Exoplanet imaged around Sun-like star
I just saw this on Bad Astronomy, and almost jumped out of my chair. Astronomers from the University of Toronto have published an infrared image of what they have tentatively identified as a planet orbiting a distant young star. This is only the second time such a discovery has been made, and the first was of a five-Jupiter mass planet orbiting a brown dwarf, a failed star that barely shines. This new finding is – if confirmed – even more amazing because the star is reasonably similar to our own Sun.
The primary star of this system is very young, probably about 5 million years old or thereabouts, slightly smaller and cooler and more orange than the Sun. The picture to the right shows the bright primary and a tiny reddish speck in the upper left corner of the picture… that’s the planet. The planet has the mass of about eight Jupiters, making it a really large gas giant. Also, characteristics of its light spectrum show the planet is hot, with a surface temperature of 1800 K.
The kicker in this story is that the planet is about 330 Astronomical Units (AU) from its primary. That is very far out, compared with other star systems astronomers have found so far. For comparison, Neptune – the most distant true planet in our star system – only averages about 30 AU from the Sun, and Neptune is very cold… about 63 K (only 63 metric degrees above absolute zero) at its cloud top. This weird hot Jupiter is more than 10 times farther from its little sun, and its cloud tops are roasting at an incandescent 1500 Celsius. It probably looks like a lurid ball of embers spinning in the darkness.
How can such a planet exist? Well, for one thing this planet appears very young. Still hot and fluffy from its recent accretion, its layers of atmosphere haven’t cooled and settled into a smooth ball of clouds like Jupiter or Saturn. This newly observed world is still radiating with the heat of its formation.
This might not be what it appears to be. The authors’ conclusions are not yet confirmed. This planet would be at an exteme distance from its star, and according to what we know about how solar systems form, no planet that large should be that far out. There shoundn’t be enough concentrated material at that distance during system accretion. The planet could have been slung out there by an interaction with another (yet unseen) planet in its system, but there’s no evidence yet for that. The authors present a convincing case that the object isn’t another star, much closer, or a rogue planet that just happened to get in the shot. So for now it’s an astronomical puzzle, but an exciting one, and one that might just point the way to many more pictures of distant worlds yet unseen.