Wednesday, October 23, 2013

1010 Extrasolar Planets

Figure 1. View from an imaginary exomoon of an imaginary exoplanet orbiting an imaginary binary star by Luis Calcada, reigning master of astro-art.

The ones and zeroes in my headline are not a binary expression of the number more commonly known as diez, ash’ra, dus, desyat’, or shr. No, those digits are in good old base ten, and they’re telling us that the census maintained by the Extrasolar Planets Encyclopaedia has reached vertiginous heights: as of yesterday, one thousand and ten planets have been detected around stars other than our Sun. More than a hundred were reported just in the past three months in a big statistical surge.

So now we can point to 1,010 different alien worlds where it’s night right now. Given the frequency of tight orbits and tidally locked rotation, most of those nights will last forever.

Since I did a descriptive survey of the full extrasolar population in July, I’ll hold off on an update until the end of the year. I just want to observe this moment in history and share it with whoever is reading.

But I can’t resist a few geeky observations. Of the hundred-odd objects of planetary mass reported between July 1, when the census reached 900, and October 22, when it jumped from 999 to 1010, only 16 were discovered by radial velocity (RV) observations. Four others were identified by microlensing, and two were imaged (not counting several brown dwarfs that were also photographed). All the rest – 83 planets – were discovered in transit, and more than three-quarters of those were captured by a single instrument: our beloved but now lamented Kepler spaceborne telescope.

Considering this imbalance in returns, RV has apparently assumed minority status among planet-seeking methods, while transit surveys have become the principal way to find new worlds. Just five years ago, when the exoplanet census broke 300, transit detections accounted for 17% of all detections, while RV was at 78%. Now those numbers are 39% vs. 53%.

Most of the recent bounty of transiting planets comes to us courtesy of Kepler. As mission scientists predicted when data collection ended catastrophically this past May, so many observations were already in the pipeline that analyses could go on for years to come, with new exoplanets continuing to emerge from the light curves just as they have over the past several months. Those predictions have been amply confirmed.

The influx of new transiting objects is bound to slow down eventually, since the data are finite. But it’s hard to see how RV can pick up the slack, unless a space-based RV observatory of unprecedented precision and longevity is lofted into orbit soon. Sadly, I don’t know of any such mission in the works. The James Webb Space Telescope, in development for almost 20 years, may finally launch in five more years - but that launch date isn't guaranteed, and RV observations are likely to be a small part of the JWST agenda, even if it does become a reality someday.

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