Could an extraterrestrial civilization endowed with technology similar to ours have detected or be about to detect the Earth by the transit method?
An alien civilization with technology similar to ours would be unable to detect Earth by direct imaging. that same civilization I have it very, very difficult to discover our world with the method of radial velocity. But we think of the most fruitful procedure to date, that of transits or eclipses. Would it serve to find our planet from the depths of space?
interesting eclipses
The photometric method, or of transits, it only works when, by chance, the orbital plane of the planet coincides with the line of sight. In this case, the planet passes before its star at each turn, a transitand this causes a very faint eclipse, a drop in apparent brightness that may or may not be detected.
Extrasolar planetary systems have randomly oriented orbital planes, and therefore for a planet to transit its star on every turn as viewed from the Solar System would seem a highly unlikely coincidence by this method.
To the previous difficulty is added that of the period. A signal that is repeated every four days, like Dimidio’s, is more likely to be picked up. But you have to accumulate data over several orbital periods to confirm the existence of the planet, so it would be at least two years away for Earth and well over twenty for Jupiter.
In addition, in those very long time intervals, in which continuous observation would have to be maintained, the transits occupied a brief fraction. For the aliens, the Earth would cross the solar disk in less than 13 hours and Jupiter in a day and a quarter.
The terrestrial planets detected up to now by the transit method have been found around stars much smaller than the Sun, which greatly increases the depth of the eclipses until bringing it within the range of sensitivity of current instruments.
Plato!
But advances in space photography have been announced, which should make it possible to capture the photometric signal due to the eclipse caused by planets similar to Earth when they transit before stars similar to the Sun. These improvements are being implemented in a space mission of the European Space Agency which, if successful, will mean a huge advance in the search for worlds like Earth: the satellite Plato.
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The dish should fly in the year 2026 and aims for a photometric precision of 34 ppm. This puts at your fingertips a not inconsiderable sample of stars like the Sun around which worlds similar to Earth could be found. If alien technology follows our lead, it could take one in two hundred civilizations a brightness or so to pick up the photometric signature of our transits across the Sun using an instrument like Plato.
Now, if they detect us, would they know if our world is habitable?