Scientists have made giant leaps in honing techniques for finding worlds outside of Earth’s solar system, detecting new ones on the order of hundreds every year.
The number of confirmed exoplanets — planets orbiting stars other than the sun — has risen to 5,539, with 10,000 more candidates under review. Most of these are in the Milky Way, though scientists think they discovered the first planet within another galaxy two years ago.
Statistically speaking, the growing tally only scratches the surface of planets believed to be in space. With hundreds of billions of galaxies, the universe likely teems with many trillions of stars. And if most stars have one or more planets around them, that’s an unfathomable number of worlds.
What scientists are learning is that alien worlds are like snowflakes, each with its own distinct characteristics. There are water worlds, rogue planets, planets with multiple sunsets, volcanic worlds, and planets with weird clouds.
With the new James Webb Space Telescope, getting to know these worlds should become profoundly easier. The leading infrared space observatory will spend about a quarter of its time studying exoplanets. Knowing what’s in another planet’s atmosphere can tell scientists a lot about a world, including whether it could be hospitable to life.
A world straight out of Star Wars
Credit: NASA Goddard Space Flight Center / Chris Smith (USRA) illustration
Back in the 1970s when Star Wars debuted, scientists weren’t sure if a world like Luke Skywalker’s Tatooine — a planet orbiting two stars with majestic twin sunsets — even existed.
Not only are these worlds real, astronomers don’t have to look in a galaxy far, far away to find them.
The discovery, published in Nature Astronomy in June, is called BEBOP-1C, short for Binaries Escorted By Orbiting Planets. It is one of only a dozen circumbinary star systems known to host planets so far.
The planet, thought to be a gas giant like Uranus or Saturn, was found accidentally, 1,300 light-years away in the constellation Pictor. Its year lasts 215 Earth days, and it weighs 65 times more than our planet, according to the study.
Despite its imposing mass, BEBOP-1C is still roughly 20 percent the weight of Jupiter. Its two stars orbit each other every 15 days, according to NASA. One is about 10 percent more massive than the sun; the other is cooler, dimmer, and only one-third the sun’s mass.
The exoplanet with a controversy
Credit: Amanda Smith illustration
Astronomers led by the University of Cambridge used the Webb telescope this year to study the atmosphere of an intriguing exoplanet and found a slight, but potentially exciting, new chemical signal.
The detection was for dimethyl sulfide, a molecule produced by phytoplankton — or microalgae — in Earth’s waters. Because there is no other known way for the substance to be produced on our planet, some scientists suggest it could be an indicator of life if it is found in other worlds, said Nikku Madhusudhan, one of the researchers. Future studies will attempt to validate this tenuous detection.
But the new findings for exoplanet K2-18 b stirred controversy, with skeptics criticizing the weakness of that signal and other claims from the research, such as the belief that the planet is a water world with a hydrogen-rich atmosphere. The planet lies about 120 light-years away from Earth toward the constellation Leo.
Scientists discovered atmospheric water around K2-18 b with Hubble, Spitzer, and Kepler space telescope observations in 2019. The new Webb observations revealed evidence of other life-indicating molecules, such as methane and carbon dioxide. Those chemicals, coupled with the absence of ammonia, are consistent with predictions for an ocean under a temperate hydrogen-rich atmosphere on K2-18 b, the authors of the new study say.
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The world with glittering clouds of quartz crystal
Credit: NASA / ESA / CSA / Ralf Crawford (STScI) illustration
Scientists discovered a gigantic, puffy world, where high-flying clouds are peppered with quartz crystals, a first-of-its-kind detection in an exoplanet’s atmosphere.
Researchers, including several from NASA, used the Webb telescope to study the planet WASP-17 b about 1,300 light-years away. While using the transmission spectroscopy method, they learned the exoplanet’s clouds contain pointy hexagonal prisms like those found in geodes on Earth — the primary difference being that each is likely only about 10 nanometers wide. That’s about one-millionth of one centimeter.
“We knew from Hubble [Space Telescope] observations that there must be aerosols — tiny particles making up clouds or haze — in WASP-17 b’s atmosphere, but we didn’t expect them to be made of quartz,” said David Grant, a researcher at the University of Bristol, in a statement. The team’s study was published in the Astrophysical Journal Letters in October.
Unlike mineral particles found in Earth’s clouds, the quartz detected in the clouds of WASP-17 b don’t come from a rocky surface — they come from the atmosphere itself. That’s possible because WASP-17 b is 2,700 degrees Fahrenheit, and the pressure where they form high in the sky is only about one-thousandth of the level experienced on Earth’s surface. In these conditions, solid crystals can form directly from gas, without going through a liquid phase first, Grant said.
Mirror exoplanet, the shiniest of them all (so far)
Credit: Ricardo Ramírez Reyes (Universidad de Chile) illustration
Astronomers have found a Neptune-sized world covered in metallic clouds, making it the largest known mirror in the galaxy so far.
The exoplanet LTT9779 b‘s clouds, mostly made of the same stuff as sand and glass and other metals like titanium, are highly reflective. New detailed measurements by the European Space Agency’s Cheops satellite indicate this planet reflects 80 percent of the light from its host star. By comparison, Earth only reflects about 30 percent of sunlight.
