Some Of the most interesting question about planet 9 (answered!)
Q: If true, could this be the first of many such planets that we find?
A: Actually, yes, that’s possible. There is a lot of space outside of the Kuiper belt but still within the gravitational influence of the sun. There could be several small planets out there. The wide field infrared survey has ruled out anything as large as Saturn or bigger, though.
Q: Would such a discovery make it easier to find other Kuiper belt objects, or it would still leave too many variables to do so?
A: To find this planet they’re going to have to take a lot of long exposure images of a good chunk of the sky. They will likely find quite a few other objects in that region while they look for it. Some will possibly be in the Kuiper belt, and others could be like Sedna and Eris, and be in the space past the Kuiper belt.
Q: Wouldn’t those planets temps be basically at near absolute zero?
A: No. Just because it’s far from the sun doesn’t mean it can’t be hot itself. We know it isn’t, but for its mass it would need to be a gas giant about Neptune’s size, which means it has enough mass to pressurize the lower levels and its core to keep it hot. Along with that, it’s fluctuation of gravity as it approaches and retreats from Sol are enough to give it some internal movement like our own core because of tidal pulls from the Luna. We’ve ruled out anything of Saturn’s size or larger because it’s heat signature would be measurable without really looking for it, but the mass it would require for the calculations to work would place it somewhere between Neptune and Uranus in size, and therefore gaseous and about 20% cooler than we’ve been searching for.
On top of which, space isn’t cold. Cold isn’t a thing, its a lack of heat, which means the energy must transfer somewhere. There is no medium for it to transfer, so an object in space loses heat by losing its own mass. Space stations have to worry about cooling from all the instruments and body heat, not staying warm like you see in movies. Now eventually, after several billion years between galaxies a planet earth’s size could lose all its heat energy, but not one still circling a star, and nothing will reach absolute zero on its own until the heat death of the universe.
Q: How do we know it must be a gas giant? Is there something inherently impossible for a planet of that mass to be rocky?
A: Yes, actually. At a certain point a rocky planet’s mass becomes unsustainable. That’s why most rocky extrasolar planets are called Super-Earths, because Earth is already decently large.
Q: It sounds like we have some circumstantial data and solid math supporting its existence, but no actual observations of the planet:
“We have pretty good constraints on its orbit,” Dr. Brown said. “What we don’t know is where it is in its orbit, which is too bad.”
Is our next step to actually figure out where it is? Given its extremely large orbit, what are some observation techniques applicable for the kinds of distances we’re talking about?
If that’s not our next step, what is?
A: they would need an extremely powerful telescope to spot it. The only one capable is Subaru, which they are intending on using to look for it, the Astronomer who found it (Brown) estimates it would take 5 years to locate it.
Q: For a sense of scale, how far out would voyager 1 or 2 be on that map? Would either have reached the aphelion of planet IX yet?
A: Voyager 1, the farthest space probe from Earth, is about 133 AU away from us. This new planet would have a closest approach of around 200 AU, meaning Voyager 1 is about 2/3 of the way to the closest point in this planet’s orbit. If you were to send a probe out from Earth today at the speed Voyager has been going at, you would get to its closest approach in about 58 years.
Q: Theoretically, what would be the maximum distance an object could orbit the sun before gravity is no longer strong enough to allow for a repeating orbit? And to add, is there a minimum or maximum mass that object would have to be?
A: The mass of the orbiting object won’t matter (provided it’s significantly smaller than the mass of the Sun itself, of course – another star makes things complicated).
You’re basically asking for the radius of the Hill sphere of the Sun. Someone on this forum post calculated that it’s 2.37 light years, anything orbiting farther out than that would tend to have its orbit disrupted by tidal effects from the galaxy’s mass and from other passing stars.
In practice it’s probably smaller than that, since something orbiting 2.37 light years away would be very tenuously bound to the Sun indeed. The Oort cloud is theorized to have comets orbiting up to around 1.5-2 light years out, that’s probably the max.
