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NASA’s TESS Mission Finds Its Smallest Planet Yet

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Posted June 28, 2019

NASA’s Transiting Exoplanet Survey Satellite (TESS) has discovered a world between the sizes of Mars and Earth orbiting a bright, cool, nearby star. The planet, called L 98-59b, marks the tiniest discovered by TESS to date.

The three planets discovered in the L98-59 system by NASA’s Transiting Exoplanet Survey Satellite (TESS) are compared to Mars and Earth in order of increasing size in this illustration. Credits: NASA’s Goddard Space Flight Center

The three planets discovered in the L98-59 system by NASA’s Transiting Exoplanet Survey Satellite (TESS) are compared to Mars and Earth in order of increasing size in this illustration. Credits: NASA’s Goddard Space Flight Center

Two other worlds orbit the same star. While all three planets’ sizes are known, further study with other telescopes will be needed to determine if they have atmospheres and, if so, which gases are present. The L 98-59 worlds nearly double the number of small exoplanets — that is, planets beyond our solar system — that have the best potential for this kind of follow-up.

NASA’s Transiting Exoplanet Survey Satellite has confirmed the tiniest planet in its catalog so far — one of three discovered around a bright, nearby star called L 98-59. As shown in the illustrations in this video, all could occupy the “Venus zone,” the range of distances from the star where a Venus-like atmosphere is possible. The outermost planet also has the potential for a Neptune-like atmosphere. Credits: NASA’s Goddard Space Flight Center

“The discovery is a great engineering and scientific accomplishment for TESS,” said Veselin Kostov, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the SETI Institute in Mountain View, California. “For atmospheric studies of small planets, you need short orbits around bright stars, but such planets are difficult to detect. This system has the potential for fascinating future studies.”

A paper on the findings, led by Kostov, was published in the June 27 issue of The Astronomical Journal and is now available online.

NASA’s newest planet hunter, the Transiting Exoplanet Survey Satellite (TESS), stares for a month at a time at sectors of the sky, watching for dips in the light from stars as planets pass in front of them, called transits. TESS will map 13 sectors each in the southern and northern sky. Credits: NASA’s Goddard Space Flight Center

M dwarfs like L 98-59 account for three-quarters of our Milky Way galaxy’s stellar population. But they are no larger than about half the Sun’s mass and are much cooler, with surface temperatures less than 70% of the Sun’s. Other examples include TRAPPIST-1, which hosts a system of seven Earth-size planets, and Proxima Centauri, our nearest stellar neighbor, which has one confirmed planet. Because these small, cool stars are so common, scientists want to learn more about the planetary systems that form around them.

L 98-59b, the innermost world, orbits every 2.25 days, staying so close to the star it receives as much as 22 times the amount of energy Earth receives from the Sun. The middle planet, L 98-59c, orbits every 3.7 days and experiences about 11 times as much radiation as Earth. L 98-59d, the farthest planet identified in the system so far, orbits every 7.5 days and is blasted with around four times the radiant energy as Earth.

Illustration of NASA’s Transiting Exoplanet Survey Satellite. Credit: NASA's Goddard Space Flight Center

Illustration of NASA’s Transiting Exoplanet Survey Satellite. Credit: NASA’s Goddard Space Flight Center

None of the planets lie within the star’s “habitable zone,” the range of distances from the star where liquid water could exist on their surfaces. However, all of them occupy what scientists call the Venus zone, a range of stellar distances where a planet with an initial Earth-like atmosphere could experience a runaway greenhouse effect that transforms it into a Venus-like atmosphere. Based on its size, the third planet could be either a Venus-like rocky world or one more like Neptune, with a small, rocky core cocooned beneath a deep atmosphere.

One of TESS’s goals is to build a catalog of small, rocky planets on short orbits around very bright, nearby stars for atmospheric study by NASA’s upcoming James Webb Space Telescope. Four of the TRAPPIST-1 worlds are prime candidates, and Kostov’s team suggests the L 98-59 planets are as well.

The TESS mission feeds our desire to understand where we came from and whether we’re alone in the universe.

“If we viewed the Sun from L 98-59, transits by Earth and Venus would lead us to think the planets are almost identical, but we know they’re not,” said Joshua Schlieder, a co-author and an astrophysicist at Goddard. “We still have many questions about why Earth became habitable and Venus did not. If we can find and study similar examples around other stars, like L 98-59, we can potentially unlock some of those secrets.”

TESS is a NASA Astrophysics Explorer mission led and operated by MIT in Cambridge, Massachusetts, and managed by NASA’s Goddard Space Flight Center. Additional partners include Northrop Grumman, based in Falls Church, Virginia; NASA’s Ames Research Center in California’s Silicon Valley; the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts; MIT’s Lincoln Laboratory; and the Space Telescope Science Institute in Baltimore. More than a dozen universities, research institutes and observatories worldwide are participants in the mission.

Source: NASA

 

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