Most planets have a low “albedo,” referring to the amount of light they reflect, either because they have an atmosphere that absorbs a lot of light or their surfaces are dark or rough.
“Imagine a burning world, close to its star, with heavy clouds of metals floating aloft, raining down titanium droplets,” said James Jenkins, astronomer at Diego Portales University and CATA in Chile, in a statement. He co-authored a paper on the new research that appeared in the journal Astronomy & Astrophysics in October.
Its shininess isn’t the only strange thing going on. The exoplanet is also the only known world of its size and mass orbiting so close to its star. A year on LTT9779 b is just 19 hours, according to ESA. This means it lives in what’s known as the “hot Neptune desert,” scientists say.
This TRAPPIST planet couldn’t hack it
Credit: NASA / ESA / CSA / Joseph Olmsted (STScI) illustration
When astronomers conducted a Webb study of TRAPPIST-1B this year, they found its size was likely the closest thing in common with Earth.
The rocky exoplanet about 41 light-years away doesn’t appear to have an atmosphere and is a toasty 450 degrees Fahrenheit, according to a paper published in the journal Nature. So, just the right temperature for a dystopian book-burning future, anyone?
Scientists have eagerly awaited an opportunity to study the TRAPPIST-1 solar system, a family of seven Earth-sized planets orbiting a red dwarf, a tiny but violent type of star commonly found in the Milky Way. They’ve speculated that one or two of the TRAPPIST worlds, discovered six years ago, could be habitable.
Though TRAPPIST-1B isn’t likely to support life, researchers are just getting started on their studies of this intriguing star system. They are looking forward to learning about some of the other planets, particularly its neighbor TRAPPIST-1E, the fourth from the star. It is thought to be the right distance to allow liquid water to form into lakes and oceans on the planet’s surface.
An Earth twin that hints at an atmosphere
Credit: NASA / ESA / G. Bacon (STScI) illustration
Astronomers are taking a closer look at another rocky exoplanet, GJ 486 B, relatively close to our solar system at just 26 light-years away in the constellation Virgo. Discovered two years ago, it’s about 30 percent larger than Earth, orbiting a red dwarf every 1.5 days.
Despite being so close to its host star and having a scorching temperature of about 800 degrees Fahrenheit, the planet shows signs of having water vapor — a hint that the alien world may have an atmosphere swaddling the planet. And atmospheres are critical for shielding a planet from ultraviolet solar radiation, maintaining habitable temperatures, and creating the pressure needed for liquid water.
But could it be a mirage?
Another possible explanation for the vapor detected by Webb is that water is coming from the outer layer of the nearby star, cooler than the sun, and not from the planet at all. Scientists will need more observations to determine if the exoplanet indeed has an atmosphere and how much water is present. Without an atmosphere, life — at least the type able to flourish on Earth — wouldn’t exist.
Water vapor has been discovered on gassy exoplanets before, but never for a rocky or terrestrial planet akin to Earth, Mars, Mercury, and Venus.
A lava world half hidden in dark shadow
Credit: NASA’s Goddard Space Flight Center / Chris Smith (KRBwyle) illustration
An intriguing world sits just on the cusp of the so-called Goldilocks zone, the region around a host star where it is not too hot and not too cold for liquid water to exist on the surface of planets.
That’s, in part, why scientists are interested in LP 791-18 D, a temperate world about the size of Earth orbiting a small red dwarf star 90 light-years away in the southern constellation Crater.
But if it sounds like paradise, consider that the exoplanet is packed with volcanoes, with half the planet in perpetual daylight while the other half sits in constant darkness. These extreme conditions may combine to provide the necessary ingredients for the planet to have an atmosphere. Many planetary scientists believe volcanic activity is key for a life-sustaining world because the release of gasses during an eruption contributes to the atmosphere and can help a planet maintain moderate temperatures.
Astronomers want to get observation time on the Webb telescope to conduct an atmospheric study of the exoplanet. Discoveries of water and methane, for example — important ingredients for life as we know it — could be signs of potential habitability or biological activity.
A planet with terrifying sand clouds
Credit: NASA / ESA / CSA / Joseph Olmsted (STScI) illustration
The clouds over a newly discovered world 40 light-years from Earth swirl with sizzling, gritty flecks of sand.
On VHS 1256 B, it’s a perpetual, blistering sandstorm. Up in the clouds, temperatures reach a scorching 1,500 degrees Fahrenheit. And when the clouds get too heavy, rainstorms likely pelt the planet with the sandy mixture, astronomers say.
Though the exoplanet‘s days are only two hours shorter than ours, it takes 10,000 Earth-years to make a complete trip around its two stars. That’s right: BEBOP-1C (See the first exoplanet in this story) wasn’t the only world spied this year in a binary system. But given how far away the world is from its stars — about four times farther than Pluto is from the sun — the light sources would be pretty dim.
Just another recent example of how otherworldly clouds can be totally different from the pillowy water vapor clouds of Earth.
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