Astronomers have discovered a star system with three Earth-mass planets located just 12 light years away from Earth. This is therefore the closest known multi-planet system to Earth so far.
An artist's impression of a red dwarf star [Image by NASA]
The planets orbit a red dwarf star called YZ Ceti in the constellation Cetus. Interestingly, though YZ Ceti is quite close to the sun, we can't see it from Earth with the naked eye. As a red dwarf, YZ Ceti is quite small and relatively cool. The star is just about 8.5% the size of our sun, with less than 1/5000th the luminosity. YZ Ceti is also uncommonly close to another star, Tau Ceti, at a distance of just 1.6 light years.
Since this discovery is quite fresh still, there is still more information to learn about the star system and its newly-discovered planets. There may be more planets in the system, and astronomers may still find something interesting about the planets themselves.
YZ Ceti's location on the Cetus constellation [Image by Calle Cool]
What we know about the three Earth-mass planets so far is that their mass is similar to that of Earth. The innermost planet has a mass equivalent to 0.75 times Earth's mass, while the middle and outermost planets have a mass of 0.98 and 1.14 times Earth's mass, respectively.
Red dwarf star planets typically orbit quite close to their star. The innermost planet has a distance of just 0.016 AU away from its star, the middle planet has 0.021 AU, while the outermost planet has 0.028 AU. 1 AU is equivalent to the distance of the Earth from the sun. With such short distances, the orbits don't take very long. The innermost, middle, and outermost planets have orbits lasting 1.97, 3.06, and 4.66 days, respectively.
Researchers say that, based on the findings, there may be a fourth planet in the system. The fourth planet's mass is possibly 0.47 times that of Earth, with an orbit that lasts just 1.04 days. If this small fourth planet does exist, it may be among the smallest exoplanets ever found.
Astronomers used the High Accuracy Radial velocity Planet Searcher (HARPS) at the European Southern Observatory (ESO) in Chile to make the discovery. HARPS uses a technique called radial velocity method to detect exoplanets.
What else is the YZ Ceti star system hiding?
Though these planets have masses similar to Earth's, let's not get our hopes up that they'd be suitable for life. It seems that the planets aren't in the habitable zone, being so close to their star. Planets in the habitable zone are the ones on which liquid water can form, which indicates that the planet is possibly habitable. Planets that close to their star have temperatures that are too high for liquid water—and therefore life—to form.
Still, this is an important discovery. Since it's so close to our own star system, we can make further observations on the planets and on YZ Ceti itself with relative ease. Red dwarves like YZ Ceti are also the most common kind of star there is, making up 70% of known stars. Astronomers may also find out more about the three Earth-mass planets and find something beneficial to space exploration efforts.
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