> 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?
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.
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.
Try looking out the back of your head for the planet hiding right behind you. Once you figure out that you have to turn around, the planet might not be there anymore :) We could build telescopes & point them in every direction though!
Well, yes. True. Not spectacularly informative though.
But speaking purely in terms of human eye sensitivity this has been confirmed in an indirect way at least: the faintest star visible to the human eye (under perfect conditions) is comparable in light intensity.
EDIT: also, sky lanterns https://en.wikipedia.org/wiki/Sky_lantern
The planets we're detecting are all large, and relatively close to their stars - so much so that we can observe the star's brightness changing, as the planet passes in front of the star, or that we can observe the gravitational wobbles of the star, as the planet orbits it.
We would not be able to detect a Planet 9 orbiting around, say, Alpha Centauri.
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.
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!
We detect planets in other systems by seeing them pass in front of the host star, or we detect them radiating IR, or if exoplanet is really big, with small orbit, it's gravitational influence on the host star (I.e. see it 'wobble').
In all cases, exoplanet is quite close in orbit to star.
By contrast, if a big planet is orbiting sun, but really far away (>x100 earth-to-sun-distance), it'd be to cold to detect it radiating any IR, it'd be too far to see obvious effects of it's gravity.
Plutos wikipedia page seems to support this (under mass estimates).
Ps when its discovered, can the planet start with a P so the rhymes still work?
Observations of Neptune in the late 19th century led to a prediction that there was another planet, beyond Neptune, that was also affecting the orbit of Uranus. Pluto was discovered -- accidentally -- during the search for that predicted 9th planet.
It was later discovered that (a) Pluto isn't nearly massive enough to explain the observed perturbations, and (b) the observations were explained without the need for another planet when more accurate mass measurements were made.
(The hypothesized Planet Nine is too far away to have a significant effect on the orbits of Uranus and Neptune.)
How was Neptune predicted from observations of its own orbit? Am I not parsing this correctly?
My Very Educated Mother Just Served Us... Nothing!
Very unsatisfying. But my aged brain cant remember the others :(
Mein Vater erklärt mir jeden Sonntag unsere neun Planeten.
In case anyone is wondering what the new one actually is, the mom now serves nachos.
> 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.
What am I missing in this context?
The problem is space is big, and space is dark, so its hard to find things that don't generate their own light.
Its orbit has between 200 and 1200 times the distance from the Sun as Earth (it's an ellipse), and it takes 10 to 20 thousand years to revolve around the Sun once.
Depending on where it is currently on this orbit, it might be that we will need to wait for better technology or for it to plainly get closer to Earth before we can find it.
Surely you can work out where it will likely be in the sky.
That gives them strip of sky to search through. A strip that unfortunately goes past some bright things - like the Milky Way.
To add to the problem. Objects in the outer solar system are spread out more vertically in their orbit. ( Like Pluto which dips far above and below the intermediate plane.
This means there is a relatively large area of they sky it could be in. Due to it's distance, it is not going to reflect much visible light at all either. So instead of being able to just scan across a the invariable plane looking for it we have to look in a large swath of the sky for something very dim, moving very slowly.
There probably are NO "nearby known entities". Planet 9 is probably further away than most detectable objects. The only reason it would possibly be found while "nearby" objects would not is because it's bigger.
And it's probably so far away that its gravitational tug is very slight on the big planets that are easy to measure. The article mentioned it may tug the outer gas giants by a "dozen meters" off course from models having no Planet 9 in them. That requires a really powerful "ruler" to detect.
Edit - clarification.
A small correction, white dwarfs are not produced by supernovae but by main sequence stars running out of fuel.
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.
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.
I understand you'd like to focus on objects in hydrostatic equilibrium. Pluto, Ceres, the Moon, and Titan are really neat, but something happens when you tell their life stories: you end up referencing one or more of the eight heavyweights. By contrast, these smaller objects just don't get referenced very much when we talk about other bodies' life stories.
The large scale structure and history of the solar system has just 8 known characters that really matter, and that's what the definition of the planet captures.
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.
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).
A very good laser has a beam divergence of tenths of milliradians, or 0.01 degrees. At the radius of planet 9, this is a very large beam, and we'd have a hard time putting out enough power to compete with the sun.
Furthermore, the sky has an area of 40,000 square degrees. Our little laser beam projects a circle with an area of 0.0000785 square degrees. You'd need to aim at 500 million spots to see the whole sky.
That's smaller than I expected. To convert that into human scale sqrt(500 million) = 22360, in millimeters that's around 22 meters (72 ft).
So if we had a square wall 22 meters by 22 meters we could paint a grid of 1 mm by 1 mm squares on it and end up with around 500 million squares.
Then we'd need to stand there in front of the wall with a laser pointer and shine the laser at each individual square and check the light bouncing back at us.
And there's uncertainty in whether your measurement is accurate.
And there's a background of other illuminated squares that can interfere with your readings.
And you're spinning while this is going on.
And the target square is continually moving. You might have just missed it.
1. Build a Dyson sphere around the sun.
2. Capture all the mass in the solar system to build a giant freaking laser.
3. Use the energy to from the Dyson sphere to power the laser.
4. Melt your entire civilization.
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.
Edit - podcast link https://www.preposterousuniverse.com/podcast/2018/08/27/epis...
In all seriousness, that would definitely kill any possibility. Sweeping an entire orbit at the resolution needed to hit something smaller than Uranus/Neptune would take eons.
