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I'm an ex-NASA scientist - these are the planets where alien life really could exist
A water world ruled by octopus-like creatures.
A planet divided by light and dark where the sun never rises.
And a lava hell where molten rock rains from the sky.
These are not descriptions of foreign worlds in science fiction novels, these are some of the 'exoplanets' most likely to be harboring aliens right now.
Dozens of these exoplanets - planets that orbit stars outside our solar system - which have been classified as 'potentially habitable' or 'Earth-like' have been documented in tantalizing detail in a new book.
Humanity is in a 'new golden era of exploration,' according to Dr. Lisa Kaltenegger, whose new book explores what science now knows about how distant worlds in our galaxy could support life. Above an artist envisions Proxima Centauri b - a planet where the sun never rises or sets
One of our solar system's nearest neighbors, the star system Proxima Centauri is just 4.25 light-years away. It's 'most likely to be habitable' world, Proxima Centauri b (illustrated above), is tidally locked with its host star, preventing the rotational day to night cycle we know on Earth
In 'The Worlds That Shook Science', by Dr. Lisa Kaltenegge, a former NASA mission reviewer, writes that astronomy breakthroughs in the past three decades have meant we are living in 'a completely new golden era of exploration'.
Since 1992, when the first exoplanet was discovered, there have been 5,000 more confirmed in our galaxy alone.
Of them, 70 have just the right ingredients for life to exist.
Given that some of them are 17,000 lightyears - which would take 6.9 million years to get to on the fastest man made machine, NASA’s Juno probe - Dr Kaltenegge says humanity's next challenge will be to summon the creativity needed to actually detect and communicate with alien lifeforms.
'I hope to convey just how difficult the search for alien life will be,' Dr. Kaltenegger writes in her book. 'We might not even recognize it when it is staring us in the face.'
A staggering 5,000 planets outside of our solar system have now been discovered, since the first of these 'exoplanets' — a Jupiter-like gas giant named 'Dimidium' — was first documented in 1992.
'Solving the puzzle of these new worlds requires using a wide range of tools like cultivating colorful biota in our biology lab [...] and reaching back into the long history of Earth's evolution for clues on what to search for,' she explained.
Dr. Kaltenegger, who is also the founding director of the Carl Sagan Institute at Cornell University and professor, said Earth will have to become 'our laboratory' as we test new ideas about how life could evolve differently out in the galaxy.
Right now, according to the University of Puerto Rico's Planetary Habitability Laboratory, 29 of the rocky exoplanets identified are the most likely to support life, or at least life as we know it on Earth.
Roughly another 41 more, astronomers report, appear to be 'water worlds' — or mini-versions of our own solar system's planet Neptune — making them each possible, but less likely, candidates for alien life as well.
NASA's massive, $10 billion James Webb Space Telescope (JWST), which launched in 2021 and collects light from distant space with a mirror over six-times the size of its famous predecessor, Hubble, has led to a bonanza of these new exoplanet discoveries.
'The JWST is the first telescope capable of capturing just enough light with its 21.3-foot (6.5-meter) mirror to explore the chemical composition of the atmosphere of other rocky worlds,' Dr. Kaltenegger told Big Think.
'Size,' she noted, 'is the key to collecting light.'
'Imagine a bucket: the larger it is, the more rainwater it can catch [...] The telescope's mirror operates the same way: the larger it is, the more light it can collect.'
According to Dr. Kaltenegger, signs of extraterrestrial life on other world's are 'written in a planet's light—if you know how to read it.'
As the light from distant stars pass through or bounce off an exoplanet's atmosphere, as she put it, 'the chemical makeup of the atmosphere of an alien world is encoded in the light that arrives at my telescope.'
Most distant planets, like that lava world, CoRoT-7 b, 489 light-years from Earth, would be too punishing in its endless magma heat to ever support life.
