A ninth planet after all?

[Glaurung]

Astronomers from Caltech have published indirect evidence for the existence of a previously unknown planet in our solar system. It's calculated as having about 10 times the mass of the Earth (somewhat less than Uranus or Neptune), and a very distant orbit with a period of at least 10,000 years.

There's a summary in a BBC News article, and the full scientific paper online as well.

[comrade_general]

Pics or it didn't happen.

[Glaurung]

I think quite a lot of astronomers' time will now be spent trying to get those pictures - it's not actually a planet until we can see a little dot moving against the sky, day by day.

[comrade_general]

I won't be convinced until we stick a probe up its a.

[Glaurung]

Sending a probe would be nice (and there's probably someone in NASA or ESA already thinking about how to do it), but it would take a long time to get there. "Planet Nine" could be anywhere between 200 and 1,200 astronomical units from the Sun (the radius of the Earth's orbit is 1 AU). For comparison, Pluto's orbit takes it between about 30 and 50 AU from the Sun, and New Horizons took nine and a half years to get there. Unless we can achieve much higher probe speeds than we have so far, a Planet Nine probe is likely to take well over 50 years to get there

[comrade_general]

We can use impulse engines.

[SaidaiSloth]

All I want is for it to be called Dorris.

[Glaurung]

We can use impulse engines.

Indeed: any drive system that would run reliably for months or years at a time, even at very low power, would make an amazing difference to space exploration. Unfortunately it would probably be a lot bigger than current space probes, and would probably have to be manufactured in space to be remotely economic.

[comrade_general]

Well really it just needs a burst of speed and then ability to make course corrections and then slow down. A basic impulse engine would harness a nuclear explosion to generate sudden thrust. We have plenty of nukes already, just need to blow one up in space and keep the probe from getting destroyed by it.

[Glaurung]

Drives powered by nuclear explosions (known, more prosaically, as nuclear pulse propulsion) have in fact gone through quite a lot of theoretical development - the first work was done by Project Orion at General Electric in the 1950s and 60s, which is why such drives are often known as Orion drives. They appear in science fiction from time to time, most memorably for me in Larry Niven and Jerry Pournelle's novel Footfall.

Meanwhile, closer to the original topic, today's xkcd is relevant.