Our Solar System has 127 probable planets and 500+ possibles

It is estimated that there may be 200 dwarf planets in the Kuiper belt of the outer Solar System and possibly more than 10,000 in the region beyond. The International Astronomical Union (IAU) has accepted four as official dwarf planets: Pluto, Eris, Haumea, and Makemake, as well as Ceres in the inner Solar System.

Philip Metzger has recently published a case that all dwarf planets are planets. The qualifying feature of a dwarf planet is that it “has sufficient mass for its self-gravity to overcome rigid-body forces so that it assumes a hydrostatic equilibrium (nearly round) shape” is enough to categorize as a planet.

We have 8 official planets and one or two likely planet 9 and 10 candidates which have some evidence but have not been found.

According to Mike Brown of Thu Jun 21 2018 there are:
10 objects which are nearly certainly dwarf planets,
16 objects which are highly likely to be dwarf planets (not recounting the certain),
39 objects which are likely to be dwarf planets (not recounting certain and highly likely),
88 objects which are probably dwarf planets (without recounting above categories)
573 objects which are possibly dwarf planets (without recounting above categories).

Current observations are generally insufficient for a direct determination as to whether a body meets this definition. A dwarf planet may not be the satellite of another body, even though several moons (such as Titan) are larger than the recognized dwarf planets.

Based on a comparison with the icy moons that have been visited by spacecraft, such as Mimas (round at 400 km in diameter) and Proteus (irregular at 410–440 km in diameter), Michael Brown estimated that an icy body relaxes into hydrostatic equilibrium at a diameter somewhere between 200 and 400 km.

Ceres is thought to be the only dwarf planet in the asteroid belt. 4 Vesta, the second-most-massive asteroid, appears to have a fully differentiated interior and was therefore in equilibrium at some point in its history, but it is not today. The third-most massive object, 2 Pallas, has a somewhat irregular surface and is thought to have only a partially differentiated interior. Brown has estimated that, because rocky objects are more rigid than icy objects, rocky objects below 900 kilometers (560 mi) in diameter may not be in hydrostatic equilibrium and thus not dwarf planet.

In 2010, Gonzalo Tancredi presented a report to the IAU evaluating a list of 46 candidates for dwarf-planet status based on light-curve-amplitude analysis and the assumption that the object was more than 450 kilometres (280 mi) in diameter. Some diameters are measured, some are best-fit estimates, and others use an assumed albedo of 0.10. Of these, he identified 15 as dwarf planets by his criteria (including the four accepted by the IAU), with another nine being considered possible. To be cautious, he advised the IAU to “officially” accept as dwarf planets the top three not yet accepted: Sedna, Orcus, and Quaoar. Although the IAU had anticipated Tancredi’s recommendations, they have not responded.

Mike Brown considers a large number of trans-Neptunian bodies, ranked by estimated size, to be “probably” dwarf planets. He did not consider asteroids, stating “In the asteroid belt Ceres, with a diameter of 900 km, is the only object large enough to be round”.

The terms for varying degrees of likelihood he split these into:

Near certainty: We are confident enough in the size estimate to know that each one of these must be a dwarf planet even if predominantly rocky.

Highly likely Anything larger than 600 km is all but certainly round. Even objects significantly smaller are likely round. The predicted and/or measured size of an object in this category would have to be grossly in error or the composition would have to be primarily rocky in order for it not to be a dwarf planet.

Likely: Anything icy larger than 500 km is highly likely to be round. But the size uncertainties are large enough that some of these objects could, in reality, be small enough to be less certain.

Probably: All icy satellite larger than 400 km are round, so we expect these objects to be round if the size estimate is correct.

Possibly: We don’t know where the transition from non-round to round occurs, but in icy satellites it is between 200 and 400 km. Objects this size in the Kuiper belt could thus possible be round, but we don’t know. Probably not: Below 200 km no icy satellite are round. We expect the same in the Kuiper belt. A few of these object could be bigger than expected, however, and could turn out to be large enough to round themselves.

