By Ian Steadman, Wired UK

The Kepler space telescope has spotted the most tightly packed exoplanet system yet, with five planets orbiting around the star KOI-500 within a fraction of the distance between Mercury and our Sun.

[partner id="wireduk" align="right"]The system was discovered by Darin Ragozzine, a planetary scientist at the University of Florida at Gainesville, and his team. It's roughly 1,100 light-years from us, in the direction of the constellation Lyre. Its five planets are each slightly larger than the Earth, but their orbits are remarkably close to KOI-500 – 150 times smaller than the orbit of the Earth. That's even less than the orbital distance of Mercury. Yet despite flying around so fast that it's only a manner of Earth days for each "year," they exist in an orbital resonance that keeps them from crashing into each other or falling into the star.

Ragozzine presented the discovery to the annual meeting of the American Astronomical Society's Division for Planetary Sciences in Reno, Nevada, as reported by Space.com. The planets orbit their star in (going from innermost to outermost) 1.0, 3.1, 4.6, 7.1, and 9.5 days each, respectively, and each planet is between 1.3 and 2.6 times the size of the Earth. The outer four planets exist in a kind of orbital resonance, which sees them return to a set formation every 191 days – that seems to keep them from being knocked out of orbit by each others' gravitations and hurled either farther out into the system or into the star to burn up.

It's a unique planetary relationship – four planets is the largest number of bodies found so far existing in resonance with each other. The astronomers think it might have come about thanks to the way they migrated in toward KOI-500, slowly spiraling in as the system formed out of planetary dust until it reached a point of equilibrium. It's quite a young system, perhaps only a billion years old, and while KOI-500 has a similar mass to our Sun its diameter is only three-quarters the same size.

Yet again Kepler has surprised us with its discoveries, after discovering other planets orbiting nearer to stars than we thought safe or possible, and finding planets orbiting around a binary star system too. Even more bizarre, just yesterday Wired UK reported on an amateur astronomer who found a planet orbiting a binary star system with another pair of stars orbiting around the three bodies further out, which nobody had expected to find.

It's increasingly feeling like our own Solar System is a bit of an oddity in its structure, but then we haven't been looking for planets for that long – Kepler only went into operation in 2009, and it's found over 2,000 stars that possibly have planets orbiting them in just that short time. Probably the one thing we can be sure of is finding our immediate galaxy is even more ridiculous than we ever imagined.

Source: Wired.co.uk

Image: Artist's concept of a small planetary system around a different star. NASA