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The search for alien life is something that has gripped the world for decades. While telescopes point up at the sky and scan the recesses of space, probes like Voyager 1 are traveling incredible distances in the hopes of finding extraterrestrial life. But where can such life be found? What are the ideal conditions for aliens to live in? And how similar would their planets be to ours?
Click through this gallery to find the answers hidden in interstellar space.
There are estimated to be up to one septillion stars in the known universe (that’s a one followed by 24 zeros!). And each of these stars could potentially have a dozen planets orbiting. So, how can we find alien life? The first step is to look closer to home.
The Earth is pretty much the perfect place to live, astronomically speaking. The existence of water and a stable atmosphere has created an ideal environment for life to thrive.
The distance of a planet from its star is crucial in understanding a planet’s viability in supporting life. Earth is located perfectly in what is called the Habitable Zone, where conditions are neither too hot, nor too cold to support life.
The Habitable Zone is also called the Goldilocks Zone, named after the fairy tale. In the story, Goldilocks chooses between three sets of items and ignores the ones that are too extreme (large or small, hot or cold), instead settling for the one that is “just right.”
Venus, which is similar to the Earth in mass, is too close to the Sun to be viable for life. Planetary scientists believe that Venus may have had surface water once, but the planet is now choked by carbon dioxide and a temperature of 864°F (462°C).
Mercury is even closer to the Sun than Venus, not to mention that it is too small and doesn’t even have an atmosphere to support life.
By understanding the criteria for the Goldilocks Zone, astronomers were able to figure out that there could be as many as 40 billion planets orbiting in habitable zones of the Milky Way.
So far, astronomers have only been able to confirm 1,780 planets beyond our solar system. And of those planets, only as many as 16 are located in their respective habitable zones.
In order for atmospheric pressure to be just right, a planet will need to be between 0.1 and 10 times the Earth’s mass. This is a very narrow habitable zone, especially when you consider how many planets in the universe are hundreds of times bigger than ours.
In 2007, the scientific community was abuzz with news of Gliese 581c, the first Super-Earth in the Goldilocks Zone. However, it was soon discovered that the planet’s surface conditions were brutally similar to Venus.
An Earth-sized exoplanet by the name of Kepler-186f was discovered in 2014, orbiting in a red dwarf star’s habitable zone. Astronomers are still trying to determine whether the planet can support life.
The closest exoplanet to Earth is Proxima Centauri b, which is in orbit around the closest star to the Sun, about four light years away. But although it is a Goldilocks planet, scientists are unsure whether it has an atmosphere.
Although a planet’s Goldilocks zone and atmosphere are important in understanding its habitability, this isn’t where it ends. Planets must meet a plethora of other criteria, including the ability to sustain liquid water.
Mars is the only other planet in our solar system that is within the habitable zone. But the right atmospheric pressure can only be found at the planet’s low elevations, and there has been no confirmation that the planet has any liquid water.
Hypothetically, dry planets could retain water via oases, which would mean that such planets can orbit closer to a star and outside the Goldilocks Zone.
It has been theorized that Earth’s oceans came into existence after icy bodies impacted our planet and subsequently melted. Other such planets could exist.
Planetary natural satellites, or moons, could also potentially be habitable. But these moons must be located within the Goldilocks zones of their host planets, and they must orbit far enough that they do not become volcanic worlds like Jupiter’s moon Io.
Jupiter’s fourth-largest moon, Europa, is thought to be home to a water ocean trapped beneath the planet’s surface, which could potentially harbor alien life.
Earth’s magnetic field is an example of another important criterion that determines the viability of life, as it shields the planet’s surface from radiation and cosmic rays. Other planets would need a similar field to allow complex life to flourish.
To date, astronomers have been unable to find any star that matches the Sun, a phenomenon called a solar twin. This has created much difficulty in the scientific community in finding extraterrestrial life that is similar to ours.
But what types of alien life could we potentially find? It has been largely accepted that carbon-based lifeforms are the only viable ways in which life can exist.
Many scientists have criticized the idea that alien life must be constructed from carbon. Hypothetically, extraterrestrials could be made up of vastly different elements that allow them to survive in places that are inhospitable to humans.
Saturn’s largest moon, Titan, is home to hydrocarbon lakes that could potentially support life. Titan is the only other object in space that has been discovered to have surface liquid.
Physicist Enrico Fermi (1901–1954) theorized that we haven’t encountered alien life because intelligent life is either rare or only just emerging in the universe.
Other physicists have claimed that we haven’t encountered alien life because we’re late to the party. Essentially, they say that extraterrestrials have mostly died and the universe is expanding too far for us to find their remains.
Many anthropologists and astronomers believe that humankind is alone in the universe because of the Great Filter. Basically, there are so many improbable steps for life to evolve intelligence that it is unlikely to occur again.
Other scientists have hypothesized that extraterrestrial life does exist, but they are avoiding humanity in order to allow our primitive existence to unfold without intervention. Either way, space is a large frontier that may very well hold alien life.
In April 2025, astronomers have uncovered the strongest evidence to date of possible extraterrestrial life. Using the James Webb Space Telescope, they detected two specific gases in the atmosphere of exoplanet K2-18 b. These gases, found thanks to the telescope's advanced instruments, are known on Earth to be produced solely through biological processes, typically by microscopic marine organisms like phytoplankton. Researchers emphasized that while the discovery is promising, it does not confirm the presence of actual living organisms. They caution that further observations are needed to verify the findings and rule out non-biological explanations. Still, the detection marks a significant step forward in the search for life beyond Earth.
Sources: (National Geographic) (NASA) (Astronomy.com) (Earth How) (Harvard John A. Paulson School of Engineering and Applied Sciences )
See also: The greatest discoveries and advancements in the history of astronomy
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LIFESTYLE Astronomy
The search for alien life is something that has gripped the world for decades. While telescopes point up at the sky and scan the recesses of space, probes like Voyager 1 are traveling incredible distances in the hopes of finding extraterrestrial life. But where can such life be found? What are the ideal conditions for aliens to live in? And how similar would their planets be to ours?
Click through this gallery to find the answers hidden in interstellar space.