But here are just three of the distant star systems whose exoplanets have offered teasing clues in their light that they may hold undiscovered extraterrestrial life.
'Orange dwarf' star Kepler 62 (above), roughly 980 light-years from Earth, has at least two likely water worlds orbiting around it: Kepler 62-e and Kepler 62-f. According to a 2015 NASA report, Kepler 62-f is one of the 'most promising planets discovered' for supporting ET life
Kepler-62 - a star system of global oceans
'Life that never left the oceans could be fascinatingly weirder than we could ever imagine,' Dr. Kaltenegger writes in 'Alien Earths.'
And the 'orange dwarf' star Kepler-62, roughly 980 light-years from our solar system, has at least two likely water worlds orbiting around it: Kepler 62-e and Kepler 62-f.
Both exoplanets are between the sizes of Earth and Neptune, with Kepler 62-f being one of the 'most promising planets discovered' for supporting extraterrestrial life according to a 2015 NASA research document. But what might live there?
'The octopus-like creatures, heptapods, envisioned in the Ted Chiang's 1998 science-fiction novella Story of Your Life, the basis of the 2016 movie Arrival, cross my mind when I think about large ocean worlds,' Dr. Kaltenegger said.
In the 2016 sci-fi drama, from director Denis Villeneuve of this year's blockbuster Dune adaptation, tall, tentacled alien creatures teach a human linguist played by Amy Adams a language that literally changes her perceptions of space and time.
'The octopus-like creatures, heptapods, envisioned in the Ted Chiang's 1998 science-fiction novella Story of Your Life, the basis of the 2016 movie Arrival, cross my mind when I think about large ocean worlds,' Dr. Kaltenegger said of exoplanets Kepler 62-e and Kepler 62-f
In the 2016 sci-fi drama, from director Denis Villeneuve of this year's blockbuster Dune adaptation, tall, tentacled alien creatures teach a human linguist played by Amy Adams (pictured above) a language that literally changes her perceptions of space and time
Any advanced beings on Kepler-62's water worlds would mostly likely be equally trippy and mind-expanding, according to Dr. Kaltenegger, although she is skeptical about their ability to master space travel like the beings in Chaing's story.
'Life on these worlds would be under water with no easy access to metals, to electricity, or fire for metallurgy,' she said soon after NASA's Kepler space telescope first discovered the worlds.
'Nonetheless, these worlds will still be beautiful blue planets circling an orange star,' the astrophysicist added, 'and maybe life's inventiveness to get to a technology stage will surprise us.'
Even without advanced spacefaring life, Dr. Kaltenegger holds out hope that the Kepler-62 worlds may one day be excellent human tourism destinations.
'These worlds could be some of the best surfing spots in the cosmos,' she said.
Just 40 lightyears away from Earth, a tightly packed cluster of exoplanets circling the red sun Trappist-1 appears to have three neighboring worlds nestled within its 'habitable zone' - and they all could support life, according to Dr. Kaltenegger. Above, Trappist-1 by a NASA artist
Trappist-1 - sunset worlds of glowing algae
Just 40 lightyears away from Earth, a tightly packed cluster of exoplanets circling the red sun Trappist-1 appears to have three neighboring worlds nestled within its 'habitable zone' — and they all could support life, according to Dr. Kaltenegger.
'How much farther along our space-travel capacity would be,' she wonders in Alien Earths, 'if there was another habitable world orbiting our Sun, let alone several.'
Of the seven exoplanets closest to Trappist-1, named Trappist-1b through Trappist-1h, two have most caught the attention of astronomers for their mild temperatures and other 'just right' characteristics: Trappist-1e and Trappist-1f.
With a mass just under 70 percent the size of Earth, Trappist-1e orbits its sun from just 2.7 million miles away — a mere fraction of the 93.6 million miles between Earth and the sun.
Trappist-1f, which is just four percent larger than Earth orbits the star from not much farther out, just 3.6 million miles away.