The table also lists the estimated albedo used to determine the size or the calculated albedo from the measured size. Also listed is the absolute magnitude, which in this case refers to how bright the object would be if you were looking at it while you were standing on the surface of the sun and the object were at the distance of the earth. As in the rest of astronomy, smaller magnitudes are brighter and every 5 magnitudes represents a factor of 100.

40 thoughts on “Our Solar System has 127 probable planets and 500+ possibles”

  1. I was thinking in the farther term. Of course, we don’t have the technology for that now and probably won’t for several decades. For the moment being, it will be enough to send manned BFRs or more evolved ships to orbit these places, every time farther and farther from home. Venus will probably be one of the first visited planets after Mars. But humans there will remain in orbit for a while, sending automated probes down the atmosphere and surface as you say. I have no idea when humans will go to Jupiter or Saturn, but I expect it to be a few decades after we visit Mars and Venus. The difficulties for such a trip are significantly more than those for Mars and Venus, taking a couple of years to several in every direction at least. But I do believe people will dare to go one day. Just for the adventure’s sake. Probably in something that will drop from orbit, aero-brake, deploy parachutes and finally, balloons, take a peek of a few hours/days and then go back to orbit with some staging rocket, jettisoning the rest. The kind of daredevil mission the first space explores would have thought, but with the technology and facilities of that future time, with people probably waiting for them safely in orbital settlements to cheer their return.

    Reply
  2. I was thinking in the farther term. Of course we don’t have the technology for that now and probably won’t for several decades.For the moment being it will be enough to send manned BFRs or more evolved ships to orbit these places every time farther and farther from home. Venus will probably be one of the first visited planets after Mars. But humans there will remain in orbit for a while sending automated probes down the atmosphere and surface as you say.I have no idea when humans will go to Jupiter or Saturn but I expect it to be a few decades after we visit Mars and Venus. The difficulties for such a trip are significantly more than those for Mars and Venus taking a couple of years to several in every direction at least.But I do believe people will dare to go one day. Just for the adventure’s sake. Probably in something that will drop from orbit aero-brake deploy parachutes and finally balloons take a peek of a few hours/days and then go back to orbit with some staging rocket jettisoning the rest.The kind of daredevil mission the first space explores would have thought but with the technology and facilities of that future time with people probably waiting for them safely in orbital settlements to cheer their return.

    Reply
  3. I’ll note only that the gas giants are also supposed to have ridiculously high winds and terrible storms. So floating colonies will have serious difficulties there, even if the tech was developed.

    Reply
  4. I’ll note only that the gas giants are also supposed to have ridiculously high winds and terrible storms. So floating colonies will have serious difficulties there even if the tech was developed.

    Reply
  5. Something that *might* be worth doing is have robotic airships gathering samples from the surface & bring them up to a floating habitat for analysis by human scientists. Of course AI & remote control might be good enough to control the floating lab from orbit, before we have humans near Venus.

    Reply
  6. Something that *might* be worth doing is have robotic airships gathering samples from the surface & bring them up to a floating habitat for analysis by human scientists. Of course AI & remote control might be good enough to control the floating lab from orbit before we have humans near Venus.

    Reply
  7. It’s really difficult to imagine science on Venus that requires a human presence. At most you might, as has been proposed for Mars, have a manned orbiter to control robots on the planet (or in its atmosphere in Venus’ case) with low communications latency, and to observe these planets at a safe distance.

    Reply
  8. It’s really difficult to imagine science on Venus that requires a human presence. At most you might as has been proposed for Mars have a manned orbiter to control robots on the planet (or in its atmosphere in Venus’ case) with low communications latency and to observe these planets at a safe distance.

