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Why Can’t We Find Planet Nine?
- umeshunni 8y agoRelevant XKCD: https://xkcd.com/1633/ https://xkcd.com/1633/
- bkohlmann 8y agoGreat graphical depiction. one question: Why do dwarf plants on the right have an upward sloping diameter as you get farther out? Isn't a dwarf defined by an absolute diameter cutoff (i.e. above which it's a true planet, below which it's not)? or is there a formula that takes into account distance from something?
- janzer 8y agoThe difference in definition between a planet and a dwarf planet is just that a dwarf planet has not cleared debris from it's orbit. So not directly dependent on the mass, diameter etc. I'm unsure why the further would orbits require a larger size though; my guess is something to do with longer, slower orbits needing more mass to get rid of the debris.
- JumpCrisscross 8y ago> I'm unsure why the further would orbits require a larger size though Stern–Levison's Λ finds a body's ability to scatter smaller masses out of its orbital region over a period of time equal to the age of the Universe scales inversely with its semi-major axis [1]. (A circle's semi-major axis is its radius [2].) This is most simply because a wide orbit contains more volume than a small orbit. [1] http://www.boulder.swri.edu/~hal/PDF/planet_def.pdf http://www.boulder.swri.edu/~hal/PDF/planet_def.pdf [2] https://en.wikipedia.org/wiki/Semi-major_and_semi-minor_axes https://en.wikipedia.org/wiki/Semi-major_and_semi-minor_axes
- zaroth 8y agoIs Pluto the black circle with the question mark or is that “Planet Nine”? Not marking Pluto on this would ruin it for me, even if it’s in the “Dwarf Planet” box.
- Raphmedia 8y agohttps://www.explainxkcd.com/wiki/index.php/1633:_Possible_Undiscovered_Planets https://www.explainxkcd.com/wiki/index.php/1633:_Possible_Un...
- zaroth 8y ago“Pluto, no longer considered a planet (it was the ninth until 2006), is not marked on the chart, but it would be below Neptune just outside the pink region (2,300 km diameter and 30-50 AU away).“ Yeah, that sucks.
- krylon 8y agoDo not take this the wrong way, but I am always a little confused about people feeling about the whole planet-dwarf_planet thing so strongly. Pluto is still out there, just as it was a hundred years ago, when nobody knew it existed. And just recently, NASA sent a probe Pluto's way, that managed to amaze me, an outspoken Pluto-hater[0]: Turns out that Pluto is much more complex than people had anticipated. Who cares what the IAU decides to call it? It is what it is. You could call a rose a turd, and it still would not smell as badly. ;-) [0] Okay, I do not hate Pluto. I just wish NASA, ESA or whoever would send a couple of probes to Uranus and Neptune. I feel very strongly about this.
- chrispeel 8y agoMike Brown, Konstantin Batygin, and Surhud More just spent time at the Subaru telescope looking for Planet Nine. This thread summarizes their search and what they'll do if they don't find it: https://twitter.com/plutokiller/status/1071978898458464256 https://twitter.com/plutokiller/status/1071978898458464256
- breck 8y agoVery cool, thanks. > I didn't expect to get so much data; need new disks drives Anyone know how much data they'd get in 7 days, and what models they'll run on it to search for planet 9?
- sandworm101 8y agoIt isn't terribly complicated. They take images of a particular patch of sky on two different days, then xor them against each other to detect differences. Those differences are a moving object, something associated with our solar system rather than the (relatively) non-moving stars in the background. That gives you a detection and an angular speed, from which you can make assumptions about distance (stuff in orbit further away moves slower, really far away and it can seem to move in reverse). Then you wait six months for earth to be on the other side of its orbit and take some more pics based on your previous guesses about the orbit. That lets you triangulate for a better distance estimate. Combine all the estimates and you can match it to a reasonable orbit. Do that over and over and you get an increasingly accurate estimate of the true orbit. And from distance+brightness+composition you get a size/mass.
- breck 8y agoThanks! I was wondering if the devil is in the details--if the datasets are so large (petabytes+?) that there are millions of these "differences", most of which are false positives from factors like atmospheric noise or equipment issues, and what the computing challenges were sifting through it all...Or perhaps as you hint it is relatively straightforward after all.
- fhood 8y agoI am an idiot who doesn't know anything about astronomy, and I always assumed that if you were looking for something like planet 9 you would attempt to deduce its position from the gravitational effects it might have on nearby known entities. What am I missing in this context?
- aurailious 8y agoI'd guess there is very few nearby known entities and those that are in the area are too far to be precise enough.
- Avshalom 8y agoThats how its existence is inferred but there are enough additional bodies that it's a chaotic signal. Then even if you do know where to look that doesn't guarantee you'll spot a relatively small dark object.
