2023-04-25 10:37:29
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 would have a very, very difficult time discovering our world with the radial velocity method. But let’s think about the most fruitful procedure to date, that of transits or eclipses. Would it serve to find our planet from the depths of space?
Eclipses interestelares
The photometric, or transit, method only works when, by chance, the orbital plane of the planet coincides with the line of sight. In that case the planet passes its star at each turn, a transit takes place, and this causes a very faint eclipse, a drop in apparent brightness that might or might 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 very 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 data must be accumulated over several orbital periods to confirm the planet’s existence, so it would take at least two years 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 occupy a very short 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 photometry have been announced that 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 that, in case if successful, it will be a huge breakthrough 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 steps, it could take one in two hundred civilizations more or less five years to capture the photometric signal of our transits before the Sun using an instrument like Plato.
Now, if they detect us, would they know if our world is habitable?
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