Hot News for Hot Jupiters
Those mysterious warm and hot jupiters may have been coerced into very close orbits by big planets orbiting in a different plane.
When exo-planet hunting began in earnest decades ago with equipment that actually had the ability of finding one, there was much talk about finding rocky planets like the earth. We, of course, did not yet have the ability of finding earth twins as we do now. Earth-sized planets were simply too small to tug their parent stars in any discernible way. They were likewise too small to block enough of the light of their star in any way we could detect. Giant gas planets however had none of these problems and that is why they were the first exoplanets found.
The first one found orbiting around a main-sequence star is called 51 Pegasi b. This was a historical moment but, as often happens in science, this discovery raised a whole slew of new questions because 51 Pegasi b was not where it was supposed to be. It was in an orbit insanely close to its star, an amazing one eighth the distance that our own Mercury orbits the sun. Being so close, its annual trip around its star took a mere 4 days. These were dubbed Hot Jupiters for obvious reasons.
It clearly could not have formed there because the gas would have been far too thin in those environs for enough to accumulate around a gas giant. Theory says that the planet must form beyond the so-called frost line where temperatures are low enough for rock and gasses and ices to accrete onto these behemoths. From there they would have to migrate inwards towards the star. It was soon determined that gravitational interactions between the planet in these exo solar systems must be the most likely way to move one of these gas giants. But how does that work exactly?
Well, one way this could have happened was recently announced by researchers at the University of California at Berkley. They examined 6 exoplanetary systems, each with a Warm Jupiter and another large but more distant planet. Warm Jupiters are just what you might imagine. They are farther away than the hot ones but still within the frostline. For each system they ran a 1,000 simulations until they noticed a pattern. In those systems in which both planets were at an angle to each other (35 to 65 degrees), the outer large planet was able to gravitationally nudge the gas giant into a yet closer orbit. Over time, this process could eventually turn a warm jupiter into a hot one.
This is fascinating on multiple levels. First of all, it shows that a large planet orbiting in a completely different plane around its star could actually cause a gas giant to careen towards its star….and by careen I mean slowly move over many millions of years. Secondly, it shows that we may be a little biased in thinking that all or most solar systems are essentially flat discs in terms of planetary rotation. Clearly many if not most of them are but a surprising number may contain these oddball planets that don’t orbit the way the others do. How that happens is another mystery though it is likely caused by gravitational interactions that eject it into another orbital plane.
Finally, this is important not only because it could help elucidate the evolution of solar systems in general, it could actually help us determine the likelihood of life itself in this universe. After all, having jupiter-sized planets mowing down the inner terrestrial planets as it make its way to its sun is not very conducive to life.
Image Credit: ESA, NASA and G. Tinetti (University College London/ESA) )