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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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  — 

Picture a world made out of cotton candy, and you canadd “super-puff” to the list of weird and wonderful exoplanet types. This new type of exoplanet is the lowest density ever found outside of our solar system.

When astronomers used the Hubble Space Telescope to study the Kepler 51 star system, which is about 2,400 light-years away from Earth, they spotted something unusual: puffy planets orbiting a sun-like star in the system first seen by NASA’s Kepler mission in 2012. But new observations by Hubble allowed researchers to better understand their mass and density.

This artist's illustration shows WASP-121b, a distant world that is losing magnesium and iron gas from its atmosphere. The observations represent the first time that heavy metals have been detected escaping from a "hot Jupiter," which is a large, gaseous exoplanet that orbits very close to its host star. WASP-121b's orbit is so close that the star's gravity is nearly ripping the planet apart, giving the planet an oblique football shape. CREDIT NASA, ESA, and J. Olmsted (STScI)
This artist's illustration shows WASP-121b, a distant world that is losing magnesium and iron gas from its atmosphere. The observations represent the first time that heavy metals have been detected escaping from a "hot Jupiter," which is a large, gaseous exoplanet that orbits very close to its host star. WASP-121b's orbit is so close that the star's gravity is nearly ripping the planet apart, giving the planet an oblique football shape. CREDIT NASA, ESA, and J. Olmsted (STScI)
NASA/ESA/J. Olmsted

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“They’re very bizarre,” said Jessica Libby-Roberts, a graduate student in the Department of Astrophysical and Planetary Sciences at the University of Colorado Boulder. Libby-Roberts is one of the authors of a study that will publish in The Astronomical Journal about the exoplanets

The three planets in the system each have a density less than 0.1 grams per cubic centimeter of volume, according to the researchers.

“We knew they were low density,” she said. “But when you picture a Jupiter-sized ball of cotton candy – that’s really low density.”

Although they’re the size of Jupiter, mass-wise the planets are a hundred times lighter.

Intrigued, the astronomers attempted a closer look to understand the atmospheres of two of the planets – but the atmospheres were cloaked by an opaque layer at a high altitude.

The three Kepler planets compared with planets in our solar system.
The three Kepler planets compared with planets in our solar system.
NASA/ESA/STSci

“It definitely sent us scrambling to come up with what could be going on here,” Libby-Roberts said. “We expected to find water, but we couldn’t observe the signatures of any molecule.”

The researchers estimate that lightweight gases like hydrogen and helium are responsible for the puffy worlds. But a methane haze is also in the mix, causing the obscuring atmospheric layer. This isn’t unlike Saturn’s moon Titan, which has a dense, hazy atmosphere that’s nearly impossible to peek through.

“This is an extreme example of what’s so cool about exoplanets in general,” said Zachory Berta-Thompson, study co-author and an assistant professor at the University of Colorado Boulder. “They give us an opportunity to study worlds that are very different than ours, but they also place the planets in our own solar system into a larger context.”

Astronomers have found a white dwarf star which appears to be surrounded by a truncated disc of gas. The disc was probably created from a gas planet being torn apart by its gravity.
Astronomers have found a white dwarf star which appears to be surrounded by a truncated disc of gas. The disc was probably created from a gas planet being torn apart by its gravity.
Mark A. Garlick/University of Warwick

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The exoplanets may also be rapidly shedding their gas because they’re dumping billions of tons of material per second into space. If this keeps up over a billion years, the big puffy planets will shrink down significantly, the researchers said.

The system itself is fairly young, universally speaking, at only 500 million years old. Our solar system is 4.5 billion years old.

“A good bit of their weirdness is coming from the fact that we’re seeing them at a time in their development where we’ve rarely gotten the chance to observe planets,” Berta-Thompson said. “This system offers a unique laboratory for testing theories of early planet evolution.”