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The minor planet center is the clearing house of observations of objects in our solar system. They have announced a new dwarf planet today. This object appears

The minor planet center is the clearing house of observations of objects in our solar system. They have announced a new dwarf planet today. This object appears to be in a very eccentric orbit (0.948), and with an H magnitude of 3.55, so it is likely hundreds of km in diameter. Ceres for reference has a H magnitude of 3.33 (smaller H is bigger diameter). If you want to know what H means: https://en.wikipedia.org/wiki/Absolute_magnitude#Solar_System_bodies_(H) https://en.wikipedia.org/wiki/Absolute_magnitude#Solar_Syste...

gus_massa 1y ago
> hundreds of km How big is that compared with other dwarf planets/ Moons? If you sort all dwarf planets by size, which position does this take (approximately)? Pluto -> 2300 Km Ceres -> 950 Km Fobos(Mars) -> 25 Km
- ddahlen 1y ago
  Depends on the albedo, if the H magnitude is a good measurement, then it is probably between 300-700km. These are rough bounds, its highly dependent on how reflective it's surface is (albedo). With an orbit somewhere around 28k years, it reached perihelion in about 1931, at 45 au from the Sun.
  - kbelder 1y ago
    So it's roughly in the closest 200-year period out of 28,000 years. That means it spends 99.3% of it's orbit further away than now, and thus harder to find. Simplistic odds would seem to imply that there's over a hundred more dwarf planets just like this but further away, so we just haven't seen them.
    - hnuser123456 1y ago
      I really hope we can get some more sensitive and wider telescopes to look deeper into the Oort cloud. At those distances, sunlight is comparable to a full moon or less, surface temperatures are only tens of kelvin. And yet they're still less than 1% of the distance to the next star.
  - gus_massa 1y ago
    [I'm lost with all the recent discoveries.] Assuming 500Km, is in in the top 10 by size/mass[1][2]? Top 100? Top 1000? Top 1000000? [1] Yes I know it's not the same. Whatever criteria is easier to measure. [2] I guess not top 10, but I have no idea about the current knowledge of the long tail. Fake Edit: I took a look at https://en.wikipedia.org/wiki/List_of_possible_dwarf_planets https://en.wikipedia.org/wiki/List_of_possible_dwarf_planets So between 20 and 30???
  - liamwire 1y ago
    Your comment was the one that really made all of this sink in, thanks. Wow.
- hinkley 1y ago
  This thread is making me realize that The Expanse has me pronouncing planetoids in Belter.
  - temp0826 1y ago
    Beltalowda!
bediger4000 1y ago
Does the 0.984 eccentricity orbit imply anything? That's close to eccentricity of 1, which is a parabolic path, not gravitationally bound to the sun.
- deleted 1y ago
  [deleted]
- hnuser123456 1y ago
  Going off the SMA and eccentricity, part of its orbit is "relatively" close to the sun, ~ 45 AU, about 1.5x the distance to Neptune (~ 30 AU), and the other half of its orbit is very, very far away, ~ 1700 AU, over 50 times the distance to Neptune, but still less than 1% of the distance to the next star. When it's in the faraway part of its orbit, it is moving very slowly, probably only tens of meters per second, but it's still close enough to the sun to eventually fall back in for another loop. However, if something else dense enough got close enough out there, it would be easily perturbed and have its whole orbit altered, or even be ejected. But interstellar space is pretty void of wandering solid bodies, so it keeps falling back towards the sun.
  - SJC_Hacker 1y ago
    > But interstellar space is pretty void of wandering solid bodies, so it keeps falling back towards the sun. As far as we know ... we don't know how many rogue planets are out there ... mayb be as numerous as the number of stars or even greater
    - hnuser123456 1y ago
      After I posted that, I did some more research to see how typical it is, over longer time periods, that our nearest star is about 4 ly away. That seems to be about average spacing for our part of the galaxy, but it turns out in a little over a million years, a star about half the size of the sun will pass around 0.15 ly away or 10,000 AU, which is far outside the kuiper belt, but solidly though the middle of the inner oort cloud, and will leave a wake of scattered comets and asteroids, some of which will rain down on Earth. https://en.wikipedia.org/wiki/Gliese_710 https://en.wikipedia.org/wiki/Gliese_710
evil-olive 1y ago
