My short bio: Konstantin: One of my absolute favorite things to do is to space out and think about planets. This works out pretty well, because I get paid (in American dollars) to do exactly that. A year and a half ago, my friend Mike and I decided to use our powers of deduction to demonstrate, once and for all, that there is no such thing as planet X. While successful, we also discovered evidence for planet 9 along the way. Other things I do when professor-ing include working with students and postdocs to understand the interiors and orbits of planets around other stars, as well as teaching classes on planetary physics. When I’m not working on science, I enjoy making music, running, hiking, snowboarding, surfing, flying remote control airplanes, and hanging out with my wife and daughter. I also have a cat, who is my social media representative, and his twitter handle is @kbatygin.

Mike: I like to consider myself the Emperor of the Dwarf Planets. Unfortunately, the International Astronomical Union chooses not to accept my self-designation. I did, at least, discover most of the dwarf planets that we now recognize. These days I spend much of my time at telescopes continuing to search for new objects on the edge of the solar system in hopes of piecing together clues to how planetary systems form. When not staying up all night on mountain tops, I also teach a few thousand student in my free online MOOC, "The Science of the Solar System." Or write the occasional book. I have won a slew of fancy prizes, but my favorite honor is that I was once voted one of Wired Online's Top Ten Sexiest Geeks. But that was a long time ago, and, as my wife never ceases to point out, it was a very slow year for sexy geeks. You can stalk me on Twitter @plutokiller.

My Proof:

Hello, Reddit! Mike and Konstantin here to answer your questions about our discovery of Planet Nine. We are here until 3:00 PM EST, so ask away! All of our answers will come from the "caltechedu" account, and Mike's answers will begin with "MB", and Konstantin's will begin with "KB."

3:05 PM EST / 12:05 PM PST - We have concluded the AMA as of now, and won't be answering any more questions. Thanks, everyone, for some excellent conversation!

Comments: 249 • Responses: 65  • Date: 

dummyhoy1720 karma

How do you know the apparent alignment of the Sedna-like objects we know about isn't the product of observational bias? In other words, how do you know there's not something about that part of the solar system (or the sky, or our telescopes, or whatever) that made it easier to spot the Sedna-like objects we've found? How do you know there aren't dozens more Sedna-like objects in random orientations that we just haven't seen yet?

Also, Mike and, do your cats play with "Da Bird"- the feather-on-a-fishing-poll toy?

caltechedu30 karma

MB: This is a great question. We have tried really hard to correct for observational biases, but this is, in my opinion, that most uncertain part of the whole work. The human brain is really really good at finding patterns even when they aren't there. You try to overcome these pitfalls by replicating results and making further predictions. Time will tell if the replication occurs (we think it will!), but, as of now, we've already had one successful set of predictions which has come true. So we're convinced enough that we are right that we're willing to stand up and say so, but, late at night, when I can't sleep, I worry about human brains and pattern matching. Time will definitely tell.

Also: the #OMGKITTENS love the feather-on-a-pole.

koosekoose20 karma

Have you ever played kerbal space program? You really should.

caltechedu23 karma

KB: Ok - after I finish AMA

BlueFire1919 karma

What is your favorite sci-if movie, book, or video game?

caltechedu43 karma

KB: I absolutely loved Deus Ex: HR and the Mass Effect series. I think sci-fi video games are an awesome way to connect scientific progress with entertainment.

Cenodo16 karma

Could the planet have moons, and if so, how big could they be?

caltechedu30 karma

It could definitely have moons. That will be one of the first things we look for when we spot it. Whether or not it has moons might give us good clues to exactly how it got there.

