Video: Watch the mysterious transit in action
The heavens have aligned in a way never seen before, with two exoplanets overlapping as they cross their star. The phenomenon is so new it doesn鈥檛 yet have a name.
of the University of Tokyo, Japan, and colleagues used data from the to probe KOI-94, a star seemingly orbited by four planets. A planet passing in front of a star, or transiting, causes the star鈥檚 light to momentarily dim: that鈥檚 how Kepler spots exoplanets. Two planets transiting at the same time dim the star even more, but if they also overlap there is a momentary increase in brightness as the planets cover less of the star.
This latter light pattern is exactly what Hirano鈥檚 team saw. It seems that one planet candidate, KOI-94.03, passed in front of the star and then the innermost candidate, KOI-94.01, passed between the two.
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As both candidates must still be confirmed, another explanation for the light show is that a single planet passed in front of a dark starspot. But there is no evidence for spots on the surface of the star.
Exosyzygy mouthful
The uncertainty hasn鈥檛 stopped speculation over what to call the event. Hirano favours 鈥減lanet-planet eclipse鈥�, but that implies the total covering of one body by another:
KOI-94.01 is thought to be larger than KOI-94.03, so parts of all three bodies were visible. Another option is 鈥渄ouble transit鈥�, but that can include cases where two planets don鈥檛 overlap.
For that reason, 鈥渙verlapping double transit鈥� is favoured by of the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, who in 2010 suggested looking for the light pattern that Hirano鈥檚 team has now seen. That鈥檚 a mouthful, but not as hard to say as his other suggestion, 鈥渆xosyzygy鈥�, a play on the general term for three celestial bodies in a row, 鈥渟yzygy鈥�.
Now that we have seen two planets lining up in front of their star, what are the chances of spotting three? 鈥淭hat is basically never going to happen,鈥� says Ragozzine. While Kepler has seen a few solar systems with three planets transiting simultaneously, the odds of them all lining up are extremely low.
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