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CosmosUp | July 16, 2019

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Another Earth may be 150 Light Years Away

Another Earth may be 150 Light Years Away
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On January 6, astronomers announced the discovery of eight new planets in the so-called Goldilocks zone. This is at a distance from a star where the temperatures are just right for liquid water to exist, a condition thought to be necessary for life to begin. In recent times, scientists have found more and more planets in this zone, and some of them are earth-like with rocky cores and possibly atmospheres.


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In last week’s harvest, a team of international astronomers led by Ian Crossfield, an astronomer at the University of Arizona has discovered three planets just slightly larger than Earth about 150 light years away orbiting a cool red M-dward star about half the size and mass of our Sun. The outermost planet orbits in the “Goldilocks” zone.

The star, EPIC 201367065, is a cool red M dwarf about half the size and mass of our Sun. At a distance of 150 light-years, the star ranks among the top 10 nearest stars known to have transiting planets. The star’s proximity means it’s bright enough for astronomers to study the planets’ atmospheres to determine whether they are like Earth’s atmosphere and possibly conducive to life.

This cartoon shows the three newly discovered extrasolar planets (right) casting shadows on their host star that can been seen as eclipses, or transits, at Earth (left). Earth can be detected by the same effect, but only in the plane of Earth's orbit (the ecliptic)

This cartoon shows the three newly discovered extrasolar planets (right) casting shadows on their host star that can been seen as eclipses, or transits, at Earth (left). Earth can be detected by the same effect, but only in the plane of Earth’s orbit (the ecliptic)


Crossfield said the discovery is exciting, first of all, because it helps validate the worth of K2 — a resurrected mission of NASA’s Kepler Space Telescope that positioned the crippled spacecraft to look for signs of transiting planets around nearby stars.

Kepler project scientist Steve Howell said the K2 mission was pitched by scientists to NASA as a way of finding “high value” planets by recording the slight diminution of light when they pass in front of bright stars in its field of view.

Howell, describing the discovery, said the original Kepler mission gathered “fabulous results,” identifying thousands of exoplanets. The only drawback, he said, is that most are very faint — too far away for detailed study.

Crossfield’s team developed a computer program to search K2 data for nearby targets and found these three planets recently.

The three planets are 2.1, 1.7 and 1.5 times the size of Earth. The smallest and outermost planet, at 1.5 Earth radii, orbits far enough from its host star that it receives levels of light from its star similar to those received by Earth from the sun, said UC Berkeley graduate student Erik Petigura. In order from farthest to closest to their star, the three planets receive 10.5, 3.2 and 1.4 times the light intensity of Earth, Petigura calculated.

“There is a very real possibility that the outermost planet is rocky like Earth, which means this planet could have the right temperature to support liquid water oceans.”

The next step will be observations with other telescopes, including the Hubble Space Telescope, to take the spectroscopic fingerprint of the molecules in the planetary atmospheres.

“If these warm, nearly Earth-size planets have puffy, hydrogen-rich atmospheres, Hubble will see the telltale signal,” Petigura said. The discovery is all the more remarkable, the researchers said said, because the Kepler telescope lost two reaction wheels that kept it pointing at a fixed spot in space.

Bottom Line: Kepler was reborn in 2014 as ‘K2’ with a clever strategy of pointing the telescope in the plane of Earth’s orbit, the ecliptic, to stabilise the spacecraft. Kepler is now back to mining the cosmos for planets by searching for eclipses or ‘transits,’ as planets pass in front of their host stars and periodically block some of the starlight. Kepler sees only a small fraction of the planetary systems in its gaze: those with orbital planes aligned edge-on to our view from Earth. Planets with large orbital tilts are missed. Accounting for other types of stars as well, there may be 40 billion such planets galaxy-wide.

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Pre-print paper: http://goo.gl/AE3vYU.

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