Searching for exoplanets is like trying to spot the Invisible Man: Since you can't actually see him, you have to look for clues he's left in the spaces he passes through. Astronomers have gotten pretty good at this: With nothing but shadows and gravitational traces to go on, they've picked out more than 450 planets beyond our solar system.

Now astronomers are targeting an even slipperier quarry: all-but-undetectable Earth-sized planets orbiting near the Jupiter-sized ones they've already fingered. They've found the Invisible Man; now they're looking for his invisible dog.

This morning, at the Boston meeting of the Division of Dynamical Astronomy, invisible dogs were barking out of every PowerPoint. Here's the idea: A planet casts a shadow as it passes between its star and the Earth. If the planet circles the star every five days, for example, telescopes back at Earth will see that the star dims every five days, like clockwork. But if astronomers could measure the timing more closely, to within a few minutes or even seconds, they might find that the timing isn't quite perfect. Because maybe--just maybe--there's another unseen planet (pdf) in the system that is changing the course of the shadow-planet's orbit. 

Planet-hunters call those orbital glitches "transit timing variations," or TTVs, because astronomers love acronyms. Some planetary systems might have TTVs big enough to show up in data from telescopes like Kepler, but it will take a little luck: the biggest signals should come from planets orbiting in the same plane, and the TTVs get an extra boost when the time it takes one planet to orbit is a tidy ratio of the time it takes for the other planet to circle round.

Astronomers haven't discovered any "invisible dogs" this way yet, but Kepler is perfectly positioned to catch the first one. Stay tuned!

User Comments:

Hello, I am new to twitter, and recently began researching (sciences) privately and in school, I am premajoring in a Tech. School then transfering for a bach. in Meteoroligcal/Atmosphere (UNCC). I'm looking to make long term science friends to chat with and learn from.

The following explains my passions:

"Sciences of my planet to improve the future of mankind is my desire, while Sciences of the Cosmos is my sarcastic grin; while enjoying play time" ...

I believe that the chances for life on other earth like planets. would have to be more than we think, for little is really known how other galaxies operate.
Although most galaxies seem to be spiral or eliptical, with some to be coliding galaxies,(irregular) we barely have cracked the surface of how our galaxy operates.
The reason I am saying this, 500 years ago, humans thought they knew everything (gods, climate in scale, stars, and everything else imaginable). What's to say 500 years from now, we understand dark matter, smbh(super massive black wholes) more in depth, find more moons that could be habitabal, (maybe even more than earth like planets) and understanding if the galaxy expands, then someone (or something) has a jump start in techology and we may one day get to find out :)

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