Cenodo13 karma

Could you elaborate? What would a lack of moons indicate, for example? Or a Saturn-style mess o' moons?

caltechedu23 karma

MB: We think P9 was flung out of the Uranus/Neptune region early on. Our guess is that it wouldn't have had time to have formed moons at the time. So if no moons => early ejection. What if it has moons? Either late ejection OR moons forming when it was far away. If they formed far away they might be very different.*

  • warning: rampant speculation.

notjabba16 karma

Would the existence of a planet so far away from the sun open up possibilities for new ways of slingshotting spacecraft outside of the solar system?

caltechedu22 karma

I had never thought of this, but there was a very nice article written last week interviewing a few people about the possibilities (short answer: probably not). Anyone remember the link?

strozykowski13 karma

Mike: How many white, fluffy cats, if concentrated and placed in the same orbit as the theorized Planet 9, would it take to be visible by a human-made telescope (either terrestrial or space-based)?

caltechedu23 karma

MB: approximately 10 earth masses of cats. Although I find that orange cats tend to be larger, so it might be easier to find enough of them.

lswanson10 karma

Hi Konstantin and Mike!

Given that the possible new planet would potentially solve the problems with the orbits of the other observed objects discovered so far, what would this do to the probability of additional, similar mass objects out there? Does it mean it's a lot less likely there's anything else, at least in the nearby area?

Is there any current thinking or would you care to speculate as to how large bodies would behave outside of the heliopause? Would they be more likely to retain some sort of tenuous (or even strong?) atmosphere, or maybe have other effects due to increased cosmic rays, for example?

caltechedu14 karma

It certainly not implausible that additional objects can exist beyond the orbit of P9. However, there is no current evidence for their existence.

Bodies on sufficiently expansive orbits can be affected by Galactic tides, so there is a different orbital behavior that occurs there. In terms of atmospheric retention, there seems to be no problem with atmospheric retention even relatively close to the host stars (like many exoplanets we observe) so I don't think the huge orbit makes too big of a difference.

vnangia7 karma

Given the distances involved, wouldn't we see significant differences in the atmosphere at perihelion and aphelion? I got the sense from an NH briefing that even Pluto has a much thicker atmosphere closer to the sun than at aphelion and unless 9 is generating a lot of heat internally, isn't it likely the atmosphere freezes and falls to the ground? Kind of like Vinge's on-off star, now that I think about it.

caltechedu12 karma

It's an interesting question. The amount of energy obtained from the Sun is quite tiny anywhere in its orbit, so my gut feeling is that the atmospheric heating is overwhelmed entirely by internal heating.

blue_bomber5089 karma

If I were to train on that planet in order to defeat Kakarot, how many times Earth's gravity would I be training in?

caltechedu16 karma

KB: !!!! interestingly, the surface gravity of this object is not too different from the Earth's. I think once again Kakarot might end up having the upper hand.

PS Frieza - next time you post on reddit, don't hide behind an anonymous-looking handle.

nobodyspecial9 karma

If p9 exists, why wouldn't it have shown up in the WISE survey?

caltechedu15 karma

KB: not bright enough in intrinsic heat for WISE and too far for reflected light. WISE would have found it if it was at perihelion.

escherbach8 karma

If an astronomer actually observes the planet wouldn't he/she be the "discoverer"? You have just made a mathematical prediction of its existence haven't you?

caltechedu24 karma

MB: hard for me to guess. Urbain le Verrier is generally credited with "discovering" Neptune, though he predicted and Galle actually observed it. It doesn't matter much to me: I just want to see.

Ghostryder1227 karma

At this point, what is required to have the ability to physically see the suspect planet?

caltechedu14 karma

MB: The planet is faint, but no hopelessly so, we think. Based on where we think it likely is in its orbit, we are going to need a couple of the biggest telescopes in the world (the Subaru telescope, is my favorite), but with these we definitely have a chance.

sissipaska7 karma

How hard is it to keep this kind of finding as a secret before publishing it officially?

