Exoplanet scientists and enthusiasts spend a lot of time trying to find, measure and understand distant planets that can — under specific conditions — be detected as passing in front of their host star. A majority of the 4000-plus exoplanets discovered so far were indirectly detected this way, by measuring the diminishing of stellar light as the exoplanet passes between the star and us.
In a conceptual turnaround, two researchers have now asked the question of how common it might be for beings on distant exoplanets to be able to similarly detect and measure Earth as it transits in front of our sun.
Astronomers call this special vantage point in space – the point from which Earth transits can be seen – the Earth transit zone. Because the cosmos is dynamic and ever-changing, they looked for not only stars that are in that zone now, but have also passed through over the past 5,000 years and will in the next 5,000 years.
“From the exoplanets’ point-of-view, we are the aliens,” said Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell University.
“We wanted to know which stars have the right vantage point to see Earth, as it blocks the sun’s light. And because stars move in our dynamic cosmos, this vantage point is gained and lost.”
How many stars (and their orbiting planets) have this proper vantage point, have had in the past and will in the future?
In Kaltenegger’s paper, published in Nature with Jackie Faherty of the astrophysics department of the American Museum of Natural History, the numbers reported are quite low.