LP 791-18d: The Earth-Sized Planet Covered in Volcanoes
Imagine a world just like Earth in size but completely covered in erupting volcanoes. That world exists and astronomers have found it. It is called LP 791-18d and it sits about 90 light-years away from us.
It is one of the most exciting planet discoveries in recent years and scientists are still learning from it today.
What Is LP 791-18d?
LP 791-18d has a radius of just 1.03 times that of Earth and a temperature range roughly between 27 and 127 degrees Celsius on parts of its surface. So in terms of pure size it is almost a perfect copy of our planet. But that is where the similarities end.
The planet orbits a small red dwarf star and astronomers believe it is likely carpeted with volcanoes similar to Jupiter’s moon Io which is the most volcanically active body in our solar system.
The discovery was published in the journal Nature and was led by a large international team of astronomers.
How Did Scientists Find It?
Researchers discovered the planet using data from NASA’s Transiting Exoplanet Survey Satellite (TESS) and the retired Spitzer Space Telescope as well as multiple ground-based observatories.
Two other planets in the same star system had already been found back in 2019. LP 791-18d was hiding in the data and the team pieced together its existence through careful analysis.
Why Is This Planet So Volcanic?
This is the really interesting part. The volcanoes are not random. They are caused by gravity.
At their closest the two planets in the system are only 1.5 million kilometres apart which is 33 times closer than Mars and Earth ever get to each other. Each close passage produces a gravitational tug on planet d making its orbit less circular and more elliptical.
Along this elliptical path planet d is slightly deformed every time it goes around the star. The astronomers calculated that this deformation produces a lot of heat inside the planet that needs to escape through intense volcanic activity.
Think of it like squeezing a stress ball over and over again. Eventually the inside heats up from all that pressure. That is exactly what is happening inside LP 791-18d every single orbit.
Could It Support Life?
This is the question everyone wants answered. The honest answer is: maybe on parts of it.
LP 791-18d is tidally locked meaning one side permanently faces its star while the other side stays in constant darkness. Tidal locking combined with the significant amount of volcanic activity suspected across the planet could enable LP 791-18d to sustain an atmosphere and allow water to condense on its night side.
The dark side of the planet could theoretically be cool enough for liquid water to exist. And where there is liquid water there is at least the possibility of life as we know it.
As co-author Jessie Christiansen at the NASA Exoplanet Science Institute explained a big question in astrobiology is whether tectonic or volcanic activity is necessary for life. LP 791-18d may help answer that question.
What Did the James Webb Space Telescope Find?
Here is where things get even more interesting. Scientists did not stop at the discovery. They kept studying this star system.
Astronomers from the Trottier Institute for Research on Exoplanets used the James Webb Space Telescope to study LP 791-18c the larger planet in the same system.
They found it has a hazy atmosphere unlike any of its planetary siblings showing that planets that appear nearly identical at first glance can diverge dramatically in their cloudiness chemistry and history.
A separate 2025 study used detailed atmospheric models to further examine LP 791-18d itself focusing on how tidal heating from its orbital configuration could shape the kind of atmosphere it might develop.
Scientists are actively using JWST to build a fuller picture of this entire planetary system. LP 791-18d is next on the list.
How Does It Compare to Venus and Earth?
LP 791-18d gives scientists a rare chance to study how volcanoes shape a whole planet over time. Venus is the best example we have in our own solar system. Runaway volcanic emissions created a greenhouse effect on Venus that made it one of the most hostile places in the solar system with surface temperatures hot enough to melt lead.
Earth on the other hand has had volcanic activity throughout its history and it actually helped create the atmosphere and conditions that allowed life to thrive. LP 791-18d sits somewhere in between and studying it helps scientists understand which path a volcanic planet might take.
Why Does This Discovery Matter?
Finding a planet like LP 791-18d matters for several reasons.
Volcanic activity recycles gases and minerals between the interior and the surface of a planet. This process played a huge role in making Earth habitable. Seeing it happen on another world helps scientists understand how common or rare Earth-like conditions really are across the galaxy.
The discovery of an Earth-size planet in the habitable zone that is potentially volcanically active is a huge step forward in the search for life outside the solar system according to researcher Mohamad Ali-Dib who called on the scientific community to use the JWST to learn more about its atmosphere.
Quick Facts About LP 791-18d
Distance from Earth: About 90 light-years
Location in the sky: Southern constellation Crater
Planet size: Nearly identical to Earth (1.03 times Earth’s radius)
Planet mass: 0.9 times Earth’s mass
Orbit: Tidally locked around a red dwarf star
Volcanic activity: Likely as intense as Jupiter’s moon Io
Discovered using: NASA TESS, Spitzer Space Telescope, ground observatories
LP 791-18d is one of the most fascinating planets ever found. It is basically Earth’s volcanic twin sitting 90 light-years away. It is being cooked from the inside out by gravity and it might still have the right conditions for water on its dark side.
As the James Webb Space Telescope continues observing this system scientists expect to learn much more. We may be looking at a planet that shows us exactly what Earth or Venus might have looked like billions of years ago and what other rocky worlds around distant stars could become.
The universe keeps surprising us and LP 791-18d is proof of that.