Edit: Like this:

caltechedu13 karma

MB: Pretty hard. By the day of the announcement several dozens of people knew about it. It's hard to not want to tell someone (i.e., I had to call my Mom and tell her!), and it just takes a little for it to leak out all of the way. We didn't really know whether this one would hold or not!

nickjudge427 karma

Are they any alternate hypothesis (even at a very, very low probability) that could explain the orientation of the orbits of the 6 objects in the Kuiper belt? Other than random chance, of course?

caltechedu13 karma

MB: I think the best alternative explanation is random chance. It's the one I worry about the most. We tried really really really really really really hard to come up with others, but couldn't. Can someone else? We shall see. We hope that people are currently hard at work trying!

dummyhoy177 karma

Do you think we overemphasize crewed space exploration versus uncrewed probes?

caltechedu9 karma

MB: I think they both have their places. I grew up on Saturn V rockets and Apollo missions and found them the most inspirational things around. But for science, I don't think you can beat the robots.

vnangia7 karma

Which would you rather fight? One hundred cat-sized planets or one planet-sized cat?

caltechedu11 karma

KB: I fight with a planet-sized cat at home on a daily basis (because he gets hungry), so I'll take the hundred cat challenge.

loxs6 karma

Do you think there could be a link between Planet Nine's orbital period and the Milankovitch Cycles?

caltechedu13 karma

MB: No! Planet Nine is just too far away to have any but the most minuscule effects on the earth.

SaltySeaDodger6 karma

As you found it, do you get to name the planet?

caltechedu14 karma

We actually think that the discovery of a new planet in the solar system will be such a momentous occasion that there should be some way that more than just 2 or 3 or 4 people get to name it. It should be part of a larger societal discussion. However that works.

sandygrains6 karma

Theoretically, could P9 be Tyche? Wasn't that predicted to sit around 15,000 AU? Could WISE rescan to search for Tyche, now with a lower mass?

caltechedu12 karma

KB: Tyche was predicted at 15000AU. P9 has a semi-major axis of approximately 700AU. Even if there is a massive object far out in the Oort cloud, it is not P9.

KarenD20166 karma

Ann-Marie Madigan from Berkeley is giving a lecture today suggesting the orbital oddities you observed can be explained by "a (tilted and highly-inclined) disk of minor planets, at least two orders of magnitude more massive than the Kuiper Belt awaiting discovery at hundreds of AU." Did you examine this possibility in your mathematical models? How does a massive planet make more sense? Maybe a massive cat? ;-)

caltechedu16 karma

KB: I'm familiar with Ann-Marie's work. I genuinely think their discovery of the "inclination instability" is awesome - such dramatic progress rarely happens in celestial mechanics. At the same time, we have observations that rule out the existence of so much mass in the extended scattered disk of the Kuiper belt. So I doubt the inclination instability actually applies to the Kuiper belt. Interestingly, our first thoughts were also along the lines of self-gravity (different mechanism from that proposed by Ann-Marie) when we started this project a year and a half ago, but we abandoned that direction. Plus my cat kept demanding a planet.

PM_ME_YOUR_UFOs5 karma

Is it possible for Planet Nine to be a captured rogue planet?

caltechedu8 karma

KB: It's not out of the question.

I_Just-Blue_Myself2 karma

so this planet could have developed in another solar system, been ejected and then trapped by ours? what are the odds of something like that happening?

caltechedu8 karma

KB: It depends on a number of factors - was the sun a binary early on in its history (most sun-like stars are)? what was the birth cluster like? Capture is an interesting scenario, but simulations are needed to put a number on the probability.

MattBaster5 karma

Although the majority of our planets were named after ancient Greek and Roman gods, I’ve read that you are hoping to officially name this planet “George”. Although “George” goes way back historically, why push for such a widely used, conventional and rather… boring name?

caltechedu9 karma

KB: George is an inside (outside?) joke between Mike and I. When P9 is caught on camera, we will not actually push for George. :)

VirFalcis5 karma

Will the James Webb Space Telescope be able to help in the search for Planet 9?

caltechedu11 karma

MB: It will do no good for the search, but it will be AWESOME for studying Planet Nine once we find it.

dummyhoy174 karma

Did you two do this work on your own, or did you have (a few, dozens, hundreds) of grad students working with you? How many people knew about your result before you published the other day?

caltechedu10 karma

MB: Konstantin and I really did do all of this with just the two of us. It was super fun.

I would guess hundreds of people knew by publication day. There were paper referees, editors, type setters, reporters, my Mother, etc.

hramos4 karma

Have you been able to predict the current location of Planet Nine? If so, is the level of accuracy such that observing this planet is within the grasp of amateur astronomers?

caltechedu10 karma

MB: We now know the orbital PATH, but not the location along the path. We think that we have already ruled out the parts of the path where Planet Nine is bright enough for amateurs, so we are turning to some of the biggest telescopes on the planet.

