Artistic recreation of an alien landscape. (Creative Commons image seen on Wikimedia – credit Daampjeee).
In this blog I have spoken countless times about exoplanets, or planets that orbit stars other than the sun. As a good fan of astrobiology, I have followed the progress of our astronomers in inferring the presence of other nearby worlds, in the hope that one would be capable of supporting life as we know it.
The golden age came with the performance of the Keppler space observatory, which in the short time in which it remained operational was able to discover thousands of exoplanets. Now, we all hope that the James Webb Space Telescope will finally be launched into space later this year (if it doesn’t suffer further delays) and that its incredible potential will help us study the atmospheres of some promising worlds in our neighborhood.
But today I come to tell you about an exercise totally contrary to our search for habitable worlds in the galactic proximity. Indeed, a couple of scientists (the astronomer Lisa kaltenegger and the astrophysicist Jackie Faherty) have joined forces to try to find out which of the exoplanets closest to Earth would be a good vantage point to observe us using the transit method. That is, for what living beings could we be aliens?
In order not to make the job too big and complicated, Kaltenegger and Faherty decided to narrow the search for nearby star systems to a distance of 100 parsecs around. With the help of the European Space Agency’s Gaia catalog – a highly accurate database that stores the positions and motions of nearly 1.7 billion stars in the Milky Way – the pair of scientists identified 1,715 nearby star systems, from which any well-equipped alien astronomer could have observed Earth transiting the surface of the solar disk for the past 5,000 years.
Among all these exosystems stood out 46, because it is close enough to Earth to be able to clearly intercept a technological signal of human origin. It should be remembered that these signals, in the form of radio and television broadcasts, began to reveal our presence in the cosmos 100 years ago.
But they didn’t stop there. The pair of researchers continued to filter information until they reached a number of nearby worlds, with potential for life, from which they could have observed the terrestrial transit and captured our radio emissions. Outcome? According to your estimate there are a total of 29 worlds within that circle of 100 parsecs around our solar system, from which so-called technologically advanced aliens could have observed us and inferred our presence. All hypothetically clear!
Among those 29 worlds aspiring to be an alien observation tower from which to spy on us, stands out a red dwarf in the constellation Virgo called Ross 128, which is “a stone’s throw away” on the galactic scale, just 11 light years away. This star is known to have a planet with an approximate mass of two earths. Any well-equipped astronomer in this world could have observed our passage in front of the sun for 2,000 years. Curiously, for 900 years our hypothetical astronomer would have lost his observation window, when varying our relative positions.
Other worlds to highlight are the two that orbit the star Teegarden, another red dwarf located about 12.5 light years away, in the constellation Aries. Although currently the transit of the Earth is not visible from both exoplanets, in just 29 years the situation will change, placing the hypothetical Teegardenian astronomers in a privileged position to spy on us.
Finally, it would be convenient to talk about another family of candidate exoplanets to be a point of observation for humans. We refer to the seven worlds that orbit the star Trappist-1 (an ultra-cool dwarf star located 39.13 light years away in the constellation Aquarius). We know that at least four of them are within the habitable zone, although according to Kaltenegger and Faherty, the hypothetical alien astronomers of these worlds will have to wait 1,642 years for our positions to vary, allowing them to observe the transit of the Earth in front of the sun. .
I recognize that there will be those who consider these astronomical exercises somewhat useless. After all the various SETI projects that scientists have carried out have never discovered man-made radio emissions reaching us from nearby stars. Even so, I find them interesting because they give us useful information for future observing missions, such as the one to be undertaken shortly by the aforementioned James Webb Space Telescope.
Can you imagine what we would feel observing another intelligence that in turn observes us?
Kaltenegger and Faherty’s work has been published in Nature.
I found out by reading The Guardian