> This object appears to be in a very eccentric orbit (0.948) from [0]: > Before its demotion from planet status in 2006, Pluto was considered to be the planet with the most eccentric orbit (e = 0.248). Other Trans-Neptunian objects have significant eccentricity, notably the dwarf planet Eris (0.44). Even further out, Sedna has an extremely-high eccentricity of 0.855 due to its estimated aphelion of 937 AU and perihelion of about 76 AU > ... > Comets have very different values of eccentricities. Periodic comets have eccentricities mostly between 0.2 and 0.7, but some of them have highly eccentric elliptical orbits with eccentricities just below 1; for example, Halley's Comet has a value of 0.967 so possibly an ignorant question, as someone who's interested in astronomy but doesn't follow it very closely - when this is categorized as a dwarf planet, does that include "it might be a comet" as a possibility? or have they already ruled it out as a possible comet through other observations? 0: https://en.wikipedia.org/wiki/Orbital_eccentricity#Examples https://en.wikipedia.org/wiki/Orbital_eccentricity#Examples
- mandevil 1y ago
  Dwarf planet versus comet/asteroid hinges on mass, basically its "enough mass to be roughly round" (technically it's called "hydrostatic equilibrium"). Back from the 1810's to the 1870's or so, most people considered Ceres, Vesta, and things like that to be planets- they were bodies that wandered around the solar system, that meant they were planets. When the numbers started to get into the 20's, everyone decided to create a new category, "asteroid" (Greek for 'star-like') and put all of the smaller things in that. So when Pluto was discovered in 1930 it was slotted right into the planet category. Pluto was discovered mostly by accident, because Clyde Tombaugh was amazing at working the blink comparator, and finding the one dot that moved in between the two pictures of the night sky a few days apart. However, by the 1990's and 2000's you had computers and digital cameras, which are even better than Clyde at finding things that move, and quickly the number of planets started to go up- and it was clear that once we had thoroughly mapped the ~~Oort Cloud~~ (meant Kuiper Belt, see below) etc. we would have dozens of planets. And so once again astronomers decided to create a new category, just like they had with asteroids a century earlier. This time they drew the line in such a way that Ceres got moved from asteroid to dwarf planet- it has enough mass to be roughly round, so after over a century of being an asteroid it became a dwarf planet. This is how things always work in science: we discover something, then we discover more of them, and re-categorize everything based on the new discoveries. It's just more noticeable with Pluto because reciting the planets is done by every schoolkid in a way that they don't for subatomic particles or for species of voles or whatever.
ddahlen 1y ago
If you want to view the orbit: https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2017%20OF201&view=VOP https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2017%...
- araes 1y ago
  Thanks, it helps quite a bit to be able to visualize what they're talking about. Out at 90 AU, and by the year 3000 is out at 500 AU, and that's still not anywhere near maximum distance. Looked like it was going to be 10,000+ years orbits or longer, and probably out at several 1000 AU at maximum. Little skeptical it would even orbit normally with how heavily eccentric it is, and the extreme distance at maximum. Way... out beyond the heliopause / heliosheath / termination shock.
  - zamadatix 1y ago
    The fun part is the ~1700 AU aphelion is still not far enough out to be part of the Oort cloud. https://science.nasa.gov/solar-system/oort-cloud/facts/ https://science.nasa.gov/solar-system/oort-cloud/facts/
    - jessriedel 1y ago
      Well, the preprint announcing the discovery describes its orbit as extending to "the inner Oort cloud" even though aphelion is 1630 au. https://arxiv.org/abs/2505.15806 https://arxiv.org/abs/2505.15806
  - jessriedel 1y ago
    > and probably out at several 1000 AU at maximum. The preprint announcing the discovery lists the semi-major axis as 838 au, so the major axis is 1676 au and aphelion is about 1630 au. https://arxiv.org/abs/2505.15806 https://arxiv.org/abs/2505.15806
- mwaitjmp 1y ago
  Does anyone know if this has its PE in alignment with the other Sedna type objects found? I think there is a tendency for them to have their PE out to one side and the AP out to the other giving a fairly obvious pattern indicating another larger object is shepherding the others into their orbits.
d_silin 1y ago
Most likely a https://en.wikipedia.org/wiki/Detached_object https://en.wikipedia.org/wiki/Detached_object

