Potential super-Earth found orbiting the nearest star from our sun

In 2016, astronomers found a potentially habitable planet called Proxima b around the star Proxima Centauri, which is only 4.2 light-years from Earth. Now, researchers have traced a second signal they believe belongs to a super-Earth orbiting the same star, increasing the intrigue of this neighboring planetary system and its potential.

An artists's conception shows planet LP 791-18d. The volcanically active planet, which is a similar size to Earth, was discovered by NASA's Spitzer Space Telescope.

This artist's illustration depicts the rocky exoplanet GJ 486 b, which orbits a red dwarf star located 26 light-years away from Earth. Astronomers have detected hints of water vapor in the system, but they can't be sure if it signifies a planetary atmosphere or if it's part of the star.

This illustration shows an Earth-size exoplanet called TOI 700 e, discovered orbiting the small, cool M dwarf star TOI 700, which is located 100 light-years away. Its other Earth-size sibling, TOI 700 d, can be seen in the distance.

TOI 700 d is the first potentially habitable Earth-size planet spotted by NASA's planet-hunting TESS mission.

Artist's impression of the exoplanet WASP-121 b. It belongs to the class of hot Jupiters. Due to its proximity to the central star, the planet's rotation is tidally locked to its orbit around it. As a result, one of WASP-121 b's hemispheres always faces the star, heating it to temperatures of up to 3000 degrees Celsius. The night side is always oriented towards cold space, which is why it is 1500 degrees Celsius cooler there.

This artist's impression shows a close-up view of Proxima d, a planet candidate recently found orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The planet is believed to be rocky and to have a mass about a quarter that of Earth. Two other planets known to orbit Proxima Centauri are visible in the image too: Proxima b, a planet with about the same mass as Earth that orbits the star every 11 days and is within the habitable zone, and candidate Proxima c, which is on a longer five-year orbit around the star.

The discovery of a second exomoon candidate hints at the possibility that exomoons may be as common as exoplanets.

This artist's impression shows the football-shaped planet WASP-103b (left) closely orbiting its host star.

This image shows double-star system b Centauri and its giant planet b Centauri b. The star pair is the bright object at top left. The planet is visible as a bright dot in the lower right. The other bright dot (top right) is a background star.

This artist's rendering shows a Jupiter-like planet orbiting a dead white dwarf star 6,500 light-years away from Earth. The planet survived the violent phases of stellar evolution leading to the star's death.

This artist's illustration shows the night-side view of the exoplanet WASP-76b, where iron rains down from the sky.

Astronomers have identified a new class of habitable planets, which they call Hycean planets. These are hot, ocean-covered planets with hydrogen-rich atmospheres.

This artist's illustration shows L 98-59b, one of the planets in a planetary system 35 light-years away from Earth. This planet has half the mass of Venus.

In this artist's illustration, two gaseous exoplanets can be seen orbiting the bright sun-like star HD 152843.

An artist's rendering of TOI-1231 b, a Neptune-like planet about 90 light years away from Earth.

This artist's conception depicts a violent flare erupting on the star Proxima Centauri as seen from the viewpoint of a planet orbiting the star called Proxima Centauri b.

After losing its gaseous envelope, the Earth-size core of an exoplanet formed a second atmosphere. It's a toxic blend of hydrogen, methane, and hydrogen cyanide that is likely fueled by volcanic activity occurring beneath a thin crust, leading to its cracked appearance.

This illustration shows the metaphorical measuring of the density of each of the seven planets in the nearby TRAPPIST-1 system. New measurements have revealed the most precise densities yet for these planets and they're very similar -- which means they also likely have similar compositions.

This artist's illustration shows the view from the furthest planet in the TOI-178 system.

This artist's illustration shows TOI-561b, one of the oldest and most metal-poor planetary systems discovered yet in the Milky Way galaxy. Astronomers found a super-Earth and two other planets orbiting the star.

This massive and distant exoplanet, called HD106906 b, has an elongated and angled orbit that causes it to take 15,000 Earth years to complete one lap around its twin stars.

This is an artist's impression of a free-floating rogue planet being detected in our Milky Way galaxy using a technique called microlensing. Microlensing occurs when an object in space can warp space-time.

This is an artist's impression of exoplanet WASP-189 b orbiting its host star. The star appears to glow blue because it's more than 2,000 degrees hotter than our sun. The planet, which is slightly larger than Jupiter, has a tilted orbit around the star's poles rather than its equator.

For the first time, an exoplanet has been found orbiting a dead star known as a white dwarf. In this artist's illustration, the Jupiter-sized planet WD 1856 b orbits the white dwarf every day and a half.

This illustration shows a carbon-rich planet with diamond and silica as ts main minerals. Water can convert a carbon-rich planet into one that's made of diamonds. In the interior, the main minerals would be diamond and silica (a layer with crystals in the illustration). The core (dark blue) might be made of an iron-carbon alloy.

This image shows a young sun-like star being orbited by two gas giant exoplanets. It was taken by the SPHERE instrument on European Southern Observatory's Very Large Telescope. The star can be seen in the top left corner, and the planets are the two bright dots.

