EDIT: After reading the comments in this discussion, many of which are addressed in the NYT article, I'd say the NYT article is almost certainly worth reading.
I really like the people and format of HN. Unfortunately these kinds of posts (random gifs, memes, video links) really detract from it. Luckily they only come up sporadically and when they do they're quickly gone.
The answer is that Pluto isn't some sort of classification issue.
The proper answer is that Pluto is a planet because of historical reasons (by fiat). By definition, it is a planet, and the asteroids in the asteroid belt are simply asteroids.
From then on, you can apply the rules of a "planet" later on to other bodies, like this one.
> The proper answer is that Pluto is a planet because of historical reasons (by fiat)
I disagree that Pluto should somehow have this distinction. Along with all of the reasons it shouldn't be considered a planet under the current definition, it was only discovered in 1930 so it's not like we've been seeing this dot in the sky since humanity was in caves.
Even if I were to agree, then Ceres should also be considered a planet since it was discovered earlier.
Well, then I say it's fair to assume they are not considering the dwarf planets as planets. If they did, they would not have called it the ninth planet as you have pointed out.
We have been looking for a "missing" objects for a while. The nemesis star theory says the sun has a brown dwarf companion. This object would interact with the Oort Cloud instead of the Kuiper belt. But this theory has been pretty much refuted.
This theory definitely looks more promising. Finding eccentric Kuiper belt objects, and aligning them with a missing object seems to be a good bet. Giving the object an orbit should make the search easier, and we will probably have a conclusion one way or another within a few years.
In searching for Tyche, the WISE missions ruled out the possibility of anything larger than Saturn (95x the mass of Earth) out to about 10000 AU and anything larger than Jupiter (317x the mass of Earth) out to about 26000 AU. WISE was able to detect objects the size of Neptune (17x the mass of Earth) out to about 700 AU, so it should be possible to find the object proposed by the Caltech astronomers here (10x the mass of Earth at around 600 AU). I don't know if WISE's current condition would allow it to perform such a search, as it's completely out of coolant.
* The WISE survey might only find Planet X at it's nearest approach. Kevin Luhman has redone the survey using the most sensitive WISE bands that only cover a narrow area of the sky and hasn't found Planet X.
* They reviewed the Catalina Sky Survey and eliminated most of the areas they'd expect Planet X.
* The Pan STARRS site survey didn't find Planet X.
Conclusion: Planet X is at aphelion, difficult to find with the Milky Way as a (stunning) backdrop.
I wonder how their conclusions match with David Nesvorny's paper predicting a 5th planet having been ejected from the Solar System: http://arxiv.org/pdf/1109.2949v1.pdf
> Planet X is at aphelion, difficult to find with the Milky Way as a (stunning) backdrop.
I would have assumed that planets are easier to detect when they have a backdrop? That the light can be blocked, partially blocked, bent, .. Isn't that the case?
I'm not sure if you're referring to the tansit technique where a planet passes in front of a star multiple times which allows to determine the size and distance from the detectable dips in brightness.
This technique wouldn't work well with a backdrop since it never passes in front of the same star twice.
I'm also not sure if we can resolve the planet optically i.e. 1) it will always be smaller than a pixel of the telescope sensor 2) the pixels of the telescope sensor always collect light from the backdrop even if the planet is dead center on the group of pixels.
When you detect the light of a planet without backdrop both problems would be much smaller because then you can actually see some tiny dark blurry object moving relative to the stars around it in the image.
You're thinking about one of the ways extrasolar planets can be detected, when they cross in front of their parent star (transit photometry) or when they're imaged using light magnified or redirected by a massive foreground object (gravitational microlensing). I don't think we have the capability to detect something in this solar system eclipsing a background object (whether that's a star or a galaxy or whatever else is out there).
Not an astronomer, but my impression is that microlensing couldn't be used to detect objects in our own solar system, but I don't see any reason why eclipsing of distant stars couldn't be used... it would be far too rare to be practical to find a planet, though.
