NASA’s Kepler Spacecraft Discovers Tiny Exoplanets

By  //  May 21, 2013

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Smallest Planets Yet Detected

ABOVE VIDEO: Kepler is the first NASA mission capable of finding Earth-size planets in or near the habitable zone, which is the range of distance from a star where the surface temperature of an orbiting planet might be suitable for liquid water. Launched in 2009, Kepler has been detecting planets and planet candidates with a wide range of sizes and orbital distances to help scientists better understand our place in the galaxy. (Beadledom911)

BREVARD COUNTY • KENNEDY SPACE CENTER, FLORIDA – NASA’s Kepler mission scientists have discovered a new planetary system that is home to the smallest planet yet found around a star similar to our sun.

The planets are located in a system called Kepler-37, about 210 light-years from Earth in the constellation Lyra. The smallest planet, Kepler-37b, is slightly larger than our moon, measuring about one-third the size of Earth. It is smaller than Mercury, which made its detection a challenge.

The newly discovered planet Kepler-37b is slightly larger than our moon, measuring about one-third the size of Earth. (Image courtesy of NASA/Ames/JPL-Caltech)

The moon-size planet and its two companion planets were found by scientists with NASA’s Kepler mission to find Earth-sized planets in or near the “habitable zone,” the region in a planetary system where liquid water might exist on the surface of an orbiting planet. However, while the star in Kepler-37 may be similar to our sun, the system appears quite unlike the solar system in which we live.

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 three-quarters the size of Earth. Kepler-37d, the farther planet, is twice the size of Earth.

The first exoplanets found to orbit a normal star were giants. As technologies have advanced, smaller and smaller planets have been found, and Kepler has shown even Earth-size exoplanets are common.

“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.”

NASA’s Kepler spacecraft blasted off in March 2009 from Launch Complex 17-B at Cape Canaveral Air Force Station. (Image courtesy of NASA)

SAME SIZE STAR

Kepler-37’s host star belongs to the same class as our sun, although it is slightly cooler and smaller.

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 research team used data from NASA’s Kepler space telescope, which 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.

SOUND WAVE BENEATH THE SURFACE OF THE STAR

An artist's conception compares planets in the Kepler-37 system to the moon and planets in our solar system. (Image courtesy of : NASA/Ames/JPL-Caltech)

An artist’s conception compares planets in the Kepler-37 system to the moon and planets in our solar system. (Image courtesy of : NASA/Ames/JPL-Caltech)

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.

NASA’s Kepler spacecraft blasted off in March 2009 from Launch Complex 17-B at Cape Canaveral Air Force Station. (wikipedia.org image)

NASA’s Kepler spacecraft blasted off in March 2009 from Launch Complex 17-B at Cape Canaveral Air Force Station. (wikipedia.org image)

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.

NEW MILESTONE

With the very high precision of the Kepler instrument, astronomers have reached a new 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 3 percent accuracy, which translates to exceptional accuracy in the planet’s size.

NASA’s Kepler spacecraft blasted off in March 2009 from Launch Complex 17-B at Cape Canaveral Air Force Station.

Its mission is specifically designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-size and smaller planets in or near the habitable zone and determine the fraction of the hundreds of billions of stars in our galaxy that might have such planets.

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