Aliens are closer than ever: There are habitable planets located less than 20 light-years away from us.

HD 20794 d is the name given to the planet located in the constellation Eridanus. It is situated 19.7 light years away and lies within the habitable zone of its star—meaning it is at a distance where conditions are warm enough for liquid water to exist on its surface. Evidence supporting the planet's existence has been presented by a large international team of scientists (47 members, including some of our compatriots) in a scientific article recently published in the journal Astronomy & Astrophysics (A&A).

Dr. Michael Cretignier from Oxford University, who discovered initial hints of HD 20794 d's existence back in 2022, describes the planet as potentially habitable—at least theoretically, but with considerable confidence. Uninvolved astronomers have classified this discovery as "momentous," suggesting it raises hopes that we may soon be able to not just reach extraterrestrials, but actually observe them. HD 20794 d is located practically next door—in cosmic terms, of course.

If neighbors are within 20 light years, powerful next-generation telescopes will allow us to see them. If not the beings themselves, then at least signs of their existence.

The chances that the newly discovered planet is indeed habitable are quite promising. The star it orbits resembles our Sun—somewhere between G and M types. Such stars typically exhibit stable behavior, unlike red dwarfs, which have recently been found to host planets within their habitable zones.

Red dwarfs have created life-sustaining conditions on planets located very close to them—small, dim, and relatively cool stars. On some of these "close" planets, a year lasted only a couple of Earth weeks. However, that isn’t the main concern. Most red dwarfs exhibit very erratic behavior, periodically emitting flares of tremendous power. Life cannot withstand such torrents of lethal radiation—even an atmosphere and protective magnetic field cannot save it.

The star around which HD 20794 d orbits has not been observed exhibiting such erratic behavior; it is roughly the same distance from the planet as the Earth is from the Sun—on average, a bit more. A year on this planet lasts 647 days, which isn’t exceptionally long. The catch is that HD 20794 d follows an elongated elliptical orbit, bringing it alternately closer to the outer and inner boundaries of the habitable zone—subjecting it to cold winters and scorching summers. Frigid temperatures, akin to those in Yakutia, can suddenly give way to sweltering heat.

The green disc represents the habitable zone. The planet oscillates between "heat" and "cold," approaching and retreating from its star.

Approximately two-thirds of the year on HD 20794 d is quite comfortable, but for humans like us, it would be challenging. Literally. Scientists have determined that the planet has a mass equivalent to six Earths—such planets are referred to as super-Earths. The exact diameter in comparison to ours is still unknown, as astronomers have yet to ascertain that. However, it is safe to say that there would be ample space for several civilizations like ours.

The conclusions were drawn from analyzing data obtained using the HARPS, ESPRESSO spectrographs, and the TESS space telescope.

The HARPS (High Accuracy Radial Velocity Planet Searcher) is installed at the European Southern Observatory in Chile. It searches for planets by detecting anomalies in stellar motion. If a star has planets, their gravitational influence causes the star to wobble. The star’s speed changes, and these fluctuations are precisely recorded by the detector. The current accuracy allows for the detection of planets smaller than Earth—HARPS responds to changes in the star's speed of just 30 centimeters per second.

HD 20794 could be a desert planet—like Dune. And habitable, like it.

Photo: Shutterstock.

ESPRESSO (Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations) operates in a similar manner. This instrument is even more sensitive, with improved spectral resolution—it works in conjunction with the Very Large Telescope (VLT) in Chile. It specifically searches for rocky exoplanets.

The TESS (NASA Transiting Exoplanet Survey Satellite) space telescope detects changes in the light of stars, whose brightness diminishes when planets transit across their disks—if such planets exist, of course. Scientists carefully analyze the parameters and, upon confirming the "discovery," begin to investigate what the identified planet is like.

BY THE WAY

Extraterrestrials can be comfortable even in deserts

HD 20794 d may very well resemble the desert planet Arrakis from the sci-fi blockbuster "Dune," adapted from Frank Herbert's "Dune Chronicles." And that would be great. This would further enhance the likelihood that the discovered planet is habitable.

Desert planets can be quite suitable for life. This conclusion was reached by Kevin Zahnle from NASA's Ames Research Center and Yutaka Abe from the University of Tokyo, as reported in the journal Astrobiology.

Scientists modeled the climate on planets larger than Earth. Without altering the atmosphere or the length of days, they removed oceans and vegetation from the surface, leaving deserts with oases and hiding water underground—just like on Arrakis.

The result showed that the habitable zone of "desert" planets could be three times wider than that of planets like ours, which have abundant liquid water on their surfaces. Additionally, these planets may be more reliable and stable in terms of climate response to cosmic whims.

Scientists determined that a "water" planet (like ours) would turn into an icy sphere if its "heating" level dropped to 72 percent of what Earth currently receives from the Sun. In contrast, a "desert" planet could sustain life even if the heat flow fell below 58 percent.

Conversely, what if "heating" increases? Water would evaporate from the coldest areas of a "water" planet—the poles—if the energy flow from its star reached 135 percent. A "desert" planet would retain liquid water at its poles even when the energy level is at 170 percent.

In other words, the elliptical orbit of HD 20794 is not as critical as it may seem. "Desert" planets can support life, whether they are farther from their star or closer than we currently imagine.