Scientists on Monday said they have discovered traces of a gas called phosphine through the clouds of Venus, indicating a sign of potential life beyond Earth, findings published in journals reported. Venus has long been overlooked in the search for extraterrestrial life as its atmosphere is comprised almost entirely of carbon dioxide and described as hellish.

While scientists did not discover actual life forms, they noted that on Earth phosphine is produced by bacteria thriving in oxygen-starved environments. A team first spotted the phosphine using the James Clerk Maxwell Telescope in Hawaii and confirmed it using the Atacama Large Millimeter/submillimeter Array or ALMA radio telescope in Chile.

“When we got the first hints of phosphine in Venus’s spectrum, it was a shock,” Professor Jane Greaves, an astronomer at Cardiff University, leader of the team who made the discovery said. Greaves said that it was the first time phosphine had been found on a rocky planet other than Earth.

While Venus has been compared to Earth for some similarities including size and proximity to the sun, the planet’s atmospheric pressure is 92 times Earth’s sea level pressure, and has an average temperature of 464 degrees Celsius. It has an extremely dense atmosphere and hardly any water at all.

Meanwhile, Massachusetts Institute of Technology molecular astrophysicist and study co-author Clara Sousa-Silva, said it was “an extraordinary discovery”. “I should emphasise that life, as an explanation for our discovery, should be, as always, the last resort,” Sousa-Silva added. “This is important because, if it is phosphine, and if it is life, it means that we are not alone. It also means that life itself must be very common, and there must be many other inhabited planets throughout our galaxy.”

The team concluded that their research provided evidence “for anomalous and unexplained chemistry” on Venus, according to AFP.

Alan Duffy, an astronomer from Swinburne University and lead scientist of The Royal Institution of Australia, said it all other possible non-biological means should be ruled out first before believing that the phosphine was produced by lifeforms.

Mars and other giant planets have got more attention in the past as scientists sought signs of life elsewhere in the solar system.