These planets have varied widely, and many of them are incredibly large compared to the analogs we are familiar with in our home system. Super-Jupiters and super-earths are among the many discoveries, and for good reason: at the distances we have to look for them, planets are very faint compared to their stars and usually must be detected by indirect viewing, such as the dimming effect they have on their stars when they transit between them and our sight.
Despite these limitations, scientists have learned much about how much diversity exists in star systems throughout the universe, including the idea that planetary formation seems to be more common than not during the lifecycle of the stars. However, one key component has eluded scientists over the decades: a glimpse of planetary formation itself.
While astronomers have been able to extrapolate from existing data a good idea of how planets coalesce from orbiting debris around newly-born stars, the process yet to be observed. That is, until now.
This past week a team of scientists, headed by Stephanie Sallum of University of Arizona and Katherine Follette of Stanford University, announced that they discovered a planet going through the process of formation.
The planet in question is a gas giant not unlike Jupiter or Saturn, albeit far younger. The team of scientists photographed it forming around the star LkCa 15, which is 450 light years from our own system. The planet, dubbed LkCa 15 b, is estimated to orbit its star at a distance of 16 astronomical units (AU). One such unit is the distance the Earth orbits the Sun, or 93 million miles.
The picture itself shows the hydrogen-rich planet shining brightly within a transition disk, the name for the dust and debris that collects around a young star and eventually can give birth to planets when it accumulates over time.
"This is the first incontrovertible detection of a planet still in the process of forming – a so-called 'protoplanet'," Follette, a postdoctoral researcher at Stanford and co-author of the study, said in a release. "I was pretty excited as soon as I processed the data, but I wanted to be cautious. I was pretty sure I had found something interesting, but in this field we're always chasing objects that are just at the edge of what we can detect. The really cool thing is that it survived all of our tests to make sure it was real."
"The difference in brightness between a star and a young exoplanet is usually comparable to the difference between a firefly and a lighthouse," Follette continued. "It's very hard to isolate the light from the planet when it is so faint and so close to the star from our point of view. But, because we could focus on a special color of light where the planet is glowing very brightly, the signal was significantly stronger than what we normally look for."
The LkCa 15 system was observed by the scientists using the Large Binocular Telescope in Arizona. While the researchers are excited about this breakthrough, they still the biggest discoveries in their field are still ahead of them. Namely, a solar system with an exoplanet (or more than one) that can conceivably harbor life. While our current technology can detect the largest planets orbiting distant suns, advances have yet to be made to pick up their smaller neighbors. Until then, likely earth-like candidates might still be hidden from our view by their stars’ immense light.
"One of the fundamental human questions is whether we're alone or unique," Follette said. "It's cool to look at Jupiter-like exoplanets like LkCa 15 b, but ultimately we're trying to push the technology to be able to detect Earth-like exoplanets. I've always been inspired by the famous 'pale blue dot' image of Earth taken by Voyager as it passed Saturn. We'd really like to do that someday for a planet around another star, and this sort of work is moving us in that direction."
By Trent Townsend
Actulal image of newborn planet LCKa15b forming