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posted by martyb on Thursday July 02 2020, @06:39PM   Printer-friendly
from the gas-giant-without-the-gas dept.

Bizarre new planet is largest known rocky world, 40 times as massive as Earth

About 730 light-years away, not far on the scale of our galaxy, an utterly bizarre planet orbits a sun-like star. Big, dense, and tightly tethered to its home star, the planet is unlike anything astronomers have yet seen—either in our own solar system or afar.

The roasted world known as TOI-849b is the most massive rocky planet ever observed, with as much as 40 Earths' worth of material crammed inside. Perplexingly, TOI-849b's tremendous bulk suggests that it should be a giant, gassy world like Jupiter, yet it has almost no atmosphere. Explaining how such a world emerged challenges what scientists understand about how planets grow.

[...] The planet betrayed its presence by crossing the face of its star and briefly blotting out a smidgen of starlight. Those fleeting, shadowy transits revealed that the alien world circles its star every 18 hours, meaning that its surface temperature is a sweltering 2800°F.

TESS observations also showed that the planet is about 3.4 times as wide as Earth, or 85 percent as wide as Neptune—making it a world of unusual size for its position so close to its star. Up until now, astronomers have primarily observed hot Jupiters or much smaller super-Earths in such tight orbits, and nothing has populated what's known as the hot-Neptune desert.

"There really are no planets of that mass there," Fortney says. TOI-849b is the right radius to be a hot Neptune, but its mass is two to three times larger.

Further observations of the host star's gravitational wobble, made with the HARPS instrument at the La Silla Observatory in Chile, determined that while TOI-849b is roughly as wide as Neptune, it is at least twice as massive. All that bulk means TOI-849b is extremely dense. The rocky planet might have a thin veneer of atmosphere, probably composed of hydrogen and helium—but not nearly as much gas as a world that hefty should hold on to.

Chthonian planet.

Also at University of Warwick and BBC.

A remnant planetary core in the hot-Neptune desert (DOI: 10.1038/s41586-020-2421-7) (DX)


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  • (Score: 1) by khallow on Friday July 03 2020, @04:21AM

    by khallow (3766) Subscriber Badge on Friday July 03 2020, @04:21AM (#1015673) Journal

    That doesn't make sense because the lost material shouldn't have proportionally more momentum than what is left behind.

    Well, for the hot Jupiters, it is. We're not speaking of a little material. We're speaking of a considerable portion of the planet over millions of years. And it's leaving with well over the escape velocity of the planet.