- badloginagain 8y agoThe article states that's exactly what they're doing. They believe there's a planet nine based on its effect on other objects, and have a theoretical orbital range modeled from those gravitational effects. The problem is space is big, and space is dark, so its hard to find things that don't generate their own light.
- fhood 8y agoAh ok, I guess I just overestimated the level of precision they were working with.
- benj111 8y agoWasn't Pluto predicted before it was discovered? And wasn't the mass of Pluto less than what was predicted? Plutos wikipedia page seems to support this (under mass estimates). https://en.m.wikipedia.org/wiki/Pluto https://en.m.wikipedia.org/wiki/Pluto Ps when its discovered, can the planet start with a P so the rhymes still work?
- jonathankoren 8y agoAfter the demotion of Pluto, I rather liked this mnemonic: My Very Educated Mother Just Served Us... Nothing!
- benj111 8y agoI'm just stuck on "My Very Easy Method Just Speeds Up Naming....." Very unsatisfying. But my aged brain cant remember the others :(
- 0003 8y agoI just use SUN. MVEMJ is so ingrained into my memory, but the more distant gas giants I forget! :P
- _kst_ 8y agoI use the names of the planets to remember the mnemonic.
- tzjmetron 8y agoHehehe. To be honest, I never got mnemonics myself. The original data seem far easier to remember.
- novaleaf 8y agoI recited the planet names to my kids as toddlers using the tune of Brahms' Lullaby. I think it helped them.
- jonathankoren 8y agoSame.
- jkingsbery 8y agoSince Pluto is clearly Planet Nine, I'm assuming this was written before 1930. (I'm only being a little facetious. According to https://www.amazon.com/Chasing-New-Horizons-Inside-Mission-ebook/dp/B076H7LK8Y/ref=sr_1_1?ie=UTF8&qid=1545245406&sr=8-1&keywords=new+horizons https://www.amazon.com/Chasing-New-Horizons-Inside-Mission-e..., plenty of scientists consider Pluto a planet still.)
- OscarCunningham 8y agoMost definitions that make Pluto a planet would make it Planet Ten, because Ceres would also be a planet.
- mcv 8y agoIn the 19th century, Ceres, Pallas, Juno and Vesta were all considered planets for a while. At some point the solar system had 12 planets. Until people realised it was nuts to consider all asteroids planets. Just like what happened with Pluto upon the discovery of more Kuiper Belt objects.
- Zardoz84 8y agoPluto is a MINOR planet
- zaroth 8y agoThey’ll just find it, add it as a “planet”, then discover dozens or hundred of others just like it that aren’t on the same orbital plane as our first 8, and demote it again.
- Rooster61 8y agoUnlikely. My understanding of the gravitational breadcrumbs we have seen indicate a much larger body (~10x Earth's mass, like a smaller ice giant similar to Uranus/Neptune), one that would almost certainly clear out the area around it through accretion. It would be very surprising to see something with that kind of mass still sharing an orbital neighborhood of other similar bodies.
- garmaine 8y agoIt is in the Kuiper belt. It hasn’t cleared it’s neighborhood. (But then the definition of “planet” you are referencing is utterly uselesss and misapplied already anyway.)
- bronson 8y agoIt has to clear the Kuiper belt? That's a tall order!
- garmaine 8y agoWho knows. The definition is vague to the point of uselessness. Pluto, apparently, is not a planet because it hasn't cleared Neptune out of its orbit. But then by symmetry neither has Neptune cleared Pluto out of its orbit, so if we're to have any consistency then we can't call Neptune a planet either. Oops. The reality is that the IAU definition of "planet" was a very poor decision made by people who aren't planetary scientists. The geophysical definition is much better: an object large enough to assume spherical shape from its own gravitational force acting on its constituent material, and too small to have initiated fusion and be a star. So Pluto is a planet, as is Ceres, the Moon, and a thousand other known objects.
- JamesUtah07 8y agoFrom Mike Brown's Twitter: > My biggest fear, though, is the Milky Way galaxy. There are SO MANY stars that we tend to avoid even looking there. But our predicted region goes through the Milky Way. So we are going to have to deal. We're testing a little of that this week, (Dec 9) If it is indeed in that region it may be a long time before we detect P9. But I'm optimistic that they'll find it in their latest survey they did. Mike Brown is extremely experienced at finding objects in the outer solar system so if he's confident that they'll find it soon than so am I.
- DoctorOetker 8y agocould it not be seen as an advantage? in reflection we have fourth power, but in obstruction its inverse square of the distant (group of) stars?
