SJAA Ephemeris December 2010 | SJAA Home | Contents | Previous | Next

The Last Month in Astronomy


07-NOV-2010 • Eris shrinkage • Dear Pluto, First, on behalf of the planet or at least the astronomers or maybe just on behalf of amateur astronomers on my block, sorry for belittling you lately. Yes, we always understood that it is us not you. You didn’t change. We demoted, no, make that, modified your status to that of “dwarf planet”. As Neil deGrasse Tyson says, if you were in orbit around 1 AU then you would have a cometary tail and “that’s no way for a planet to behave”. But Dr. Tyson, on a recent episode of “The Big Bang Theory” claimed he didn’t stick it to you, the International Astronomy Union did. Yet, his preeminence dwarfs other astronomers. Oops, used the “d” word again. We did have good intentions. We knew that there are a lot of objects like you out there 40 AU or more away from Sol. And we figured someday we would find an object even larger than you and we either let everybody be a planet or we get pedantic about it. This would not have felt so unseemly except that it makes scientists look like they don’t know anything. If you can’t get the definition of a planet correct how much faith can we put into cosmology? And it’s not like astronomers were going to go back and fix the misnamings that have accumulated over centuries: planetary nebulae (nothing to do with planets), Alpha Orionis (Betelgeuse is not brighter than Rigel), quarter moon (when it looks half lit), novae (not “new” stars, dying stars). But righteous indignation was rampant when Eris was discovered and it was bigger than you. Ooops, again. Turns out Eris is probably smaller than you. Some occultation measurements performed by telescopes in Chile made that determination. Alas, this doesn’t mean we are going to restore your previous planetary status anytime soon. If ever. For all the reasons why please see Mike Brown the original discoverer of Eris. He says that this must mean that you are less dense than Eris. And if that is true then you might not be related at all. Now what?

05-NOV-2010 • Hartley Studied • The Deep Impact mission has completed part 2 of its mission. It came within 435 miles of Comet Hartley. This mission is officially called EPOXI - a combination of two instruments. Hartley 2 is the fifth comet nucleus to be imaged and the first time two comets were studied with the same hardware.

29-OCT-2010 • Mars Gullies from CO2 • Researchers have tracked changes in gullies and tracked them to CO2 frost. This is because the changes appear during Martian winter, a time when liquid water is unlikely. Instead, it appears that the carbon dioxide frost accumulates at the top of a dune that eventually gets thick enough to cause a small avalanche.

28-OCT-2010 • Largest Neutron Star • A neutron star has been found that is twice the mass of the sun. The pulsar is PSR J1614-2230 which rotates 317 times per second. The mass measurement works best when a companion star is present and in this case the companion orbits once per 9 days. In addition, the companion is in an orbit that is nearly edge-on from Earth. This causes radio waves to undergo a delay called the Shapiro Delay. This discovery makes some theories more likely and others less so. Winners are that short-duration gamma ray bursts can come from neutron stars and that they can be used to study gravitational waves. Losers are that free quarks can be found in a neutron star core and that they might contain other subatomic particles.

28-OCT-2010 • How Many Earths • Sometimes the statistics tell a story that arrives before the rest of the evidence. For example, we know that the odds are you are more likely to die from an asteroid hitting Earth than you are from a terrorist act. This is true despite the fact that no human (that we know of) has ever been killed by an asteroid. Here’s another one. 23% of all Sun-like stars should have Earth mass planets. But we haven’t found any yet. That new statistic comes from Geoff Marcy and Andrew Howard from UC Berkeley. Their reasoning goes something like this: for every 100 sun-like stars, we detect 1-2 Jupiters, maybe 6 Neptunes, and about a dozen super-Earths (3-10 Earth masses). At that rate, you should end up with 23 planets in the range of .5 to 2.0 Earth masses. Compare this to some estimates of the factors in the Drake Equation. One factor is the number of stars that have planets and another factor is the number of those planets that can support life. Some put each factor at one over ten so those two factors come out to 1%. Can it really be 23% instead? Okay, not quite an apples-to-apples comparison but wow!

27-OCT-2010 • THEMIS becomes ARTEMIS • Two spacecraft have been given new assignments. The two THEMIS spacecraft were supposed to study that solar wind as it moves past the Earth. The problem is that the spacecraft, intended to be in the Earth shadow only 3 hours at a time, found themselves in shadow 8 hours during some orbits and the electronics suffered. So the instruments were moved to the Lagrangian points 1 and 2 and they have been renamed ARTEMIS.


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