Is our solar system missing a planet?

Possibly, according to some scientists who are trying to understand the early days of Sol and friends.

One way that researchers study events like the creation of the solar system is to model what might have happened using computer software. The basic idea works like this: We know a decent amount about the physical laws (like gravity) that govern the creation of planets and the formation of a solar system. So scientists can take those laws, and program them into a virtual universe that also includes other real-world data ... like what we know about the make-up of the Sun and the planets orbiting it. Then, they recreate history. Then they do it again. Over and over and over, thousands of times, the scientists witness the creation of our solar system.

It doesn't happen the same way each time. Just like you can get a very different loaf of bread out of multiple attempts and baking the same general recipe. But those recreations start to give us an idea of which scenarios were more likely to have happened, and why. If our solar system tends to form in one way and resist forming in another, we have a stronger basis for assuming that the former way was more likely to be what really happened.

That's what you're seeing in this study, which Charles Q. Choi writes about for Scientific American.

Computer models showing how our solar system formed suggested the planets once gravitationally slung one another across space, only settling into their current orbits over the course of billions of years. During more than 6,000 simulations of this planetary scattering phase, planetary scientist David Nesvorny at the Southwest Research Institute in Boulder, Colo., found that a solar system that began with four giant planets [as ours currently has] only had a 2.5 percent chance of leading to the orbits presently seen now. These systems would be too violent in their youth to end up resembling ours, most likely resulting in systems that have less than four giants over time, Nesvorny found.

Instead, a model about 10 times more likely at matching our current solar system began with five giants, including a now lost world comparable in mass to Uranus and Neptune. This extra planet may have been an "ice giant" rich in icy matter just like Uranus and Neptune, Nesvorny explained.

Read the rest


  1. A shredded “ice giant” rich in icy matter just like Uranus and Neptune might explain the abundance of icy chunks in our solar system, still bombarding Earth and her siblings.  Might have “caused” our atmosphere.

    1. This is an entirely different thing than the idea that some mystical planet is going to turn back up and destroy Earth or raise our consciousness or whatever. Neither I, nor the researchers, are promoting that idea. 

      1. But you realize people are looking for a reason to drink themselves into self-prophecy this coming weekend, right?

        And now, a completely unrelated post about volcanoes.

  2. Interesting.  I’ve always been suspicious of the asteroid belts positioning, but then again – Jupiter IS sooo dense.

  3. Not sure if their model is expecting Neptune in its current orbit or not as part of the 2.5% chance.  I thought it was well-accepted that Neptune may have formed inside of Jupiter’s orbit and got thrown out beyond Saturn later on.

  4. The thing that nibbles at me about these studies is the tendency to assume “well, the more probable thing must be the thing that happened”. 2.5% isn’t odds I’d want to hang my habitable planet on by any stretch, but it only needed to happen once, here, for it to be the “actual history”.

    I’m not sure that at this point it’s anything more than interesting theorycrafting, and as mentioned I wouldn’t bet on 2.5%. But it does make me wonder if there’s just more variables we need in our models.

      1. But these kinds of studies of course are not only concerned with our Solar System. These probabilities are fascinating and totally what science is all about. In generalisation lies the truth science has to offer, no? Our system may be an edge case, finding that it is, or isn’t is only part of the knowledge we can gain.

  5. I notice that the diagram does not include Counter-Earth. Perhaps the Priest-Kings are at work in eliminating planets from our awareness, rather than from our solar system?

  6. We have been watching Jupiter eat other parts of the solar system for decades. I just wonder how much blowback would have been felt on Earth if a Neptune sized planet got eaten. Could its moons have escaped? Say it had a moon the size of Triton, could that be pluto?

    1.  This is actually a thing in Mass Effect; there’s one solar system that has one planet, a rather large and hungry gas giant.

  7. I find it a bit sad that BoingBoing is “dark” as it were to the Electric Universe theories of cosmology.  Something definitely worth looking into.

  8. Instead of proving an ad hoc suggestion of a lost planet, this study by may be a coffin nail in the accretion model of planet formation and a back-handed affirmation of the competing gravitational-collapse model of planetesimal, planet and star formation, also known as gravitational instability (GI).

    Stars are known to form predominantly in binary pairs by GI, and a recent hypothesis suggests that the ‘cold’ classical Kuiper belt binaries also formed by GI. (Nesvorny and Youdin, 2010) (The same David Nesvorny.)

    Why should planets be any different? An alternative hypothesis unifies binary planetesimals and stars formed by GI with planets.

    Planets may also form by GI as binary pairs, not in the circumbinary protoplanetary disk, but rather deep down in the binary stellar realm in horseshoe libration orbits around the L4, L3 and L5 Lagrangian points of the binary stellar pair. Then core-collapse perturbation causes the binary planets to spiral out while the close-binary stellar and planetary pairs spiral in.

    The binary planets spiral in to merge and form solitary planets, and most binary stars likewise spiral in and merge to form luminous red novae (LRNe), like the hypothesized merger of the binary stellar pair that merged at 4.567 Ga to form our Sun, creating the short-lived radionuclides, calcium aluminum inclusions (CAIs) and chondrules of our early solar system.

    Nesvorny, David, Youdin, Andrew N., Richardson, Derek C., (2010), Formation of Kuiper Belt Binaries by Gravitational Collapse, The Astronomical Journal 140 (2010) 785, doi:10.1088/0004-6256/140/3/785

  9. >”We know a decent amount about the physical laws (like gravity) that govern the creation of planets and the formation of a solar system. ”

    Oh, we do? Can you tell me then what Gravity is? as I was under the impression this is one of the most important mysteries modern Physics is still trying to answer ;)

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