Q: Considering its distance, how long do you think until we have a clear image of it equivalent to the ones of Pluto? Would it be something achievable in our lifetimes?
A: Achievable technologically and achievable politically are different things. As soon as we actually find this guy we could build a probe and launch it but the question is will our government pony up that kind of money. Would still be years away with a probe. Voyager 1 was launched in 1977 and is just over 130AU away. This planet seems to be about 150AU away from the sun at it’s closest point.
Q: How certain are we that this really exists? Can odds be estimated at this point, or is it too early for that?
A: We demonstrate that the perihelion positions and orbital planes of the objects are tightly confined and that such a clustering has only a probability of 0.007% to be due to chance, thus requiring a dynamical origin.
That is, specifically, the probability of happening to observe the alignments of perihelia and orbital pole orientations of a sample of six trans-Neptunian objects not significantly perturbed by Neptune, if their distributions were random. This can be taken to show that the orbital distributions of these objects are non-random, and are presumably influenced by an outside source.
Determining whether a planetary perturber is the correct explanation to the above improbability cannot yet be definitively stated, as the current data is very limited.
Q: So let’s say this planet was a gas giant when it was ejected (if that’s what happened).
What would have happened to its atmosphere that far from the Sun? Or do we know it’s a terrestrial planet?
A: At the expected mass, it’s most likely an ice giant like Uranus and Neptune with a thick atmosphere of mostly hydrogen and helium. Hydrogen is a gas down to 14K, and helium down to 4.5K, so I don’t think the atmosphere would have frozen even that far from the Sun.
Q: What are they going to name it?
A: The planet has not been discovered yet, it’s only theorized to exist. But this is by far the best evidence we’ve had to date that suggests an additional large planet exists.
My point is, we’re far away from naming anything at this point.
Q: How can we identify planets thousands of light years away but not one within our own solar system?
A: The planets we are observing around distant stars can be detected in a few ways.
The planet is massive like Jupiter and orbits very near its host star, causing the star to wobble slightly. We can detect the wobble, and thus predict the mass and orbit of the planet.
The planet eclipses its host star. We can see a very small dip in the brightness of the star. From this dip, we can determine the size of the planet from how much light it blocks, and we can determine the orbit from the rate at which it crosses its star’s disk.
Sometimes the planet is very large, and orbits close enough to be well lit but too far to cause a massive wobble. In this case, we can directly observe it.
I’m sure there are more, but these are the main ones. The problem with detecting this planet is that we are looking from the inside out.
Imagine standing in the center of a massive stadium. You think there is a person somewhere in the back 10 rows, but you aren’t sure. It is dark outside, and the only source of light is a modestly sized flashlight you brought with you. To add to the difficulty, you are limited to looking through a drinking straw.
If you were looking down into the stadium from say, a blimp, it would be much easier to spot the person’s exact location. As you’re floating around the stadium, you may have a brief glimpse of that person blocking the flashlight in the center.
Q: any chance that it could be a brown dwarf?
A: No. The Wide-Field Infrared Survey Explorer (WISE) recently completed a survey finding that no objects larger than Saturn exist in the region where there’s evidence for this new Planet Nine. If it exists it’s likely the size of Neptune or smaller, definitely not a brown dwarf which would be many, many times the mass of Jupiter.
Q: If our new “Planet-X” is confirmed, what was happening on Earth the last time it passed by?
A: If in passed by you mean the last time it was still over 200 times farther from the Sun than the Earth, that’s hard to say. It hasn’t actually been discovered, yet, so we don’t know where in its orbit it is right now. It could be at its closest approach in its possibly 15,000 year orbit today, or it could be at its farthest point making its last close approach 7,500 years ago.
Q: Given current propulsion technology and a large enough budget, what is the fastest that a probe could reach a planet this distant?
A: New Horizons took 9 years to reach Pluto. This planet is probably at least 20 times farther away, so well over a century.