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Space Science

Core of a Gas Planet Seen For the First Time (bbc.com) 47

Posted by BeauHD from the first-of-its-kind dept.
A team of astronomers has discovered what they think are the rocky innards of a giant planet that's missing its thick atmosphere. Their findings have been published in the journal Nature. The BBC reports: Its radius is about three-and-a-half times larger than Earth's but the planet is around 39 times more massive. In this size range, the planet would be expected to have a significant component that's gas. Yet it has a density similar to Earth, appearing to be mostly rocky. The object, called TOI 849 b, was found circling a star much like the Sun that's located 730 light-years away. The core orbits so close to its parent star that a year is a mere 18 hours and its surface temperature is around 1,527C. Researchers aren't sure whether the core lost its atmosphere in a collision or just never developed one.

If it was once similar to Jupiter, there are several ways it could have lost its gaseous envelope. These could include tidal disruption, where the planet is ripped apart from orbiting too close to its star, or even a collision with another planet late in its formation. If it's a "failed" gas giant, this could have occurred if there was a gap in the disc of gas and dust that it emerged from, or if it formed late, after the disc ran out of material.
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Core of a Gas Planet Seen For the First Time More

Core of a Gas Planet Seen For the First Time

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  • Too close to its primary, too hot, and you couldn't even mine it.

  • My first instinct was that being that hot and that close to a much more massive object, it could have lost its atmosphere because it simply had enough energy to get to Lagrange point L1 and be pulled away by the star. Since that's not mentioned, presumably my instinct is wrong. Any planetary cosmologists here to tell me how many orders of magnitude away from plausible that idea is?

    • The reason the atmosphere of the planet is gone is called "solar wind", it is a constant stream of protons radiating from the star, which heated the atmosphere of the planet up and blew it away.

      • It's not clear to me from the article how they determined it had an atmosphere in the first place. It's a massive rock very close to its sun, and they're not sure if it lost its atmosphere or never developed one. So how does this make it a candidate for being a gas giant core more than any other rock near a star?

        • It's the mass of the exoplanet, which is far higher than should be possible for a rocky body. If our theories of planet formation are correct, it's reasonable to draw the conclusion that it was a gas giant that had its atmosphere either torn away by the solar wind or there was some other significant event like a collision that blew off its atmosphere.

          • Ah-ha, this is very useful. I went back and read the article and it isn't that I missed it, they just don't mention it at all. I feel like that's a critical piece of information here!

            • It's a pretty cool object, if you think about it. At least for Jupiter and Saturn, there's no firm boundary between atmosphere and core, just points where pressure and temperature increase that matter is compacted in fuzzy zones. To imagine Jupiter having its atmosphere shredded, left with the ultra-compressed core would be cool. There are theories that Jupiter's rocky core is surrounded by a shell of metallic hydrogen (hence it's massive magnetic field, the planet's core is like a monster dynamo). But that

    • Re: (Score:1)

      by eeloon ( 6270492 )

      That's actually a really good idea. In general, material can escape not just by passing the Lagrange-1 point, but by passing in any direction beyond the boundaries of its Roche lobe [wikipedia.org]. (The L1 point is the inner apex of the Roche lobe.)

      To actually (fail to) answer your question: I don't know whether it's significant it is in this case, but this process - Roche lobe overflow - is important for the loss of mass from stars in binary systems.

    • Yeah solar wind seems like the obvious explanation (ala Mars' supposed loss of atmosphere). So it's strange that the article doesn't explain why the layman's most likely guess was rejected.

      It's a bit like saying "This car crashed into the yard is a mystery to investigators, they suspect it may have fallen from an airplane." : Raises many questions.

      In of itself, explaining why investigators suspect an unusual cause without explaining why they 'jumped' to the unusual explanation seems lacking in the report

  • That the athmosphere was simply blown away be the intense solar wind, a flare, or something else that a 1500 degree intensity brings with it?

    • Yeah, pretty sure the scientists never thought of that. Luckily, you were here to point that out, or they might have been puzzling over this for years....
      • You seem to be confused about the difference between the scientists and the journalists who very likely left that information out of their article. But if the scientists don't address that possibility in their paper, they deserve to be called out for it.... it doesn't matter if it "occurs" to you or not if you don't include it.
  • You can't be 3x the size and 39x the mass while having similar densities. The densities would have to be over an order of magnitude apart, this is pretty basic math.

  • "Its radius is about three-and-a-half times larger than Earth's but the planet is around 39 times more massive." Yes, if its radius is 3.5 times larger than Earth's then its volume is 3.5^3 times larger, i.e. around 43 times larger. The "but" is misleading :) Clarified later by comparing densities but surely there was a simpler way.

    • Re: (Score:2)

      by Mal-2 ( 675116 )

      "It has about 43 times the mass of the Earth but similar density, making the core 3.5 times the radius of Earth."

      A lot of it has to do with what order the writer wants to reveal the data to the reader, though.

    • Re: (Score:1)

      by Tablizer ( 95088 )

      Usually the larger a rocky body is the denser it is due to gravity such that volume extrapolation alone cannot be used. But I don't know what the typical density factor is, though, other than it's not trivial.

  • People who know their astronomy probably have a good explanation for this sort of thing, but ignorant me never understood why Jupiter is considered a gas giant, rather than a rocky planet with a very big atmosphere.