    Reply
  9. I was thinking in the farther term. Of course, we don’t have the technology for that now and probably won’t for several decades. For the moment being, it will be enough to send manned BFRs or more evolved ships to orbit these places, every time farther and farther from home. Venus will probably be one of the first visited planets after Mars. But humans there will remain in orbit for a while, sending automated probes down the atmosphere and surface as you say. I have no idea when humans will go to Jupiter or Saturn, but I expect it to be a few decades after we visit Mars and Venus. The difficulties for such a trip are significantly more than those for Mars and Venus, taking a couple of years to several in every direction at least. But I do believe people will dare to go one day. Just for the adventure’s sake. Probably in something that will drop from orbit, aero-brake, deploy parachutes and finally, balloons, take a peek of a few hours/days and then go back to orbit with some staging rocket, jettisoning the rest. The kind of daredevil mission the first space explores would have thought, but with the technology and facilities of that future time, with people probably waiting for them safely in orbital settlements to cheer their return.

    Reply
  10. I was thinking in the farther term. Of course we don’t have the technology for that now and probably won’t for several decades.For the moment being it will be enough to send manned BFRs or more evolved ships to orbit these places every time farther and farther from home. Venus will probably be one of the first visited planets after Mars. But humans there will remain in orbit for a while sending automated probes down the atmosphere and surface as you say.I have no idea when humans will go to Jupiter or Saturn but I expect it to be a few decades after we visit Mars and Venus. The difficulties for such a trip are significantly more than those for Mars and Venus taking a couple of years to several in every direction at least.But I do believe people will dare to go one day. Just for the adventure’s sake. Probably in something that will drop from orbit aero-brake deploy parachutes and finally balloons take a peek of a few hours/days and then go back to orbit with some staging rocket jettisoning the rest.The kind of daredevil mission the first space explores would have thought but with the technology and facilities of that future time with people probably waiting for them safely in orbital settlements to cheer their return.

    Reply
  11. I’ll note only that the gas giants are also supposed to have ridiculously high winds and terrible storms. So floating colonies will have serious difficulties there, even if the tech was developed.

    Reply
  12. I’ll note only that the gas giants are also supposed to have ridiculously high winds and terrible storms. So floating colonies will have serious difficulties there even if the tech was developed.

    Reply
  13. Something that *might* be worth doing is have robotic airships gathering samples from the surface & bring them up to a floating habitat for analysis by human scientists. Of course AI & remote control might be good enough to control the floating lab from orbit, before we have humans near Venus.

    Reply
  14. Something that *might* be worth doing is have robotic airships gathering samples from the surface & bring them up to a floating habitat for analysis by human scientists. Of course AI & remote control might be good enough to control the floating lab from orbit before we have humans near Venus.

    Reply
  15. It’s really difficult to imagine science on Venus that requires a human presence. At most you might, as has been proposed for Mars, have a manned orbiter to control robots on the planet (or in its atmosphere in Venus’ case) with low communications latency, and to observe these planets at a safe distance.

    Reply
  16. It’s really difficult to imagine science on Venus that requires a human presence. At most you might as has been proposed for Mars have a manned orbiter to control robots on the planet (or in its atmosphere in Venus’ case) with low communications latency and to observe these planets at a safe distance.

    Reply
  17. However, a breathable nitrogen oxygen mix is a lifting gas in the Venus atmosphere, but that is not the case for any of the gas giants, so the floating habitat idea is much more practical for Venus. Whether we would ever want to do more with Venus than we currently do with Antarctica is another matter.

    Reply
  18. However a breathable nitrogen oxygen mix is a lifting gas in the Venus atmosphere but that is not the case for any of the gas giants so the floating habitat idea is much more practical for Venus.Whether we would ever want to do more with Venus than we currently do with Antarctica is another matter.

    Reply
  19. However, a breathable nitrogen oxygen mix is a lifting gas in the Venus atmosphere, but that is not the case for any of the gas giants, so the floating habitat idea is much more practical for Venus. Whether we would ever want to do more with Venus than we currently do with Antarctica is another matter.

    Reply
  20. However a breathable nitrogen oxygen mix is a lifting gas in the Venus atmosphere but that is not the case for any of the gas giants so the floating habitat idea is much more practical for Venus.Whether we would ever want to do more with Venus than we currently do with Antarctica is another matter.

