Colossal exoplanet is one of the most massive super-Earths ever discovered: ScienceAlert

A newly discovered exoplanet just 200 light-years away could shed new light on one of planetary science’s weirdest mysteries.

At about 1.8 times the Earth’s radius, the named object TOI-1075b ranks among the largest examples of a super-Earth exoplanet we have found to date. This too sits firmly in what we call the small planet radius deviation; an apparent deficit of planets between 1.5 and 2 Earth radii.

Slightly Smaller Rocky Super-Earths Was found. Thus, slightly larger worlds swelled with puffy atmospheres, known as mini Neptunes. But between the two, it’s something of a desert.

That extra girth isn’t any puff either. The mass of TOI-1075b is 9.95 times that of Earth. It’s far too heavy for a gaseous world; at the inferred density, the exoplanet is likely to be rocky, like MercuryEarth, Marchand Venus. This feature makes it an ideal candidate for probing theories of planetary formation and evolution.

The radius deviation of minor planets was only identified a few years ago, in 2017, when we had a quite a large catalog of exoplanets (extrasolar planets or planets outside the solar system) for scientists to notice a pattern. For exoplanets located in some proximity to their stars, very few worlds have been found to straddle this gap.

There are several possible explanations for this; the main one seems to be that below a certain size, an exoplanet simply doesn’t have the mass to hold an atmosphere against evaporating radiation so close to the host star. According to this model, exoplanets in space should therefore have a fairly large atmosphere composed mainly of hydrogen and helium.

Enter TOI-1075b. It was detected in data from NASA’s exoplanet-hunting telescope, TESS. Short for Transiting exoplanet study satellite, TESS looks for faint, regular dips in the light of other stars that suggest those stars are orbiting an exoplanet. Astronomers can also determine the radius of this exoplanet based on how much light from the star is attenuated.

The SSET data suggested that the orange dwarf star TOI-1075 orbited an exoplanet about 1.72 times Earth’s radius, with an orbital period of about 14.5 hours. This caught the attention of astronomer Zahra Essack of MIT, who studies super-hot Earths. At this ray and at this proximity, the then-candidate world met the criteria of a ray gap world.

The next step in trying to understand the nature of this exoplanet was to weigh it. This involves taking advantage of a different effect an exoplanet has on its host star: gravitational. 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 a star wobbles ever so slightly in place, and astronomers can detect it in small changes in starlight.

If we know the mass of the star, these changes can be used to estimate the mass of the planet shaking the star. TOI-1075 has a mass and radius about 60% of that of our own Sun, so Essack and his colleagues were able to accurately calculate the mass of the exoplanet at 9.95 Earth masses. And their precision measurements of the size gave 1,791 Earth radii.

If you know the size and weight of an object, then you can calculate its average density. And the TOI-1075b? Turned out to be an absolute chonk. It has a density of 9.32 grams per cubic centimeter. That’s nearly twice Earth’s density of 5.51 grams per cubic centimeter, making it a contender for the densest super-Earth on the books.

An exoplanet in the mass gap should have a substantial hydrogen and helium atmosphere. The density of TOI-1075b is incompatible with a substantial atmosphere. It’s very curious. But what the exoplanet might have instead is potentially even more fascinating.

“Based on the predicted composition of TOI-1075b and its ultra-short orbital period, we do not expect the planet to have retained an H/He envelope,” the researchers write in their article.

“But, TOI-1075b could have either: no atmosphere (bare rock); a vaporous metal/silicate atmosphere with composition defined by magma-ocean vaporizing at the surface since the equilibrium temperature of TOI-1075b is hot enough to melt a rock surface; or, especially at the lower end of its allowable average density range, possibly a thin H/He or CO₂ or another atmosphere.”

Yes, you read that right. TOI-1075b is so hot (because it’s so close to its star) that its surface could be an ocean of magma that produces an atmosphere of vaporized rock.

The good news here is that we might find out. as we have seen only recently, JWST is very good at scrutinizing the atmospheres of exoplanets. Pointing it to TOI-1075b should reveal whether it has a thin atmosphere, a silicate atmosphere, or no atmosphere at all – and that information could reveal a previously unknown quirk of planet formation and evolution, and how super-Earths lose their gas.

The team’s research was accepted in The Astronomical Journaland is available at arXiv.