SageWaterDragon4 karma

Would it be possible to directly observe the planet in any way that would let us resolve it as more than a dot? Considering how long it took for New Horizons to reach Pluto, I doubt we could get a probe out there during my lifetime.

caltechedu16 karma

MB: HST should be able to see it a few pixels across. Not a lot, but a few.

We've been talking with people about ways to get there more quickly. The trick is to go straight at the sun and then blast every engine should have when you are super close and use that for a monster slingshot. Then coast 20 years and arrive at Planet Nine. Sign me up.

9tenalp4 karma

Wouldn't P9 also exert gravitational perturbations on Neptune and maybe even Uranus? Even if these effects are tiny, wouldn't we nonetheless be able to see them in the data (simply because we observed those planets for a very long time, thus determining their ephemerides with very high level of accuracy)?

caltechedu7 karma

MB: Yes, but tiny tiny tiny effects. We are actually looking into whether or not these tiny effects could be measured with ultra-precise measurements from spacecraft. Stay tuned.

19chickens4 karma

What's your favourite kind of cat?

On a non-cat question, what kind of planet (other than the mass estimates) is IX?

caltechedu11 karma

KB: My cat is my favorite type of cat. P9 is likely a slightly smaller brother of Uranus and Neptune. Probably similar composition overall.

caltechedu7 karma

MB: My cats are better than Konstantin's cat. Because I have 4 of them. Because we are a crazy cat family.

Marine_Mustang3 karma

Could Planet 9 be found before LSST comes online? Will LSST's work be the definitive answer for how many other objects could be in the solar system?

caltechedu7 karma

MB: Maybe! We are certainly looking hard and hope to not have to wait until 2023. But, if we don't find it before LSST, then LSST will find some many other objects being affected by Planet Nine that I think it will essentially tell us exactly where to search.

derbecrux3 karma

How long will it take to receive an actual image of planet nine?

caltechedu4 karma

KB: If we are optimistic, a couple years. However, if the planet is hiding in front of the galactic plane, then the search might take up to a decade.

wxmeddler3 karma

From what I've read, the confidence that you have in Planet Nine is 3 sigma. How would you or other astronomists be able to raise this confidence interval further (ex. 5 sigma)? Is this even possible? If not, what technologies or other research would need to be undertaken to capture these other data points?

caltechedu11 karma

MB: It is critical to find more objects like the 11 that make up the pattern in the sky that we see. Every new object that fits the pattern continues to increase our confidence. Alternatively, if we find new distant Kuiper belt objects which don't fit the pattern that we see, then WE ARE WRONG. Which, we think, makes this a nice, easily falsifiable theory.

finnyboy6653 karma

How does it feel to be the man behind Pluto's demise?

caltechedu13 karma

Actually it feels great. As both an astronomer AND an educator, this has given me a great chance to explain to people how science works, how the solar system works, and how discoveries are made.

vnangia2 karma

Reading your paper, I didn't get a sense of whether 9 can explain the Kuiper Cliff. Can it? If not, what do you think is causing that, assuming it isn't observational bias?

caltechedu7 karma

KB: At least in its current configuration, P9 does not influence the Kuiper Cliff directly. The Kuiper Cliff might be representative of the primordial edge of the solar nebula. But really, it's still a puzzle.

snotpocket2 karma

Re planet 9, is it plausible that a passing star caused these KBOs to orbit like this?

Or can we rule that out based on the relatively low eccentricity of the orbits of the first 8 planets?

caltechedu7 karma

KB: If you invoke a stellar fly-by, it MUST be 'recent,' and the probability of that is rather low. If you leave these orbits to evolve under the gravitational influence of the known giant planets (so a solar system without P9), they will randomize in about half a billion years. So flyby is not exactly a satisfactory answer.

runswithbees2 karma

Planet 9 seems like huge object to have flying around in the inner Oort cloud!

