The 13 Most Interesting Exoplanets in the Milky Way

The James Webb Space Telescope recently found a “prime target for future atmospheric characterization” in this exoplanet orbiting a red dwarf star 100 light-years away. Like many other exoplanets, researchers discovered this one because it is blocking some of the star’s light every time it passes in front of it.

Based on this information, researchers know that this world is 70 percent bigger than ours—earning it the nickname “super-Earth”—and that it orbits quite rapidly, once about every 11 days. Its density could indicate a deep ocean surface, in addition to a rock and metal composition, like our planet.

Surprisingly, water could make up 30 percent of TOI-1452b’s mass, a far greater proportion than Earth’s 1-percent water mass (despite water covering 70 percent of our planet’s surface).

Webb’s Near-Infrared Spectrograph (NIRSpec) enabled detailed observations of the exoplanet WASP-39 b and found clear evidence of carbon dioxide in the atmosphere. It’s the first time this gas, familiar on Earth, has been detected on another planet outside the solar system. The 3- to 5.5-micron range, which is in the infrared portion of the transmission spectrum, is useful not only for detecting carbon dioxide, but also water and methane, which are indicators for potential life.

At about 1,600 degrees Fahrenheit, WASP-39 b is a hot gas giant 700 light-years away, with a mass about one-quarter that of Jupiter, but with a diameter 1.3 times greater. It orbits rather fast and close to its Sun-like star—every 4 Earth days, it completes a lap.

The rugby ball-shaped WASP-103 b is the first non-spherical exoplanet discovered. Whipping around its star in less than a day, tidal forces on the planet have pressed it into a rugby ball shape, researchers report.

The European Space Agency’s CHaracterising ExOPlanet Satellite, or Cheops, discovered the strange planet within the constellation Hercules. Twice Jupiter’s size, WASP-103 b is quite close to its star, WASP-103, whose gravitational influence tugs at it continually.

Perhaps even more surprising then, is that the planet seems to be moving farther away from its star with each orbit. Maybe it’s too close for comfort.

More than 300 light-years from Earth, a gas giant and its companion planet orbit an extremely young, Sun-like star, only about 17 million years old. Its planets must also be brand new, and in their infant state, they radiate a glow that we can see with our ground-based telescopes.

That makes TYC 8998-760-1 b quite a rare phenomenon, because most of the time, starlight at least partially obscures the planets themselves. The Paranal Observatory in the Atacama Desert in Chile, found this exoplanet.

There’s a chance TYC 8998-760-1 b may be a brown dwarf, kind of between a failed star that never got big or hot enough to keep burning and a regular planet. Still, it’s a behemoth, at 14 times the mass of Jupiter.

Barnard’s Star is famous less for the planets it has than for the planets it doesn’t have. Let me explain.

The star, the fourth closest to us, has been the subject of a heated back-and-forth in astronomy circles since the 1960s as to whether or not it has planets. The current answer is no. But for at least 10 years, following an official announcement by Peter van de Kamp in 1963, many people believed the answer was a resounding yes, and that Barnard’s Star had two gas giants orbiting it.

Van de Kamp never gave up on his claims, but Hubble observations showed them to be impossible in the late 1990s.

But here’s the thing: Hubble didn’t rule out that Barnard’s Star could have planets. It ruled out large planets at certain distances from the ancient sun. It’s not out of the question that a rocky world or even a Neptune-sized ice giant could be there.

Future exoplanet surveys may answer the question once and for all ... or just spur on more controversy.

We’ve discovered planets around sun-like stars for 20 years. But we’ve known of planets outside our solar system for a little longer ... they just happened to be radically different than any kind of solar system we’d conceived of. Like, say, around the remnant of a supernova.

The first exoplanet discovered still holds the record for being the least massive. PSR B1257+12 A—also called PSR B1257+12 b—is barely bigger than the moon, orbiting the harsh environment of a pulsar. The planets in the system were discovered in 1994 by the tug they gave on their home star.

Pulsars are known as cosmic timekeepers, sometimes called the “most accurate clocks in the universe.” But something was making the beat of PSR B1257+12 just a little off. It was determined that the culprits in question were two planets, including this one. A third was later found, and claims to a fourth were made and subsequently retracted.

While 51 Pegasi b wasn’t the first planet discovered, it was the first confirmed planet around a sun-like star. Even so, it was nothing like any planet we knew. This giant world completes a swift orbit of its star every few days. It kicked off the discovery of many “hot Jupiters,” gas giants in orbits even tighter than Mercury’s.

In 2015, the atmosphere of 51 Pegasi b was characterized in the visible spectrum, another first. Instead of just observing 51 Pegasi b’s silhouette as it passes in front of its home star, we can study things like the planet’s actual mass or orbital inclination by looking at the visible light it throws off.

This may seem like small potatoes compared to how much we know about most of the planets in our own solar system, but when you’re talking about an exoplanet that’s 50 light-years away, this is valuable and fresh information.

The name PSR B1620-26 b, like many other exoplanets, doesn’t quite roll off the tongue. But this is the oldest planet known, at somewhere around 12.7 billion years old. That’s just a little younger than the universe itself.

The ancient planet orbits both a pulsar and an ultra-dense white dwarf, itself another supernova remnant. The two stars orbit each other while the gas giant orbits around the gravitational center of those dense dance partners.

It’s only 15 light-years away. It’s small enough to be rocky, though far, far larger than Earth. But don’t pack your bags yet: Gliese 876 d is a hellish world.

Its day is a shade less than an Earth day in length, but its orbit is just a fraction of Mercury’s distance from the sun. It is hot, hot, hot. But the 2005 discovery of the planet is important for showing there are rocky worlds beyond our solar system.

There’s a problem with classifying smaller exoplanets: We’ve seen a number of planets out in the void that are bigger than Earth but smaller than Neptune. But here in our solar system, we have nothing of the sort. That makes it hard to guess what these worlds might be like. At what size is something more likely to be a rocky planet, like Earth or Mars? At what size do they become more like ice giants, like Uranus and Neptune?

There’s little to no debate with Kepler-11 f, a confirmed mini-Neptune. Its density hints at a Saturn-like atmosphere with only a small rocky core. It created a class of “gas dwarves” that are unseen in our home solar system.

Kepler-452b is almost definitely the most Earth-like planet found thus far. Its star is the size of the sun, its year is just a shade longer than ours, and it’s a little bit bigger than our planet, but firmly in the habitable zone of the star.

There are only a few problems: It’s more than 1,000 light-years away, so we’ll never get there. And it’s 1.5 billion years older than Earth, meaning its host star may have grown enough to make the planet currently uninhabitable. Long ago, though, this could have been our twin.

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