Earth is in sight of exoplanets

06/25/2021 at 8:00 AM CEST

New research has been able to determine that, if they existed, other civilizations in thousands of worlds beyond our solar system can see us and follow our evolution on Earth, using the same knowledge of the universe that we have.

Our Sun is just one of approximately 200 billion stars that exist in our galaxy. And we have discovered that there are also at least 3,200 planetary systems hidden in that myriad of suns that populate the Milky Way, around which 4,171 exoplanets swing.

The distances that separate us from these exoplanets, so called because they are located outside our solar system, are considerable: the closest, called Proxima Centauri b, is 4.23 light years from Earth, in the constellation Centaurus.

The most distant exoplanet known to date is called OGLE-2005-BLG-390Lb and orbits a sun that is 21,526 light years from Earth, in the constellation Sagittarius, near the center of the Milky Way. At the time of discovery it was the most Earth-like exoplanet.

We have known about them by regularly observing the brightness of the stars they orbit: at a certain moment they betray the passage of an exoplanet between us and that remote sun.

Reverse observation

Reverse observationNew research, developed at Cornell University, has calculated whether, in the same way that we have located exoplanets, any of them could have observed or be observing the Earth.

And the surprise has been great: it identified a total of 2,034 nearby solar systems, in a range of 326 light years from us, in which, if some of its exoplanets were inhabited and with a technology equivalent or superior to ours, someone could having realized that the Earth is inhabited by another civilization.

The Earth has been exposed to the observation of 1,715 star systems for 5,000 years (somewhat after the appearance of cities) and will be for another 319 more star systems in the next 5,000 years, according to the calculations of this research.

For this reason, if some civilization hypothetically inhabited one of those exoplanets, it would have had enough time to realize that we are here, and, if it has not already done so, it has plenty of time to realize it in the future.

Related Topic: The moons of nomadic exoplanets could harbor water and life

They can perceive us

They can perceive usAnother significant piece of information from this research: of the 2,034 solar systems identified, 117 of the best placed to observe us are less than 100 light years from Earth.

What’s more, 75 of those 117 solar systems are in the front row to see us in the best possible way since we began transmitting radio waves in 1879, a clear signature of our civilization that some exoplanets could have captured.

Forty-six of the exoplanets have even had an extensive observing time of ours in the last 100 years. However, 313 of them have lost the ability to image the Earth.

“Our analysis shows that even the closest stars generally spend more than 1,000 years at a vantage point where they can see the Earth’s transit,” explains one of the researchers, Lisa Kaltenegger, in a statement.

“If we assume the opposite is true, that provides a sufficient timeline for nominal civilizations to identify Earth as an interesting planet,” he adds.

Many possibilities

Many possibilitiesThis research concludes that in the vast majority of the 2,034 solar systems analyzed, the transits of the Earth could be detected today, with significant nuances.

In 66% of stars, observable Earth transits would last at least 10 hours, increasing the chances of detection. Only in 868 of those solar systems will it take more than 10,000 years before transits of our planet can be detected.

The conclusion of this research indicates, on the one hand, something that we had not realized: in the same way that we desperately search for signs of intelligent life inside and outside the solar system, other hypothetical civilizations could also be registering our presence in this corner of the Milky Way.

On the other hand, it also concludes that, wherever you look, the chances that someone outside our solar system could have noticed that we are here are really considerable, if intelligent life exists beyond our planet.

Another intelligence watching us?

Another intelligence watching us?A separate question is to know if in those privileged places to observe our planet there is a possibility that life exists. The researchers note that about 10 percent of the identified solar systems are similar to our Sun.

Another hundred stars are brown dwarfs, with little chance of harboring life (at least in the known way), since their habitable zone is very narrow. The rest are larger and smaller stars, including 75 white dwarfs, which are already in the terminal state.

On the exoplanets that orbit many of these stars, the authors of this research estimate that there will be more than 500 with the ability to be similar to Earth. And they highlight that seven stars, within the radius of 325 light years, have confirmed planets.


ReferencePast, present and future stars that can see Earth as a transiting exoplanet. L. Kaltenegger & JK Faherty. Nature volume 594, pages505–507 (2021). DOI: https: //

Top photo: Earth seen from within the Solar System. NASA / JPL-Caltech / Space Science Institute

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