This artist's impression shows a Neptune-sized planet in the Neptunian Desert. It is extremely rare to find an object of this size and density so close to its star.

This is an artist's impression of the multiplanetary system of newly discovered super-Earths orbiting a nearby red dwarf star called Gliese 887.

The newly discovered exoplanet AU Mic b is about the size of Neptune.

This artist's impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. Proxima b is a little more massive than the Earth.

This is an artist's illustration of an exoplanet's atmosphere with a white dwarf star visible on the horizon. The starlight of a white dwarf filtered through the atmosphere of an exoplanet that's orbiting it could reveal if the planet has biosignatures.

This is an artist's illustration of the Kepler-88 planetary system, where one giant exoplanet and two smaller planets orbit the Kepler-88 star. The system is more than 1,200 light-years away.

Weird and wonderful planets beyond our solar system

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Proxima Centauri is the closest star to our sun. It’s a low-mass red dwarf star known as an M-class dwarf. The star is in a triple star system known as Alpha Centauri, including binary pair Alpha Centauri AB. All of these stars are within the Centaurus constellation.

After the discovery of the first planet around Proxima Centauri, researchers speculated about the existence of another planet in the system. Astronomers used the Atacama Large Millimeter/submillimeter Array of telescopes in Chile to trace light signals that appeared to be coming from that direction.

The authors of a new study, published Wednesday in the journal Science Advances, were able to look at more than 17 years of radial velocity data from the well-studied star system and determine if the signal belonged to an orbiting planet.

The radial velocity method is based on gravity and the Doppler effect, in which light increases or decreases in frequency as a source and observed objects move toward or away from each other.

An artist's concept of GJ180d, which is the nearest temperate super-Earth to us that is not tidally locked to its star, making it more likely to be able to host and sustain life. CREDIT Illustration is by Robin Dienel, courtesy of the Carnegie Institution for Science.

Related article A cold Neptune and two super-Earths are among newly found exoplanets around nearby stars

Stars don’t remain completely still when they are orbited by planets; they move in small circles as a response to the pull of gravity from the planets. These movements change the light wavelength of the star, going between red and blue depending on the location of the planet. Tracing the shifts can help astronomers find planets.

The researchers can’t rule out that the signal could be due to activity of the star’s magnetic field, but the signal they traced occurred over a period of 1,900 days – a strong indicator that a planet is present.

“Even the closest planetary system to us may retain interesting surprises,” said Fabio Del Sordo in an email, study author and postdoctoral researcher in the department of physics at the University of Crete. “Proxima Centauri hosts a planetary system that is much more complex than we knew, and we do not know how many unknown features are waiting to be discovered.”

Meet the planet neighbors

The newly discovered second planet, Proxima c, is likely a super-Earth with a mass larger than Earth’s but smaller than Uranus and Neptune. The researchers estimate that it completes an orbit of Proxima Centauri every 5.2 Earth years.

The first planet found around the star, Proxima b, is six times smaller and is 30 times closer to its star, which also makes it warmer, the researchers said.

Proxima b is 1.3 times the size of Earth and orbits its star every 11.2 days. It is in a close orbit of Proxima Centauri: only 5% of the distance between the Earth and the sun. They are even closer together than Mercury and the sun. But because its star is much cooler and fainter than our sun, Proxima b has a temperature that is suitable for liquid water to exist on the surface without evaporating.

Given the proximity to its star, Proxima b is also subject to less pleasant factors like ultraviolet and X-ray flares that are 100 times the intensity of what Earth receives from the sun. If there is life on the planet, it would be affected by this radiation, but it is pure speculation as to what kind of effect.

This artist's impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears in the image to the upper-right of Proxima itself. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface.

Related article Closest potentially habitable planet to our solar system found

Even though Proxima b is within the habitable zone of its star, meaning liquid water could exist on the surface, that doesn’t mean it’s actually habitable. And the radiation it likely faces has likely stripped away key elements for life like hydrogen, oxygen and nitrogen.

The newly discovered planet is intriguing because further study could reveal how low-mass planets form around low-mass stars, the researchers said. And this particular planet flips the typical theory of super-Earth planet formation on its head.

It’s beyond the “snowline” of the system, which suggests any water on the planet would be frozen. Super-Earths typically form near the snowline, but not beyond it.

Related article TESS mission spots Earth-size potentially habitable planet and 'Tatooine' system

“The formation of a super-Earth well beyond the snowline challenges formation models, according to which the snowline is a sweet spot for the accretion of super-Earths, due to the accumulation of icy solids at that location,” said Mario Damasso, study author and postdoctoral researcher at Italy’s National Institute for Astrophysics. “Or it suggests that the protoplanetary disk was much warmer than usually thought. In general, there’s nothing preventing the existence of Proxima c there where we spot it, but the formation and evolutionary history is a subject worthy of deeper investigation.”

The European Space Agency’s Gaia mission, which is creating a 3D mission of our galaxy, could help refine the signal of the second planet and provide more answers in the future.

“Proxima Centauri is the nearest star to the sun, and this detection would make it the closest multiplanetary system to us,” Del Sordo said.