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

A new exoplanet found 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 Earth, the object named TOI-1075b ranks among the largest examples of super-Earth exoplanets we have found to date. also sits firmly in what we call minor planet radius gap. an apparent deficit of planets between 1.5 and 2 Earth radii.

Slightly smaller rocky super-Earths have been found. Thus, slightly larger worlds have accumulated with inflated atmospheres, known as mini-Neptunes. But in between, it’s something of a desert.

That added girth is no slouch either. The mass of TOI-1075b is 9.95 times that of Earth. This is very heavy for a gaseous world. at compact density, the exoplanet is likely to be rocky, like Mercury, Earth, Mars, and Venus. This peculiarity makes it an ideal candidate for investigating theories of planetary formation and evolution.

The minor planet radius gap was only discovered a few years ago, in 2017, when we had a large enough catalog of exoplanets (extrasolar planets or planets outside the Solar System) for scientists to notice a pattern. For exoplanets in a certain proximity to their stars, very few worlds have been found that cross 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 maintain an atmosphere against evaporative radiation so close to the host star. According to this model, exoplanets in the gap should therefore have a fairly large atmosphere consisting mainly of hydrogen and helium.

Enter TOI-1075b. It was spotted in data from NASA’s exoplanet-hunting telescope, TESS. Short for Transiting Exoplanet Survey Satellite, TESS looks for faint, regular dips in the light of other stars that indicate those stars are being orbited by an exoplanet. Astronomers can also tell the radius of that exoplanet based on how much of the star’s light it dims.

The TESS data showed that the orange dwarf star TOI-1075 was orbited by an exoplanet about 1.72 times the radius of Earth, with an orbital period of about 14.5 hours. This caught the attention of MIT astronomer Zahra Essack, who studies hot super-Earths. At this radius and proximity, the then-candidate world fit the criteria for a gap-radius world.

The next step in trying to understand the nature of this exoplanet was to weigh it. This involves leveraging a different effect an exoplanet has on its host star: gravity. Most of the gravity in a star-planet interaction is provided by the star, but the planet also exerts a tiny gravitational pull on the star. This means that a star wobbles very slightly on location, and astronomers can detect this in 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 planet rocking the star. TOI-1075 has a mass and radius of about 60 percent that of our own Sun, so Essack and her colleagues were able to accurately estimate the exoplanet’s mass at 9.95 Earth masses. And their precision measurements of size returned 1,791 Earth radii.

If you know how big something is and how heavy it is, then you can calculate its average density. And the TOI-1075b? It turned out to be an absolute chock. It has a density of 9.32 grams per cubic centimeter. This is nearly double Earth’s density of 5.51 grams per cubic centimeter, making it a contender for the densest super-Earth in the books.

An exoplanet in the mass gap should have a substantial hydrogen-solar atmosphere. The density of TOI-1075b is inconsistent with a substantial atmosphere. This is very strange. But what the exoplanet could hold is potentially even more exciting.

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

“But TOI-1075b could either have: no atmosphere (bare rock), metallic/silicic vapor atmosphere with a composition formed by the vaporizing magma-ocean at the surface, since the equilibrium temperature of TOI-1075 b is quite high to melt a rocky surface or, especially at the low end of its allowed average density range, possibly a thin H/He or CO2 or other atmosphere’.

Yes, you read that right. TOI-1075b is so hot (from being so close to its star) that its surface could be a magma ocean producing an atmosphere of vaporized rock.

The good news here is that we can learn. As we saw just recently, JWST is very capable of looking at the atmospheres of exoplanets. Pointing it at TOI-1075b should reveal whether it has a thin atmosphere, a silicic atmosphere, or no atmosphere at all – and that information could reveal some previously unknown quirks of planet formation and evolution, and how super-Earths lose their gas.

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

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