Three new planets have been discovered that are only 40 light-years away and are thought to be the best places to look for life outside our solar system.

According to the report released in the journal , the planets are of similar size and temperature to Venus and Earth, and are orbiting an ultra-cool dwarf star now known as the TRAPPIST-1, named after the telescope used to look at it. The star is in the Aquarius constellation and the planets are considered to be potentially habitable.

The two closest planets have orbital periods of about 1.5 and 2.4 Earth days, respectively, while the third planet could have an orbital period as low as 4.5 days or as high as 73 days.

鈥淭his really is a paradigm shift with regards to the planet population and the path towards finding life in the universe,鈥� said Emmanuel Jehin, co-author of the study, adding that the existence of these 鈥渞ed worlds鈥� was always just theoretical, until now.

The planets are referred to as 鈥渞ed worlds鈥� due to the dark red colour reflected off of the TRAPPIST-1, a star barely larger than Jupiter. As an ultra-cool dwarf star, it has a temperature of less than 2,700 kelvin -- more than 2,000 C -- making it half as hot as the sun.

The closest two planets are nearer to the TRAPPIST-1 than the Earth is to the sun, meaning that they receive four times and twice, respectively, the amount of radiation received by the Earth. However, the third planet, and farthest from the TRAPPIST-1, is thought to receive less radiation than the Earth.

The first two planets are too close to the star to be considered in the habitable zone although they could have habitable regions, while the third planet could be within the zone.

鈥淪ystems around these tiny stars are the only places where we can detect life on an Earth-sized exoplanet with our current technology,鈥� said Michael Gillon, the lead author of the report. 鈥淪o if we want to find life elsewhere in the universe, this is where we should start to look.鈥�

The planets were found when scientists used the Belgian TRAPPIST telescope to observe the star and noticed it seemed to be fading at regular intervals. This indicated that there were objects passing between the star and the Earth, which ended up being the three Earth-sized planets.

The TRAPPIST telescope is at the ESO鈥檚 La Silla Observatory in Chile and is a prototype for a larger project called SPECULOOS that will be installed at the ESO鈥檚 Paranal Observatory, also in Chile.