Artist's concept of Titan surface beneath its foggy atmosphere. Courtesy NASA. Click to embiggenate.
Astronomer Mike Brown of CalTech (who tweets under the name PlutoKiller) has a fascinating discussion on his blog about fog banks hovering over Titan’s south pole. Titan, if you haven’t been following outer solar system news, is the largest moon of Saturn. It has this thick atmosphere hanging over a frigid surface which itself boasts pools of hydrocarbons in the form of liquid and ice. The hydrocarbons are in the form of ethane (on the surface) and now it appears that the methane forms fog banks in the atmosphere. Methane breaks down in the presence of sunlight to make ethane, so this whole thing seems to point to some sort of cycle between atmosphere and surface on Titan.
I say “seems” because, as Mike discusses, there’s a lot of atmospheric science work to be done to completely understand what’s happening on this shrouded world to make methane clouds form. Want to know more and see a cool pic? Run over to Mike’s blog and read what he has to say. He also has a link to his science paper outlining the fogbank on Titan and a nice, insightful discussion on peer review of his paper — and he invites folks knowledgeable in the Titan atmosphere to review his paper before it goes to publication. How cool is that!
So, did you see any Perseids last night? We went out after midnight and saw maybe 20 before the Moon’s brightness lit the sky up too much. There were several really bright blue-white ones flaring across the sky and a lot of smaller flashes that went by pretty quickly. Did you know that each time you see a meteor flare in the sky, you’re seeing the vaporization of something that likely formed well before the planets did? That may have been the leftovers of a stellar explosion long before our Sun was born? Meteors are usually always bits of dust and grains thrown off by comets as they round the Sun, or are the crumbs of ancient collisions between asteroids. Those crumbs and bits of dust are scattered along the comet’s path, and occasionally they intersect with Earth. Those that aren’t bounced off the top of the atmosphere come heading straight in. As these bits of cosmic debris blast speed through the air, they get heated and vaporized — giving off light in the process. That’s what we see as a meteor.
There’s debris scattered throughout the solar system, the leftovers from the formation of the planets, moons, rings, and Sun. Of course, it’s spread very thin — chances are if you were going through interplanetary space you’d encounter little of it, but it’s out there. However, when it encounters Earth, that’s when things get all flashy and bright for these little bits of dust. Think about that the next time you’re out stargazing and see that telltale flash of light go across the sky. You’re watching the demise of something that’s likely OLDER than this planet.
Planetary Billiards
Artists' impression of what the WASP-17 system might look like. Courtesy KASI/CBNU/ARCSEC (Click to embiggen.)
Speaking of planetary systems, there’s a new world joining the ever-growing list of exoplanets out there. A team of scientists from the United Kingdom’s Wide Angle Search for Planets (WASP) project and the Geneva Observatory Extrasolar Planet Search program announced today that they found a giant planet they named WASP-17. It’s orbiting around a star about a thousand light-years away. That in itself would be sort of ho-hum in these days of “oh, gee, there’s another planet out there — how about finding us an Earthlike one” attitude from the press — but this planet is orbiting is star the “wrong” way. That is, it’s in a retrograde orbit, moving opposite the direction of anything else that’s in orbit around the star. This is a big honkin’ clue that something happened to knock the planet out of the orbit it formed in and send it careening like a billiard ball off in an entirely different orbit. The best guess is that WASP-17 had a close encounter with an even bigger planet during the often-violent period of planetary formation around the star. It’s a dangerous time for objects orbiting newly formed stars — things smash into each other, forming larger planets or grinding smaller objects to dust.
Not only is this planet headed the wrong way, but it’s huge — and that’s also a clue to its violent experiences in the past. As it got shoved into its current highly elliptical retrograde orbit, WASP-17 experienced some intense tidal interactions (caused by the gravitational pull of the star, perhaps, and at least by nearby objects). Those tides alternately compress and stretch the planet, which has the density of polystyrene (think foam cups), which heats it up (same as at Io, the volcano world orbiting Jupiter here in our own solar system). Heating causes bloating, and voila — you get WASP-17.
This discovery doesn’t just tell astronomers about that particular system however — it also gives really good insight into what conditions were like when the Sun and planets formed 4 billion years or so ago. It wasn’t just a “here’s a Sun, here are some planets, now start evolving” kind of thing. The process is long, drawn out, involves lots of crashes of objects, and apparently, some cosmic billiards!
