Two newly discovered exoplanets demonstrate the detail at which planets orbiting other stars can be studied using instruments like the Spitzer Space Telescope and Kitt Peak National Observatory.
GJ 1252b – a planet with likely no atmosphere
The Spitzer Space Telescope’s IRAC2 4.5 μm channel took measurements of an exoplanet called GJ 1252b over ten eclipses of its host star. GJ 1252b is a “super Earth” rocky planet that was discovered orbiting an M-type dwarf star about 66 light-years from Earth in 2020.
Using these measurements, researchers published a paper in The Astrophysical Journal Letters saying that GJ 1252b does not have an atmosphere – or, rather, any atmosphere it has is, as the paper described it, “substantially thinner than the atmosphere of Venus” at less than 10 bar.
Earth has an atmospheric pressure of about 1 bar at sea level. Venus’ atmosphere at surface level is typically about 90 bar.
Modeling of the chemical composition of GJ 1252b indicates that no atmosphere at all is a plausible explanation for the eclipse measurements that the Spitzer Space Telescope returned. Most of the uncertainty in the less-than-10-bar figure seems to depend on the chemical composition of any atmosphere that GJ 1252b might have. If the atmosphere contains mostly carbon monoxide or carbon dioxide, the atmospheric pressure might be less than one bar – less than Earth at sea level.
In any case, GJ 1252b is so close to its host star that it’s plausible that any atmosphere it has probably got blasted off through intense heat and its host star’s activity. Red dwarfs can spew out a lot of activity like flares, which can strip a planet of its atmosphere.
The planet is close enough to its star that its surface temperature can reach 1410 degrees K (about 2078 Fahrenheit) – hot enough to melt gold, silver, and copper.
“The planet could have 700 times more carbon than Earth has, and it still wouldn’t have an atmosphere. It would build up initially, but then taper off and erode away,” said Stephen Kane, UCR astrophysicist and study co-author.
TOI-3757 b – The Marshmallow World
…Okay, TOI-3757 b probably isn’t literally made out of marshmallow. However, scientists say that it has the average density of one, making it one of the least dense known exoplanets.
This exoplanet orbits a red dwarf star about 580 light-years away from Earth. Like GJ 1252b’s host star, TOI-3757 b’s star is a small but potentially volatile star.
“Giant planets around red dwarf stars have traditionally been thought to be hard to form” due to atmosphere-stripping solar flares produced by red dwarfs, said Shubham Kanodia, the lead author of the paper published in The Astronomical Journal.
According to current models, gas giants have a rocky core about ten times the mass of Earth. Scientists have found exoplanets that might have once been the cores of gas giants, but they settled into an orbit that was too close to their stars and their thick envelope of atmosphere was stripped away by a cranky host star.
However, TOI-3757 b might have avoided that fate by forming its big rocky core more slowly than most gas giants. A lack of heavy elements in its host star was a likely contributing factor. This delayed the exoplanet’s chance to accumulate the gases in its thick atmosphere, explaining its low density.
The exoplanet’s orbit may also be slightly elliptical, which can cause the atmosphere to bloat through excessive heating.
The researchers observed TOI-3757 b using the WIYN 3.5-meter Telescope at Kitt Peak National Observatory in Arizona.
Could more sensitive instruments improve our ability to study exoplanets?
It is crazy to think about what might be out there that we haven’t found yet because we don’t have sensitive enough scientific instruments yet. The James Webb Space Telescope was launched in October 2021 and is already finding galaxies that we previously missed from not having sensitive enough instruments. It can do this with the most sensitive infrared instrument launched to date.
Better instruments – and better modeling – could improve our ability to study distant exoplanets. According to the research paper co-authored by Stephen Kane, a more detailed model might be needed to get a better picture of GJ 1252b’s atmosphere – if it even has one. And better instruments could do better than get brief glimpses of it as it transits its host star.
Of course, you may be wondering, But why, though? It’s easy to get into the deep philosophical questions: Could there be life somewhere else in the universe? Where could it be, is it intelligent, and could it be asking the same questions about life on a planet called Earth? Could we travel to those other planets someday?
When it boils down to it, though, exoplanets are pretty darn cool. Someday, we might build a space telescope that’s actually capable of taking detailed pictures of some nearby ones.