interstellar t is k notes on pluto charon talk and pluto mission sci space readers can skip the first paragraph yesterday in response to henry spencer s question about the temperature of a blackbody in interstellar space i said dust grains acts as blackbodies and they re at k well i was dead wrong our local interstellar dust expert bruce draine has informed me that dust grains aren t good radiators in the far ir which is why they are so warm actually the ambient radiation field from distant stars can bring a true blackbody to only or kelvin sorry henry and anyone else i misled obviously time for me to take another ism class in other news alan stern of the southwest research institute gave a talk on the pluto charon binary system yesterday he gave a brief overview of the currently accepted system parameters volume ratio of about mass ratio about or so plus lots more and then gave his thoughts on the formation of pluto charon his idea is that there were lots and lots of small planetesimals in the outer solar system with masses distributed as a power law of some kind over time the planetesimals accreted into larger bodies most got scattered out of the solar system by close encounters with jupiter and saturn but many accreted into the gas giants especially uranus and neptune a large planetesimal was captured by neptune we call it triton captured how perhaps by a collision with a smaller already existing neptunian moon perhaps by a very close passage through neptune s atmosphere mondo aerobraking he notes that the two recently discovered kuiper belt objects qb and fw plus chiron and pholus are all about the same mass and he identifies this group as one accretion down from the larger bodies of triton and pluto charon pluto charon he thinks formed when an impacting body hit proto pluto knocking some material into a ring around pluto which later accreted in charon similar to ideas about the formation of earth s moon there is good evidence from spectra that the surfaces of pluto and charon are very different pluto has methane frost charon doesn t which can be used as evidence for the impact theory he believes that there may be around pluto to chiron sized objects remaining in a relatively stable dynamical zone just outside neptune s orbit beyond au or so qb and fw are the first members of this population to be found in his model note that such bodies will be very dark since if their surfaces are covered with methane frost it will have photolyzed into very dark long chain hydrocarbons by now the reason that pluto has such a high albedo around i think is that its surface warms up just enough around perihelion to sublimate and when the atmosphere freezes out again thirty years later it forms bright new frost so any bodies much farther away than au are going to be very hard to see i hope i haven t made any errors in the transcription if you see a howling mistake it s undoubtedly mine not his by the way he s one of the top guns behind the pluto fast flyby mission i think and said that the current plans are to use a titan to send the probe on just about a rectilinear trajectory to pluto we were speaking loosely at the time he d like to use a proton which gives a slightly smaller velocity but costs much less his figures million for titan launches there will be two separate probes launched separately or million for proton launches he told a story about how the soviets originally offered to sell proton launches for million each but were forced to increase their prices in the us in order to be allowed in the marketplace i m just telling you what he said michael michael richmond this is the heart that broke my finger richmond astro princeton edu
