An impossible giant in a dangerous neighborhood
Astronomers have barely got used to the idea of giant planets in close orbits around their sun, when the next surprise awaits them: a specimen the size of Jupiter, which should not have formed in the complicated system of its three suns.
Everything starts with a cloud. Ice, dust, and gas gradually gather into a protoplanetary disk that rotates and condenses. At its center, matter will eventually collapse into a new star, while at the edges there is a chance to form smaller celestial bodies. Rocky planets such as Mercury, Venus, Earth and Mars are formed close to the young Sun. Farther out, at least three times the distance of Earth's orbit, cores of solid material pull in gases with their gravity and grow into gas giants. Jupiter and Saturn began their existence in this way. And so each planet has its history and its well-established place in the solar system.
Then astronomers took a closer look. About ten years ago, what they saw through their telescopes upset the beautifully harmonious theory of the formation of planetary systems. 51 Peg is the name of the heavyweight villain that, despite its enormous mass, orbits unashamedly close to its star, at just one twentieth of the mean distance between Earth and the Sun (the astronomical unit, AU). Impossible that it could have survived this close, not to mention the fact that there couldn't have been enough matter in those regions to form 51 Peg in the first place. And yet he was and is there. How so?
Good advice was expensive, but given a little time scientists have credible explanations for even crazy observations. 51 Peg originally got its start at a suitable distance and later migrated towards the star as a completed gas giant, was the idea. The theoretical world was in order again.
Until Maciej Konacki of the California Institute of Technology cast his gaze through the Keck I telescope at the star HD 188753 in the constellation Cygnus. In fact, the object, 149 light-years away, is a system of three stars. Two of them orbit each other so closely they're almost indistinguishable, and this binary system orbits the main star just 12.3 AU away - about the distance between the Sun and Saturn. A complicated web of gravitational forces results, not a good area for planets. But this is exactly where Konacki discovered a planet with around 1.14 Jupiter masses, whizzing around the single star once every 3.35 days.
Impossible, because the three stars would have catapulted him out of his orbit long ago. Impossible, because the binary system would have trimmed the dust disk of the single star to a meager remainder with an extension of 1.3 AU and thus robbed the material for such a planet. Impossible, because something like that couldn't be in our solar system.
But the universe seems to care little about the objections - and so the astronomers are again faced with a lot of question marks. A reason for hangover? Not at all, write Artie Hatzes from the Thuringian State Observatory and Günther Wuchterl from the Friedrich Schiller University in Jena. Such a discovery may represent an important step in truly understanding the formation of our solar system - and other systems. Because one thing seems obvious: nature knows more than one recipe for baking planets. Now we have the chance to take a look at the second page in the cookbook.