The planetary system WASP-47 is highly popular at the moment, following the K2 discovery of two more transiting exoplanets, and the radial-velocity detection of a longer-period outer planet, in addition to the orginal hot Jupiter, WASP-47b.
But here’s an additional curiosity: WASP-47 is so close to the plane of our own solar system, aligned to better than 0.26 degrees, that Earth would be seen to transit from WASP-47!
Christopher Burke, of the SETI Institute, has produced this graphic of an Earth transit as seen from the location of WASP-47.:
And, supposing that the inhabitants of the WASP-47 system had a spacecraft like Kepler, this is what the transit they might record would look like:
Of course it is only speculation that there are inhabitants of WASP-47, though, with four planets known so far in the system, there might be some planet or moon that is inhabitable. If they had detected Earth, they might then point their biggest telescope at the next transit, and perhaps find free oxygen in Earth’s atmosphere, and so deduce that Earth has life.
Chris Burke suggests that WASP-47 is a very good SETI target; they might already know about us!