The Terrible Weather on 6 Exoplanets
David A. Aguilar/Harvard-Smithsonian Center for Astrophysics
Of the more than 900 exoplanets—planets outside our solar system—discovered to date, none, not a single one, appears to be a nice place to visit or live. If anything, descriptions of most of these far-flung bodies sound like a walking tour of hell. There’s the planet where glass falls from the sky, or the one where temperatures spike so quickly that they generate supersonic megastorm.
These weather reports are educated guesses, of course, culled from measurements of the apparent mass, infrared output, chemical makeup, and position of each exoplanet. Though the majority of these alien worlds tend to be astonishingly large and hot, that’s more a function of how our space-based and terrestrial telescopes search—big and blazing stands out better than Earth-sized and temperate, and planets with a tighter, closer orbit are more likely to catch our attention by crossing in front of a star. Here are the exoplanets whose estimated weather conditions are as detailed and evocative as they are terrifying, all further reminders of how uniquely livable our own planet is. (Note: There are exoplanets with less harsh or extreme characteristics, but whose weather is even more speculative.)
1. Baking and Breezy: Kepler-76b
Our first selection (above) is, in many ways, the archetypical exoplanet—its name is exceedingly dull, an indication of the telescope that spotted it (NASA’s space-based Kepler telescope, in this case) and the star system it resides in (it’s the “b” planet in the Kepler 76 system). It’s also what astronomers call a “hot Jupiter,” a gas giant with at least as much mass as our own resident behemoth, but with a much higher temperature. Kepler-76b’s hotness comes from its cozy proximity to its own star, circling it every 1.5 days (compared to 4332 days for Jupiter). The result is a world whose surface doesn’t rotate—it’s tidally-locked, like our Moon—but whose blisteringly hot winds do, carrying the 3600-degree Fahrenheit temperatures on its star-facing side around to the “dark” side in a constant, planet-wide gale.
2. Blue Skies, with a Chance of Glass: HD 189733b
HD 189733b's blue sky is caused by silicate particles in the atmosphere that form into droplets of glass, which cast a bluish tinge. Researchers studying the planet with the Hubble space telescope determined not only its unique, cobalt-blue hue, but the fact that its glass rainfall is whipping across the planet at some 4500 mph. And like Kepler-76b, this silicate-scoured deathtrap is a tidally-locked hot Jupiter—though with its permanently dark side averaging around 1500 degrees Fahrenheit, it’s comparatively temperate.
3. Bad World Rising: Kepler-36b
One of a slim minority of exoplanets discovered that happen to be rocky, Kepler-36b has a turbulent orbital relationship with its neighboring world, 36c. Every 97 days that planet, a “hot Neptune” (like a hot Jupiter, but smaller) gas giant comes perilously close to 36b, roughly five times the distance between the Earth and the Moon. Astronomers paint the spectacle as undoubtedly glorious, with the purple gas giant looming some 2.5 times larger (in diameter) than our own moon. Unfortunately, these picturesque swing-bys would likely trigger cataclysmic—by our standards—seismic activity, as gravitational forces stretch the two planets, triggering even more volcanic activity on 36b, a planet already defined by its lava flows and 1300-degree Fahrenheit temperatures. (The image above shows what 36c might look like from 36b.)
4. A Song of Ice-Cold Rocks and Fire: CoRoT-7b
Like many confirmed exoplanets, CoRoT-7b is close enough to its parent star to be both hotter than anyone’s interpretation of hell (up to 4700 F, to be specific) and tidally-locked, with one hemisphere cooking under a stellar heat lamp. CoRoT-7b is a strange case, though. It’s rocky, so its heat isn’t distributed throughout the planet, as is the case with some gas giants, keeping its dark hemisphere at somewhere around minus 350 F. Weirder still, astronomers believe that 7b’s combination of scorching heat and mineral-rich atmosphere could result in a rainfall of rocks, on both the frigid and lava-soaked sides.
5. High Winds, Green Sunset: HD 209458b
European Space Agency and Alfred Vidal-Madjar (Institut d'Astrophysique de Paris, CNRS, France)
The most interesting thing about HD 209458b isn’t that it’s so ludicrously windy—nearly 4500 mph, similar to the speeds estimated in the glass-blasted upper reaches of HD 189733b—but that it's leaking. Although its atmosphere includes significant amounts of carbon monoxide, sodium, and other elements, the gas giant’s close proximity to its star seems to be tearing the planet’s hydrogen free. HD 209458b could be losing as much as 500 million kg of hydrogen per second, which might be visible in a long, comet-like tail. Anyone somehow lurking within the atmosphere, however, wouldn’t necessarily be able to see that trail, though researchers have described what it might be like to watch the sunset from HD 209458b—a eerie progression from blue to green, no doubt complimented wonderfully by that scouring carbon monoxide super-breeze.
6. Explosions in the Sky: HD 80606b
Most days on HD 80606b are simply nightmarish—980 degrees Fahrenheit, with unimaginable pressures due to its mass (four times that of Jupiter). But every 114 or so days, the gas giant’s hugely elliptical orbit brings it point-blank with its star. Over six hours, the temperature rises by some 1000 degrees, and the atmosphere essentially explodes. As the star gets 1000 times brighter, the sudden heat births titanic superstorms, with winds topping 11,000 mph. These atmospheric shockwaves wrap around the planet as it rockets back along its pinched orbital circuit, away from the heat source that creates perhaps the most violent weather system ever discovered.