What I Learned Today

Today I attended a fascinating talk by Dr. Michelle Thaller about the Spitzer infra-red telescope and the search for exoplanets. I love hearing about the ongoing discoveries of planets orbiting around other stars. This is cutting-edge observational science! The first exoplanet was detected in 1995; before that, they were only hypothetical.

Spitzer is an IR telescope that orbits the Sun, lagging behind the Earth in its orbit. This lets it observe out away from the IR signal of the Earth and Moon. Dr. Thaller opened the talk with some fun (and fascinating even if you’ve seen an IR camera before!) demos showing how in IR, you can see through some things (black plastic bags) but not others (optically transparent glasses). She noted that the Earth’s atmosphere is opaque in IR, which helps explain both the greenhouse effect and why you need a space-based telescope to observe the universe in IR. More than that, since dust is opaque optically but often transparent in IR, Spitzer has given us our first views deep into the center of our own galaxy (dust blocked optical telescopes’ view into the Milky Way). We subsequently learned that we live in a barred spiral galaxy (previously thought to be just a spiral).

Spitzer doesn’t have the resolution to pick out individual planets orbiting other stars, but it can detect a swept-out gap in a stellar disk that can indicate where a planet has formed. That can guide more detailed investigations for exoplanets, such as astrometry and radial-velocity studies. You can browse a catalog of discovered exoplanets, sorted by their method of discovery or an even more attractive atlas of the planets and their stars. We’re currently up to 326 (from 1, only 13 years ago!). You can follow along with the latest planetary discoveries at PlanetQuest, and even download a desktop/Dashboard widget tracking the exoplanet tally.

The talk was exceedingly well timed. Just yesterday, it was announced that the first ever images of exoplanets had been recorded: Fomalhaut b by Hubble and three planets around HR 8799 by ground-based telescopes Keck and Gemini, using adaptive optics (see more pictures here). The full scientific papers are available here (AAAS subscription needed for full text PDF):

• Optical Images of an Exosolar Planet 25 Light-Years from Earth by Kalas et al.
• Direct Imaging of Multiple Planets Orbiting the Star HR 8799 by Marois et al.

Despite this pile of planetary discoveries, the hunt is still on for “Earth-like” planets: similar to our home world in terms of mass, size, temperature, and atmospheric composition. It’s bound to happen soon!