Back in January of 2010, the Kepler Space Telescope was checking out a four-planet system called KOI-94, when it noticed something weird. Additional observations and recent analysis suggest that what Kepler saw was a double exoplanet transit, and since nobody's ever seen this before, astronomers have had to invent a brand new term to describe it: behold, an exosyzygy.
A syzygy (which as far as I can tell is pronounced exactly how it's spelled) is an alignment of three celestial bodies in a row. It's most commonly used to refer to eclipses: when you've got the Earth, Moon and Sun all lined up to make a solar eclipse or a lunar eclipse, that's a syzygy. An exosyzygy is the same thing, except with exoplanets lining up around alien stars.
The Kepler telescope is specifically designed to spot exoplanet eclipses. This is, after all, how it finds exoplanets: it looks for changes in brightness when exoplanets pass in front of, or behind, their stars. When an exoplanet passes between its star and the telescope, for example, there's a small drop in brightness, and Kepler can detect that. Apparently, what Kepler saw around KOI-94 was a drop in brightness, followed by another drop in brightness, followed by an increase in brightness, another drop, and then two more increases. That's some serious weirdness, but here's what astronomers think was going on:
- An exoplanet passes in front of the KOI-94 star, and the star dims slightly.
- A second exoplanet also passes in front of the KOI-94 star, and the star dims even more.
- The second exoplanet passes behind the first, and the star brightens a little bit, since there now appears to be just one exoplanet in between us and the star.
- The second exoplanet comes out of eclipse, and the star dims.
- Both planets pass out from in front of the star, and the brightness bumps up twice, back to normal.
And here's what the light curve looks like:
You could also call this phenomenon an "overlapping double transit," if you want to be all boring about it.
We should mention that these exoplanets have not been confirmed to be, you know, exoplanets, so there's still a possibility that there might just be one planet and some darker sunspots that are fooling us into having to make up awesome new words. But an exosyzygy does seem to be the most likely explanation, and we're in favor of anything that will help us win at Scrabble.