    Reply
  21. I was thinking in the farther term. Of course, we don’t have the technology for that now and probably won’t for several decades.

    For the moment being, it will be enough to send manned BFRs or more evolved ships to orbit these places, every time farther and farther from home. Venus will probably be one of the first visited planets after Mars. But humans there will remain in orbit for a while, sending automated probes down the atmosphere and surface as you say.

    I have no idea when humans will go to Jupiter or Saturn, but I expect it to be a few decades after we visit Mars and Venus. The difficulties for such a trip are significantly more than those for Mars and Venus, taking a couple of years to several in every direction at least.

    But I do believe people will dare to go one day. Just for the adventure’s sake. Probably in something that will drop from orbit, aero-brake, deploy parachutes and finally, balloons, take a peek of a few hours/days and then go back to orbit with some staging rocket, jettisoning the rest.

    The kind of daredevil mission the first space explores would have thought, but with the technology and facilities of that future time, with people probably waiting for them safely in orbital settlements to cheer their return.

    Reply
  22. I’ll note only that the gas giants are also supposed to have ridiculously high winds and terrible storms. So floating colonies will have serious difficulties there, even if the tech was developed.

    Reply
  23. Something that *might* be worth doing is have robotic airships gathering samples from the surface & bring them up to a floating habitat for analysis by human scientists. Of course AI & remote control might be good enough to control the floating lab from orbit, before we have humans near Venus.

    Reply
  24. It’s really difficult to imagine science on Venus that requires a human presence. At most you might, as has been proposed for Mars, have a manned orbiter to control robots on the planet (or in its atmosphere in Venus’ case) with low communications latency, and to observe these planets at a safe distance.

    Reply
  25. That’s interesting, I didn’t know that the “surface” gravity of some gas giants was in the same range as Earth. There’s a case to be made for floating colonies then, like what’s been proposed for Venus.

    Reply
  26. That’s interesting I didn’t know that the surface”” gravity of some gas giants was in the same range as Earth. There’s a case to be made for floating colonies then”””” like what’s been proposed for Venus.”””

    Reply
  27. That’s interesting, I didn’t know that the “surface” gravity of some gas giants was in the same range as Earth. There’s a case to be made for floating colonies then, like what’s been proposed for Venus.

    Reply
  28. That’s interesting I didn’t know that the surface”” gravity of some gas giants was in the same range as Earth. There’s a case to be made for floating colonies then”””” like what’s been proposed for Venus.”””

    Reply
  29. However, a breathable nitrogen oxygen mix is a lifting gas in the Venus atmosphere, but that is not the case for any of the gas giants, so the floating habitat idea is much more practical for Venus.
    Whether we would ever want to do more with Venus than we currently do with Antarctica is another matter.

    Reply
  30. The gravity of Uranus and Neptune are also very close to that of Earth, but like Venus if you go down far enough to reach some sort of “surface” you’ll be crushed by the atmospheric pressure.

    Reply
  31. The gravity of Uranus and Neptune are also very close to that of Earth but like Venus if you go down far enough to reach some sort of surface”” you’ll be crushed by the atmospheric pressure.”””

    Reply
  32. The gravity of Uranus and Neptune are also very close to that of Earth, but like Venus if you go down far enough to reach some sort of “surface” you’ll be crushed by the atmospheric pressure.

    Reply
  33. The gravity of Uranus and Neptune are also very close to that of Earth but like Venus if you go down far enough to reach some sort of surface”” you’ll be crushed by the atmospheric pressure.”””

    Reply
  34. Plenty of room and resources in this Solar System for those that know how to live in space and earn a living off floating rocks. In my belief, all this brouhaha about going to Mars is a cultural fad, that will go away shortly after we go there. The real life for humans in space, will be in rotating habitats in free fall/orbit. Given those are the only ones that could provide all the elements for a healthy human life: energy, resources available with affordable energy expenditure, low radiation and most importantly, gravity. No other planet but Venus and Saturn can provide us with gravity levels near those of Earth, but Venus is a hell in most other respects and Saturn has no solid ground to stand on, besides of being quite hellish on its own. Both will be visited by humans in due time, but not for living. If we learn to live in rotating habitats, with whatever energy sources and resources we can get from asteroids, we can live practically anywhere, including these many frigid planets or planetoids, which will become important sources of resources in the far future.

