Feeds

New research cuts Kepler's exoplanet count by one third

Look out for those 'astrophysical false positive' impostors

Intelligent flash storage arrays

A new study has shown that the number of exoplanets – planets outside of our solar system – discovered by NASA's Kepler may be inflated by over a third.

The Kepler team's "Table of confirmed planets" (their emphasis) in that spacecraft's slice of the sky now stands at 105. According to the criteria used by NASA's Exoplanet Archive, there are 817 exoplanets out there, and Exoplanet.eu's catalog currently includes a total of 853 exoplanets (one more than last week) in 672 planetary systems – but what are a few extra planets among friends?

But all those numbers are likely wrong, according to an article published in the Thursday edition of the prestigious science rag, Nature.

The article, "Extrasolar planets: Astrophysical false positives", by University of St. Andrews astronomy professor Andrew Collier Cameron, cites a recent paper in the journal Astronomy & Astrophysics that painstakingly examined the masses of 46 Kepler candidates and determined that a full 35 per cent of them were, as the title of Cameron's paper suggests, "astrophysical false positives."

The careful examination of those candidates was done using the SOPHIE spectrograph at the Observatoire de Haute-Provence outside Marseille, France. According to Cameron, what the French astroboffins discovered was that some of what Kepler had identified as giant, fast-moving gas planets orbiting their host stars were instead impostors.

To understand why the French team labeled those candidates as astrophysical false positives, it's instructive to remember that Kepler makes its planetary observations by detecting minute differences in the light of a host star as the disk of a candidate planet crosses – or transits – its own disk.

The false positives that the paper posits are of three types: first, brown dwarfs or stars with masses that are less than 10 per cent of our Sun; second, "blended stellar binaries" in a three-star system whose strongly occluding eclipses are made to appear less strong – and more exoplanetary – due to the addition of the light from the third, brighter star; and simple two-star systems whose eclipses "graze" one another, thus mimicking the lessening of light caused by a planetary transit.

Diagram of how exoplanet 'false positive' identifications can occur

One actual exoplanetary transit; three 'astrophysical false positives' (click to enlarge)

The French estimate of a 35 per cent false-positive rate – well, actually 34.8 per cent, plus or minus 6.5 per cent, if you want to be precise – is substantially higher than an earlier projection, published last year, which had predicted that 90 per cent of the candidates it analyzed would have a false-positive rate of less than 10 per cent, and over half would have a rate of less than 5 per cent.

As Cameron notes, however, problems with this more-optimistic false-positive estimate were soon revealed, based on the fact that it didn't sufficiently take into account the effects of the third type of impostor, the "grazing binaries".

"We should not, however, expect the story to end here," Cameron writes. "Estimates of the true fraction of planetary systems among Kepler candidates over the full range of transit depths and orbital periods are only as good as our understanding of the binary-star population."

As is true in 99.99 per cent of scientific studies, more research needs to be done. Only after much further study and boffinary head-scratching will astrophysicists be able to accurately sort the true exoplanet wheat from the astrophysical false positive chaff. ®

Providing a secure and efficient Helpdesk

More from The Register

next story
GRAV WAVE DRAMA: 'Big Bang echo' may have been grit on the scanner – boffins
Exit Planet Dust on faster-than-light expansion of universe
SpaceX Dragon cargo truck flies 3D printer to ISS: Clawdown in 3, 2...
Craft berths at space station with supplies, experiments, toys
That glass of water you just drank? It was OLDER than the SUN
One MEELLION years older. Some of it anyway
NASA rover Curiosity drills HOLE in MARS 'GOLF COURSE'
Joins 'traffic light' and perfect stony sphere on the Red Planet
Mine Bitcoins with PENCIL and PAPER
Forget Sudoku, crunch SHA-256 algos
Big dinosaur wowed females with its ENORMOUS HOOTER
That's right, Doris, I've got biggest snout in the prehistoric world
Japanese volcano eruption reportedly leaves 31 people presumed dead
Hopes fade of finding survivors on Mount Ontake
Canberra drone team dances a samba in Outback Challenge
CSIRO's 'missing bushwalker' found and watered
prev story

Whitepapers

A strategic approach to identity relationship management
ForgeRock commissioned Forrester to evaluate companies’ IAM practices and requirements when it comes to customer-facing scenarios versus employee-facing ones.
Storage capacity and performance optimization at Mizuno USA
Mizuno USA turn to Tegile storage technology to solve both their SAN and backup issues.
High Performance for All
While HPC is not new, it has traditionally been seen as a specialist area – is it now geared up to meet more mainstream requirements?
Beginner's guide to SSL certificates
De-mystify the technology involved and give you the information you need to make the best decision when considering your online security options.
Security for virtualized datacentres
Legacy security solutions are inefficient due to the architectural differences between physical and virtual environments.