back to article Warm, wet, mysterious... sound familiar? Ah, yes, you've heard of this second Neptune, too

A strange, distant planet HAT-P-26b has an atmosphere full of water vapor, hydrogen and helium – and could change how scientists think of planet formation. The exoplanet is hovering 437 light years away from Earth, orbiting a dwarf star twice as old as the Sun. It was found in 2011, and on Friday this week, more light was shed …

  1. Anonymous Coward
    Anonymous Coward

    I was confused, so I looked it up. Metallicity, it turns out, is astronomer-speak for "everything it's made of that isn't hydrogen or helium". As opposed to metallic hydrogen; which is what happens when you squeeze the crap out of hydrogen and which gas giants contain rather a lot of, so I'm told.

    One is a technical term and the other is stuff you're unlikely to encounter while alive and neither have very much to do with the sort of things you tend to think of as metallic.

    1. handleoclast

      To a first approximation

      To a first approximation, every every element in the periodic table is a metal (the vast majority of elements are metals).

      To a first approximation, everything in the universe is either hydrogen or helium (the vast majority of the universe is one or other of those).

      Therefore, to a first approximation, everything in the universe that isn't hydrogen or helium is a metal.

      You have to use a second approximation to start considering things like carbon, oxygen, nitrogen and chlorine.

      1. Anonymous Coward
        Anonymous Coward

        Re: To a first approximation

        Almost makes sense when you put it like that; but surely when you make your first approximation, you should run it through some sort of common-sense filter?

        Every element in the periodic table isn't a metal...you have carbon; noble gases; less noble gases that scratch their bollocks at the dining table; and various other bits and pieces. Everything in the universe clearly isn't hydrogen or helium because carbon is quite important to those very beings wot are doing the approximating; and without oxygen they turn blue and fall over. And so on. Silicon!

        On the plus side, I have learned about order of approximation. Surely if your first-order approximation leads to a clearly untrue statement, then you should bin it and try something else? Which still leaves me confused about the term metallicity.

        1. handleoclast
          Boffin

          Re: To a first approximation

          To a first approximation, if you think that first approximations should lead to a true statement then your thinking is flawed.

          All scientific understanding is an approximation. Sometimes a very good one. Sometimes one that does not apply in rare circumstances. Newtonian gravity and mechanics is a very good approximation that fails in some circumstances. If you're designing particle accelerators or navigation satellites then you need Einsteinian relativity, otherwise Newton does just fine. Even with theories which give very good results and have no known exceptions we cannot prove (or even know) that they're true because new evidence or thinking could cause them to be supplanted.

          In the case of first-order approximations all we ask is that they provide answers that are close enough to be useful. Often all they have to do is let you decide if something might be feasible (so try a more accurate approximation) or clearly impossible (so no need to do all the extra calculations).

          You're right that a lot of the elements important to us are not metals. That doesn't alter the fact that most of the universe is hydrogen and helium. From periodictable.com's abundances we get hydrogen 75%, helium 23%. All the others add up to 2%. So, to a first approximation, the universe is hydrogen and helium.

          Excluding hydrogen and helium, there are 15 non-metals in the periodic table and 7 metalloids. If you class metalloids as non-metals that means 70 out of 92 elements are metals. Class metalloids as metals and that means 77 out of 92 elements are metals. English doesn't have a word meaning "every element but hydrogen and helium" so when you're looking at stellar spectra to see what's in stars, after you exclude hydrogen and helium lines then most of the lines you see are due to metals. This is expecially true because elements with high atomic numbers are metals and have large numbers of transition levels. What you're going to see in a star's spectrum is mostly hydrogen, helium and metals.

          It's only when you look at the second-order approximation that things change. Oxygen, carbon and neon are most abundant after helium. Iron after them. Then silicon (metalloid) and magnesium. Then sulfur and argon. Etc.

          And then you get to the third-order approximation. During planet formation, a lot of the lighter gases were driven away from the inner accretion disc by the solar wind, so our planet is has a massive iron (relative abundance in universe 0.11%) and nickel (0.006%) core.

          To a first approximation, the universe is hydrogen, helium and metals. Especially if you spend a lot of time studying stellar spectra. A geologist would give you a different answer for planet earth.

          1. stephanh

            Re: To a first approximation

            Yeah, when astronomers talk about "metals" they mean everything except hydrogen and helium.

            So for an astronomer, oxygen is a "metal".

            1. Anonymous Coward
              Anonymous Coward

              Re: To a first approximation

              Fair enough. And bewilderment is my default state anyway. Makes for a fun party game too..."to a first approximation planet Earth is all water therefore we are all fish" and so on.

              EDIT: ...or should that be plankton?

              1. Bernard M. Orwell

                Re: To a first approximation

                "...or should that be plankton?"

                Nah, we're all just wet.

                1. Anonymous Coward
                  Anonymous Coward

                  Re: To a first approximation

                  :)

                  My above post came out more sarcastic than was intended. Thank you handleoclast for your explanation.

                  TBH; it's not easy to get my head round science rolling with something that's demonstrably false just because it works. I always thought that the entire point of science was to get at the raw, distilled, it-was there-before-you-and-it'll-be-there-after-you truth. "True until something better comes along",is easy. "True this week" in turbulent subjects, no problem. "It's bollocks but it seems to work" just seems....unscientific, somehow.