    Reply
  35. Plenty of room and resources in this Solar System for those that know how to live in space and earn a living off floating rocks.In my belief all this brouhaha about going to Mars is a cultural fad that will go away shortly after we go there.The real life for humans in space will be in rotating habitats in free fall/orbit. Given those are the only ones that could provide all the elements for a healthy human life: energy resources available with affordable energy expenditure low radiation and most importantly gravity.No other planet but Venus and Saturn can provide us with gravity levels near those of Earth but Venus is a hell in most other respects and Saturn has no solid ground to stand on besides of being quite hellish on its own.Both will be visited by humans in due time but not for living.If we learn to live in rotating habitats with whatever energy sources and resources we can get from asteroids we can live practically anywhere including these many frigid planets or planetoids which will become important sources of resources in the far future.

    Reply
  36. Plenty of room and resources in this Solar System for those that know how to live in space and earn a living off floating rocks. In my belief, all this brouhaha about going to Mars is a cultural fad, that will go away shortly after we go there. The real life for humans in space, will be in rotating habitats in free fall/orbit. Given those are the only ones that could provide all the elements for a healthy human life: energy, resources available with affordable energy expenditure, low radiation and most importantly, gravity. No other planet but Venus and Saturn can provide us with gravity levels near those of Earth, but Venus is a hell in most other respects and Saturn has no solid ground to stand on, besides of being quite hellish on its own. Both will be visited by humans in due time, but not for living. If we learn to live in rotating habitats, with whatever energy sources and resources we can get from asteroids, we can live practically anywhere, including these many frigid planets or planetoids, which will become important sources of resources in the far future.

    Reply
  37. Plenty of room and resources in this Solar System for those that know how to live in space and earn a living off floating rocks.In my belief all this brouhaha about going to Mars is a cultural fad that will go away shortly after we go there.The real life for humans in space will be in rotating habitats in free fall/orbit. Given those are the only ones that could provide all the elements for a healthy human life: energy resources available with affordable energy expenditure low radiation and most importantly gravity.No other planet but Venus and Saturn can provide us with gravity levels near those of Earth but Venus is a hell in most other respects and Saturn has no solid ground to stand on besides of being quite hellish on its own.Both will be visited by humans in due time but not for living.If we learn to live in rotating habitats with whatever energy sources and resources we can get from asteroids we can live practically anywhere including these many frigid planets or planetoids which will become important sources of resources in the far future.

    Reply
  38. That’s interesting, I didn’t know that the “surface” gravity of some gas giants was in the same range as Earth. There’s a case to be made for floating colonies then, like what’s been proposed for Venus.

    Reply
  39. The gravity of Uranus and Neptune are also very close to that of Earth, but like Venus if you go down far enough to reach some sort of “surface” you’ll be crushed by the atmospheric pressure.

    Reply
  40. Plenty of room and resources in this Solar System for those that know how to live in space and earn a living off floating rocks.

    In my belief, all this brouhaha about going to Mars is a cultural fad, that will go away shortly after we go there.

    The real life for humans in space, will be in rotating habitats in free fall/orbit. Given those are the only ones that could provide all the elements for a healthy human life: energy, resources available with affordable energy expenditure, low radiation and most importantly, gravity.

    No other planet but Venus and Saturn can provide us with gravity levels near those of Earth, but Venus is a hell in most other respects and Saturn has no solid ground to stand on, besides of being quite hellish on its own.

    Both will be visited by humans in due time, but not for living.

    If we learn to live in rotating habitats, with whatever energy sources and resources we can get from asteroids, we can live practically anywhere, including these many frigid planets or planetoids, which will become important sources of resources in the far future.

    Reply

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