Nasa’s Spitzer telescope has found seven Earth-sized planets orbiting around a single star.

All of the newly found exoplanets could have liquid water, while three of them are located in the habitable zone.

Located around 235 trillion miles from Earth, the latest discovery is so far the biggest number of habitable-zone planets found around a single star outside the solar system.

Nasa Science Mission Directorate Washington associate administrator Thomas Zurbuchen said: “This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life.

“Answering the question ‘are we alone’ is a top science priority and finding so many planets like these for the first time in the habitable zone is a remarkable step forward toward that goal.”

Known as Transiting Planets and Planetesimals Small Telescope (TRAPPIST-1), the new exoplanet system is situated in the constellation of Aquarius.

“This discovery could be a significant piece in the puzzle of finding habitable environments."

Last May, researchers announced the discovery of three planets in the TRAPPIST-1 system.

Using several ground-based telescopes, Nasa’s Spitzer telescope had confirmed the existence of two of these planets and discovered five additional ones, increasing the number of known planets in the system to seven.

Nasa noted that it has measured the sizes of the seven planets and developed first estimates of the masses of six of them.

Based on their densities, all of the TRAPPIST-1 planets are appear to be rocky.

Nasa is carrying out further observations to determine the nature of the planets.

Image: Artist's concept shows what each of the TRAPPIST-1 planets may look like, based on available data about their sizes, masses and orbital distances. Photo: courtesy of Nasa/JPL-Caltech.