By Ashley Strickland, CNN
Published 5:07 PM EDT, Wed May 17, 2023
An artists's conception shows planet LP 791-18 d, which may be volcanically active. Similar in size to Earth, the planet 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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Astronomers have found an Earth-size planet that isn’t like Earth at all.
Instead, the exoplanet, called LP 791-18 d, is likely covered in volcanoes and may experience eruptions with the same frequency as Jupiter’s moon Io, the most volcanically active place in our solar system, according to researchers.
Data from NASA’s planet-hunting Transiting Exoplanet Survey Satellite, the retired Spitzer Space Telescope and ground-based telescopes was used to find the exoplanet. A study detailing the findings was published Wednesday in the journal Nature.
LP 791-18 d is located about 90 light-years from Earth in the Crater constellation, where it orbits a small red dwarf star.
Two other known planets also orbit the star, including LP 791-18 b, which is estimated to be 20% bigger than Earth, and LP 971-18 c, about 2.5 times Earth’s size and more than seven times its mass. And astronomers believe the massive planet LP 971-18 c might be contributing to the newly detected exoplanet’s possible volcanism.
As the two objects orbit their star, LP 971-18 c and the newfound exoplanet LP 791-18 d closely pass each other, allowing the gravitational pull of the larger planet LP 971-18 c to tug on planet d and reshape its orbit. With each trip around the star, planet d’s path shifts, becoming slightly more oval-shaped. The elliptical revolutions cause the interior of the planet to heat up, driving volcanic activity.
This phenomenon is similar to what occurs on Io, caught in a gravitational crossfire between Jupiter and its larger moons.
But there is no direct evidence yet to prove that volcanoes exist across LP 971-18 d.
“We don’t know that there are any volcanoes here,” said study coauthor Ian Crossfield, associate professor of physics and astronomy at the University of Kansas in Lawrence, in a statement. “All we know is that this is a small planet that’s experiencing a straight-up periodic stretching due to its orbit around its star and near the other planets. That might cause lots of volcanoes like on Jupiter’s moon Io, which is the most volcanically active thing in our solar system. We know about that because we’ve sent things nearby and taken pictures. There’s not yet that kind of clear evidence yet with LP 791-18 d.”
Future observations of the planet could provide more data as astronomers continue the search for potentially habitable Earth-size planets.
Volcanic activity and planetary atmospheres
Astronomers estimate that LP 791-18 d falls within the inner edge of the habitable zone, the distance from a star where a planet is warm enough to support liquid water on its surface.
“LP 791-18 d is tidally locked, which means the same side constantly faces its star,” said study coauthor Björn Benneke, professor of astronomy at the Trottier Institute for Research on Exoplanets at the University of Montreal, in a statement. “The day side would probably be too hot for liquid water to exist on the surface. But the amount of volcanic activity we suspect occurs all over the planet could sustain an atmosphere, which may allow water to condense on the night side.”
Although volcanic activity sounds like an impediment to water and potential life, it may actually help the planet maintain an atmosphere. Volcanoes can drive interactions between the interior and exterior of a planet.
“A big question in astrobiology, the field that broadly studies the origins of life on Earth and beyond, is if tectonic or volcanic activity is necessary for life,” said study coauthor Jessie Christiansen, a research scientist at NASA’s Exoplanet Science Institute at the California Institute of Technology in Pasadena, in a statement. “In addition to potentially providing an atmosphere, these processes could churn up materials that would otherwise sink down and get trapped in the crust, including those we think are important for life, like carbon.”
Astronomers are intrigued by how volcanic activity can drive changes on planets. Venus, similar enough in size to Earth to be called its twin, may have once been more like our world.
“On Venus, volcanic carbon dioxide stayed in the atmosphere, pushing the planet into a runaway greenhouse state,” said study coauthor Stephen Kane, professor of planetary astrophysics at the University of California Riverside, in a statement. “Today, surface temperatures on Venus are more than 850 degrees Fahrenheit (454.4 degrees Celsius) — as hot as a wood-fired pizza oven — and odds of life there are slim. But it may not always have been that way. Volcanoes might be a big piece of the puzzle about what actually happened on Venus. Planets like LP 791-18d can shed important insights into how volcanoes shape planetary environments with time, including those of Venus and Earth.”
The search for planetary atmospheres
The larger planet LP 971-18 c is already on the list of targets that the James Webb Space Telescope will observe in the future, and now the study team believes that the newly spotted planet d is also a prime candidate. Astronomers are using the Webb telescope to search for signs of atmospheres around exoplanets and peer into them to determine the chemicals that make up these extraterrestrial atmospheres.
The discovery of LP 971-18 d points to the importance of data collected by space telescopes. The planetary system was one of the last observation targets of the Spitzer Space Telescope before the observatory was retired in January 2020.
“It is incredible to read about the continuation of discoveries and publications years beyond Spitzer’s end of mission,” said Joseph Hunt, Spitzer project manager at NASA’s Jet Propulsion Laboratory in Pasadena, California, in a statement. “That really shows the success of our first-class engineers and scientists. Together they built not only a spacecraft but also a data set that continues to be an asset for the astrophysics community.”