Our solar system is pretty neat and orderly. Yeah, it has some issues, but in general we can make some broad statements about it: the planets all orbit the Sun in the same direction, for one thing, and they also orbit pretty much in the same plane. If you look at the system from the side, the orbits would all look flat, like a DVD seen from the side.
That’s left over from the formation of the solar system itself, which happened when a cloud of dust and gas collapsed into a disk. The planets formed from that disk, so they all orbit in roughly the same plane. We see other systems forming in the same way, so we assume that when we look at those planets, they’ll also have all their planets in a plane.
Oops. Maybe not so much. Astronomers have just announced that they’ve confirmed a system where the planets are not all aligned this way, and in fact the planets are titled relative to each other by as much as 30°!
Will Baird reproduced the below useful comparison map of our planetary system and Upsilon Andromedae's. I wouldn't have thought it stable, honestly.
[T]he amazing thing is that it looks like Ups And c and d are in wildly different orbits: instead of being almost exactly in the same plane as expected, they are tilted relative to one another by 30°! The illustration on the right compared those orbits with those of planets in our own solar system, and you can see how weird this is.
[. . .]
In the case of Upsilon Andromedae, we have some culprits. The data hint that there may be a fourth planet orbiting the star. It’s not clear if it’s there or not, but if it has an elliptical orbit it could gravitationally affect the inner planets. There’s also the red dwarf star orbiting farther out. Far more massive than a planet, its gravity may have some effect on the system as well. It’s also certainly possible that there are other influences we haven’t seen or thought of yet. [Update: I just got off the phone with the team who did this research, and Rory Barnes told me that a strong possibility as well is that there were more planets in the system initially. They would have interacted via gravity, and affected each others' orbits. A likely scenario is that a planet with about ten times the mass of Jupiter could have messed up the orbits of the other two, then been ejected out of the system. This is a common outcome when you have lots of massive objects in one system.
This has obvious implications for life, as noted at Wired Science.
When astronomers talk about the “habitable zone,” they mean the shell around a star where the temperatures are right for liquid water. Any closer, and oceans will boil. Any farther, and the planet will freeze. But this definition assumes that most planets have roughly circular orbits, like the Earth and most other planets in the solar system.
“What we know from studying exoplanets is that that is definitely not the rule,” said Rory Barnes of the University of Washington at the meeting of the American Astronomical Society in Miami. Many of the 454 exoplanets discovered to date have highly elliptical orbits, meaning the planets are not always the same distance from their parent star. Thanks to this uneven geometry, the planet spends more time closer to its star, which tends to make for warmer planets.
Adding another planet, especially a bullying Jupiter-sized planet, can mess with orbits and make a once-hospitable planet move in and out of the habitable zone over time. Using computer simulations of several hypothetical planetary systems, Barnes showed that a giant neighbor can pull an Earth-like planet’s orbit like a rubber band, shifting it from circular to elliptical and back to circular again in as little as a few thousand years.
Still, there is hope.
Barnes’ simulations predicted more-dire consequences for extrasolar planets near the edge of their habitable zones, though. If the planet is on the cooler edge of the habitable zone, it could go through cycles of freezing and thawing. If it’s on the warmer side, the temperature could fluctuate from comfy to boiling from one millennium to the next.
“The inner edge is much more dangerous,” Barnes said. All the water could boil off and be lost forever, or the warming planet could experience a “runaway greenhouse” effect and end up a scorched wasteland like Venus.
But it’s not all bad news. Barnes suggests that some planets we might dismiss as snowballs could just be going through an eccentric phase.
“Our own Earth has gone through stages of glaciation — we call them snowball Earth phases — and we managed to pull out of it,” he said. “On a planet like that, on the outer edge, you will have reservoirs of life, and there will be habitats that will persist.”</i>
Barnes is referring to the Snowball Earth theory, which suggests--apparently with good reason--that there have been periods of time when the Earth was locked into periods of tens of millions of years in which it has been completely glaicated. Science fiction writers have depicted life on worlds with similar if less extreme cycles, most notably Brian Aldiss in his Helliconia series, set on a planet with very long seasons, dipping from coldest winter to warmest spring over two thousand years.