Archive for February, 2012

Get the money

February 28th, 2012 3 comments

It’s likely that everyone who reads this site has already seen the new Kepler candidates paper. Drawing on 16 months of photometric data, and importantly, on significant improvements to the reduction pipeline, it gives details on 2,323 planet candidates. The cumulative planet candidate table, in particular, makes for interesting reading.

In true Gordon Gekko style, I ran the new candidates table through my valuation formula (see here, here, and here.)

A screenshot of the results, for candidates with valuations greater than ten dollars are shown below. KOI 2650.01 and KOI 2124.01, assuming that they hold up, are both million dollar worlds. The total value of the current catalog is 10.9M.

Categories: worlds Tags:

Planets orbiting Barnard’s Star

February 25th, 2012 2 comments

Hey! Did you see the New York Times article about the discovery of a Jupiter-like planet orbiting Barnard’s Star?

The subtly out-of-date fonts are really the only indication that the above article, which was printed on April 19th, 1963, is nearly a half century old. Certainly, the blandly uninformative expert commentary and the worn-smooth assertion that the new finding adds support to the conviction of astronomers that a great many solar systems exist, some of them possibly supporting life, are both still fully serviceable.

The erstwhile planet(s) orbiting Barnard’s star were the fruit of thousands of astrometric measurements of photographic plates taken from 1938 through 1962 by Dr. Peter van de Kamp and his students from Swarthmore College’s Sproul Observatory. During the 1960s, the existence of van de Kamp’s planets were generally accepted by the astronomical community, and they only began to drift out favor during the 1970s. As explained in this interesting historical review of exoplanet detection, it’s now clear that the apparent astrometric motions of Barnard’s Star over the years can be correlated with telescope adjustments. Modern radial velocity measurements from UVES at the VLT and from the HET telescope show quite definitively that van de Kamp’s planets don’t exist:

Indeed, there must now be enough radial velocity observations of Barnard’s star to put some very interesting limits on any planets that might be lurking in the system… Given that the star is so bright (for a red dwarf) with V=9.5, highly charismatic, and visible from La Silla, I think it’s safe to say that for orbital periods of less than ~100 days, the largest planets that could be hiding there have masses roughly twice that of Earth.

Broadly speaking, the non-hydrogen/helium mass of a planetary system is ~0.02*0.016*Mstar*(10**[Fe/H]). We therefore don’t expect to find bruisers of planets orbiting Barnard’s Star, which has only ~14% of the Sun’s mass, and has a metallicity of order 10-30% that of the Sun. Given what we now know about the galactic planetary census, an educated guess is that Barnard’s star harbors several roughly co-planar planets, none larger than 1.5 Earth masses, with orbital periods less than 100 days. In fact, I think there’s an even chance that within the next four years, we could be reading about just such a system in the New York Times.

Categories: worlds Tags:

Regular systems of satellites

February 19th, 2012 10 comments

Following the 1846 discovery of Neptune by Urbain J. J. LeVerrier of France and Johann Galle of Germany, the British astronomical establishment — the Rev. James Challis, the Astronomer Royal George Biddell Airy, and Sir John Herschel — found themselves in rather hot water. Diffidence, seeming indifference and miscommunications had deprived Britain of a very tangible emblem of national prestige. In the damage-control scramble that ensued, Herschel wrote urgently to William Lassell, a wealthy brewer in Liverpool who owned a 24-inch telescope, exhorting him to search for satellites “with all possible expedition!”. Lassell was on task. A mere 17 days after the announcement of Neptune’s existence, he had discovered Triton, thus handing his countrymen a victory in the losers’ bracket rounds.

The quick discovery of Triton occurred in large part because astronomers were conditioned as to what to expect. Jupiter, Saturn and Uranus all host regular satellite systems in which the orbital periods of the satellites are measured in periods lasting days to weeks, and in which the mass ratio of the satellites to the primary is of order two parts in 10,000. These rules of thumb hold quite nicely, despite the fact that Jupiter has more than 20 times the mass of Uranus.

Much of the bewilderment that has accompanied the discovery of extrasolar planets stems from the fact that planets found orbiting other stars don’t bear much resemblance to configuration of our own planetary system. First, hot Jupiters. Then giant planets on highly eccentric orbits with periods of a few hundred days. And now, the realization that over half of the sun-like stars in the solar neighborhood are accompanied by planets with masses in the superEarth/subNeptune range and orbital periods of less than 100 days. It’s now clear, in fact, that our own solar system is unusual at least at some modest level, and perhaps at quite a significant level.

As hordes of new planets pile into the candidate tables at, the correlation diagrams are really beginning to show the true features of the galactic planetary census. The classic log-log mass-period diagram is a good example. Here’s one that’s (already) two months out of date:

The lower-right portion of the above diagram is incomplete, and there are a whole slew of observational biases at work, but nevertheless, the relatively depopulated divisions between the superEarth/subNeptunes, the hot Jupiters and the eccentric giants are real features of the planet distribution. There’s truth in the fact that one can sometimes overlook the forest for the trees. By smearing vaseline on the laptop screen and taking a cell-phone photograph, one obtains a better sense of the outlines of the forest:

It’s interesting to adjust the log-log mass-period diagram so that the y-axis charts the planet-to-star mass ratio rather than planetary mass (an advantage of logarithms is that concerns regarding the difference between M and Msini are effectively academic). With this plotting scheme, Earth and Jupiter are still off the guest list, but remarkably, the regular satellites of the Jovian satellites adhere to the same distribution as the superEarths and subNeptunes:

A comparison that’s made all the more dramatic with the inclusion of the Kepler multiple-transit candidates:

A coincidence? I don’t think so.

Categories: worlds Tags: