[HN Gopher] Possible new dwarf planet found in our solar system
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Possible new dwarf planet found in our solar system
Author : ddahlen
Score : 84 points
Date : 2025-05-21 18:32 UTC (4 hours ago)
(HTM) web link (www.minorplanetcenter.net)
(TXT) w3m dump (www.minorplanetcenter.net)
| ddahlen wrote:
| 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_Syste...
| gus_massa wrote:
| > _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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| [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_dwar
| f_planets So between 20 and 30???
| hinkley wrote:
| This thread is making me realize that The Expanse has me
| pronouncing planetoids in Belter.
| temp0826 wrote:
| Beltalowda!
| bediger4000 wrote:
| 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.
| hnuser123456 wrote:
| 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.
| evil-olive wrote:
| > 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
| mandevil wrote:
| 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.
| epicureanideal wrote:
| Very informative, thank you!
| AStonesThrow wrote:
| > thoroughly mapped the Oort Cloud
|
| So it's interesting that the Oort Cloud is often mentioned
| as a real thing. Surely there are plenty of bodies
| discovered which are orthogonal to its existence, but
| Oort's "Cloud" itself still enjoys only the status of
| hypothesis and not reality.
|
| https://en.wikipedia.org/wiki/Oort_cloud
|
| Sadly, even Wikipedia editors seem unable to distinguish
| between the formal definitions of "hypothesis" vs. "theory"
| when delivering such a scientific article.
| codethief wrote:
| Oh wow, looks like I'm one of today's lucky 10,000!
| Thanks so much!
| mandevil wrote:
| You are correct, I meant to say Kuiper Belt, not Oort
| Cloud, pulled the wrong thing out of my memory. Unlike
| the Oort Cloud, we are doing a good job of mapping KBO's
| as we speak.
| throwaway2k255 wrote:
| If the Oort Cloud is so relatively close to Alpha
| Centauri, is there a chance that Alpha Centauri also has
| its own cloud that overlaps with it?
| hinkley wrote:
| And that, boys and girls, is how Neil deGrass Tyson got
| Pluto demoted. (I kid).
| naikrovek wrote:
| I still think he did it because he wanted to have his
| name on something significant. He's a science
| communicator, not a researcher, and he's not going to be
| making any discoveries. So he's gotta change something
| that already exists to have his name on something that
| everyone knows. He had the power to change its status, so
| he did. I think that's all it was. I hope I'm wrong but
| I've never heard a really GOOD reason to undo something
| that was so commonly known and taught. The definition for
| "planet" could change and Pluto could have been left
| alone, grandfathered in, in a way. There's a reason it
| was discovered first. It's huge compared to other dwarf
| planets.
|
| There's no reason that Pluto couldn't have remained a
| proper planet. It's big enough to be round _and_ its
| largest moon is big enough to be round. Mars doesn't have
| _any round moons._ Mars is still a planet.
| XorNot wrote:
| Isn't that kind of the issue though? Pluto's moon isn't
| just round it's about half the size of Pluto itself such
| that the Pluto-Charon system orbits around a point in
| space between the two bodies.
| naikrovek wrote:
| Jupiter and the sun orbit a barycenter, too. Jupiter is a
| planet.
| calmbell wrote:
| Eris is essentially the same size as Pluto and has a
| larger mass.
| naikrovek wrote:
| Then ADD Eros. Don't remove Pluto.
| xp84 wrote:
| > The definition for "planet" could change and Pluto
| could have been left alone, grandfathered in, in a way
|
| This doesn't sound like a science way of doing things.
| The definition of planet would have to be literally
| changed to add "Or has to have been discovered before
| 19XX" in order to keep Pluto without becoming an
| unbounded set. If you're annoyed at all the pedants
| correcting kids or anyone else talking about the nine
| planets, I'd take it up with them for uselessly debating
| such a fine distinction, like a chemist arguing about the
| word "Sodium" on a Nutrition Facts label.
|
| I would argue the colloquial definition has indeed been
| changed in the above way, in that most people would say
| that what Mars, Venus, and Pluto have in common is
| they're all planets, and only a few would remember the
| odd factoid that the dwarf planet designation was
| created.
|
| It's okay for the colloquial definition to be different
| than the scientific one. There isn't any use case where
| that will harm anyone. It's not like we're chartering
| flights to "All Planets" where space tourists are going
| to be ripped off, limited to 8 planets by the
| technicality and missing out.
| naikrovek wrote:
| You're probably right, but I still think there's room for
| things like this.
|
| What's a "moon" versus a "planet"? Earth is a moon of
| Sol, is it not? Why is having a lot of planets a problem
| in the first place? Why do we have to restrict the
| definition at all? If 2-3 stars are at the center of a
| star system, are the planets in that star system planets,
| or something else? What if they're small?
|
| This whole scene is ripe for people who want to put their
| stamp of opinion on something to go nuts arbitrarily.
| rantallion wrote:
| > What's a "moon" versus a "planet"? Earth is a moon of
| Sol, is it not?
|
| Planets orbit stars. Moons orbit planets. That's a clear
| and easy distinction. Planet vs dwarf planet isn't so
| clear to most.
| xp84 wrote:
| What's a "moon" versus a "planet"? Earth is a moon of
| Sol, is it not?
|
| We already have the word "satellite" for "things that go
| around other things" right? I think "moon" is just
| "satellite of a planet" for convenience in discussing
| that subset.
|
| > Why is having a lot of planets a problem in the first
| place?
|
| I think keeping the number manageable is explicitly
| something we keep around to help kids grasp the main
| entities in the solar system. If we just said "there are
| 235 planets" it would be silly to try to teach them all,
| so we'd probably just settle for "The top 10 biggest
| planets" or something. Having a definition instead of a
| number to bound the set isn't much less arbitrary than
| teaching the "top 10," but since the long tail clearly
| starts after #8, "Top 8" would be the only guaranteed
| stable set to give special treatment to, which is what
| we've arrived at with the official definition.
| metalman wrote:
| I prefer to think that Pluto got denounced, and may yet
| be rehabilitated.MPAPA
| hinkley wrote:
| That wiki page needs some work. The section you linked to
| describes the eccentricity as a ratio, however the top of the
| page describes 0 as perfectly circular and 1 as an escape
| trajectory.
|
| If it were a ratio then 0 would be escape and 1 would be
| circular.
| ddahlen wrote:
| If you want to view the orbit:
|
| https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2017%...
| d_silin wrote:
| Most likely a https://en.wikipedia.org/wiki/Detached_object
| java-man wrote:
| Sorry for a stupid question: could it be "the planet X", or is it
| too light / in a wrong orbit?
| porkbrain wrote:
| No, according to Wikipedia Planet Nine is expected to have
| about 5 earth masses.
| dotancohen wrote:
| This is not planet X. This is smaller than other, closer,
| bodies that we already know of.
| squidsoup wrote:
| And I just put the kettle on for the Anunnaki, what a pity.
| mandevil wrote:
| This is a good question to ask. It can't be, for the reasons
| you guessed.
|
| This is not the first time this sort of thing has happened.
| When Pluto was found by Clyde Tombaugh he was looking for
| Planet Nine, which Percival Lowell had calculated must be
| present based on the orbits of the outer planets. But it was
| quickly realized that Pluto was too small and in the wrong
| orbit for it be Lowell's deduced planet. (And even then they
| worked with a too high estimate of Pluto's mass, it wasn't
| until the 1978 discovery of Charon that we got a good estimate
| of Pluto's mass. It is hard to get a good mass estimate without
| something else in orbit around it.)
|
| The Pioneer and Voyager missions gave us much better estimates
| of the masses of the gas giants, and my understanding is that
| if you go back and redo Lowell's calculations with those
| correct masses, his planet disappears. That's my best guess as
| to Planet X, that our constants are wrong in some way, but
| we'll see.