Skepticism is warranted, but keep in mind that Mike "pluto killer" Brown, one of the authors, has an impressive track record. He discovered Eris and Sedna.
If it holds up, this is fantastic. Given how interesting the Pluto system has turned out to be, I can only fantasise about a potential super-earth system relatively nearby.
However, to be completely pedantic: would this actually be a planet? Or still a dwarf planet, despite its massive size? Keep in mind that the definition of planethood is not only that it's large enough to be rounded by its own gravity, but that it has also "cleared its orbit". I get the impression that this would cut through broad swathes of the still-cluttered Kuiper belt, and thus would only qualify as a "dwarf" despite its massive size.
I checked the original papers for references to whether it had cleared its orbit, and couldn't find any. Correct me if I'm wrong?
The criteria for clearing an orbit are apparently somewhat involved[1]. It can't just be a matter of no other bodies having the same distance from the sun or Pluto would disqualify Neptune and Jupiter would be disqualified by its trojans. Because the planets in these cases mass so much more than other other nearby bodies those other bodies dance to the planet's tune and aren't counted against the planet in terms of clearing it's neighborhood. But if you look at the large bodies in the asteroid belt or the TNOs then their influence is very much mutual.
It's not entirely obvious if the new body would be a planet under the listed criteria since I don't think we have a good handle on the total trans-Neptunian population. In fact by Soter's µ criteria we might just need a single Pluto-sized object to cross this planet's path to disqualify it.
I was misremembering Pluto's mass as being 1/10 of Earth's when it's really 1/500th. It would take a large number of TNOs to push this hypothetical object from being a planet to being a dwarf planet.
For those that won't click through, a very short explanation given by the author: "Is Planet Nine gravitationally dominant? I think it is safe to say that any planet whose existence is inferred by its gravitational effects on a huge area of the solar system is gravitationally dominant."
He then goes on to give a more technical argument.
From what I understand, it has cleared the space but there are still harmonic crossings that can't be cleared. Interesting challenge to the new definition - must the orbit be clear, or only clear sailing through the orbit.
I don't seem to have a grasp of our visibility of our solar system. We can see a number of the planets with the naked eye, a number of the moons with binoculars and a few hundred $/£/€/.. telescope. Yet even with these great big radio telescopes, antenna arrays, Hubble, etc, we seem to be quite unaware of what's in our neighbourhood. Anyone have figures of how much we've surveyed?
It's all about distances. The planets we can see with the naked eye are at most 11AU from us (Saturn is at 10AU at aphelion).
For comparison, Neptune is never closer than about 29AU to us. Brightness goes down as the square of the distance. But it gets worse, because that's brightness at given source brightness. Planets don't radiate intrinsically; they reflect sunlight. And sunlight brightness drops off as the square of distance from the sun. Which is to say that even if they were the same size and albedo (they're not), Neptune would appear about 81 times dimmer than Saturn to us. Oh, also (linear) angular size goes down linearly with distance. So if you want to see the two planets as disks of the same size, you need to have a field of view three times narrower, which means you need 9 times as many of them to cover the sky. And if you want the same amount of light gathered, you have to spend 81 times longer gathering it, per the above brightness calculation.
All of which is to say that the time needed to do an "equivalent" sky survey N times further away (within the solar system, where all the illumination is coming from the sun) scales as N^6. And planets do move, so you might still miss one if you survey a place where it's not yet, then take a while to get to where it used to be, such that it has moved. This is why Neptune was found via its gravitational interactions followed by a survey of a small part of the sky, not brute-force observation.
Anyway, back to the topic at hand, the proposed Planet Nine orbits 20 times farther out than Neptune. 20^6 is 64 million. So if we assume we've pretty much surveyed everything out to the radius of Neptune's orbit at some resolution, and then spent about 64000 times as much time surveying stuff out to the distance Planet Nine is proposed to be at, at the same resolution (I doubt we have), then we've probably surveyed about 0.1% of the stuff out there.
