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Kepler confirms 1,284 new planets

The announcement more than doubles Kepler’s confirmed exoplanets and suggests that, somewhere out there, we’ll discover another Earth.

This artist's concept depicts select planetary discoveries made to date by NASA's Kepler space telescope. Image credit: NASA/W. Stenzel

This artist’s concept depicts select planetary discoveries made to date by NASA’s Kepler space telescope. Image credit: NASA/W. Stenzel

Scientists say that they’ve now confirmed that 1,284 objects observed outside Earth’s solar system by NASA’s Kepler spacecraft are indeed planets. Announced yesterday (May 10, 2016) in the Astrophysical Journal, it’s the largest single announcement of new planets to date and more than doubles the number of confirmed planets discovered by Kepler so far to more than 2,325.

And it means that – of the nearly 5,000 total exoplanet candidates found to date – more than 3,200 have been verified (2,325 by Kepler, and the rest by other means). Go Kepler!

Ellen Stofan is chief scientist at NASA Headquarters in Washington. She said:

This announcement more than doubles the number of confirmed planets from Kepler. This gives us hope that somewhere out there, around a star much like ours, we can eventually discover another Earth.

The Kepler mission finds planets by the transit method; that is, it looks for a brief dip in a star’s light as planets previously hidden in their stars’ glare pass in front of the stars (much like the May 9 Mercury transit across the face of our sun). False positives are common. They can result from – for example – smaller, dimmer stars orbiting larger, brighter companion stars.

That’s why validation is needed.

During the May 10 announcement, the scientists explained a new technique developed by Princeton astrophysicist Timothy Morton, who is lead author of the Astrophysical Journal paper. It’s a statistical analysis method that can be applied to many planet candidates simultaneously. Morton’s method essential compares values from previous exoplanet observations to current measurements. Writing in Wired, Nick Stockton explained:

His method uses paired simulations, comparing values from previous exoplanet observations to current measurements. The first compares the flicker in question to other confirmed signatures of both exoplanets and imposters. The second simulation determines whether—given what scientists know about the total distribution of exoplanets in the Milky Way—the flicker in question makes sense as an exoplanet. Combined, the two simulations assign each flicker a statistical probability of being an exoplanet.

Timothy Morton said:

Planet candidates can be thought of like bread crumbs. If you drop a few large crumbs on the floor, you can pick them up one by one. But, if you spill a whole bag of tiny crumbs, you’re going to need a broom. This statistical analysis is our broom.

The researchers used an automated software developed at Princeton known as Vespa that allows scientists to efficiently determine if a Kepler signal is caused by a planet. Vespa computes the chances that a Kepler signal actually came from a certain type of planet. Automated software such as Vespa is necessary because of the sheer amount of Kepler data and the similarity that some planetary signals — especially those of larger planets — have to other objects such as stars that orbit each other. The graph above shows the type of planets newly verified by Vespa (orange) compared to the number of those planets previously confirmed (blue). Vespa more likely verified smaller planets because of their prevalence and unambiguous signal; signals thought to come from less common Jupiter-sized planets were more likely to actually emanate from stars. Image credit: NASA

The researchers used an automated software developed at Princeton known as Vespa that let scientists to determine if a Kepler signal is caused by an exoplanet. Vespa computes the chances that a Kepler signal actually came from a certain type of planet. Automated software such as Vespa is necessary because of the sheer amount of Kepler data and the similarity that some planetary signals — especially those of larger planets — have to other objects such as stars that orbit each other. The graph above shows the type of planets newly verified by Vespa (orange) compared to the number of those planets previously confirmed (blue). Vespa more likely verified smaller planets because of their prevalence and unambiguous signal; signals thought to come from less common Jupiter-sized planets were more likely to actually emanate from stars. Image via NASA

Scientists from Princeton University and NASA analyzed the Kepler space telescope’s July 2015 planet candidate catalog, which identified 4,302 potential planets. For 1,284 of the candidates, the probability of being a planet is now greater than 99 percent – the minimum required to earn the status of “planet.” An additional 1,327 candidates are more likely than not to be actual planets, but they do not meet the 99 percent threshold and will require additional study. The remaining 707 are more likely to be other astrophysical phenomena. This analysis also validated 984 candidates previously verified by other techniques.

In the newly-validated batch of planets, nearly 550 could be rocky planets like Earth, based on their size. Nine of these orbit in their sun’s habitable zone, which is the distance from a star where orbiting planets can have surface temperatures that allow liquid water to pool. With the addition of these nine, 21 exoplanets now are known to be members of this exclusive group.

Natalie Batalha is co-author of the paper and the Kepler mission scientist at NASA’s Ames Research Center in Moffett Field, California. She said:

They say not to count our chickens before they’re hatched, but that’s exactly what these results allow us to do based on probabilities that each egg (candidate) will hatch into a chick (bona fide planet).

This work will help Kepler reach its full potential by yielding a deeper understanding of the number of stars that harbor potentially habitable, Earth-size planets – a number that’s needed to design future missions to search for habitable environments and living worlds.

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Launched in March 2009, Kepler is the first NASA mission to find potentially habitable Earth-size planets. For four years, Kepler monitored 150,000 stars in a single patch of sky, measuring the tiny, telltale dip in the brightness of a star that can be produced by a transiting planet.  Image via Kepler mission.

Launched in March 2009, Kepler is NASA’s first mission to find potentially habitable Earth-size planets. For four years, it monitored 150,000 stars in a single patch of sky, measuring tiny, telltale dips in the brightness of star produced by transiting planets. After going into – and then out of – Emergency Mode earlier this year, Kepler is now pursuing an extended mission called K2. Image via Kepler mission.

Bottom line: Scientists from Princeton University and NASA have confirmed that 1,284 objects observed outside Earth’s solar system by NASA’s Kepler spacecraft are indeed planets. Reported in The Astrophysical Journal on May 10, it is the largest single announcement of new planets to date and more than doubles the number of confirmed planets discovered by Kepler so far to more than 2,300.

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Eleanor Imster

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