These alien worlds orbit so close to Trappist-1 — a so-called 'ultracool dwarf star,' whose light is 2,000-times dimmer than our own sun — that one year's around the star only takes a few days.
A 'year' on Trappist-1e is not even a full week, just 6.1 days, a little longer than a year on Trappist-1f, which takes 9.2 days to complete its orbital cycle.
'This planetary system is so tightly packed that planets Trappist-1d and Trappist-1f would both appear as large as our moon in the night sky of the middle planet Trappist-1e,' Dr. Kaltenegger said, likely becoming cultural touchstones for any alien civilizations millennia before they could come to meet their nearest alien neighbors.
Some scientists, in fact, think there's a solid chance that alien life on Trappist-1e could be studying our own planet from a distance, if they had telescopes in operation as sophisticated as NASA's James Webb telescope.
Johns Hopkins University astrobiologist Jacob Lustig-Yeager and his colleagues poured atmospheric data about planet Earth into a simulation of the distant, watery exoplanet and found that an alien version of the JWST could likely detect mankind.
Even from their perch 40 light-years away, just such a telescope launched into orbit by aliens on TRAPPIST-1e could pick out light-signatures of molecules in our atmosphere that indicate technologically advanced life: specifically, pollutants.
'Chlorofluorocarbons (CFCs),' Lustig-Yeager and his team wrote in their paper, 'have been proposed as technosignatures due to their many industrial applications and infamy catalyzing the destruction of [the ozone layer] O3.'
Poking a flashlight passed the border onto the dark side of Proxima Centauri b, Dr. Kaltenegger argues, could likely lead to the discovery of many species evolved to generate light themselves. Above, Earth's own bioluminescent algae - off the coast of Jervis Bay, Australia
Proxima Centauri - the sun never sets
One of our solar system's nearest neighbors, the star system Proxima Centauri is just 4.25 light-years away, or about a tenth of the distance of star systems like Trappist-1.
It's 'most likely to be habitable' world, Proxima Centauri b, is tidally locked with its host star, meaning in Dr. Kaltenegger's words that it's a planet 'where the sun never sets or rises.'
She imagines that life congregates around the ring of permanent dusk, or permanent dawn, depending on one's perspective, that separates the light and dark sides of Proxima Centauri b — enjoying just the right amount of its star's solar energy to survive.
'Red puffy clouds fill an orange sky, high above the purple moss that dots the few exposed islands on the horizon,' she writes in Alien Earths. 'Waves break on the small stretches of shore, glittering in the red light from the sun overhead.'
Poking a flashlight passed the border onto the dark side of Proxima Centauri b, Dr. Kaltenegger continues, could likely lead to the discovery of many species evolved to generate light themselves.
Theorizing on the glowing life of Proxima Centauri b, Dr. Kaltenegger writes 'in the gloom, you can just make out tiny bright specks of light, a biofluorescent glow that paints a slightly green sheen on the eerily alien landscape' Above, Earth's dramatic fluorescent green algae in Iceland
'In the gloom, you can just make out tiny bright specks of light,' she envisions, 'a biofluorescent glow that paints a slightly green sheen on the eerily alien landscape.'
In 2016, Dr. Kaltenegger and her Cornell colleague, Dr. Jack O’Malley-James, tested another possible reason that life on Proxima Centauri b might glow: a biological shield that could protect its species from its host stars often dramatic solar storms.
'For the duration of a flare, the planet should glow, and that change could be strong enough to detect on planets around nearby flare stars,' Dr. O’Malley-James said of their research, published in the Monthly Notices of the Royal Astronomical Society.
The theory was just one example of how Dr. Kaltenegger and her peers have put into practice the idea of using Earth's weirdest life to imagine the variety of alien life light-years away.
'Like creatures in the deepest, darkest parts of Earth's oceans,' as Dr. Kaltenegger framed it in her new book, 'they are strangely familiar and yet not at all.'