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  — 

Just 40 light-years from Earth is a planetary system that has intrigued scientists since its discovery in 2016.

While some of the planets in this system will be observed by the upcoming James Webb Space Telescope, scheduled to launch in October, researchers continue to uncover new details that make TRAPPIST-1 even more distinct.

The planets, which are too small and faint to be seen by any current ground or space-based telescopes, have such similar densities that they may have equally similar compositions, new research has suggested.

Given that these planets are about 8% less dense than Earth, researchers have taken a stab at trying to understand how much iron, oxygen, magnesium and silicon these planets contain.

The study published last week in The Planetary Science Journal.

The TRAPPIST-1 system includes seven planets, all rocky and similar in size to Earth – and the most planets like this found orbiting one star. In contrast, the planets in our solar system vary both in size and composition, including smaller rocky planets like Venus, Mercury and Earth and giant gaseous ones such as Jupiter and Saturn.

The TRAPPIST-1 system is a reminder that no two planetary systems are alike.

This graphic shows the TRAPPIST-1 planetary system.
This graphic shows the TRAPPIST-1 planetary system.
NASA

Astronomers announced in February 2017 their discovery of the seven Earth-size planets orbiting a star 40 light-years from Earth. Initially, the researchers only identified three planets around the star in 2016, but they used multiple telescopes and discovered the other four planets using the transit method – measuring dips in starlight as planets passed in front of the star.

The seven exoplanets were all found in tight formation around an ultracool dwarf star called TRAPPIST-1, and the planets bear the TRAPPIST name – which the researchers borrowed from their favorite beer.

These planets are so close to their star that they would all fit within the orbit of Mercury around the sun, which is the closest planet in our solar system to our host star. This proximity means that if you were to stand on the surface of one of these planets, the other planets in the system would appear like large moons in the sky.

This NASA poster shows what it might look like to stand on the surface of TRAPPIST-1e and glimpse its neighboring planets in the sky.
This NASA poster shows what it might look like to stand on the surface of TRAPPIST-1e and glimpse its neighboring planets in the sky.
Courtesy NASA/JPL

Astronomers were able to obtain precise measurements of the masses and diameters of the TRAPPIST planets using the transit method, which also enabled them to determine the planets’ densities.

Their densities are so close that there is no more than a 3% difference between them, the researchers concluded.

02 exoplanet wet 0106
Friedlander-Griswold/GSFC/NASA

Related article New way of detecting oxygen on exoplanets could help find life

Even though these exoplanets are only 8% different in density from Earth and Venus, this difference suggests that the TRAPPIST planets are made differently. The researchers determined that they could be similar to Earth in every element with the exception that the composition of the seven planets could be 21% iron while Earth is 32% iron.

The iron in the TRAPPIST planets could contain more oxygen, which would actually form iron oxide – otherwise known as rust.

In our solar system, Mars gets its telltale red hue from iron oxide on the surface. Despite this, Mars has an iron planetary core, much like the other rocky planets in our solar system of Venus, Mercury and Earth.

If the TRAPPIST planets contain more of this oxidized iron, they would not include solid iron cores, which could account for the density difference.

This illustration shows three possible interiors of the seven rocky exoplanets in the TRAPPIST-1 system.
This illustration shows three possible interiors of the seven rocky exoplanets in the TRAPPIST-1 system.
NASA/JPL-Caltech

Researchers believe that a combination of lower iron content, as well as some iron oxide, accounts for the difference between the TRAPPIST planets and Earth.

The TRAPPIST system has intrigued scientists for many reasons, and this suggestion about their composition is one of the latest findings.

Astronomers previously have suggested that some of the planets orbiting the TRAPPIST-1 star are in the star’s habitable zone, meaning some of the middle planets could be at the right surface temperature to support liquid water, and perhaps life, on their surfaces.

The closest planets would be too hot and the furthest planet from the star may be covered in ice.

Astronomers have estimated that TRAPPIST-1 is between 5.4 billion and 9.8 billion years old, meaning it could be nearly twice as old as our own solar system, which formed 4.5 billion years ago.

This photo shows Northrop Grumman's huge full-scale model of the James Webb Space Telescope. It is being displayed for the public, free, January 27-February 5, 2017, at Super Bowl Live, in Houston, TX near Discovery Green. Other NASA science and tech will be represented as well. More info on the exhibits:
This photo shows Northrop Grumman's huge full-scale model of the James Webb Space Telescope. It is being displayed for the public, free, January 27-February 5, 2017, at Super Bowl Live, in Houston, TX near Discovery Green. Other NASA science and tech will be represented as well. More info on the exhibits:
Alberto Conti

Related article This telescope is our next great detective in the universe

When some of the TRAPPIST planets are observed by the James Webb Space Telescope in the future, astronomers could learn if these planets have atmospheres and if so, what those atmospheres contain.

“The night sky is full of planets, and it’s only been within the last 30 years that we’ve been able to start unraveling their mysteries,” said study coauthor Caroline Dorn, an astrophysicist at the University of Zurich, in a statement.

“The TRAPPIST-1 system is fascinating because around this one star we can learn about the diversity of rocky planets within a single system. And we can actually learn more about a planet by studying its neighbors as well, so this system is perfect for that.”