As of today astronomers have detected 4,326 planets orbiting other stars. Most are indirect detections made by measuring the tug the planet exerts on its host sun or by a drop in the star's brightness when the planet passes in front of it. Only a tiny fraction of these extrasolar planets have been directly photographed because most are hidden in the overwhelming glare of the stars they orbit.
We have even fewer images of multi-planet systems similar to our own solar system. Only two such systems have been directly observed, both of which orbit stars very different from our sun. The photo you see above is the firstshowing multiple exoplanets around a sunlike star. TYC 8998-760-1 is located 310 light years away in the southern constellation Musca the fly. Although its mass is virtually identical to the sun's it's a much younger version of our star with an age of just 17 million years. The crusty old sun has been around for more than 4.5 billion years, making it 250 times older.
"This discovery is a snapshot of an environment that is very similar to our solar system, but at a much earlier stage of its evolution," says Alexander Bohn, a PhD student at Leiden University (the Netherlands), who led the new research published inThe Astrophysical Journal Letters.
The image was made with an instrument called SPHERE (Spectro-Polarimetic High contrast imager for Exoplanets REsearch) which snaps extremely sharp photos by correcting for blurriness due to atmospheric turbulence. It also has the ability to block most of a star's light, so it can detect faint planets orbiting nearby. SPHERE photographs these systems in infrared light, which we sense as heat. Older planets, such as those in our solar system, are too cool to be found with this technique. Young planets are hotter (due to heat from gravitational contraction — they're still shrinking), and so glow brighter in infrared light.
The two gas giants orbit TYC 8998-760-1 at distances of 160 and about 320 times the Earth-sun distance, much further away from their host star than Jupiter or Saturn, which lie at only 5 and 10 times the Earth-sun distance, respectively. The team also found that the two exoplanets are much heavier than our solar system's planets, the inner planet having 14 times Jupiter's mass and the outer one six times.
A few weeks prior to the release of the photo SPHERE took an equally stunning image of what astronomers believe is a planet in the process of being born. Spirals of gas and dust signal the presence of baby planets that "kick" the gas to create waves. As the planet revolves around the central star the waves morph into a spiral. The innermost region of the spiral includes a 'twist that scientists believe marks the spot where a planet is forming.
"It corresponds to the connection of two spirals — one winding inwards of the planet's orbit, the other expanding outwards — which join at the planet location," said co-author Anne Dutrey (Astrophysics Laboratory of Bordeaux, France). "They allow gas and dust from the disk to accrete (coalesce) onto the forming planet and make it grow."
By studying these examples of young solar systems we hope to gain a better understanding of how our own formed and evolved to its present state.