              2. Martin Budden Silver badge

                Re: To a first approximation

                "...or should that be plankton?"

                Depends how fast the current is moving. Even a whale is plankton if the current is strong enough that the whale can't swim against it.

  2. Your alien overlord - fear me

    Heavy planets are made up of the lighter elements. Huh?

    1. Anonymous Coward
      Anonymous Coward

      Bigger planets. Gas giants and the like. So they would be heavier if you could find a set of scales big enough. Less dense, but massier, if that helps.

      1. SkippyBing

        'Less dense, but massier, if that helps.'

        So Chunk from The Goonies?

      2. Pedigree-Pete
        Pint

        Massier...

        Have an upvote just for massier. Kudos for not saying "much more massier". PP

    2. Frumious Bandersnatch

      Less massive planets would have a harder time holding onto lighter elements thanks to solar winds and the like. The lighter elements will obviously be higher up in the atmosphere, making them more likely to be stripped away over time. More massive planets are better at keeping hold of these because gravitational forces are higher, but there are no doubt several other reasons as well (like distance from the star).

      1. allthecoolshortnamesweretaken

        Or whether a planet has a magnetic field or not.

  3. handleoclast
    WTF?

    I'm stupid

    We think that the process of planet formation puts more of the heavy elements into smaller planets

    Which just goes to show how stupid I am. It's all so obvious now. There's a cosmic cake-frosting device that squirts heavy elements onto small planets. Which are lighter than heavy planets because they are composed mainly of heavy elements whilst the heavy planets are composed mainly of light elements.

    I'm still a little confused, but I expect it will make even more sense as I approach a state of alternative sobriety later.

  4. John Smith 19 Gold badge
    Thumb Up

    " it may be telling us that there’s more to planet formation than we expect."

    Depends what the full theory says about such planets.

    If it says "impossible" then it's clearly wrong since this work proves it's not.

    If it says "Unlikely but possible given certain parameters" then the question is wheather this solar system meets those parameters, assuming they can be measuered. If it does then the theory is still sound. If not (or they can't be measured) there's more work to be done.

    Exciting times.

    1. Steve Knox

      Re: " it may be telling us that there’s more to planet formation than we expect."

      Based on what I understand of current theory (and I understand that I do not understand enough),

      I believe it says "we don't know what parameters could produce a planet like this."

      So not so much that it's wrong but that it's incomplete. Not surprising since until recently our sample size for planetary observations was less than 10 entities in a single environment.

      This finding exemplifies why I fully support searching for and investigating exoplanets. I bear no illusions that we will visit any of these planets in the foreseeable future, but understanding the possibilities and how they come to be helps understand both the overall physics of the universe and the specific physics of our locality.

      1. Rattus Rattus

        Re: "less than 10 entities in a single environment"

        *twitch*

        Fewer than.

  5. Anonymous Coward
    Anonymous Coward

    This all seems rather obvious

    As the article says, heavier planets are able to hold onto a gassy atmosphere, which means lower levels of metallicity by default. The larger the body, the more gas it can collect, the less that a rocky/metallic core way down deep can impact the overall metallicity percentage.

    It makes sense there would be exceptions with lower metallicity like this one, presumably because there just happened to be less supernova debris available in the system where the planet formed (planets forming around Population I stars would have zero metallicity, because heavier elements didn't yet exist when the system formed)

    What would be an interesting and unexpected find would be gas giants with a significantly HIGHER metallicity than what we've observed so far.

  6. Zog_but_not_the_first
    Boffin

    Some reassurance...

    ... that there is still some intelligent life on this planet.

    1. Tom 7

      Re: Some reassurance...

      Always in the wrong bloody jobs though!

  7. Tom 7

    There's obvious and there's obvious. Planetary 'theory', or the stuff I've seen seems to make very sweeping assumptions which are mainly necessary to make the maths a bit easier - i.e. possible. Things like flat rotating disks of matter that form the star and planets. When you look around the skies the chance of these things happening seem pretty slim.

    We are only now spotting planets around other stars and none of them seem to support such simple models as being of much use and looking at clouds of matter from supernovae that might form systems suggests the models are a bit simple - but we've got to start somewhere! Now we are getting to the point where we can run simulations of system formations we then have to make models to run and test.

    Its not rocket science - its a lot lot harder.

    1. Tom 7

      RE There's obvious and there's obvious

      https://www.newscientist.com/article/2130188-earth-may-have-been-born-in-a-huge-flare-up-of-the-young-sun/ for more complications.

  8. G R Goslin

    Weight/Mass

    I do wish that people would not talk of the weight of a planet. Jupiter has a high mass, not a high weight

  9. Anonymous Coward
    Anonymous Coward

    High mass?

    Bless you my son.

  10. Faux Science Slayer

    "Does the Sun Have a Surface" by Dr Pierre Robitaille, on YouTube

    In his video...."On the Validity of Kirchoff"....Dr Robitaille explains modern empirical evidence on the

    errors of Planck, Stephan, Boltzman and Kirchoff 'laws' of radiation. His Sun Surface series

    explains the goofy "Hydrogen Ball" hypothesis. We have been systematically lied to about everything.

    1. Pompous Git Silver badge

      Re: "Does the Sun Have a Surface" by Dr Pierre Robitaille, on YouTube

      "We have been systematically lied to about everything."
      Do you include yourself in that statement Faux?

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