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During the past ten years, astronomers have identified more than 200 planets relatively close to our Solar System. Most orbit around high-mass stars. Some are massive, with orbits lasting for as little as 1.2 days. These large bodies have been dubbed 'hot Jupiters', because their surface temperatures measure more than 1,000 kelvin. To find out whether similar planets exist further afield, scientists used the Hubble Space Telescope to probe the distant star-filled centre, or galactic bulge, of the Milky Way. They found 16 planetary candidates and identified a new class — ultra-short-period planets (USPPs). These orbit around low-mass stars, and their orbits last for less than one day (see page 534). Nature spoke to Kailash Sahu from the Space Telescope Science Institute in Baltimore, Maryland, to get the stellar scoop.

What is so intriguing about hot Jupiters?

What is most impressive is that they can survive for billions of years despite being very close to the star they orbit. If they were any closer than where the hottest Jupiters have been found, they probably wouldn't survive. No one expected Jupiter-sized planets to exist so close to stars, and hot Jupiters are abundant — they make up about 10% of all planets discovered so far. We think they form far from a star and migrate inwards.

Are you optimistic that the extrasolar bodies you identifed will be confirmed as planets one day?

We believe at least 45% are genuine planets. And we have measurements for two candidates that support a planetary nature. Our best chance to confirm these as planets will be through the James Webb Space Telescope, due to be launched in 2013.

Why have ultra-short-period planets not been found until now?

USPPs occur around low-mass stars, perhaps because the proximity of USPPs to their parent stars limits the size of star they can orbit. So far, ground-based telescopes have looked at more than 200 low-mass stars. But many more stars need to be monitored to find the right combination of low mass and high metal content that is known to be most likely to support USPPs — in part because nearby stars typically have low metal contents.

Is a day in the life of an ultra-short-period planet like a galactic 'Groundhog Day'?

The world of a USPP would be very different from ours. Such planets are so close to their star that they are likely to be tidally locked. And it would always be day on one side of the planet and night on the other. For a change in weather you might have to travel to a different part of the planet!