I can't tell you what the actual number is, unfortunately, but I suspect the answer is we haven't really done very good systematic surveys out at that distance.
Shouldn't it be fourth power of distance (N^4) not sixth? For objects beyond the diffraction limit (i.e., objects whose radius cant be resolved), visibility is determined by total light reaching the observer. Angular size isn't important. (And, if anything, diffusing a fixed amount of light over a larger solid angle makes it harder to see.)
If you're just trying to see all the objects, then yes, N^4. But if you're trying to figure out whether they're planets, you need to either resolve disks or take multiple observations to observe motion. I don't have a good feel for how the latter scales with N in practice...
When it comes to small (-er than, say, Jupiter) bodies in the distant outer Solar system, here's one relevant piece of information:
Because these bodies' light is purely reflected solar light, whose brightness drops as the sun-object distance squared (d^2), their brightness as seen from Earth drops as the sun-object distance to the fourth power (d^4), making them incredibly faint.
Like the parent, this seems odd that just now in 2016 we find there might be another planet in our own solar system when planets are being discovered in other solar systems and galaxies all the time.
There's this from the article:
"For the first time in over 150 years, there is solid evidence that the solar system's planetary census is incomplete."
It's our _own_ solar system and we just now found this massive thing?
One of the main methods we use for finding planets in other systems is watching for them to cross our view of the star -- basically, looking for a star to slightly dim in a periodic fashion, something akin to an eclipse.
With objects in our own system that don't emit light of their own and are much farther away from the sun than we are, they'll never block the light from the sun. If by sheer luck they happen to pass in front of another star and temporarily block it, it's still difficult to figure out what the object was, how fast it was moving, and so on and therefore difficult to correlate with "something in our own system".
Keep in mind, the solar system is REALLY big. "Planet Nine" is proposed to be some 55+ billion miles away, or about six hundred times as far away from the Sun as Earth is.
Well, we've not yet found it. There is just a very good case for it's existence.
Also, it's arguably easier to find planets in other solar systems because from our vantage point we can observe the stars and measures the dips in light as the planet transits the star (from our perspective). We can't do that without our own solar system given we too are orbiting the same star as the planet we would want to detect.
Also, remember this planet has an orbital period of about 10,000 - 20,000 years, according to the article. It would have just barely completed one orbit since humans started farming.
Planets are small. A planet 4x the diameter of Earth but 300+ AU away is a factor of about 1 to 1 million. That's equivalent to a single grain of sand nearly a kilometer away.
If you are going by that logic, Pluto was at least the 10th planet discovered and this is at least the 11th. Ceres was discovered before either Neptune or Pluto and spent 50 years as a "planet". It eventually went through a similar reclassification process as Pluto as other similar objects were discovered. The only reason you don't see the same controversy around its classification is because it was recategorized a century before any of us were born.
If naming was all about logic then 1/2 the places on earth would need to be renamed. Naming is about emotion, style, history, and personal preference. Even total mistakes (the Giant Squid) are grandfathered through. Galileo named the moons of Jupiter after his sponsors. I just hope this thing doesn't become "X, brought to you by iPhone8".
Something can be called "Planet X" without being classified as a planet. Take "Planet Hollywood". Incorporating planet into the name should at least protect against future reclassification.
> Ceres was the first asteroid discovered, by Giuseppe Piazzi at Palermo on 1 January 1801. It was originally considered a planet, but was reclassified as an asteroid in the 1850s when many other objects in similar orbits were discovered.
> [...]
> Ceres was assigned a planetary symbol, and remained listed as a planet in astronomy books and tables (along with 2 Pallas, 3 Juno, and 4 Vesta) for half a century.
> Batygin and Brown inferred its presence from the peculiar clustering of six previously known objects that orbit beyond Neptune.
