Newly discovered exoplanet could be the exposed core of a giant gas

A planet about 734 light-years away appears to be missing most of its atmosphere

A dense, crushed planet around a distant star could be the bare core of a giant gas.

Observations on satellite and terrestrial telescopes show that the newly discovered exoplanet has a radius nearly 3.5 times that of Earth and nearly 39 times its mass. These measurements together indicate a density almost equal to that of Earth, suggesting that the exoplanet is mostly made up of rocks. Unlike other massive planets, this planet, called TOI 849b, has a partially formed environment that is no more than 4% of its mass, according to a new study.

This environment is “completely small for a planet of this size,” says astronomer David Armstrong of the University of Warwick in Coventry, England. “It’s almost exclusively an exposed rock ball.”

The massive mass of the planet and the lack of an environmental deficiency suggest that TOI 849b could be the remaining core of a gas giant, Armstrong and colleagues reported to Nature on July 1. It may be the first exhibited giant fuel ever found.
Using NASA’s Transiting Exoplanet Survey Satellite (TESS), the team discovered TOI 849b by passing a star-shaped star about 734 light-years away. A follow-up of observations at the La Silla Observatory of the European Southern Observatory in Chile revealed that the mass of the planet is more than double that of Neptune. The combination of these observations with the inferred volume of the planet showed that TOI 849b is the thickest planet discovered to date.

The exoplanet whips around the star every 18 hours and revolves around it tightly so that its surface drops at 1,500 ° Celsius. This makes it a rare class: most planets close to their stars are Jupiter and larger, or larger and smaller. Only a few of the “hot Neptunes” have been discovered before (SN: 07/30/19).

In the standard theory of planetary formation, any rock ball that reaches about 10 times the mass of the earth or more should in vain discharge fuel from the disk of gas and dust from which it was formed (SN: 5/11 / 18). “Outside of the mass, it’s very difficult to stop her from becoming a gas giant,” Armstrong said. “You get this huge flow of gas that covers the process of creation.”

At 39 masses on Earth, TOI 849b is supposed to have this thick environment, so where is it? There are two main possibilities for lack of gas, the researchers reported. One of them is that the planet opened up space on the protoplanetary disk during its formation and therefore had a more difficult buffet to eat (SN: 5/20/20). It could have slowed the growth of the planet before it became a fuel explosion and left only one major.

Another possibility is that the TOI 849b is a giant gas but has somehow lost the atmosphere. The energy from the exoplanet star may heat the atmosphere too much for it to explode or simmer, or collisions with other planets may leave a calm atmosphere but leave the altered core.

It was “a bit early” to say that TOI 849b was definitely a holdover from a gas giant, said Elisabeth Adams, an astronomer at the Planetary Science Institute in Somerville, Massachusetts. There are other possibilities, such as the melting of rocky planets after most of the protoplanetary disk has been damaged.

However, if TOI 849b were an ancient giant, studying this planet and similar planets would help astronomers identify the centers of planets such as Jupiter and other gas giants. These nuclei are also difficult to study, hidden in their thick and smelly cocoons.

“We didn’t know how big Jupiter was and we sent the plane to Jupiter,” said Adams, who was not involved in the work.

The thin atmosphere of the exoplanet can be gases released from inside the planet itself. A look at the spectrum of starlight filtering through this atmosphere with future space telescopes could reveal what the planet has done, Adams says.

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