Three Earth-Mass Planets Have Been Found Just 12 Light-Years Away

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Scientists have discovered the closest multi-planet system around a red dwarf star to Earth. While these planets are unlikely to be habitable, they could be important worlds for future study.

The three planets were discovered around a red dwarf called YZ Ceti. It’s located 12 light-years away from Earth. They are all similar in mass to Earth, ranging from 0.75 times Earth’s mass for the innermost planet, to 0.98 for the middle, and 1.14 for the outermost.

A paper describing the findings is available on arXiv, led by Nicola Astudillo-Defru from the University of Geneva, and has been accepted for publication in Astronomy and Astrophysics Letters.

Like most red dwarf planets, they orbit much closer to their star than other planets orbiting Sun-like stars. Here, the innermost is about 0.016 AU away (1 AU is the distance from Earth to the Sun), the middle is 0.021 AU and the outermost is 0.028 AU. The orbits take 1.97, 3.06, and 4.66 days, respectively.

The discovery was made using the High Accuracy Radial velocity Planet Searcher (HARPS) at the European Southern Observatory’s (ESO) La Silla Observatory in Chile. This looks for planets by noticing the slight wobble in the star from the gravitational tug of planets, known as the radial velocity method. The masses of these worlds are the smallest ever discovered by radial velocity. All of the planets are thought to be less than 1.5 times the radius of Earth in size.

In their paper the team note there is possibly also a fourth planet in the system, which may have an even lower mass at just 0.47 times that of Earth and an orbital period of 1.04 days. This would be one of the smallest exoplanets ever discovered.

Unfortunately, none of the planets appear to orbit in the star’s habitable zone, where the temperatures would be just right for water to exist. But the existence of this system is important nonetheless.

“The system is at only 3.6 parcsecs [12 light-years], making it very attractive for further characterization,” the team writes. However, they note it is not yet known if the planets pass in front of their star with respect to Earth, known as a transit. This is a necessity for further investigation like atmospheric studies.

But while they might not be habitable, their discovery is still important. Red dwarfs are thought to be the most numerous in our galaxy, making up 70 percent of our stars (although whether they can support life in their habitable zones is another question).

As they are dimmer than Sun-like stars, it is easier to study planets in orbit around them – making discoveries like this promising targets for future study when instruments like the James Webb Space Telescope (JWST) come online.
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