I think someone should re-imagine all of Star Wars as hard Sci-fi set in the vicinity of a system like Alpha Centauri. That's still a vast setting.
Douglas Adams, The Hitchhiker's Guide to the Galaxy
The problem is that the power requirements go up sharply with distance. The amount that hits the object decreases with the square of the distance, as does the amount that’s returned. The end result is that your power requirements are proportional to the fourth power of the distance. Twice as far means you need sixteen times more power.
Now extrapolate that to something hundreds of times farther away than the closer planets....
As a quick back-of-the-envelope calculation: assuming you have a gigantic 100-meter diffraction-limited aperture, the smallest possible beam divergence for green light (550nm wavelength) is roughly 2 nanoradians. In the limit of large distances from both the earth and the sun, the area covered by that beam would already be receiving about 1GW of total energy from the sun. To outshine this you would need a laser of comparable power or more; the most powerful continuous laser I could find a reference to is only about 1MW, and was designed to destroy satellites and cruise missiles. 
I wouldn't rule out the possibility that you could detect a reflected laser beam, with sufficiently sensitive detectors, but it's hard to see what you would gain as opposed to just using sunlight.
Furthermore, lasers are by nature monochromatic, so you wouldn't really be able to do spectroscopy. At best, you could collect a few different points on the spectrum using lasers of different wavelengths.
Unless the pulses are long or frequent you get more light from an equally long exposure with sun light
Lasers are not the important part here- collimation is. The closer the illumination is to a perfect cylinder, the more visible it stays. Lasers often happen to be highly collimated, but it's not a defining feature. For instance laser diodes emit laser light in a cone 20+ degrees wide, and lenses are needed to produce a beam.
Bottom line: lasers aren't a panacea- generating a collimated beam isn't trivial, and just because we can make immensely powerful lasers that doesn't mean they are collimated.
> 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.
There isn't really any tell-tale spectrum available- obviously you need something below X-rays, because those will be absorbed rather than reflected. In practice you also need something above millimeter waves, because those are also absorbed but more importantly the collimation of an EM source is inversely proportional to its wavelength. So millimeter waves are ~2000x less collimated than visible light, unless you use a massive antenna.
Just above millimeter waves are infrared waves, and just below X-rays are ultraviolet waves. Along that entire range, the sun is very active, so any light is going to be washed out against that background. You don't really get to rely on the spectra being unique.
> 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)
The reflected light of the laser has to be brighter than the suns reflection over the entire area of the object you're trying to see. For an Earth-sized object at 1000 AU, that's 174 gigawatts. Not only do you have the impossible task of actually hitting the object, you need to have a hundred nuclear reactors powering a single source the entire time you do it.
I'd also then guess that a radar setup instead of visible light might work better, but that's also got resolution issues and would need a gigantic and incredibly sensitive receiver to start picking things up.
Space based systems for doing all this would probably work better since they wouldn't have to contend with the rotation of the earth itself, but it'd still be hard.
The Sun on the other hand is irradiating all space at all times. Aside from eclipses, we know Planet X is currently reflecting sunlight. We just have to look at it, compare to background, look again, compare to background, and notice the movement.
Not forgotten, just glossed over. You'd need to have a receiver that is pointing at a given (admittedly massive) part of the sky over a given range of possible times that a return photon would take to traverse the gap back to earth and strike the receiver.
> We just have to look at it
You're right, but the problem is that something orbiting at that distance follows an EXTREMELY slow orbit, so it's difficult to use the method you are describing. It's quite effective for looking for asteroids/space junk, but at that distance it becomes pretty tough to spot.
Imagine looking up and seeing the feeble sunlight. Some of it gets reflected back and starts a long journey toward some telescope on Earth.
Now imagine seeing "extremely powerful laser" from earth. Some of it gets reflected ... (ditto).
For your method to work, the latter must be more powerful than the former.
In other words, if you point your laser at Mars, a Martian should suddenly find the Earth shining brighter than the sun.
I don't believe mankind possesses such power yet (thank god).
Not marking Pluto on this would ruin it for me, even if it’s in the “Dwarf Planet” box.
Yeah, that sucks.
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: 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. ;-)
 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.
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?
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.
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 . (A circle's semi-major axis is its radius .)
This is most simply because a wide orbit contains more volume than a small orbit.
(I'm only being a little facetious. According to https://www.amazon.com/Chasing-New-Horizons-Inside-Mission-e..., plenty of scientists consider Pluto a planet still.)
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.
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). 
That would take forever to pinpoint an object with a radius of a few meters (apart from its existence as a black hole).
>but seems unlikely
I'm sure it's unlikely, but how great would it be to have a small black hole in our backyard to potentially visit with a probe.
>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."
We don't understand all the mechanisms that lead to black formation. Most likely that kind of black hole would not be a result of neutron star merger or supernova, but maybe it came about through another unknown mechanism (primordial black hole?). How great would that be to find out!
>That would take forever to pinpoint an object with a radius of a few meters (apart from its existence as a black hole).
Sure, but maybe we could detect it indirectly. Maybe this tiny black hole has moons or satellites that can be detected. Or maybe we can detect it during an asteroid or comet collision.
For a non-physicist, you sure have strong opinions about what is possible and not possible.
The Hawking radiation for such a thing would be VERY visible though, so no that’s not an option.
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.
This in addition to Alan Stern's criticism of the IAU classification: https://en.wikipedia.org/wiki/Pluto#IAU_classification