For Kepler’s first four years, it stared at a patch of sky in the Cygnus constellation. As it trailed behind Earth’s on its yearly trip around the sun, Kepler constantly watched more than 160,000 stars for any hint of dimming. The size of the dimming tells scientists how the big the planet passing in front of the star is. The timing of each dimming tells you how long a year is on that planet.

Today, NASA announced the final tally of planets from Kepler’s observation of this part of the sky in the Cygnus constellation. 219 new planet candidates were added to the final tally of 4,034 candidates. More than half (2,335) are verified as exoplanets. 10 of the new candidates are about the size of Earth and orbit in their star’s habitable zones. That brings the final count of near-Earth candidates to about 50. More than 30 of them have been confirmed as exoplanets.

Mario Perez, a Kepler program scientist, talks about what makes Kepler’s observations so special. “The Kepler data is unique, as it is the only one containing a population of these near Earth-analogs – planets with roughly the same size and orbit as Earth,” said Perez. Understanding how frequent planets like our own will help NASA develop the next telescope that will directly image planets like Earth.

Today’s news about more exoplanets isn’t based on new observations. Scientists went back through all the data Kepler gathered during its first four years to make sure they didn’t miss anything. To make sure no planets were missed, the team tossed in their own simulated planet transit signals into the data set to see how many were correctly identified as planets.

Plus, scientists looked at the false signals Kepler observed during its time watching the small area in the Cygnus constellation. Stars aren’t always the steady pinpoint of light scientists expect. Fluctuations from stars can look like transits. But the scientists were able to account for this in the latest release.

“This carefully-measured catalog is the foundation for directly answering one of astronomy’s most compelling questions – how many planets like our Earth are in the galaxy?” said Susan Thompson, a Kepler research scientist at SETI.

One of these planets could be a lot like Earth. KOI-7711 sits about 1,700 light-years away. And it isn’t like most exoplanets discovered by Kepler. It has an orbital period much similar to Earth’s at 303 days.

Most exoplanets tend to have small orbital periods (less than 100 days) because it’s easier to confirm a planet when you see several transits within a short period. Scientists can’t just observe one transit and say it’s a planet. They need multiple transits to confirm what they’re seeing is a planet.

Plus, what Kepler sees is just the tip of the iceberg. We can only see transits on systems that sit on the same elliptical plane as us. Kepler is basically viewing tiny solar eclipses. If Kepler, the planet and its star don’t line up, we can’t see a transit. NASA estimates for every planet we confirm there are another 100-200 out there.

The next-generation of telescopes will tell us more about these worlds

These near-Earth planets might be around the same size and sit in similar orbits, but how Earth-like are they really? What do their atmospheres look like? That’s a question the next set of NASA telescopes will try to answer.

The James Webb Space Telescope will launch next year and will start probing for details about the atmospheres of these alien worlds.

In the mid-2020s, NASA will launch another telescope called the Wide Field Infrared Survey Telescope, or WFIRST. NASA describes this telescope as being as sensitive as the Hubble Space Telescope but with a field of view 100 times that of the famous telescope. Each WFIRST image would be like taking 100 Hubble images according to NASA.

WFIRST will come equipped with a coronagraph to block the light from the stars and capture direct images of exoplanets.

Kepler’s mission continues

Kepler is no longer observing the same patch of sky but continues to look for far-flung worlds. The recent discovery of the TRAPPIST-1 system shows the spacecraft still has a few more discoveries to make before its mission comes to an end.

Kepler should have enough fuel to last until October 2018. You can keep up on Kepler’s observing campaigns over here.



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