This raised a big red flag in my mind. This must produce a literally astronomical multiple comparisons problem. Yes they reported sigma = 3.8, but if they didn't do their multiple comparisons correction right (which I am in no position to determine), they're basically reading tea leaves.
> but if they didn't do their multiple comparisons correction right (which I am in no position to determine), they're basically reading tea leaves.
Please don't spread FUD about other people's research and then try to soften it with a disclaimer about how you're "in no position to determine" anything about the research.
If you want to offer criticism of the research, you should do the legwork to find out what the researchers did and did not do.
I don't think that they're dummies. This is one of the big unsolved problems in statistics and empiricism.[1] There is no general solution to this problem, and the practical solutions to this problem are all very particular to their field. The geneticists have certain ways for controlling for certain known problems; the neuro imagers have certain ways for controlling for certain known problems; same goes for ML, particle physics, economics, ect. I'm personally familiar with a few of these, and I know that they are very particular to their field and that they each have their own history (which is why I'm hesitant to present myself as an expert on statistic empiricism in the context of trans-neptunian planet hunting). And those histories (the ones I'm familiar with) are a parade of over confidence followed by the community establishing new things that need to be controlled for. The red flag in my mind isn't that they are following the established rigor for trans-neptunian planet hunting (I'm sure that they are, because peer-review), or that they aren't following a theoretically valid methodology (I'm sure that they are not, because it doesn't exist). The red flag in my head is that trans-neptunian planet hunting, as a field, looks like the kind of place that there would be a lot of false positives (few historical true-positives, relatively small field, relatively novel methods). I don't doubt this experiment the way a expert in trans-neptunian planet hunting would: "They should control for X, Y, and Z, but didn't!" I don't have the expertise to do that. I'm criticizing it the way a philosopher of science might: "This sort of question in this sort of field is likely to have such-and-such problems and not yet have good ways to dealing with it yet." And I do think that know enough to log that criticism.
I knew Chaz personally in undergrad and a bit since then. Though I have not read the article yet (I'm in a state of shock really) I can attest to the man. He is so kind, funny, personable, and one a heck of a guitar player. Based on his stellar work in undergrad in modeling the orbital path futures of our solar system on the Gyr timescale, I am sure he is sure of the work. (Only non humanities major to ever win the Dean's Award at UCSC, it was great work)
The man would not ever publish this unless he was sure of it. Science and time may tell him wrong, but I'm one to believe him as a friend. Both he and Olga must be on cloud nine right now! (oh wow, nine, wow!)
I mean WOW! Like, a PLANET! A frickin PLANET! None of this dwarf stuff, a full PLANET! (Not to malign all those folk's hard work in finding the dwarves either).
Jesus tapdancing christ gravy! What a day!
EDIT: Upon further reading, it may still be a dwarf planet as it has not 'cleared' it's orbit. Still, my lord, so happy for them both right now!
As for the "full" planet/dwarf planet debate, a more precise explanation that has been seen recently in many talks is "gravitational dominance of the orbit". This arises from the case of Jupiter and its trojans. The criteria is "it dominates the gravitational interactions in its neighbourhood", which such an object (affecting practically everything in the Kuiper Belt) does.
I think you're right that that's one of the chief concerns, but I think you paint it incorrectly as a technical problem. ("Multiple comparisons" as you call it. Particle physicists call it the "look-elsewhere effect": https://en.wikipedia.org/wiki/Look-elsewhere_effect )
The easy, though tedious, part of the look-elsewhere effect is to calculate a probabilisitic correction for all the various combinatorics of X objects in Y orbits over a time period of length Z that one might have seen. The hard, and borderline philosophical, part is to identify the proper reference class, i.e., what qualitatively different sorts of observations might have also considered evidence for planet nine, and how many other astrophysical searches are we running that might have given us weird results? This is really where frequentist approaches strain to be useful, and it's hard to avoid resorting to a Bayesian prior.
