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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 HiThere on Thursday July 02 2020, @08:39PM (8 children)
If you heat a proto-planet up t0 2800F, the volatiles will go away as part of the solar wind. And they'll be baked out of the components before they condense into a planet. Getting that much hard stuff in close orbit around a star is the difficult part to explain.
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(Score: 2) by Barenflimski on Thursday July 02 2020, @11:20PM
But if rodent-people-aliens populate the habital zone on the planet they may have a grande world of extraordinary size and beauty just underneath the surface!
(Score: 3, Interesting) by ese002 on Friday July 03 2020, @12:06AM (6 children)
It has long been suggested that hot jupiters formed far from the host star an then migrated sunward. Perhaps we are looking at the end stage of a jupiter after all of its volatiles boiled away, leaving only the rocky core. Mind you, I've never read anything that explained how this migration was supposed to occur.
(Score: 1) by khallow on Friday July 03 2020, @12:54AM (5 children)
(Score: 0) by Anonymous Coward on Friday July 03 2020, @02:10AM (1 child)
That doesn't make sense because the lost material shouldn't have proportionally more momentum than what is left behind. Planetary migrations in our own system are due to inter-planetary interactions, in particular when planetary orbits develop harmonic periods with other planets resulting in kinetic energy transfer between them. As an example, Jupiter and Saturn developing harmonic orbits is believed to have temporarily pushed Jupiter into the asteroid belt, causing the Late Heavy Bombardment. Either Uranus or Neptune was temporarily thrown out into the Kuiper belt as part of the same event.
(Score: 1) by khallow on Friday July 03 2020, @04:21AM
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.
(Score: 2) by HiThere on Friday July 03 2020, @02:46AM (2 children)
You're assuming that the planet formed before the volitiles left. I'm claiming the opposite. There were a bunch of stuff circling the star that hadn't yet formed into condensed planets. So there was no strong planetary gravity. Think of asteroids. That close to the star the volitiles left quickly because it was too hot for them to solidify. They even got baked out of the hunks of rock that had them as hydrates. So when the planet formed, all that was available to form it from is rocks. The strange thing is that there were enough rocks to form it.
I'm NOT supposing that this planet migrated into its current position, I'm assuming it formed there. Otherwise the problem of composition is harder.
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(Score: 1) by khallow on Friday July 03 2020, @04:22AM (1 child)
For hot Jupiters, that is indeed the case. Because there's still massive amounts of volatiles left.
(Score: 2) by HiThere on Friday July 03 2020, @01:42PM
True, but this isn't a Jupiter, this one's rocky. So it needs a different origin. It's heavy enough that it would have held onto lots of the volatiles unless they left before the planet formed.
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