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© NASA; Paul Spella / The Atlantic
One of the most exciting discoveries in astronomy began, like many things in the 1990s, with a fax machine.
Didier Queloz, then an astronomer at the University of Geneva, spent the summer of 1994 sorting through data from a new telescope technology that measured the subtle movements of stars. Such movements, the scientists had theorized, could potentially suggest the presence of planets outside our solar system, orbiting their own suns. Gravity from a distant planet could pull at its star, causing it to wobble very slightly. No one had ever discovered a so-called exoplanet in this way before, so when Queloz finally found a flickering star, he thought it might be an instrumental error. But the mysterious quiver has not disappeared. Queloz therefore sent a fax to his advisor, Michel Mayor, on sabbatical leave in Hawaii: “I think I have found a planet.
The oscillation had revealed a world half the size of Jupiter orbiting a sun-like star about 50 light years from Earth. Queloz and his team named it 51 Pegasi b, after the star it orbits. The existence of the planet was amazing in itself, but it also hinted at something extraordinary: there must be more.
And there are more — many, many more. In the years that followed, astronomers confirmed the existence of more than 4,400 exoplanets in our Milky Way galaxy. They found icy planets and burning planets, a planet with oceans of lava and a planet where it rains glass; planets whose density is reminiscent of cotton candy and a planet that literally evaporates into space. But these days, the astronomical community is no longer as enthusiastic about a single discovery as it once was. The field of “exoplanets, for the first two decades, was really in the stamp collecting phase,” Jessie Christiansen, a NASA astrophysicist who studies exoplanets, told me. “We were like, Ooh, a shiny new thing.“
Now there are enough planets to really understand what they look like. Researchers are pushing the boundaries of current technology and imagining what is possible with more powerful tools to fill in the details and apply the exo prefix to other fields: exotopography, exogeology, exoecology, exomoons. In the tiny ripples of light from distant stars, astronomers have gone far beyond just detecting new planets to examine these distant worlds with greater precision than ever before.
While 51 Pegasi b were found thanks to the movement of a star, most of the exoplanets found since have been detected by starlight. When a distant planet orbits in front of its star, it blocks out some starlight, causing the star to appear weaker to us on Earth temporarily. When astronomers observe the star long enough, noting the star’s dim light, they can confirm not only the existence of a planet, but also the time it takes for this world to orbit its sun. , the composition of its atmosphere and the temperature of its surface.
These are the basics of the exoplanet that are usually fairly straightforward to discern. But the light of other suns contains much more information than we are only beginning to understand. One astronomer, for example, examined how much starlight exoplanets reflect to study what their surfaces might be made of; ice, for example, is more reflective than water, and water is more reflective than dirt. One of the most intriguing approaches I’ve come across recently is changing the traditional method of finding exoplanets in starlight hollows. “We know that rocky planets are going to have bumpy features, and if the planet spins in front of the star, those features come in and out of view and block the star’s light more,” says Moiya McTier, an astrophysicist who has exoplanets studied. These tiny changes could suggest the presence of mountains, volcanoes, and other towering terrain.
Video: Astronomers discover three new planets, including the smallest exoplanet to date (The Independent)
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[Read: The planet that took us beyond the solar system]
Astronomers also understand the skies of exoplanets better, shooting telescopes as much as possible to observe characteristics of distant atmospheres. A planet with an atmosphere absorbs some of its star’s glow, leaving imprints on the light that eventually reaches Earth. Scientists looked at these marks for evidence of all kinds of molecular signatures in the atmospheres of exoplanets: oxygen, hydrogen, sodium, iron, and even water vapor. Some of these substances are quite common in the universe, so astronomers are now broadening their research to include more unusual biosignatures – the kind that living organisms, not chemical processes, might produce – and are finding out how they might spot their fingerprints. distinct in starlight. .
It is only recently that researchers have started looking for even more advanced indications of life on exoplanets – the radio transmissions of a society in turmoil. Breakthrough Listen, an international effort to find radio signals that could be produced by intelligent civilizations, recently teamed up with NASA’s TESS Space Telescope, which found 144 confirmed exoplanets hidden in the shards of other stars. Earth’s radio broadcasts have been floating in space for decades, carrying information about our existence. Perhaps it was the same with other planets.
Ultimately, the driving force behind exoplanet research is less about finding new types of worlds than finding a specific type: can we find another Earth? Most of the planets that astronomers have found so far, including Pegasi 51b, the subject of the fax that changed astronomy, are unlivable. We’re still looking for what Christiansen, the NASA astrophysicist, calls the “holy grail of exoplanets”: a rocky world the size of Earth, orbiting a comfortable distance from its star, where water wouldn’t freeze. or would not always evaporate, but would lap up its surface. It’s the kind of place – the only one, really – where we could confidently say that life could be born.
[Read: The curious case of the evaporating exoplanet]
Of the thousands of known exoplanets, only 165 are rocky Earth-sized worlds, which are harder to detect than giant planets made of gas. Yet the statistics are on the side of astronomers. Scientists believe that every star in the Milky Way galaxy has at least one planet, and they believe that planets nestled in their star’s habitable zone are common. As the writer Jo Marchant writes in his book The human cosmos, “While it is highly unlikely that life will occur on any particular planet, we know that in our galaxy alone there are billions of chances of it happening.”
But as is often the case in exoplanet research, technology is still catching up with theory. To test McTier’s exotopographic approach, for example, the astronomical community needs more powerful instruments than those currently in use. And astronomers can only dream of catching a glimpse of something as wonderful as the twinkle of someone else’s city lights or as spectacular as explosion shields built to protect against deadly supernovas. Despite all the new research, we are still a long way from photographing small rocky planets at higher resolution than a single pixel.
[Read: How to draw an exoplanet]
Studying exoplanets reminds me of Apollo’s landings on the moon, the only other world that humans have actually visited. When Armstrong, Aldrin, and Collins returned from their trip, they filled out a customs form, declaring the “moon” as their place of departure and declaring samples of moon rock and dust as goods. The piece of paper, a small token of the historic mission, turned the moon into a real place people could touch and walk. Humanity can visit the moon again, and maybe one day can make a real place on Mars. And we can certainly try to turn exoplanets into places in a certain way, using beautiful illustrations, says Lisa Messeri, an anthropologist at Yale who has written about how scientists can help the public view targets. scientists like exoplanets like real worlds. Maybe it can give some of us – the non-scientists who don’t spend hours peeling starlight – a fuzzy feeling. “Being able to identify the resemblance, even if it’s impossible for us to achieve, somehow shrinks the size of the universe to make us feel more connected,” Messeri told me.
But exoplanets will remain, for the foreseeable future, incredibly distant, abstract. The Earth-sized planet around our nearest star would take decades to reach, with technology capable of traveling at a fraction of the speed of light. The study of the planets beyond our solar system always comes down to a melancholy but immutable truth: much of astronomy is the pursuit of understanding everything from here on out, and there will always be limits within our grasp. .
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