"It is a step on that road to understand if there are other planets like Earth and potentially life out there", he said.

Macintosh's team used two ground-based telescopes, while the second team relied on photos from the 18-year-old Hubble Space Telescope to gather images of the exoplanets - planets that don't circle our sun.

Exciting finding

In the past 13 years, scientists have discovered more than 300 planets outside the solar system, but they have done so indirectly, by measuring changes in gravity, speed or light around stars.

The research from both teams was published in Thursday's online edition of the journal Science.

Ed Weiler, Nasa's space sciences chief, said the new photos were important and compared the effort to a hunt for elusive elephants. 

"For years we've been hearing the elephants, finding the tracks, seeing the trees knocked down by them, but we've never been able to snap a picture. Now we have a picture," he said.

But doubts still persist about whether these were the first exoplanet photos.

Others have made earlier claims, but those pictures haven't been universally accepted yet.

The photos released on Thursday have still not convinced all the experts.

Alan Boss, an exoplanet expert at the Carnegie Institution of Washington, and Lisa Kaltenegger, a Harvard exoplanet hunter, both said more study was needed to confirm the new set of photos were those of proven planets and not just brown dwarf stars.