Therefore, given Plant 9's estimated mass (10 Earth Masses) and estimated orbit of 200-1200 AU (20 times the distance of Neptune from the Sun), can we safely suggest that Planet 9 is the top culprit responsible for bringing comets into the inner solar system?

caltechedu12 karma

MB: NO! While Planet Nine seems really far away, it is actually well inside the Oort cloud, which we thinks starts at something like 10,000 AU. While P9 might cause a little modulation in what is going on, it is definitely not the main culprit, which remains the galactic tide.

lula24882 karma

If you could time travel to any year, what year would you travel to and why?

caltechedu14 karma

KB: 25 Jan 2016, 22 mins ago, so that we could relive the AMA experience

nobodyspecial2 karma

Any thoughts about crowd sourcing the search?

caltechedu3 karma

MB: Haven't thought of how, but if we can, we definitely will!

Replex2 karma

How does it feel to be in the boots of Le Verrier?


caltechedu5 karma

KB: They are smelly.

madmaxpower92 karma

do you guys watch Judge Judy?

caltechedu7 karma

KB: She was our inspiration to start this project.

sissipaska2 karma

Is there anything amateur astronomers could do to benefit finding either Planet Nine or some other hidden objects in the solar system?

I personally have been thinking about creating a semi-automated rig with tracking that would scan the night sky with a full frame camera and a bright 85/135mm focal-length lens, creating high resolution (hunders/thousands of megapixels) 360 degree panoramas. Mostly just for my own amusement, but I have also wondered if the material could be used for proper scientific research too if made available for others.

caltechedu4 karma

MB: We think that at this point we have ruled out most of the spots in the orbit where it would be bright enough for (even very advanced) amateur telescopes. We're planning on doing most of the search on the 8-m Subaru telescope.

Demidrol1 karma

How do you think it can be on this planet liquid water and oxygen in atmosphere?

caltechedu3 karma

KB: possibly in regions of higher atm. pressures.

madmaxpower91 karma

why would a ninth planet matter being that it is so far away. shouldn't we be using money for other thing?

caltechedu6 karma

MB: As humans, I feel like one of our most powerful instincts is for exploration, and without it we wither. We as a species will always be looking beyond our latest horizon to understand our world and our universe. This is what it means, to me, to be human.

MikeDiceOnBass1 karma

Have you used 3D Laser Scanning technology in your search for P9? What sorts of cutting edge technology are you excited to be using in your search?

caltechedu4 karma

KB: Not sure what you mean by 3D Laser Scanning technology (the grocery store check out line comes to my simple mind)... The best tool for this is really the Subaru telescope on Hawaii - large field of view and substantial depth.

Cunhabear1 karma

So if this is confirmed to be a planet within our solar system, is it going to be the actual ninth planet that we have been missing for years or will it be a special class of planet like Pluto?

caltechedu6 karma

MB: PLANET. Like a real planet. Because it's a real planet.

sandygrains1 karma

Do you guys believe this is the fifth planet that was flung out as described by the Nice Model?

caltechedu4 karma

MB: No; we think it happened earlier. By the time of the Nice flinging there would have been no way to have KEPT Planet Nine after it was flung outward.

sandygrains2 karma

Could you elaborate a little on why you think it was flung out much earlier?

caltechedu3 karma

KB: Early in the solar system's lifetime, the sun was embedded in a cluster of stars. Perturbations from the cluster are one way to keep the orbit of P9 bound to the sun, after gravitational scattering. After the cluster is gone, a scattered planet simply ejects.

0thatguy1 karma

When do you predict the planet will be found, if it exists? I've heard that using the Japanese telescope it would take 5 years to scan the whole area but since many telescopes will likely be searching at once, is it possible we could find Planet Nine in 2016?

caltechedu4 karma

MB: Not impossible.

sandygrains1 karma

Do we know the exact orbit of P9 around the sun, or at least enough to know just where exactly to point our telescopes to in hopes of it passing by one day? Edit: If it isn't too dim to be spotted, exactly what is the difficulty we have today except for lack of coordinates?

caltechedu3 karma

KB: We know it well enough to limit our observations to a 180 deg x 20 deg patch of sky. As we move forward, we will continue to refine our prediction with more theoretical calculations.

