious!  How exciting!  How unbelievable! To be able to dare to land on a comet..."

"We are the first to have done that and that will stay forever."

"Hollywood is good, but Rosetta is better."

Connie - But, amid the excitement, not everything was going exactly to plan.  Here's Andrew Coates again.

Andrew - Something was obviously going wrong.  You could see it in the eyes of the controllers and some frowns and so on from the control room, and we found out it had bounced to about, something like, 100 metres - a little bit more than that perhaps - away from the surface, and then came down again, bounced off the surface again, and came to rest finally in this really difficult place with boulders and next to an icy cliff, and in an orientation with one leg up in air of the lander, which you can see on the images.

Connie - The problem with this slightly awkward landing was that Philae was in a shadow; meaning no light could get to it's solar panels and the batteries only lasted two and a half days.  But it wasn't all bad news - the bouncing gave Philae exposure to different areas of the comet and it still managed to send back 80% of the data...

Andrew - Anything you get from a lander like this is actually really good information.  So we were able to get several new organic molecules identified by the mass spectrometers.  Those have never been seen in remote sensing, or in in-situ measurements of comets before and also finding that the magnetic field of the comet is non-existent and so that puts constraints on the importance of the magnetic field in the beginning of the solar system.  Now, there have been some theories about magnetism being very important in terms of bringing the early planetesimals together - these are the building blocks of planets.  And it turns out now, according to the results from Philae and the Rosetta orbiter - the combination of those two - that actually turns out not to be the case.  And so magnetism actually didn't play a role in the early solar system.

Connie - Maybe it's just me, but we've all got a bit attached to Philae.  We give it human characteristics and the idea of sending it off is so much sadder, I think, because Philae seems like a friend almost.

Andrew - So both the orbiter and the lander have their own twitter accounts and it was amazing; they were effectively giving both of them their own personality and getting Philae to contact and say - yes, I'm alive and able to be sending data. It sounded so familiar and really does make you identify with these space projects.  This is a great way of getting the public involved in space missions. I mean, they seem very remote, of course, and to actually be able to empathise with it  and be there with it almost was fantastic and a new way of doing outreach.  And I think that particular aspect of it, with Rosetta in particular, has been extremely successful.

Connie - So Philae has gone but, hopefully, not forgotten...

Andrew - Absolutely...

Connie - What's the legacy that Philae's left behind?  There will be learnings, I'm sure,  and are we going to see any more Philaes going out afterwards.  Maybe Philae babies landing on more comets?

Andrew - I'm sure we will.   And at some point people will propose more cometry landers.  There will be, you know, one type of comet which is becoming more, and more important now are main belt comets.  So this is a new type of sort of  asteroid, but it's in between an asteroid and a comet and these are objects which appear to have water, have activity, in the same way that a comet does but it's in the asteroid belt.  And so these are maybe the more likely things to have actually brought water and, possibly, organic molecules to the Earth and so, that type of object is something which will have exploration in the future, I'm sure.


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