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