The-Lying-Tree1 karma

Can you guys name the planet Pluto? That way people will finally stop complaining about how Pluto isn't a planet any more.

Okay a serious question now, approximately how large is this planet, how much mass dose it have, and do you think we will have the technology to do detailed observations of this planet in the foreseeable future?

caltechedu3 karma

MB: My daughter suggested naming it Pluto 5 years ago. When we weren't even looking for it yet.

Best calcuations: 10 times the mass of the earth, ~3 times the size of the earth. We can see it RIGHT NOW (except we don't know where to look).

Gnonthgol1 karma

I ask this to every astronomer. If you had $2B to build a telescope what would you build? Ground based, space based, what sensors and wavelengths, what field of view, what should it be used for, etc.

caltechedu5 karma

MB: I just thought about this after I bought my Powerball ticket. First $0.5B, a dedicated Subaru telescope for finding these things. Next $1M, a dedicated high resolution imaging telescope in space. Last $0.5B, money to pay people to help analyze all of the data!

escherbach1 karma

It will no doubt take a large scientific collaboration to actually physically detect this planet, is this a good analogy: you guys are like Higgs, Englert etc who "discovered" the Higgs particle theoretically, and the future collaboration is like CERN? (who made the physical detection). In which case, how should the Nobel Prize be divided up after physical detection?

caltechedu8 karma

MB: (first: there will be no Nobel Prize for this, so I'll answer about the Higgs).

I've wondered about this too WRT the Higgs. Certainly the huge amount of work and innovation and science that went into the actual discovery (confirmation?) deserves recognition. Certainly the original theory does. I think what this shows is how outdated the idea of things like Nobel Prizes for a few great individuals is.

I_smell_awesome1 karma

What are your favorite pizza toppings?

caltechedu3 karma

MB: sausage and mushrooms. The cats really the sausage.

IAmNotScottBakula1 karma

If the planet is officially discovered, is there any way we can convince you to name it "Planet Nine From Outer Space"?

caltechedu3 karma

KB: such an awesome movie. :) Check out the poster Mike Wong (a grad student at Caltech) made at

0thatguy1 karma

If Planet Nine turns out to be rocky and not gaseous, doesn't that mean it would have a smaller radius, and potentially evade detection?

caltechedu7 karma

MB: yes. seems unlikely, but, yes.

deepakagnanii1 karma


caltechedu4 karma

MB: pumpkin

Positron3111 karma

Why would there be a planet of such significant size in that part of the solar system? Wouldn't it have been closer to the sun, especially a planet of that mass?

Also, how did we discover Pluto way before discovering Planet Nine?

caltechedu9 karma

MB: (re: Pluto. Pluto is sooooo much closer it is relatively simple to find).

We suspect that Planet Nine formed very close to Uranus and Neptune, at about the same time. It then probably swung too close to Jupiter or Saturn and got flung outward.

We definitely don't think that it formed out there.

vnangia1 karma

Assuming its there, what do you think it will take to build a probe to do a flyby of 9 in terms of political will? This is on the order of TAU or Interstellar Probe, isn't it?

I fear 2014 MU 69 may be the last unvisited world we'll get closeups of in my life time - and I'm just in my 30s.

caltechedu4 karma

MB: I like to think that when we spot P9 we will want to go there so much that we will do a fast inexpensive flyby just for initial reconnaissance. But maybe I'm optimistic.

Also: Europa mission will be AWESOME

caltechedu3 karma

KB: It's a great question. I am humbled by the extent to which P9 has captured the public imagination, and my hope is that we can continue to be a society where curiosity is rewarded.

0thatguy1 karma

Is there anything similar to the WISE survey coming in the future that will be sensitive enough to detect planets of similar size to Planet Nine out to great distances?

caltechedu4 karma

No yet. But it will happen everyally.

0thatguy1 karma

How confidant are you that Planet Nine is real? If you had to put a percentage on it?

caltechedu5 karma

KB: 100000000000000000%