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Science Forum

  1. 19 Jul '14 19:27
    The ESA/NASA collaborative Rosetta spacecraft gets close to comet Churyumov-Gerasimenko next month. Then in November its lander will make physical contact with the nucleus.

    http://www.jpl.nasa.gov/news/news.php?release=2014-182

    Give me a heads-up whenever there is substantial new data, if you would.
  2. 26 Jul '14 17:34
    "Head," "body," and "neck" are terms being used to describe the shape of the comet as the probe closes in on it.

    http://www.jpl.nasa.gov/news/news.php?release=2014-243
  3. 01 Aug '14 18:24
    The comet is now seen to have a somewhat dark covering, which keeps it warmer than it would be if it were clean ice.

    http://news.yahoo.com/comet-surface-dark-crusty-deep-space-probe-suggests-155557326.html

    The spacecraft will orbit around the comet and continue doing so as the comet is warmed up enough to eject more material than the trivial amound coming off of it at its current distance from the Sun.
  4. Standard member sonhouse
    Fast and Curious
    04 Aug '14 14:18
    Originally posted by Paul Dirac II
    The comet is now seen to have a somewhat dark covering, which keeps it warmer than it would be if it were clean ice.

    http://news.yahoo.com/comet-surface-dark-crusty-deep-space-probe-suggests-155557326.html

    The spacecraft will orbit around the comet and continue doing so as the comet is warmed up enough to eject more material than the trivial amound coming off of it at its current distance from the Sun.
    Here is the latest hi res photo:

    http://phys.org/news/2014-08-amazing-photo-rosetta-comet.html
  5. 04 Aug '14 17:44 / 4 edits
    Originally posted by sonhouse
    Here is the latest hi res photo:

    http://phys.org/news/2014-08-amazing-photo-rosetta-comet.html
    It looks like a concrete boot to me.
    What does that says about my psychology? "don't mess with me"?
  6. 05 Aug '14 01:20
    Originally posted by humy
    It looks like a concrete boot to me.
    What does that says about my psychology? "don't mess with me"?
    Brussels sprout stuck to an old bar of soap, I say.
  7. 07 Aug '14 01:08 / 1 edit
    Boulders can be seen in one of the photos here--

    http://news.yahoo.com/first-comet-close-ups-rosetta-spacecraft-reveal-scientific-152257398.html
  8. Standard member sonhouse
    Fast and Curious
    07 Aug '14 11:30
    Originally posted by Paul Dirac II
    Boulders can be seen in one of the photos here--

    http://news.yahoo.com/first-comet-close-ups-rosetta-spacecraft-reveal-scientific-152257398.html
    One thing I was wondering, how much effect does the radiation from the sun have on the orbit of these objects? It is about 500 million Km from the sun and as such gets roughly 100 watts per square meter of energy from the sun, as opposed to 1355 watts per square meter of radiation hitting the top of Earth's atmosphere.

    I calculated a rough idea of the total energy received at about 1/4 of a gigawatt total on the surface of that comet. So going with 250 megawatts, how much actual force does that represent in terms of thinking of that in terms of solar sails presently in development? Obviously it would be pushing against a vast mass, even if that mass is tiny compared to Earth or the moon, it is still like a mount Everest flying through space.

    I was thinking of the fact that force would be acting on that mass for years at a time and another effect would be the thrust given by the water streaming off the comet when it is closer to the sun. It would seem to me at least part of the time the solar pressure and the rocket pressure of the water leaving the comet would add up and increase the effect of changing the orbit of this giant mountain in space.

    I wonder if you could calculate what the orbit would be without the solar pressure and see how much the orbit changes because of that pressure, I imagine it would not be a lot but it would be interesting to find out how much change it would represent.
  9. 08 Aug '14 02:25 / 2 edits
    Originally posted by sonhouse
    ... and another effect would be the thrust given by the water streaming off the comet when it is closer to the sun.
    My high school physics teacher had a rotary radiometer in the classroom. I remember him asking us to predict which way it would rotate-- shiny sides forward or dark sides forward.

    Some of us thought the latter, based on photons bouncing off the shiny side versus being absorbed on the dark side, giving a bigger impulse in reflection than in absorption.

    But as I recall things, it rotated the other way, with the teacher explaining that the expected behavior is swamped by the remnant air molecules inside the bulb (not quite a true vacuum) being flung off the relatively hot dark side faster than off the relatively cool shiny side.

    (Not that this is particularly relevant to your post; it's just that I was reminded of it.)
  10. Standard member sonhouse
    Fast and Curious
    13 Aug '14 01:19
    Originally posted by Paul Dirac II
    My high school physics teacher had a rotary radiometer in the classroom. I remember him asking us to predict which way it would rotate-- shiny sides forward or dark sides forward.

    Some of us thought the latter, based on photons bouncing off the shiny side versus being absorbed on the dark side, giving a bigger impulse in reflection than in absorptio ...[text shortened]... .

    (Not that this is particularly relevant to your post; it's just that I was reminded of it.)
    I actually have one of those things, I got it going shining a laser on it!
  11. 05 Sep '14 04:58
    A month of inactivity gets a thread locked, so I will keep bumping this one until the probe sets down on the comet in November.



    Twitter page for this comet--
    https://twitter.com/ESA_Rosetta
  12. Standard member sonhouse
    Fast and Curious
    08 Sep '14 21:36 / 1 edit
    Originally posted by Paul Dirac II
    A month of inactivity gets a thread locked, so I will keep bumping this one until the probe sets down on the comet in November.



    Twitter page for this comet--
    https://twitter.com/ESA_Rosetta
    Here is hoping they actually pull it off. There is a theory of comet building making the rounds that it is not gravity holding them together but electrical forces, Van Der Waals kind of thing. If so that little probe may be in for a big shock when it sets down, so to speak

    Future missions might want to include an electrometer to measure electrical forces in the vicinity of a comet. If there are electrical forces strong enough to hold the pieces together, it should be readily seen in the proper instrumentation but I don't think any of these probes have been equipped with such devices. It's basically a small antenna going to a very high impedance DC amplifier with 60 or 80 db of gain that can sense the presence of such fields surrounding a comet if they are there.
  13. 09 Sep '14 06:34
    http://phys.org/news/2014-09-experts-nicaragua-meteorite.html
  14. 09 Sep '14 06:56
    Originally posted by sonhouse
    Here is hoping they actually pull it off. There is a theory of comet building making the rounds that it is not gravity holding them together but electrical forces, Van Der Waals kind of thing. If so that little probe may be in for a big shock when it sets down, so to speak
    Van Der Waals forces do not result in an overall charge. You are obviously thinking of ordinary static electricity. In general, there are a number of different forces that hold molecules together and the question is which ones are the most significant. It is likely that gravity does play a significant part, but possibly not the only significant part, and possibly not event the largest part.
  15. 09 Sep '14 07:00
    Originally posted by humy
    http://phys.org/news/2014-09-experts-nicaragua-meteorite.html
    That hole looks too small for 1 ton of TNT, but then I am not an explosives expert.