- Rooster61 8y agoThis is almost certainly an oversimplified question born out of ignorance, but I've always wondered why we have to rely on the light of the Sun to find distant, dark objects. Why would it not be possible to fashion an extremely powerful laser and sweep it across the sky in an area where gravitational clues indicate a dark object may reside? Unless the object was utterly black on its surface, I'd think we would be able to monitor wherever the beam traverses and look for tell-tale spectra coming back in our direction due to the laser being scattered by a solid object's surface. Again, I know I am oversimplifying a complex problem, and I could speculate on factors that might render this impractical, such as atmospheric effects or the necessary power needed for a laser strong enough to travel to such a distant point (it might not be physically possible to create a laser large enough to exceed the light we would already see reflected back from the already formidable output of the Sun), but I don't have the requisite knowledge of physics to really make solid assumptions about such things.
- avar 8y agoRelative to planet #9 we're right next to a giant nuclear fusion powered light 700,000 km across. If it isn't lighting up the surface of planet #9 well enough for us to see it already, then we're not going to be able to construct some laser that makes a difference. That's before you get to the problem that space is ridiculously big, and sweeping it across the entirety of the surface of the imaginary sphere that might contain planet #9 would probably take millions of years (citation needed).
- Rooster61 8y ago> That's before you get to the problem that space is ridiculously big, and sweeping it across the entirety of the surface of that imaginary sphere would probably take millions of years. The scale isn't lost on me. I'm aware of how much ground would need to be covered when you get out that far, and I figured that might be a pretty damning factor. That said, you wouldn't need to sweep it across the entire surface, only enough of the surface to rule out any interfering debris between us and the object. Wouldn't take much. We would need VERY accurate models of the orbit based on effects on other bodies, but it's hard to totally rule it out in my head.
- vivekd 8y agoIt's interesting how space research technology works, right now we can detect planets around distant stars many light years away but we are still unable to detect a planet several times larger than earth that is likely orbiting our own sun. I wonder if it's possible to send a probe out beyond the orbit of Neptune and try and detect planet 9 using gravitational lensing the way we do with planets in other solar systems.
- waserwill 8y agoWhen researchers look for a planet around a star, they only need to look at a small part of our sky. Not so for nearby objects. Plus, they can exploit the fact that stars with planets nearby will exhibit patterns of brightness, etc.,—if the planet is in the right orbit, has a great deal of mass, along with other parameters.
- daveFNbuck 8y agoAlso they're not usually looking for a specific planet around a particular star. The sky is full of stars and planets to find but there's only one planet nine.
- dotancohen 8y agoWhy do you assume that there is only one planet nine? Are you using the IAU definition of a planet? If so, why assume that there even is one? And if you are using a different definition, why assume that only one single object meets those criteria? If you are willing to forego "cleared the neighbourhood" then there might be dozens of round worlds with upwards of 10^20 KG mass in the solar system. We even know of such worlds not bound to any star at all!
- tobr 8y agoEven if there are multiple undiscovered planets, there would be at most one planet nine, plus maybe a planet ten, eleven, etc.
- brlewis 8y agoI'm on my phone... Hope this link works. Around 9:30 there's a question about planet 9 and the NASA scientist says Pluto is Planet 9. https://m.facebook.com/story.php?story_fbid=257826325089507&id=79209882917&refsrc=https%3A%2F%2Fm.facebook.com%2F&_rdr https://m.facebook.com/story.php?story_fbid=257826325089507&...
- brlewis 8y agoOK the link works. The NASA scientist is Hal Weaver https://www.nasa.gov/mission_pages/newhorizons/launch/weaver-bio.html https://www.nasa.gov/mission_pages/newhorizons/launch/weaver... This in addition to Alan Stern's criticism of the IAU classification: https://en.wikipedia.org/wiki/Pluto#IAU_classification https://en.wikipedia.org/wiki/Pluto#IAU_classification
- macspoofing 8y agoWouldn't it be great if instead of a planet, this was a black hole with the mass of a planet.
- garmaine 8y agoWhich formed.... how? The Hawking radiation for such a thing would be VERY visible though, so no that’s not an option.
- macspoofing 8y ago>Which formed.... how? Indeed. Or are you implying we figured everything out and can't be surprised by anything. >The Hawking radiation for such a thing would be VERY visible though, so no that’s not an option. Don't think so. A planet size black hole would still take billions of years to 'evaporate'. It would be quite dark.
- dyukqu 8y agoI am not a physicist and I don't know if that's possible, but seems unlikely, if I understand this statement correctly: "After collapse to the neutron star stage, stars with masses less than 2-3 solar masses should remain neutron stars, gradually radiating away their energy, because there is no known mechanism for further combination, and forces between neutrons prevent further collapse."[0] Assuming Jupiter turning into a black hole, the radius of it's event horizon would be just 2.2 meters (and that's 8.7 millimeters for Earth and 3 kilometers for the Sun). [1] That would take forever to pinpoint an object with a radius of a few meters (apart from its existence as a black hole). [0]http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/blkhol.html http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/blkhol.html [1]http://astronomy.swin.edu.au/cosmos/S/Schwarzschild+Radius http://astronomy.swin.edu.au/cosmos/S/Schwarzschild+Radius
- anigbrowl 8y agoIt would indeed take forever, but the idea is exciting both because it would mean rethinking parts of physics and the thrilling possibilities of experimenting on a small black hole and the numerous interesting ways that could go wrong.
