(ORDO NEWS) — A newly discovered exoplanet just 200 light-years away could shed new light on one of planetary science’s strangest mysteries.
At about 1.8 times the radius of the Earth, the object named TOI-1075b is one of the largest examples of a super-Earth exoplanet we have discovered to date. In addition, it penetrates what we call the minor planet radius gap; apparent scarcity of planets between 1.5 and 2 Earth radii.
Slightly smaller rocky super-Earths have been found. So are the somewhat larger, puffy-atmosphere worlds known as mini-Neptunes. But in between there is something like a desert.
That extra girth isn’t everything either. The mass of TOI-1075b is 9.95 times the mass of the Earth. This is too much for a gaseous world; at the assumed density, the exoplanet is likely to be rocky, like Mercury, Earth, Mars, and Venus.
This feature makes it an ideal candidate for investigating theories of planetary formation and evolution.
The difference in minor planet radii was only identified a few years ago, in 2017, when we had a catalog of exoplanets (extrasolar planets or planets outside the solar system) large enough for scientists to notice a pattern.
For exoplanets that are in a certain close proximity to their stars, very few worlds have been found to bridge this gap.
There are several possible explanations for this; The main one seems to be that an exoplanet smaller than a certain size simply doesn’t have the mass to keep the atmosphere from evaporating radiation so close to the parent star.
According to this model, exoplanets in between should have fairly large atmospheres made up mostly of hydrogen and helium.
Enter TOI-1075b. It was discovered in data from NASA‘s TESS Exoplanet Search Telescope. Short for Transiting Exoplanet Survey Satellite, TESS looks for faint, regular dips in the light of other stars, suggesting that those stars orbit an exoplanet.
Astronomers can also determine the radius of this exoplanet based on how much the star’s light dims.
TESS data showed that around the orange dwarf TOI-1075, the exoplanet orbits about 1.72 times the Earth’s radius, with an orbital period of about 14.5 hours.
This caught the attention of astronomer Zahra Essack of the Massachusetts Institute of Technology, who studies hot super-Earths. With such a radius and proximity, the then candidate world met the criteria for a world with a rip radius.
The next step in trying to understand the nature of this exoplanet was to weigh it. This includes exploiting another effect that an exoplanet has on its star: gravity. Most of the gravity in a star-planet interaction is provided by the star, but the planet also exerts a small gravitational pull on the star.
This means that the star wobbles very slightly in place, and astronomers can detect this by tiny changes in the star’s light.
If we know the mass of the star, these changes can be used to measure the mass of the star. the planet shakes the star.
TOI-1075 has a mass and radius of about 60 percent that of our Sun, so Essack and her colleagues were able to accurately calculate the mass of the exoplanet to 9.95 Earth masses. And their precise size measurements gave 1,791 Earth radii.
If you know how big something is and how heavy it is, you can calculate its average density. And TOI-1075b? Turned out to be absolute rubbish. Its density is 9.32 grams per cubic centimeter.
That’s almost twice the density of Earth (5.51 grams per cubic centimeter), making it a contender for the densest super-Earth in the books.
An exoplanet in the mass gap must have a significant hydrogen-helium atmosphere. The density of TOI-1075b is incompatible with a dense atmosphere. This is very curious. But what the exoplanet could have instead is potentially even more exciting.
“Based on the predicted composition of TOI-1075b and the ultra-short orbital period, we do not expect the planet to have retained an H/He shell,” the researchers write in their paper.
“But TOI-1075b can either have no atmosphere (bare rock) or a metal/silicate vapor atmosphere, the composition of which is determined by the evaporating magma-ocean at the surface of the earth.
Surface, because the equilibrium temperature of TOI-1075 b is high enough to melt the rocky surface, or, especially at the lower end of the acceptable average density range, perhaps a thin H/He or CO 2 or other atmosphere.”
Yes, you read it right. TOI-1075b is so hot (due to being so close to its star) that its surface could be an ocean of magma creating an atmosphere from the evaporated rock.
The good news is that we can find out. As we have just recently seen, JWST is excellent at peering into the atmosphere of exoplanets.
Pointing it at TOI-1075b should show whether it has a thin atmosphere, a silicate atmosphere, or no atmosphere at all – and this information could reveal some previously unknown features of planet formation and evolution, as well as how super-Earths lose their gas.
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