This post has been updated to include GU Psc b, a directly imaged exoplanet announced today. More information below.
We know of more than 1,700 exoplanets. But most of these planets have been detected indirectly, by the way they darken their stars’ faces, their gentle tugs on their home stars, or by the effects of their gravity on distant starlight.
Thus, though there are many, many worlds out there, most of them are hiding from Earthly eyes. We have yet to actually see the majority of exoplanets. So, most exoplanet discoveries are accompanied by detailed artistic renderings of what that planet, or planetary system, might look like.
The few real images we have of exoplanets don’t yet contain those fantastic details: There are no clouds, no continents, no shimmering alien oceans. Instead, the images are of a few blurry pixels that represent a distant world. But hiding in those pixels is a potential flood of information – details about the planet’s size, temperature, and atmospheric composition. In the future, high-resolution direct images of planets will be crucial for helping scientists determine whether life — like planets — is common in the cosmos.
On May 12, a team of scientists reported the best picture yet of an alien planet called Beta Pictoris b, in the Proceedings of the National Academy of Sciences. Using the Gemini Planet Imager, which detects infrared radiation emitted by young, hot planets, the team was able to capture the exoplanet in a super-short, 1-minute exposure. About 63 light-years away, Beta Pictoris b is bigger than Jupiter and orbits more than 1.3 billion kilometers (about nine astronomical units) from its star. This isn’t the first image snapped of Beta Pictoris b – that was done (albeit accidentally) in 2003 – it’s just the best.
Beta Pictoris b is a fairly common observation target. Just two weeks ago, a different team of scientists calculated how fast the planet spins: 100,000 kilometers per hour. In other words, a day on the planet lasts just eight hours. Its year, however, is the equivalent of 20.5 Earth-years.
The total number of planetary systems scientists have directly imaged is very small – around a dozen. This is because it’s incredibly difficult to take pictures of such dim, relatively small, faraway objects (it’s tricky to do this in our solar system, too — we don’t have high-resolution images of Pluto, yet).
But imaging exoplanets is especially hard because of the extraordinary amount of light produced by parent stars, which overwhelm the faint reflections of their small planetary companions. It’s kind of like trying to see a blinking firefly hovering near a much larger searchlight.
So, one of the ways astronomers take images of these planets is by blocking out the host star’s light. This way, they can see the tiny, bright pixels that betray the presence of a planet. Some of the images in the gallery above have big, mostly blank circles near their centers; normally, the host star would be there, but it’s masked. Other images in the gallery are composites of the star and planet.
The Gemini Planet Imager is now systematically searching for exoplanets near some 600 stars. Maybe soon, we’ll be able to use those data to find out what kinds of molecules live in exoatmospheres, and if there are living, breathing organisms on other worlds.
Update, 10 a.m. EDT: Another directly imaged planet has been announced. In The Astrophysical Journal, a team of astronomers reports the presence of a gas giant called GU Psc b, which orbits a star 155 light-years away. The planet is pretty hefty — between 9 and 13 times as massive as Jupiter (that upper mass limit is on the boundary separating planets and brown dwarf stars). But its year is even heftier: At 2,000 times the Earth-sun distance from its star, GU Psc b’s year lasts the equivalent of 80,000 Earth-years. The immense distance between the planet and its star sets this system apart from the others detected so far; the team, led by scientists at the Universite de Montreal, is about to survey several hundred more stars and search for planets in similar orbits. I’ve added GU Psc b’s image to the gallery above. The artist’s representation of the planet is below.