- infinity0 8y agoCould "planet nine" actually just be dark matter?
- neolefty 8y agoIf you define dark matter as matter whose gravitational influence we infer but whose nature is still mysterious, then sure it is right now!
- burtonator2011 8y agoTL;DR inverse square rule... it's super dark out there!
- flareback 8y agoI hope that there is a Planet Nine. I like space related news and I think it would be an amazing discovery
- Pica_soO 8y agoI hope there is not. If its elliptic, this planet is a bringer of instability to the solar system and the most likely suspect when it comes to the death of the dinosaurs. Such planets driveby gunning the innerplanets with asteroids might be a answer to the fermi paradox.
- Pica_soO 8y agoCould a NN going over all collected data, in search for a slow moving "missing" observed objects shadow find it?
- darepublic 8y agoWhat if planet nine doesn't want to be found
- zulfishah 8y agoWere it to be confirmed, would "Planet 9" actually be classified as a Dwarf Planet?
- flukus 8y agoIt's estimated to have 10 times the mass of earth, putting it up in the Uranus and Neptune range: https://en.wikipedia.org/wiki/Planet_Nine#Size_and_composition https://en.wikipedia.org/wiki/Planet_Nine#Size_and_compositi... .
- ajmurmann 8y agoSize isn't sufficient though. It also needs to have cleared its orbit.
- flukus 8y agoIt's orbit is thought to range between 200 and 700 AU, which is well outside the Kuiper belt at 30-50 AU and well inside the Oort cloud at 2,000-200,000 AU. So barring the discovery of more stuff in that area it seems to qualify.
- skykooler 8y agoWould that explain why there's a gap between the outside of the Kuiper Belt and the inside of the Oort Cloud?
- flukus 8y agoThat would be well beyond my knowledge or ability to say. It certainly seems plausible, it may even explain the existence of the Kuiper belt, being held in the balance between Neptune and this planet much like the inner belt is by Mars and Jupiter.
- yaks_hairbrush 8y agoProbably a planet. The distinction between planet and dwarf planet turns on whether the body has demonstrated gravitational dominance. Planet Nine's existence (if it indeed exists) was inferred from alignments of other bodies' orbits, which makes for a very, very strong case that it's a planet and not a dwarf planet.
- rishav_sharan 8y agoMy layman-scifi-loving hypothesis is that its not a planet that we are looking for but the remnants of the novae which birthed the solar system. this star core is likely mostly iron and other heavier elements, and as such is incredibly dense. It will probably be a super earth only a few times the Earth's radius but with mass over 10x that of earth. While detecting gas giants is easier due to their infrared signature, one such dense star core in (or beyond) the Oort cloud would be practically invisible to us in the infrared searches and using starlight occlusion (due to its much smaller size).
- newsbinator 8y agoWhat's the best way to detect a massive iron ball in dark space? Can we ping it with radio waves?
- aruggirello 8y agoI'm afraid there are no 'wild star cores' in the Solar System backyard. A supernova remnant would either be a white dwarf, or a city-sized neutron star (possibly a black hole) with a mass larger than that of the Sun. The latter could go undetected, but can be safely excluded since in that case it would be the Solar System actually orbiting it (or anyway being affected by it - the minimum mass for a neutron star is ~1.4 Sol, and a black hole would be even larger), and we already know the Sun's path around the Milky Way to a certain extent. OTOH a white dwarf would likely take billions of years to cool off and we would be able to spot it - so no, only planetary bodies may still be lurking there undetected. Edit - clarification.
- KnightOfWords 8y ago> A supernova remnant would either be a white dwarf... A small correction, white dwarfs are not produced by supernovae but by main sequence stars running out of fuel.
- kijin 8y agoYou don't even need "a few times the Earth's radius." Assuming identical density, mass is proportional to the cube of radius. Earth already has the highest density of all the large objects in the solar system, at about 70% of the density of solid iron. An object that has the same density as Earth, but with 2x the radius, will have the mass of 8 Earths. If the object was made of solid iron, it will have the mass of over 11 Earths. That's a lot of mass in a small area.
- chiefalchemist 8y agoIs there any possibility there's more than one one Planet 9? This is, in searching for a single unseen planet, the calculations, estimates and such will be wrong if there's actually two (or more?) extra planets.