Size and albedo of the largest detected Oort-cloud object

(arxiv.org)

49 points | by belter 5 hours ago ago

19 comments

  • Simon_ORourke 4 hours ago

    11AU is close enough thank you very much

    • atemerev 14 minutes ago

      Hey, I want another Hale-Bopp, which was at 0.9 AU.

  • pmichaud 4 hours ago

    About 137km diameter, so really big, but albedo (surface brightness, basically) still similar to other comets.

    • pfdietz 4 hours ago

      This object is thankfully not coming anywhere close to Earth, but an impact of an object this size with Earth would still not sterilize the biosphere, or even evaporate the oceans.

      • perihelions 3 hours ago

        It'd certainly sterilize the vertebrate part of the biosphere: a significant part of its chemical composition (per the paper) should theoretically be CO and HCN. "Hypervolatiles" is the term the paper uses—primordial evils that can only exist in the coldest outer reaches of the Oort cloud, far away from the star that evaporates them.

        I don't know the exact numbers, but for water ice the "frost line" is at about 3 au (between Mars and Jupiter)[0]—the line inside which icy comets and ice moons, like Europa, can't form. Presumably there's analogous zones for the increasingly volatile cryogenic ices, going out into the most distant regions—a solid carbon dioxide line, a carbon monoxide line, a cyanide line... The surface of Pluto, for example, is mostly solid nitrogen, with parts of solid methane and solid carbon monoxide [1].

        [0] https://en.wikipedia.org/wiki/Frost_line_(astrophysics)

        [1] https://en.wikipedia.org/wiki/Pluto#Geology

      • LeifCarrotson 4 hours ago

        The KT impactor has been estimated to have been about 10 km in diameter and moving at 20 km/s.

        A long-period comet, like an Oort cloud object, might impact at 50 km/s, instead of the 10-20 km/s of a near-Earth asteroid.

        The physics might say that the energy might not be enough to literally vaporize the oceans or "sterilize" the biosphere, but the global ecosystem is fragile. This thing dropping on the planet would absolutely cause a mass extinction.

        • pfdietz 4 hours ago

          Oh, I didn't say the results wouldn't be utterly catastrophic. It's more a comment on just how surprisingly large an impact would be needed for sterilization.

          https://iopscience.iop.org/article/10.3847/psj/ac66e8

          (extrapolated > 700 km impactor needed for sterilization)

          • jajko 2 hours ago

            I don't think anymore absolutely 100% sterilization of all life on Earth is possible, we always end up talking about 99.999999% or similar. With exception of maybe super/hypernova of our Sun which ain't possible, or black hole passing directly through/very close to Earth, tearing apart every single atom making up this planet including all of us on quark level.

            • s1artibartfast 2 hours ago

              Colision with a planet or moon would do it, anything that turns the surface to lava really.

              • dekhn 5 minutes ago

                Deep-earth chemoautotrophs might survive that. But ultimately, if the deep subsurface exceeds 150C, it would be hard to survive.

              • sebzim4500 an hour ago

                Even then there's a chance a few tardigrades hibernate on some material that shoots up and then comes back a few years later once the earth has cooled a bit.

                • pfdietz an hour ago

                  I think they could be cooked by thermal radiation as the ejecta expands.

                  • sebzim4500 an hour ago

                    Probably most would be, but there are a lot of microorganisms and only a few need to get lucky.

      • belter 4 hours ago

        My quick back of envelope calculations...

        Imply that the kinetic energy released upon the impact of such an object, show a group sheltering at the ISS (orbit at an altitude of between 370–460 km (200–250 nmi)) or the Tiangong (orbit between 340 and 450 km (210 and 280 mi) ) would not be likely to survive the impact from ejecta thrown into their orbital altitude...

      • hinkley an hour ago

        If it’s made of the same stuff as comets, there would be some value to blowing it up, since more parts would then evaporate before impact. Right?

      • BobbyJo 4 hours ago

        "Puny rock couldn't even cook every last bacterium on our planets surface. Pathetic." - You

  • webdoodle 4 hours ago

    Is this the '9th planet' that Batygin and Brown, inferred the existence of based off the orbital tracks of smaller objects in the Oort cloud?

    https://astrobiology.nasa.gov/news/caltech-researchers-find-...

    • perihelions 4 hours ago

      No; it's about 30 million times too small. :)

    • Tuna-Fish 26 minutes ago

      No, this is way too small and close for that.