Analogously for particle physics, it's easy to compute the chance of getting a 4-sigma deviation for two different experiments in any gamma-gamma energy bins, so the after-the-fact corrections to the significant of a fluctuation in a particular bin are easy to compute. Much more difficult is to consider all the hundreds of parallel searches going on, of greatly varying levels of motivation, and correcting based on that.
I'd also observe that in terms of prior probability, "There is a ninth planet in the solar system that we have not yet detected" is probably hovering at least in the low-integer percentages, and I imagine some scientists would place it higher than that. The general idea is not a wild, far-out one by any stretch of the imagination.
I can put some bounds on them, which is all I tried to do. It is certainly not reasonable to act as if the idea there is a ninth undetected planet is some sort of one-in-a-trillion possibility.
I'm not even convinced you're correct anyhow; since I tend to accept the interpretation of probability as a statement of our knowledge of the world as good enough most of the time, we can establish a reasonable probability statement that expresses that uncertainty. We don't know everything about the universe or even our solar system but there is something about this topic that makes people start grossly overstating our ignorance.
The authors are not relying just on the improbability of that arrangement, but also on its stability. From one of the authors, on http://www.findplanetnine.com/:
"Mike and I were genuinely perplexed. Could the confinement of the orbits be due to an observational bias or a mere coincidence (after all, we are talking about six objects here - not exactly “big data”)? Thankfully, the probability of the observed alignment being fortuitous can be assessed in a statistically rigorous manner, and clocks in at right around 0.007%. Not a great gamble. Moreover, application of simple perturbation theory (or direct numerical integration) demonstrates that if allowed to evolve under the gravitational influence of Jupiter, Saturn, Uranus and Neptune, the orbits would become randomly oriented on timescales much shorter than than the multi-billion year lifetime of the solar system. So the dynamical origin of the peculiar structure of the Kuiper belt cannot be outsourced to the distant past - something is holding the orbits together right now."
So I might not have a great enough understanding but isn't 3.8 sigma not high for this kind of announcement (with the current title)? if someone wants to report finding a planet in the solar system ten times the size of Earth wouldn't they do so at more than @3.8 sigma. In particular, the prior is quite low because it would affect a bunch of other astronomical calculations, wouldn't it? So you would want the confidence that much higher....
What I mean is that in human terms, Google says the average man is 5'9" with standard deviation 2.9 inches, then 3.8 sigma (the chances of this happening by chance) are the same as the chances of finding someone 6'8". It doesn't seem unbelievable - https://answers.yahoo.com/question/index?qid=20101208183308A...
If a woman is set up on a blind date and told the guy is 6'8" would she find it like not credible?
My understnading of statistics then is that the idea that there just so happens to be a planet ten times the size of Earth in our solar system is pretty unbelievable. So I'd want the chances of it being an experimental fluke to be lower than seeing a 6'8" guy, anywhere, at any time, in any context. Because I would think that's what happens when you look at enough data.
- Aren't the chances of this being completely spurious literally exactly the same as a researcher saying "I saw a 6'8" guy somewhere", meaning anywhere, in any context?
Wouldn't you want higher evidence before stating "evidence found for ninth planet in our solar system, ten times the mass of Earth"?
No, this is just about right. The evidence they have points sharply to there being a ninth planet. Now they're saying "here's where it might be, we need help finding it!"
Once someone has a photo and an orbit, that'll be the >>3.8sigma you want, but I don't think anyone is saying anything like that yet. What they're saying is "dedicating 5 years of the pinnacle of your planetary astronomy career to looking for this thing is probably not a waste." They directly compare this to the theoretical prediction of Neptune, so I think the authors have this same interpretation of what they are doing.
Before your comment, I edited it to be much more civil and less presumptuous, my original phrasing had included "3.8 sigma is fuck-all", I was briefer, more resolute, and had just included my first link. (You can see evidence of my original phrasing if you remove the hedging I added.)
