Philae has gone to sleep

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Despite several attempts to reposition the lander to get more sunlight to its solar panels, Philae went into hibernation on Saturday.

There is still a chance the lander will come back awake, but right now the Rosetta science team considers its mission complete. Meanwhile, Rosetta will continue its flight with Comet 67P/C-G, tracking it closely for the next year as it makes its next close approach to the sun.



  • Garry

    To me it’s curious that this article (and others like it that I’ve read) haven’t addressed what might happen as the comet grows its tail; if the lander is amid the material of the tail, will the sunlight be blocked from reaching the solar panels? Will the lander itself become part of the tail? If so, will enough sunlight get through the surrounding material to power up the lander? These are drastically different scenarios, and I’m eager to see what the experts speculate might happen.

  • These factors have been discussed, but not widely. It was always expected that the presence of the dust from the tail would determine the life expectancy of Philae. As the dust increased, they expected the solar panels to get covered, thus reducing the amount of sunlight powering the spacecraft.

    It is important to note however that, from what I understand, Comet 67P/C-G does not produce a gigantic tail. Its 6.5 year orbit travels from somewhere out around Jupiter to between the orbit of Earth and Mars, so it never gets that close to the sun. This means that it doesn’t heat up that much, and that the difference between perihelion and apohelion is not as significant. See this webpage for more info.

  • Garry

    Thanks, now I understand.

    Now that I think about it, even if the lander came off the comet, it wouldn’t receive much sunlight, as the tail points away from the sun.

  • Sandra Warren

    What a shame! I was really hoping to see ongoing pictures of the surface.

  • Patrick Ritchie

    As others have noted this really calls out the need for nuclear power options for exploring areas where solar power is either weak or uncertain.

    If Philae had a power system similar to Curiosity’s (or even Viking’s) it would still be up and running and sending science data.

  • If I calculated the escape velocity on Comet 67P properly, it looks like it is about 45 cm/s. The assumption for the calculation is a spherical body, but the true result will probably not differ by more than 10% or so from this estimate [Mass of the comet is estimated about 3.14 x 10**12 kg, and the “radius” is about 2000 m].

    So, I think the atmosphere at the surface will be fairly diffuse, like a hazy day in Southern California back in 1972. A couple important questions are: 1) how sticky are the particles boiling off the surface? 2) What is the velocity distribution of those particles? The particles that are going fast will not stick around – they will escape quickly into the tail and beyond. Suppose that you use 2 x Escape Velocity as “fast”; that is approximately 1 m/s. (Barely a tithe of the speed of the fastest human on our planet). So I think the atmosphere will be fairly thin, and the sun should be able to penetrate fairly easily. I don’t think much dust will accumulate on the solar panels – it seems more likely to just bounce off (like Philae did when it hit the comet).

    But then, maybe it’s just wishful thinking – with the hope of seeing the lander power up again in a few months in the sun light! It probably will all come down to how sticky the dust is.

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