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Kepler Space Telescope Discovers 10 New Potentially Habitable Planets

ByBianca DattaNOVA NextNOVA Next

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Today, the Kepler space telescope team announced its latest list of discoveries, a total of 219 new candidate exoplanets, ten of which are rocky planets in the so-called habitable zone.

“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, Kepler research scientist in the SETI Institute, and lead author of the catalog study.

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This artist's concept depicts one possible appearance of the planet Kepler-452b, a near-Earth-size world in the habitable zone of a star that is similar to our sun.

The latest findings inch us closer to finding worlds beyond our own that can sustain life. Since the Kepler mission began in 2009, a total of 4,034 candidates and 2,335 confirmed planets have been spotted in the small slice of the sky the telescope observes, which is centered on the Cygnus constellation. To survey the entire sky, astronomers would need 400 Keplers.

Kepler measures the size of planets and their distance from stars using a technique known as transit photometry, in which the telescope watches for small decreases in the light visible from specific stars, indicating that a planet has passed in front. If a star dims at a regular interval, the Kepler team flags the signal as a candidate planet.

The announcement also revealed that Kepler data indicate two distinct size groupings of small planets as rocky “super-Earths” or gaseous “mini-Neptunes,” providing important insights on the formation of new planets.

“We like to think of this study as classifying planets in the same way that biologists identify new species of animals,” said Benjamin Fulton, lead author of the second study from this catalog. “Finding two distinct groups of exoplanets is like discovering mammals and lizards make up distinct branches of a family tree.”

This discovery sharpens the distinction between habitable and uninhabitable planets and illuminates the importance of environment in the formation of planets. Planets that are smaller (i.e. 1.5 Earth radii or less) or have less hydrogen and helium early in their lives turn into dense, rocky planets with solid surfaces, while larger planets or those with more gas turn into Neptune-like planets with no discernable solid surface and thick atmospheres. Planets with radii between these two ranges are extremely scarce.

The blue dots show planet candidates from previous Kepler results, while the yellow dots show new candidates the latest data. 10 of these new candidates are near-Earth-size, where they have a chance of being rocky with liquid water on their surface.

Exoplanets are considered habitable if they are far enough from their star to sustain liquid without freezing or boiling and thus have the potential to sustain life. This catalog brings the total candidate terrestrial exoplanets in the habitable zone up to 50. Once candidates are discovered, they are further studied to confirm that they are genuine planets, rather than erroneous signals introduced by noise from the instrumentation. At least 30 of these rocky candidates have been verified as exoplanets so far.

The nearest confirmed exoplanet in a habitable zone is Proxima Centauri b, which lies only four light years away from the Earth, or about 25 trillion miles. It is about 30% larger than Earth and orbits the star closest to our Sun, making it the closest potentially habitable planet.

Another exoplanet that stood out is KOI 7711, the closest to Earth in terms of size and distance from its sun. While scientists still need more information about its atmosphere and whether the planet harbors water, we now know that receives about the same amount of energy from its star as we do from the Sun.

Today’s announcement follows February’s discovery of a system of seven terrestrial planets, three of which were in the habitable zone. And while it adds a large cache of new exoplanets to the list, it is not as large as the results announced in May 2016, which were the largest to date.

Before Kepler was launched, we had no idea if exoplanets were rare in our galaxy. Now, we now know that, in the Milky Way, at least one exoplanet orbits in the habitable zone of every four M dwarf stars, the smallest and most common stars in our galaxy. For Sun-like stars, known as G dwarf stars, astronomers don’t have quite as detailed a survey. But of the ten newly discovered habitable planet candidates, less than half are orbiting G dwarf stars and thus could host conditions similar to our Earth.

This artist's concept depicts Kepler's smallest habitable zone planet. Seen in the foreground is Kepler-62f, a super-Earth-size planet located about 1,200 light-years from Earth in the constellation Lyra.

In a press conference today, NASA scientists explained that new craft such as the James Webb Space Telescope, which launches next year, and the existing Hubble and Spitzer space telescopes will help us better understand these new worlds, including crucial details like atmospheric content. For the next few years, at least, astronomers will still rely on transit photometry to observe these exoplanets. But by 2030, NASA scientists project that they will be able to directly image exoplanets.

These results mark the end of the first official Kepler mission, which was cut short four years ago by a second failed reaction wheel that stabilized the telescope. Its successor, K2, will survey a different patch of the sky and more and different types of stars. It “feels a bit like an end of an era, but really it’s a new beginning,” Thompson said.

Image credit: NASA Ames/JPL-Caltech/T. Pyle, NASA/Ames Research Center/Wendy Stenzel