But the downvotes meant I'm probably wrong - rather than delete I edited it to be much nicer so I could find out why I'm wrong.
Upvoted for tempering the aggression and because I agree with you. As far as I can tell your interpretations of the statistics are correct. I don't see how an argument can include information stronger than the statistics of indirect detection of the object (without direct detection).
I'm having trouble following your height example because "finding" is not well defined, and it's conflating rate of occurrence with certainty.
Being on a blind date with someone who is 6'8" is like knowing someone that won the lottery. The chance of winning the lottery is very low, but lots of people play it and chances are the winner has friends. You're unique, but have no reason to be incredulous.
This data being a coincidence is more on par with one person getting one chance to correctly predict (some of) tomorrow's lottery numbers. It's 1 in 13822.
I haven't seen the original research myself to judge, but it sounds like they're being careful about these effects. Looking at their discussion on the main page of http://www.findplanetnine.com/, the claim seems to be that this isn't "we spotted six out of the solar system's zillions of objects that formed a cluster" but rather "the unique six known objects within a certain range of orbital parameters all form a cluster in a different parameter".
More specifically, quoting from that page, "all Kuiper belt objects with orbits that do not veer into inter-planetary space and spend longer than approximately 2000 years to complete a single revolution around the Sun... trace out elliptical paths that point into approximately the same direction in physical space, and lie in approximately the same plane."
That could be just an observational coincidence, and that's where they claim the statistical figure that you've cited. I have no idea to what extent those figures account for the multiple comparisons issue, but the range of orbital parameters that I've quoted here doesn't look very fine-tuned to me. (The upper bound certainly isn't, anyway!) So it's just a question of how the lower bound was chosen. And on some level, I'm not even sure that that's an issue: an observation that's based on "the longest N bound orbits all show this pattern" feels meaningful to me even if I'm not sure in advance how big N is going to be.
The anomaly itself does not seem to be disputed. It's true that when looking for arbitrary clusters and unusual patterns you can pretty much always find something -- though it's more of a Texas Sharpshooter fallacy [1] than the kind of multiple comparisons you see in e.g. medical research -- but the paper in question [2] mentions a whole bunch of alternative theories for why the particular clustering of a bunch of rocks in the Kuiper belt is what it is, and it doesn't seem very likely to me that none of those researchers ever thought "well, gee, maybe this is all just a fluke." In fact the competing hypotheses would be my main source of skepticism – maybe it's a planet, maybe it's an entirely different phenomenon.
This is pretty solid science, even if, as others have pointed out, there's a bit of academic drama-rama and green jellybean stuff going on. In particular, their model made a prediction that they didn't set out looking for, which corresponded to existing observations. And of course, the whole hypothesis is easily testable. While they don't know where the hypothetical planet might be on it's orbit, it sounds like there's a good shot that small telescopes should be able to spot it.
Ah Planet X which is now planet IX with Pluto's demotion :-). I am guessing that you can confirm it by looking for star occulusions. Presumably the planet would blank out stars as it passed between earth and those stars. So would it be possible to find it using existing plates?
It is pretty well impossible to discover a planet by occultations. For one thing, in most parts of the sky the density of stars is pretty low. People do study occultations by known distant objects -- that provides some of the best available info on physical size and presence of atmosphere for KBO's. But in most parts of the sky, it is years in between occultations, which last just minutes. You have to be looking in the right place at the right time. And the sky is full of variable stars, so just looking for changes is hard.
They do, and at the end of the press release it says that Brown has begun an observing campaign to find the planet. Unfortunately detecting these very distant objects is very difficult. The light we see from them is reflected light from the Sun, so their apparent brightness goes as 1/r^4, not 1/r^2 like most objects. And because they are so close, there is a strong parallax from the motion of the Earth. THe consequence from this is that the object will actually drift across the image as you are taking it, smearing it out. In order to detect it you either have to take very short images so that it doesn't move too much (in which case you don't get very much light), or have some idea as to the direction of the smear so that you can correct for it. Either way it's a very hard observation to make! Fortunately if this planet is as big as they claim it to be it should be relatively easy to detect compared to Sedna and the other Kuiper Belt objects.
