This artistic rendering shows the distant view from Planet Nine back towards the sun. The planet is thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side.
So, what about that ninth planet?
Pluto, you’ll recall, was demoted to a dwarf planet because it's so small. But now a couple of scientists at the California Institute of Technology are on to what they think really IS a companion to Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
CalTech astronomer Mike Brown says he and planetary scientist Konstantin Batygin are on the cusp of a discovery, “What we think we've seen is that the very outer edge of our solar system is being pushed around by something else out there and that something else we think is the real ninth planet, this massive thing that's pushing everything around out there.”
Batygin says it's kind of like hearing a siren somewhere in the distance. You can't tell if it’s an ambulance or a fire truck, and you can't say exactly which street it's coming from. “So it’s kind of the cosmic version of that , we have a very distinct ‘echo’ that we're hearing, we have this gravitational signature of a distant planet but we haven't seen it yet and the hunt is on to detect it astronomically.”
So these planetary scientists haven't actually observed Planet 9 through a telescope. They've found evidence, that "gravitational signature," as Batygin calls it.
The suspect fits this description: “Our computer models suggest that its mass is close to 10X the mass of the earth, so it’s quite a substantial planet, its orbit is exceptionally wide, its closest pass swings in at around 250X the distance between the Earth and the Sun, at its most distant it sits at around 1,000X this distance, so it has an exceptionally elongated, long period, orbit."
Planet 9 appears to be in our solar system because there’s evidence that it’s held in orbit by the Sun's gravitational pull, “It holds it in orbit, so it goes around the sun. … even though it seems so far away to us, it's well within the solar system. It’s inside the Oort Cloud where comets live, so its far away for us but it's a very typical distance.”
If the researchers are correct, Planet 9 would put its nearest neighbor, Pluto to shame.
“I mean this is a totally different category of object. This thing is quite literally 5,000 times the mass of Pluto, so Planet 9 feels no insecurity in being compared with Pluto.”
Brown and Batygin have been poring over their data and testing their hypothesis for more than two years. But then something crystalized recently, says Brown, “There was one moment when I looked at the data we had and our computer simulations and calculations and suddenly it went from a kind of fun idea that might be true, to the moment where I actually believed it and at that moment I think my jaw hit the floor.”
So it's potentially an amazing discovery. But some NASA scientists have already said they need more proof before they welcome Planet 9 into the family.
Batygin and Brown actually welcome that scepticism. Batygin says they published their findings in the Astronomical Journal to try and get other astronomers looking up in space to help spot the planet.
“We could have kept quiet and sort of looked for this thing ourselves, and in principal we'd love to find it but it would be better if Planet 9 was discovered sooner than later rather so as a result we decided to go forward with our theoretical prediction and kind of lay out, 'Here’s the prediction of the orbit, this is where you go look in the sky to find Planet 9.'”
He adds that there’s historical precedence for this kind predicted discovery. “Neptune was calculated before it was discovered astronomically, so we feel like we’re in somewhat good company with mathematicians of the 18th century.”
“This is really the start of the search, the amazing moment will come when it’s really found,” says Brown, “but now I think everybody is at the starting line and the gun has gone off and it’s a race to see who can see it for the first time.”
That gives the rest of us the time to try and come up with name that's more original than Planet 9. As Konstantin Batygin put it, "Something as dramatic as a planet should be named by society as a whole, not by a couple of guys in southern California who are sitting around and drinking coffee."
C'mon everybody — start thinking!
Readers, what would you call Planet 9? Let us know in our comments section. Early suggestions on Twitter include David Bowie, John Lennon and William Henry Harrison (the ninth president). We're adding Curie, for Marie Curie, just because.