The Hubble space telescope has discovered 16 new planets around distant stars, Nasa revealed tonight.

Astronomers say the result suggests there are around six billion planets like Jupiter in our own galaxy. The remote worlds are much further away than any found before. They were detected circling stars in the centre of the Milky Way instead of neighbouring suns.

Five of them are unlike any planets known because they zip around their parent stars in less then one Earth day. Scientists have dubbed them Ultra-Short-Period Planets.
Hubble made the discoveries during a survey called the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS).

The orbiting telescope examined 180,000 stars in the crowded central bulge of our galaxy 26,000 light-years away. That is one-quarter the diameter of the Milky Way’s spiral disk. The results appear in tomorrow’s issue of the journal Nature.

Hubble’s field of view was only two per cent the apparent size of the Full Moon. The number of planets detected therefore suggests that the entire galaxy contains aroound six billion planets the size of Jupiter, biggest world in our own solar system.

Team leader Kailash Sahu, of Nasa’s Space Telescope Science Institute, Baltimore, said: “Discovering the very short-period planets was a big surprise. Our discovery also gives very strong evidence that planets are as abundant in other parts of the galaxy as they are in our solar neighbourhood.”

The planets were too far away to be seen directly by Hubble. Instead their existence was revealed by the dimming of their parent stars as they passed in front and eclipsed them. Experts say each planet would have to be about the size of Jupiter to block enough starlight and so be measurable by Hubble.

The new planet with the shortest orbital period, named SWEEPS-10, has a “year” only ten hours long – the time it takes to orbit its star.

The picture is an artist’s impression of one of the new planets. Credit: NASA, ESA and G. Bacon