We’re constantly learning new things about the mysteries of deep space. In April 2019, we saw the very first photo of a black hole and in February 2021, we watched the Perseverance rover touch down on Mars.
🌌 You love our badass universe. So do we. Let’s nerd out over it together.
While these incredible feats of engineering have expanded our potential to learn about our cosmos, there’s still so much outer space left to explore. Luckily, we do know some things about the mysterious, vast expanse overhead, including fun facts about our nearest planetary neighbors.
These are the nine wildest planets in the Milky Way you need to know about.
The Controversy: Barnard’s Star
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.
The First: PSR B1257+12 A
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 is barely bigger than the moon, orbiting the harsh environment of a pulsar. The planets in the system were discovered in 1992 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 third were made and subsequently retracted.
The First Around a Sun-Like Star: 51 Pegasi b
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 Oldest: PSR B1620-26b
The name PSR B1620-26b, 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.
The Rocky: Gliese 876d
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 876d is a hell 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.
The Goldilocks Zone: Gliese 581
Four comparatively small planets orbit Gliese-581. Two of them may be habitable. Gliese-581c is on the inner edge of the habitable zone, and may have suffered a fate similar to Venus, turning noxious and harsh. The other, Gliese-581d, is on the outer edge. The pair were the first announced exoplanets to be found in the “Goldilocks zone” of their star.
The “Gas Dwarf”: Kepler-11f
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 world’s might be like. At what size something is more likely to be a rocky planet like Earth or Mars? At what size do they become more like the ice giants like Uranus and Neptune?
There’s little to no debate with Kepler-11f, 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.
The Earth-Like: Kepler-452b
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.
The One We’ve Actually Seen: 1RXS J160929.1−210524
1RXS J160929.1−210524 has a very important record: the first directly imaged exoplanet. That is, the picture you see here is not an artist’s conception or a graph depicting the dip in light as the planet passes in front of its star. This is an actual image of the planet.
Most exoplanets have to be detected indirectly, such as through radial velocity, or through methods like transit detection, which look for nearly imperceptible dips in light across a planet’s surface. It would take incredible optics to find planets by telescope, something that in most cases won’t be available until James Webb Space Telescope and giant ground-based operations are online. But younger, hotter planets can be detected with the right imagers. That’s just what happened to 1RXS J160929.1−210524.
It’s more massive than Jupiter and relatively young, owing to why it could be spotted directly in the first place. Only one other orbital object, to that date, had been directly imaged–a likely brown dwarf–so this is the first time we’d seen a planet in all our years of discovering them. The picture was released in 2008.
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