Pluto formed from a billion comets?

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Scientists have come up with a new theory for the origin of Pluto, based on data from New Horizons and Rosetta, that suggests the planets formed from the accretion of a billion comets or Kuiper Belt objects.

“We’ve developed what we call ‘the giant comet’ cosmochemical model of Pluto formation,” said Dr. Christopher Glein of SwRI’s Space Science and Engineering Division. The research is described in a paper published online today in Icarus. At the heart of the research is the nitrogen-rich ice in Sputnik Planitia, a large glacier that forms the left lobe of the bright Tombaugh Regio feature on Pluto’s surface. “We found an intriguing consistency between the estimated amount of nitrogen inside the glacier and the amount that would be expected if Pluto was formed by the agglomeration of roughly a billion comets or other Kuiper Belt objects similar in chemical composition to 67P, the comet explored by Rosetta.”

This is only a hypothesis, but it is intriguing. It suggests that Pluto’s make-up came only from the outer parts of the solar system, thus constraining how much mixing between the solar system’s inner and outer regions occurred. For scientists trying to understand the formation of the entire solar system, this lack of mixing would be significant. It means that the gas giants, while migrating inward, never migrated outward.



  • Klystron

    Would this not also throw gas back on the fire whether Pluto is a planet or not, with its origins being that of KBO’s? The more we know, the more we know we don’t know!!

  • If this theory is correct then wouldn’t the density of comets in the Oort belt be about the same as asteroids are in the asteroid belt?

  • Localfluff

    The Kuiper Belt is much less dense than the Asteroid Belt. The average distance between Kuiper Belt objects has been estimated to be the same as the distance between objects in the inner Solar System! Mercury, Venus, Earth, Moon, Mars, Deimos, Phobos. If we add the few largest NEA to that, the inner Solar System is a bit denser.

    Since Pluto is in orbital resonance with Neptune, it is natural to assume that Neptune’s migration could have had something to do with the formation or evolution of Pluto. But it has been a long time and many things can have happened.

  • BSJ

    After the fly-by, they announced that Pluto had a weak comet like tail.

    I thought to myself that that would mean Pluto is really nothing more than a giant comet. I guess I’m not the only one to think so…

  • Localfluff

    @BSJ, Pluto is a comet for sure. Of it came close to the Sun it would form a huge tail. The upper size limit for a comet is somewhere between the mass of Earth and Neptune. Too large and they get a hydrogen envelope. If a big comet hit Earth the right way, it could stop our rotation, resurface the planet and bring a thick CO2 atmosphere. Maybe that’ what happened to an Earth like living Venus 0.3 billion years ago? Planetary scientists however prefer the idea of internal episodic volcanism, about which very little is known. It is indeed very unlikely that a huge comet hits a terrestrial planet.

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