In a previous life, back in the pre-CCD days I worked at an observatory searching for new asteroids. Used to be the way it was done you would point a telescope at the part of the sky directly opposite the sun (min r^4 so best chance of detection), expose a photographic plate, and repeat a few hours later. Develop the plates, mount them in a blink comparator [1] and scan manually, flipping back and forth between the plates for ~3 hours to look for anything that moved. Exclude false positives like plate blemishes (aka Eastman-Kodak Objects) or dust grains. If you see something, and it is smeared indicating motion during the exposure, mark it as a possible candidate. Revisit the same patch of sky the next night, search again. Use the datapoints to extrapolate forward, check again a couple of weeks later. If you haven't lost it (which frequently happened if it was at the limit of visibility), extrapolate back to the previous opposition (~4 years for a main belt asteroid) and search the archives for a match. If you get one, then extrapolate further back and check all previous oppositions. If you get a match on three separate oppositions, congratulations, you have a discovery.
Vastly different now - a single observation can net large numbers of asteroids and sensitivity is so much better. Still the search for this potential new planet is definitely going to be daunting given the distance.
Also, we don't know where in its orbit the planet happens to be right now. If we're lucky, it's relatively close to the sun, and it will be detectable. If we're unlucky, it's relatively far away from the sun, and it could easily be undetectable by current observatories because the orbit is so eccentric.
[Source: I saw Mike Brown give a talk on this topic at the Cal Academy of Sciences, where he hoped he was lucky...]
Note that an eccentric orbit spends most of its time out in the far reaches, since it moves much slower out there. The odds are against the happy case.
Perhaps one of the "stubby hubble" telescopes the NRO donated to NASA would be useful for this task[0]. They are essentially the hubble telescope with a much shorter focal length(hence the nickname), so one of the uses suggested for them is observing faint objects in the solar system like asteroids.
I would expect a smear with characteristics of the planet would be as effective to identify it as a single snapshot. Wouldn't the direction be well identified from indirect detection? Is the blur also less effective because of increased background exposure?
Yes, it's definitely r^4. If we assume that the planet is far from the sun compared to the earth, such that the earth-planet distance and the sun-planet distance are both approximately r, then the amount of light the planet gets from the sun is proportional to 1/r^2. Then the planet reflects that light in all directions, and the fraction of it that comes back to us on earth is also proportional to 1/r^2. 1/r^2 * 1/r^2 = 1/r^4.
Yes. The solid angle subtended by the planet (and hence the amount of reflected light) goes as 1/r^2, and then the apparent brightness of the reflected light to us goes as an additional 1/r^2. The total dependence is then 1/r^2 * 1/r^2 = 1/r^4.
The key point is that Pluto does not reflect light like a mirror, it scatters light relatively uniformly, causing more light loss to an observer than, say, a mirror that points the reflection directly at an Earth observer.
The light reaching the object from the sun drops off by 1/r^2, and then the light reaching Earth from the object drops again by 1/r^2. Since the latter light is a portion of the former, you multiply them for 1/r^4.
They do, but there are two problems. One is that that still leaves a pretty big range for possibilities for where the planet could be. The other is that we don't know where along the orbit the planet is now. Even if we knew the exact orbit of the planet simply not knowing where it was along that orbit means we'd have to scan a lot of the sky to spot it. Having a bit more ambiguity about the orbital parameters means we will have to scan much, much more of the sky to spot it.
He believed this hypothetical planet of Nibiru to be in an elongated, elliptical orbit in the Earth's own Solar System, asserting that Sumerian mythology reflects this.
