Wednesday, 27 January 2016

Pluto 2.0 – The New Ninth Planet

At several points in human history, short-sighted people have prematurely declared the end of the age of discovery. In 1900, the otherwise brilliant physicist, known to history as Lord Kelvin, allegedly claimed that “there is nothing new to be discovered in physics now; all that remains is more and more precise measurement.” Five years later, an obscure patent clerk named Albert Einstein seemingly wandered out of the woods to publish something called the “Theory of Relativity.” But Lord Kelvin shouldn’t beat himself up too badly, the New York times suggested, in 1903, that it might take mathematicians and engineers between one and ten million years to develop a true flying machine – the exact same year the Wright brothers first took to the sky. Actually, the New York Times has something of a history of being caught with their foot in their mouth, claiming in 1920 that a rocket would never be powerful enough to escape Earth’s atmosphere.

The reasons for these hilariously bad predictions are debatable. It could be that the predictors had doubt in the cleverness of mankind or fear of the unknown. It might even be that the people we remember for their lack of prescience were simply overconfident in the scientists that came before them, assuming that with such brilliant minds at work for so long, we must have completed all the work that isn’t really, very, ridiculously hard. The truth, however, is that the amount of stuff we don’t know is kind of incredible. Case in point: our own solar system.

If you think we have a pretty good understanding of things like our sun, moon, and planetary neighbours, you’ve been misled by overconfident elementary school maps of the solar system. If you don’t believe me, ask any of the map-makers who, in 2006, had to scramble to remove a lonely snowball named Pluto from the list of recognized planets. Although, now you might have a hard time getting them on the phone because they’re probably trying to figure out how to deal with the supposed real ninth planet that astronomers at the Caltech found evidence of last week.

Yes that’s right. Only a decade after pulling out their collective erasers, planet counters are preparing to adjust the planetary census once again. Researchers Konstantin Batygin and Mike Brown – the very man most responsible for downgrading Pluto to a dwarf planet – reported on January 20 that they have very good reason to believe we’ve been overlooking something substantial at the edge of our star system. Apparently, somewhere in the darkness around 25 times further away as Pluto, lurks a planet that is 10 times the mass of the Earth. So how did we miss it?

Well, for starters, saying it is 25 times further away than Pluto doesn’t really do justice to how distant this thing actually is. Pluto is 7.5 billion kilometers (4.7 billion miles) away from us. The New Horizons spacecraft, that has been sending us pretty pictures of Pluto for the past year or so, took a decade to get there. Using our fastest, most modern spaceflight technology, it would take at least half a century to get to where the uncreatively labelled 'Planet Nine' is supposedly hiding. A second, and related, reason we haven’t discovered it sooner, is that when you get that far from Earth, the Sun isn’t much more than a rather bright star in the blackness of a permanent night. That means that Planet Nine gets very little light it can reflect back to our telescopes.

In fact, we still haven’t actually discovered Planet Nine; we just have hints that it exists. Brown and Batygin have been looking at half a dozen objects located in the Kuiper Belt – Pluto’s celestial neighbourhood – and discovered that they are drifting around on a plane that is out of line with the rest of our solar system, yet seemingly in line with some other object’s gravitational force, strongly suggesting that something big and close by is bullying them with its gravity. The astronomers used a computer model to see what the gravitational effect of a large planet in the outer solar system would have on these objects and the results matched what they observed exactly. It’s a bit like looking at the ripples in a pond and inferring that something recently fell in the water. You can’t be positive, but you can be pretty sure.

So all that we are waiting for now is our first sighting. Brown predicts it could happen in the next five years, possibly. We can’t be sure though. Planet Nine’s orbit – if it exists – is massive. It takes between 12,000 and 20,000 years to orbit the Sun and astronomers will have to look at every piece of that orbit to find where it is. That is a lot of sky. Thankfully, that gives us some time to think of a better name.