Transiting Earth could be detected from nine exoplanets

Numerous exoplanet discoveries with this method have led scientists to question whether hypothetical alien civilizations with the same technological level as Earth could detect our planet passing in front of the Sun.
By Laurel Kornfeld | Sep 13, 2017
A group of scientists interested in determining how many hypothetical alien civilizations might be able to locate Earth using the transit method found just nine out of the 3,000 plus exoplanets discovered since the 1990s favorably positioned to find our planet.

The transit method is an indirect way to discover exoplanets, or planets orbiting stars other than the Sun. Because most of these cannot be directly imaged, scientists search the for regular dimming of stars' light that indicates the passage of an orbiting planet.

Each passage of a planet across the face of its star is described as a transit. Three transits occurring at regular intervals are required to confirm a planet's presence in orbit around the star.

Numerous exoplanet discoveries with this method have led scientists to question whether hypothetical alien civilizations with the same technological level as Earth could detect our planet passing in front of the Sun.

Robert Wells of the Astrophysics Research Center at Queen's University Belfast, lead author of a paper on these findings published in the journal Monthly Notices of the Royal Astronomical Society, said smaller planets, such as the terrestrials in our solar system, could be more easily seen transiting the Sun than large gas giants.

"...Since the terrestrial planets are much closer to the Sun than the gas giants, they'll more likely be seen in transit," he noted.

No alien observer using our current level of technology would be able to detect any more than three planets orbiting the Sun, co-author Katja Poppenhaeger, also of the Astrophysics Research Center, stated.

"We estimate that a randomly positioned observer would have a one in 40 chance of observing at least one planet. The probability of detecting at least two planets would be about 10 times lower, and to detect three would be a further 10 times smaller than this."

Just 68 known exoplanets are in positions from which inhabitants could detect between one and three planets orbiting our Sun. Of those 68, only nine planets, none of which are considered habitable, are in positions from which transits of Earth would be visible.

The researchers believe there are about 10 undiscovered, habitable exoplanets from which transits of Earth could be seen and plan to search for these worlds as a next step.

 

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