It reminds me about a book I read called "In Search of Planet Vulcan" (http://www.amazon.com/In-Search-Planet-Vulcan-Clockwork/dp/0...). Before Einstein, astronomers tried to explain the motion of Mercury by suggesting there might be another planet inside Mercury's orbit.
I want, by the way, an interactive map of the solar system, complete with known spacecraft, with the same UI as the KSP map. I've never met anything quite as good at visualising planetary systems.
Not that improbable. I recall that the discoverers of exoplanet Wolf 1061c, when journalists asked for a picture of the planet, gave them a screenshot from a simulation called Universe Sandbox 2.
Reading the article I didn't see a mention of a previously hypothesised fifth gas giant... so here's a link in case anyone's interested or knows something more.
At WWDC last year one of the lunchtime presentations was by Michael Brown, one of the researchers involved here. He was one of the people who proved that Pluto should not be considered a planet and went over the history of the discovery/classification of planet bodies. He also mentioned that they had some evidence of a planet body beyond Pluto due to its gravitational affect of some of the smaller bodies out there even then. Interesting to see this is finally coming to something! He has the appropriate/amusing twitter handle of http://twitter.com/plutokiller
Voyager won't escape the Sun's influence for hundreds of years. The "boundary of the solar system" is not the same as the Sun's influence (and, indeed, is somewhat poorly defined, given how many times Voyager has crossed it.)
Thanks for the link. There's a course taught on Coursera by one of the CalTech researchers, Mike Brown, if anyone is interested. It's archived but they have kept it open.
Now only if they name the ninth planet starting with a 'P', my childhood mnemonic "My Very Educated Mother Just Served Us Nine Pizzas" would finally be complete again! :D My suggestion is 'Prometheus' - sounds tragic and bad ass at the same time!
Well that would be consistent with the roman/greek names for planets and large moons. Now we have to find a stronger tie between the theory and the myth. In some article regarding this news I've read that Planet 9 might have ended in its orbit due to encounters with Jupiter/Saturn. Not exactly an eagle eating its liver, but it can be paralled to "the punishment from Zeus(Jupiter)".
:) well nicely connected with the punishment story! I would further go and say that we can draw parallels with the Kuiper Belt objects to the eagles "tormenting" Prometheus while he is chained to a "cold, lonely mountain rock" like our new mysterious planet stuck in a dark lonely corner of the solar system!
At first I thought this was another one of those planet x articles that talks about some hypothetical planet way out but then I saw that Mike Brown was involved and immediately got really excited. I hope they find something out there and we can send a probe to it in my lifetime.
10x the mass of earth is about 60% of the mass of Neptune or 80% of the mass of Uranus. So it's smaller than all of the gas giants in the system, but considerably larger than the rocky planets.
Mike Brown, the co-author of the paper reported here, discovered Eris, a KBO like Pluto, in 2005. This discovery prompted the IAU in 2006 to demote Pluto out of the realm of "planet" into a "dwarf planet".
At the time, Alan Stern's New Horizons mission to Pluto had just been launched, it finally arrived last year. Stern was incensed that NH started out as a visitor to the 9th planet and was going to end up as a visitor to one of many KBOs, and not even the largest one (Eris is more massive).
Small nitpick: "largest" refers to mean radius, "massive" refers to mass (aka weight). Pluto is the second most massive, but it is the largest. (To be fair, it is a very close call: its diameter is only ~25km larger than Eris)
I'm excited to see this story unfold, if nothing else because it's fun looking up the mythological[1][2][3] origins of the names given to new celestial bodies :)
The article quoted Brown as saying "All those people who are mad that Pluto is no longer a planet can be thrilled to know that there is a real planet out there still to be found,"
This how Qigong found the Clone Planet in Star Wars 2. Although the planet had be erased from the galactic database, it left a gravitational signature on nearby systems.
http://www.nytimes.com/2016/01/21/science/space/ninth-planet...
EDIT: After reading the comments in this discussion, many of which are addressed in the NYT article, I'd say the NYT article is almost certainly worth reading.