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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.
Also at University of Warwick and BBC.
A remnant planetary core in the hot-Neptune desert (DOI: 10.1038/s41586-020-2421-7) (DX)
(Score: 2) by bzipitidoo on Friday July 03 2020, @12:46AM (2 children)
It's very interesting, but I don't think we should be so surprised that there is a lot of variety among exoplanets.
One kind of planet I speculate could exist is a "heliopause planet". Where the solar wind stalls, could hydrogen accumulate? Of course, the heliopause is the surface of a giant sphere, with perhaps a tail, and even if some material pooled there, something else would have to concentrate it to gather up enough to make a planet before other forces scattered it into interstellar space.
(Score: 0) by Anonymous Coward on Friday July 03 2020, @02:15AM
The heliopause just means that the solar wind no longer dominates the interstellar wind. Outside* of a nebula the hydrogen density shouldn't be high enough for star formation to occur that close to the sun.
*I'm not certain that it could occur that close inside a nebula either.
(Score: 2) by takyon on Friday July 03 2020, @03:38AM
This type of planet has been hypothetical. It also seems to have more mass than the supposed mass of Jupiter's core.
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