gus_massa 1y ago

> hundreds of km How big is that compared with other dwarf planets/ Moons? If you sort all dwarf planets by size, which position does this take (approximately)? Pluto -> 2300 Km Ceres -> 950 Km Fobos(Mars) -> 25 Km

ddahlen 1y ago
Depends on the albedo, if the H magnitude is a good measurement, then it is probably between 300-700km. These are rough bounds, its highly dependent on how reflective it's surface is (albedo). With an orbit somewhere around 28k years, it reached perihelion in about 1931, at 45 au from the Sun.
- kbelder 1y ago
  So it's roughly in the closest 200-year period out of 28,000 years. That means it spends 99.3% of it's orbit further away than now, and thus harder to find. Simplistic odds would seem to imply that there's over a hundred more dwarf planets just like this but further away, so we just haven't seen them.
  - hnuser123456 1y ago
    I really hope we can get some more sensitive and wider telescopes to look deeper into the Oort cloud. At those distances, sunlight is comparable to a full moon or less, surface temperatures are only tens of kelvin. And yet they're still less than 1% of the distance to the next star.
- gus_massa 1y ago
  [I'm lost with all the recent discoveries.] Assuming 500Km, is in in the top 10 by size/mass[1][2]? Top 100? Top 1000? Top 1000000? [1] Yes I know it's not the same. Whatever criteria is easier to measure. [2] I guess not top 10, but I have no idea about the current knowledge of the long tail. Fake Edit: I took a look at https://en.wikipedia.org/wiki/List_of_possible_dwarf_planets https://en.wikipedia.org/wiki/List_of_possible_dwarf_planets So between 20 and 30???
- liamwire 1y ago
  Your comment was the one that really made all of this sink in, thanks. Wow.
hinkley 1y ago
This thread is making me realize that The Expanse has me pronouncing planetoids in Belter.
- temp0826 1y ago
  Beltalowda!

bediger4000 1y ago

Does the 0.984 eccentricity orbit imply anything? That's close to eccentricity of 1, which is a parabolic path, not gravitationally bound to the sun.

deleted 1y ago
[deleted]
hnuser123456 1y ago
Going off the SMA and eccentricity, part of its orbit is "relatively" close to the sun, ~ 45 AU, about 1.5x the distance to Neptune (~ 30 AU), and the other half of its orbit is very, very far away, ~ 1700 AU, over 50 times the distance to Neptune, but still less than 1% of the distance to the next star. When it's in the faraway part of its orbit, it is moving very slowly, probably only tens of meters per second, but it's still close enough to the sun to eventually fall back in for another loop. However, if something else dense enough got close enough out there, it would be easily perturbed and have its whole orbit altered, or even be ejected. But interstellar space is pretty void of wandering solid bodies, so it keeps falling back towards the sun.
- SJC_Hacker 1y ago
  > But interstellar space is pretty void of wandering solid bodies, so it keeps falling back towards the sun. As far as we know ... we don't know how many rogue planets are out there ... mayb be as numerous as the number of stars or even greater
  - hnuser123456 1y ago
    After I posted that, I did some more research to see how typical it is, over longer time periods, that our nearest star is about 4 ly away. That seems to be about average spacing for our part of the galaxy, but it turns out in a little over a million years, a star about half the size of the sun will pass around 0.15 ly away or 10,000 AU, which is far outside the kuiper belt, but solidly though the middle of the inner oort cloud, and will leave a wake of scattered comets and asteroids, some of which will rain down on Earth. https://en.wikipedia.org/wiki/Gliese_710 https://en.wikipedia.org/wiki/Gliese_710

