Moon Sized Exoplanet Discovered By NASA's Kepler Space Telescope

Kepler-37b, an exoplanet the size of the Earth’s moon has been discovered in a planetary system in the constellation of Lyra by NASA’s Kepler Space Telescope. The planet is the smallest planet yet discovered arouns a Sun-like star.


Kepler 37b is located, along with other planets in its star system, around 210 light-years from the Earth, as part of the constellation of Lyra. The planet is only barely bigger than our moon, being around 1/3 the size of the Earth. Considering that it’s actually smaller than Mercury, it’s impressive that we were able to detect it from so far away.

The planet, and two others in the same system, were discovered by researchers working as part of NASA’s Kepler mission. Kepler’s stated mission is to discover Earth-sized planets that reside in the ‘habitable zone’ around their star. Planets located there will theoretically be able to support liquid water on their surface. The star system that Kepler-37b is located in, though, is very different from our solar system.

“Astronomers think Kepler-37b does not have an atmosphere and cannot support life as we know it. The tiny planet almost certainly is rocky in composition. Kepler-37c, the closer neighboring planet, is slightly smaller than Venus, measuring almost 3/4 the size of Earth. Kepler-37d, the farther planet, is twice the size of Earth.”

When the search for exoplanets began, the means available meant that all we were finding was were massive gas giants. But now, as technologies have continued improving, it has become possible to to detect smaller and smaller exoplanets. This has made it very clear, that Earth-sized, and smaller, planets are very common in the Milky Way.

“Even Kepler can only detect such a tiny world around the brightest stars it observes,” said Jack Lissauer, a planetary scientist at NASA’s Ames Research Center in Moffett Field, Calif. “The fact we’ve discovered tiny Kepler-37b suggests such little planets are common, and more planetary wonders await as we continue to gather and analyze additional data.”

The star that the Kepler-37 planetary system is based around is similar to our Sun, but somewhat smaller and cooler. “All three planets orbit the star at less than the distance Mercury is to the sun, suggesting they are very hot, inhospitable worlds. Kepler-37b orbits every 13 days at less than one-third Mercury’s distance from the sun. The estimated surface temperature of this smoldering planet, at more than 800 degrees Fahrenheit (700 degrees Kelvin), would be hot enough to melt the zinc in a penny. Kepler-37c and Kepler-37d, orbit every 21 days and 40 days, respectively.”


“We uncovered a planet smaller than any in our solar system orbiting one of the few stars that is both bright and quiet, where signal detection was possible,” said Thomas Barclay, Kepler scientist at the Bay Area Environmental Research Institute in Sonoma, Calif., and lead author of the new study published in the journal Nature. “This discovery shows close-in planets can be smaller, as well as much larger, than planets orbiting our sun.”

The researchers utilized data gathered by NASA’s Kepler space telescope to discover the exoplanet. Kepler “simultaneously and continuously measures the brightness of more than 150,000 stars every 30 minutes. When a planet candidate transits, or passes, in front of the star from the spacecraft’s vantage point, a percentage of light from the star is blocked. This causes a dip in the brightness of the starlight that reveals the transiting planet’s size relative to its star.”

“The size of the star must be known in order to measure the planet’s size accurately. To learn more about the properties of the star Kepler-37, scientists examined sound waves generated by the boiling motion beneath the surface of the star. They probed the interior structure of Kepler-37’s star just as geologists use seismic waves generated by earthquakes to probe the interior structure of Earth. The science is called asteroseismology.”

“The sound waves travel into the star and bring information back up to the surface. The waves cause oscillations that Kepler observes as a rapid flickering of the star’s brightness. Like bells in a steeple, small stars ring at high tones while larger stars boom in lower tones. The barely discernible, high-frequency oscillations in the brightness of small stars are the most difficult to measure. This is why most objects previously subjected to asteroseismic analysis are larger than the sun.”

Because of how incredibly precise Kepler is, the search for exoplanets has reached an important milestone. “The star Kepler-37, with a radius just three-quarters of the sun, now is the smallest bell in the asteroseismology steeple. The radius of the star is known to three percent accuracy, which translates to exceptional accuracy in the planet’s size.”

In a related note, those in the field have voiced their thoughts that the first moon orbiting around an exoplanet is likely to be discovered this year. Several candidates have already been discovered, but remain unconfirmed as of now.

Source: NASA/Jet Propulsion Laboratory

Image Credits: NASA/Ames/JPL-Caltech

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