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

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.

Chris Smith (KRBwyle)/NASA's Goddard Space Flight Center

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.

NASA, ESA, CSA, Joseph Olmsted (STScI)

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.

NASA/JPL-Caltech/Robert Hurt

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

NASA's Goddard Space Flight Center

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.

Patricia Klein/MPIA

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.

ESO/L. Calçada

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

Helena Valenzuela Widerström

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

European Space Agency

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.

Janson et al./ESO

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.

Adam Makarenko/W. M. Keck Observatory

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

M. Kornmesser/ESO

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

Amanda Smith/University of Cambridge

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.

M. Kornmesser/ESO

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

Scott Wiessinger/NASA

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

JPL-Caltech/NASA

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.

From NRAO/S. Dagnello

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.

NASA/ESA/R. Hurt

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.

NASA/JPL-Caltech

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

L. Calçada/ESO

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.

W. M. Keck Observatory/Adam Makarenko

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.

ESA/Hubble/M. Kornmesser

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.

Jan Skowron/Astronomical Observatory, University of Warsaw

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.

ESA

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.

NASA's Goddard Space Flight Ce

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.

Shim/ASU/Vecteezy

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.

European Southern Observatory/Bohn et al.

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.

Mark Garlick/University of Warwick

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

Mark Garlick

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

NASA's Goddard Space Flight Center/Chris Smith (USRA)

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.

European Southern Observatory/M. Kornmesser

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.

Jack Madden/Carl Sagan Institute/Cornell University

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.

Adam Makarenko/W. M. Keck Observatory

Weird and wonderful planets beyond our solar system

CNN —

Five exoplanets and eight planet candidates have been found around nearby stars, including a “cold Neptune” and two super-Earths that are potentially habitable, according to a new study.

The two super-Earths, GJ180d and GJ229Ac, were found around small red dwarf stars that are 19 and 40 light-years away from our sun, while the cold Neptune was found around a similar star that’s 29.5 light-years away.

Given how close these stars are, the exoplanets found around them could be studied further by future telescopes.

The super-Earths are 7.5 and 7.9 times the mass of Earth and take 106 and 122 Earth days to complete one orbit around their stars, respectively.

The cold Neptune is similar in mass to the gaseous planet in our solar system. Previous research suggests that cold Neptunes, which can form in the icy outer regions of planetary systems, may be the most common type of exoplanet.

The new study published Tuesday in The Astrophysical Journal Supplement Series.

“GJ 433 d is the nearest, widest and coldest Neptune-like planet ever detected,” said Fabo Feng, lead study author and astronomer at the Carnegie Institution for Science.

A multitude of exoplanets, especially terrestrial planets like Earth, have been found around red dwarf stars. They’re smaller and cooler than our sun, and they’re the most common star in our galaxy. Exoplanets tend to orbit closer to these stars and still be within the star’s habitable zone, or the perfect distance for the planet to be temperate and potentially host liquid water on their surfaces.

But exoplanets around red dwarf stars pose other challenges to the potential for life. Many planets that orbit red dwarfs in the habitable zone are tidally locked, meaning the exoplanets have a very cold permanent night on one side and very hot permanent day on the other, Feng said.

“GJ180d is the nearest temperate super-Earth to us that is not tidally locked to its star, which probably boosts its likelihood of being able to host and sustain life,” Feng said.

Meanwhile, the other super-Earth, GJ229Ac, is the nearest temperate super-Earth in a system where the host star is also orbited by a brown dwarf. Brown dwarfs are known as failed stars that can’t sustain the hydrogen fusion needed to power them.

This is an artist's concept of the surface of GJ229Ac.

Robin Dienel/Courtesy of the Carnegie Institution for Science

The planets were detected using the radial velocity method. It’s 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.

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. Red dwarf stars have a lower mass than other stars, so this method is often used to detect exoplanets around them.

“We eventually want to build a map of all of the planets orbiting the nearest stars to our own solar system, especially those that are potentially habitable,” said Jeffrey Crane, study co-author and astronomer at the Carnegie Institution for Science.