evil-olive 1y ago

> This object appears to be in a very eccentric orbit (0.948) from [0]: > Before its demotion from planet status in 2006, Pluto was considered to be the planet with the most eccentric orbit (e = 0.248). Other Trans-Neptunian objects have significant eccentricity, notably the dwarf planet Eris (0.44). Even further out, Sedna has an extremely-high eccentricity of 0.855 due to its estimated aphelion of 937 AU and perihelion of about 76 AU > ... > Comets have very different values of eccentricities. Periodic comets have eccentricities mostly between 0.2 and 0.7, but some of them have highly eccentric elliptical orbits with eccentricities just below 1; for example, Halley's Comet has a value of 0.967 so possibly an ignorant question, as someone who's interested in astronomy but doesn't follow it very closely - when this is categorized as a dwarf planet, does that include "it might be a comet" as a possibility? or have they already ruled it out as a possible comet through other observations? 0: https://en.wikipedia.org/wiki/Orbital_eccentricity#Examples https://en.wikipedia.org/wiki/Orbital_eccentricity#Examples

mandevil 1y ago
Dwarf planet versus comet/asteroid hinges on mass, basically its "enough mass to be roughly round" (technically it's called "hydrostatic equilibrium"). Back from the 1810's to the 1870's or so, most people considered Ceres, Vesta, and things like that to be planets- they were bodies that wandered around the solar system, that meant they were planets. When the numbers started to get into the 20's, everyone decided to create a new category, "asteroid" (Greek for 'star-like') and put all of the smaller things in that. So when Pluto was discovered in 1930 it was slotted right into the planet category. Pluto was discovered mostly by accident, because Clyde Tombaugh was amazing at working the blink comparator, and finding the one dot that moved in between the two pictures of the night sky a few days apart. However, by the 1990's and 2000's you had computers and digital cameras, which are even better than Clyde at finding things that move, and quickly the number of planets started to go up- and it was clear that once we had thoroughly mapped the ~~Oort Cloud~~ (meant Kuiper Belt, see below) etc. we would have dozens of planets. And so once again astronomers decided to create a new category, just like they had with asteroids a century earlier. This time they drew the line in such a way that Ceres got moved from asteroid to dwarf planet- it has enough mass to be roughly round, so after over a century of being an asteroid it became a dwarf planet. This is how things always work in science: we discover something, then we discover more of them, and re-categorize everything based on the new discoveries. It's just more noticeable with Pluto because reciting the planets is done by every schoolkid in a way that they don't for subatomic particles or for species of voles or whatever.

ddahlen 1y ago

If you want to view the orbit: https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2017%20OF201&view=VOP https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2017%...

araes 1y ago
Thanks, it helps quite a bit to be able to visualize what they're talking about. Out at 90 AU, and by the year 3000 is out at 500 AU, and that's still not anywhere near maximum distance. Looked like it was going to be 10,000+ years orbits or longer, and probably out at several 1000 AU at maximum. Little skeptical it would even orbit normally with how heavily eccentric it is, and the extreme distance at maximum. Way... out beyond the heliopause / heliosheath / termination shock.
- zamadatix 1y ago
  The fun part is the ~1700 AU aphelion is still not far enough out to be part of the Oort cloud. https://science.nasa.gov/solar-system/oort-cloud/facts/ https://science.nasa.gov/solar-system/oort-cloud/facts/
  - jessriedel 1y ago
    Well, the preprint announcing the discovery describes its orbit as extending to "the inner Oort cloud" even though aphelion is 1630 au. https://arxiv.org/abs/2505.15806 https://arxiv.org/abs/2505.15806
- jessriedel 1y ago
  > and probably out at several 1000 AU at maximum. The preprint announcing the discovery lists the semi-major axis as 838 au, so the major axis is 1676 au and aphelion is about 1630 au. https://arxiv.org/abs/2505.15806 https://arxiv.org/abs/2505.15806
mwaitjmp 1y ago
Does anyone know if this has its PE in alignment with the other Sedna type objects found? I think there is a tendency for them to have their PE out to one side and the AP out to the other giving a fairly obvious pattern indicating another larger object is shepherding the others into their orbits.

d_silin 1y ago

Most likely a https://en.wikipedia.org/wiki/Detached_object https://en.wikipedia.org/wiki/Detached_object