Direct imaging of planets: Harder than it sounds

In the deeps of space there are millions of unknown stars and planets, billions of secrets, and an untold wealth of knowledge waiting for us; the only hard part is discovering them. Recently several new planets have been discovered using a less-common technique of imaging stars and planets: direct imaging.  Now to the lay-person, direct imaging seems like the most reasonable way to discover things. Just take a picture of it right? Wrong. It's extremely hard to pinpoint an area to study, because space is HUGE. It's nigh on impossible to sift through everything with a fine-tooth comb, so other methods like infrared telescopy are used, because the heat released by stars and very large planets shows up clearly in the IR spectrum.

3 massive planets found via direct imaging link

The problem with IR telescopes is that small things like planets don't show up because they don't emit enough heat to show up on the telescope. Huge planets and more recently formed planets may emit a discernible amount of IR radiation, but most smaller or older planets don't emit IR waves at a level that can be picked up by current technology. This means that other planets are found through indirect data, and it only works for planets closer than 5 astronomical units (AU) to their parent stars.

Cue direct imaging.  Direct imaging is used when the planets are outside of the bounds of IR telescopy. The most common way of using a telescope for direct imaging is by employing a coronagraph. Coronagraphs filter out the light from a star, letting a telescope detect everything around the star without being obscured by the glare from the star. Simple ones can be made from a disc cut from a piece of cardboard and held in front of the sun to block it. For purposes of finding planets, there are much more sophisticated methods of blocking light, but the same general logic applies.

Coronagraph of the sun link

Using direct imaging, scientists in 2010 were able to accurately record 3 planets orbiting around star HR 8799. This is great news, because it offers definitive proof that many other stars have planetary systems, and it proves that vortex coronagraphy is a useful tool to be used on other systems. Using direct imaging, we may be able to find closer planets or planets that more closely resemble Earth. Direct imaging is a powerful tool and using it will hopefully allow scientists to find planets all throughout the universe. If we keep our fingers crossed, maybe one of those planets will support life.

Expected motion of 3 planets compared to Jupiter, Saturn, Neptune & Pluto link

Here's a link to the research article from the team that found these planets.
Science 28 November 2008: 
Vol. 322 no. 5906 pp. 1348-1352

- Colin Downs