| hinkley wrote:
| One of the other theories for Planet X I believe has been
| debunked as absense of evidence. There are gaps in the
| _documented_ bodies orbiting the sun that could imply an
| object clearing orbits, but they were dismissed instead as
| sampling errors - there are parts of the sky that are easier
| to catalog than others, and so of course we have cataloged
| the easy parts more thoroughly. We need observation stations
| in a sun orbit to see the parts we can't see easily from an
| earth orbit.
| ChuckMcM wrote:
| "That's no moon" :-). But more seriously, just another giant lump
| of stuff swinging around the solar system. I am not an
| astronomer, so I'm not sure about some of the things I'm reading
| in that report but to me, it seems to be in the solar ecliptic.
| But its far enough away even at perigee that the only thing of
| note it might interact with would be Pluto.
|
| I suppose that flying through the Oort cloud it might
| periodically launch ice balls into the inner solar system.
| brudgers wrote:
| _only thing of note it might interact with would be Pluto_
|
| Is Pluto a planet again, or not? Honest question because I
| don't keep up on these things because they have no practical
| effect other than drama...and I try to avoid drama.
| kulahan wrote:
| No. It's smaller than other moons in our solar system. It's
| never going to be a planet again, but a planetoid, dwarf
| planet, or even asteroid is appropriate.
| rich_sasha wrote:
| It boggles my mind when I look up at the Moon, that in fact
| it's a massive rock travelling at something like 2,000 mph,
| always trying to fall onto the Earth, and missing it all the
| time.
| mgiampapa wrote:
| If my goal was to fall into the earth and kept missing I
| would be depressed too. Each try it misses by slightly more
| and it's orbital distance increases. How sad is that?
|
| Also, I like to anthropomorphize inanimate objects because
| secretly they hate it.
| yieldcrv wrote:
| its getting further away, if it helps your understanding of
| the situation better
|
| "falling into" was never part of the equation
| dabluecaboose wrote:
| > But its far enough away even at perigee
|
| Minor astrodynamics nit: "perigee" is a term specific to Earth.
| The generic term for all bodies is "periapsis", and the term
| for the Sun is "perihelion"
|
| (Astrodynamics terms generally take from the Greek, rather than
| Latin)
| astroalex wrote:
| I found the preamble at the beginning of the announcement
| charmingly dated:
|
| > The Minor Planet Electronic Circulars contain information on
| unusual minor planets, routine data on comets and natural
| satellites, and occasional editorial announcements. They are
| published on behalf of Division F of the International
| Astronomical Union by the Minor Planet Center, Smithsonian
| Astrophysical Observatory, Cambridge, MA 02138, U.S.A. > >
| Prepared using the Tamkin Foundation Computer Network
|
| Looking up the Tamkin Foundation Computer Network:
| https://www.minorplanetcenter.net/iau/Ack/TamkinFoundation.h...
|
| > The OpenVMS cluster consists of nine single-CPU workstations
| and one four-CPU server. All the machines are running the
| extremely robust and secure OpenVMS operating system. The twelve
| Alpha-based machines are arranged as an OpenVMS Cluster, allowing
| all machines to share disk storage, execution and batch queues
| and other resources, as well as simplifying system management.
|
| Assuming "Alpha-based machines" is referring to the DEC Alpha,
| these computers are ~30 years old.
| https://en.wikipedia.org/wiki/DEC_Alpha
| bastardoperator wrote:
| Could they not get more juice out of a single, modern server? I
| get porting over to a new system and migrating is a huge time
| suck and a good enough reason not to do it if everything is
| working, just seems excessive for 14 cores.
| ddahlen wrote:
| I got a bit too excited with this one, this is may not be a full
| on dwarf planet, but it is a very large object. There are only a
| small number (about 10-20) objects in our solar system of this
| size. Its the first big one we have found in a number of years.
| d_silin wrote:
| For the curious.
|
| Periapsis, au: 45.241
|
| Apoapsis, au: 1714.759
|
| Period, years: 26106.07
| d_silin wrote:
| It comes to Earth closer than Pluto, btw.
| silverfrost wrote:
| 26000 year period and yet it has still been around the sun
| 2000+ times since the dinosaurs went extinct. Make me feel a
| bit insignificant and awed at the same time.
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