    Is there a distinction I don't get, or is it a matter of convention?

    • Re: (Score:2)

      by Dr. Tom ( 23206 )
      I heard they have a huge diamond as the core, not just a pile of rocks

    • I'm by no means a professional astronomer, but here is my thought:

      The Earth's atmosphere is about 7 miles thick. The rocky part is 7,915 miles. So less than 1/1,000th is atmosphere. Earth is 99.9% rocky. Some of the rock is slightly wet, with a layer of water 0.005% the thickness of the rock.

      Jupiter: 80,000 miles of gas and 15,000 miles of rock.

      So rocky planets are 99.9% or more rock, gas planets are mostly gas.

      Further, it occurs to me that historically astronomers could see only the gas. Only later did

      • 7 miles thick? You better tell commercial pilots that they're flying in vacuum at cruise height then. Earths atmosphere is approx 100 miles thick but density decreases non linearly. It might be a logarithmic decrease, not sure, others can clarify.

        • That's actually WHY they fly there and why the 737-800 increasing the altitude from 39,000 feet to 41,000 feet is a big deal.

          To save fuel, they want to fly where there isn't much air resistance, because there isn't much air.

          Air density, as I recall, is roughly inversely proportional to altitude raised to the fifth power (actually 5.26 power), so yeah a small change in altitude makes a very big difference in pressure and density.
           

    • Re: (Score:2)

      by lgw ( 121541 )

      Most names for most things in science are wrong or misleading. Things get named when we begin to study them, not later when they're actually understood. As humans, we suck quite badly at changing names once we know what the right ones should be.

    • Re: (Score:1)

      by Tablizer ( 95088 )

      never understood why Jupiter is considered a gas giant, rather than a rocky planet with a very big atmosphere.

      Almost all planets are rocky to some degree, at least near the core. Thus, rockiness is not a distinguishing feature. Most categorizations focus on distinguishing features.

      "Gas giant" is generally a colloquial short-hand, although I suppose one could create a fairly clear-cut set of criteria based on composition ratios.

  • Isn't it great all the information we can get from something so far away? Or they're just pulling it out of their asses

    • Isn't it great all the information we can get from something so far away? Or they're just pulling it out of their asses

      The latter. We're talking about gas.

  • NO evidence that it was a gas giant (Score:3)

    by flyingfsck ( 986395 ) on Friday July 03, 2020 @09:00AM (#60257612)
    It is a big rock. TFA has zero evidence that it was a gas giant. The writer is pulling data out of vacuum, never mind thin air.

    • Re: (Score:2)

      by ytene ( 4376651 )
      Exactly this.

      I was about to post this in the form of a question, but sometimes it's good to be ninja'd.

      I got to thinking about "what other ways could a large, super-dense mass get formed? The best answer I could come up with would be that this object could be leftover matter from a supernova. Not necessarily one in this specific system; it could have actually been ejected by something remote to this system and then snagged by the star's gravity as it wandered through deep space.

      My limited understan

    • Re: (Score:1)

      by eeloon ( 6270492 )

      Most of the gas in the universe is made up of light molecules like hydrogen and helium. A small planet like Earth doesn't have enough gravity to hang on to them: our atmosphere contains only heavier molecules like nitrogen and oxygen. A larger planet has enough gravity to accumulate a thick atmosphere of hydrogen and helium, becoming a gas giant. In fact, hydrogen and helium are so common in early-stage stellar systems that this is more-or-less inevitable.

      So, the authors reason, this planet probably form

    • Re: (Score:2)

      by icejai ( 214906 )

      I'm not a planetary astrophysicist, but I imagine the thinking to be along the following idea:

      Planets can only use gravity to form. An early solar system forms out of lots of rocks, but even more gas. As planets grow larger, their ability to attract gas grows as well. As planets compete for gas, the largest ones become stars, and the rest become stuck as gas giants.

      So, a planet showing up with 39 times the mass of the earth and not seeing a gas atmosphere is a big deal.
      ie. "How did this planet get this big

  • "Its radius is about three-and-a-half times larger than Earth's but the planet is around 39 times more massive." Since mass goes up with the cube of the radius and the cube root of 39 is around 3.4 one would expect a planet with a radius of about 3.5 that of earth to be around 39 times as massive as the earth. Nothing startling about this observation though the sentence posits it as some kind of anomaly that warrants further investigation or discussion.

    • Re: (Score:1)

      by eeloon ( 6270492 )

      All other planets we've seen thus far have been either small, rocky planets (like Earth) or big, gaseous planets (like Jupiter). Our theories about how planets form are built around this observation: big planets, we think, have a strong enough gravitational field to hang on to a thick atmosphere of hydrogen and helium, whereas smaller planets can only hang on to heavier gases like nitrogen, which are much less abundant, so small planets end up with only a thin atmosphere around their rocky core.

      This is the

  • If this garbage goes on much longer without serious scientists blowing the whistle on it their entire field will be discredited.

    At best, we puny humans can observe a bit of wobble in a star, see a little occlusion in the light of that star and make observations on the intensity and wavelengths of light emitted by that star and possibly reflected off a body orbiting that star and then illuminating part of a single pixel on an imager here in our solar system. That's not really SEEING anything about the planet

    • Or the "journalist" who wrote this piece basically made up a bunch of
      statements that were only mild conjectures in the original research paper.

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