SCIENTISTS and science journalists often share a weary refrain whenever a story with a whiff of the extraterrestrial raises its head: it isn鈥檛 aliens. It is never aliens.
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While firm evidence of life beyond Earth would be the discovery of the century, we have been burned too many times before 鈥� most notably in 1996, when excitement about supposed fossils in a Martian meteorite inspired the-then US president Bill Clinton to make a statement from the White House lawn.
President Donald Trump hasn鈥檛 made any public pronouncements about the discovery of phosphine, a molecule that may have a biological origin, on Venus. Yet it has tested the resolve of the 鈥渘ever aliens鈥� crowd. Could it really be that after all the time we spent looking for life on rocky Mars, it was waiting to be discovered in the hellish clouds of Venus?
Working out what is happening there will require much more investigation, with studies of Venusian chemistry (see 鈥�To understand signs of life on Venus we must do chemistry on Earth鈥�) and a fleet of spacecraft explorers (see 鈥�Missions to confirm signs of life on Venus are already in the works鈥�) now in the planning stages. But even if we confirm that the phosphine is produced by alien microbes, not some as-yet unknown geological process, this isn鈥檛 Star Trek 鈥� we won鈥檛 be chatting to these new aliens. If we want to find intelligent life forms, we must almost certainly look further afield.
鈥淛ust because life may be common, it doesn鈥檛 follow that intelligent life awaits us in the stars next door鈥�
Here, the size of the universe is both a blessing and a curse. Our galaxy contains billions of planets, so even if the odds of life arising on a particular world are tiny, there is a good chance it has happened many times over. The possible detection of the first planet outside our galaxy (see 鈥�Astronomers may have found the first planet in another galaxy鈥�) only increases the odds.
Yet just because life may be common, it doesn鈥檛 follow that intelligent life awaits us in the stars next door. New work suggests intelligence is rare and any civilisations are likely to be thousands of light years apart (see 鈥�Why we鈥檙e in for a long wait to hear from intelligent aliens鈥�). Barring a way to break the speed limit of the universe 鈥� which, granted, isn鈥檛 an impossibility 鈥� we will probably never receive a message from another world, let alone galaxy-crossing visitors landing a flying saucer at the White House.
So even if we do find aliens, they probably aren鈥檛 going to be alien aliens. For all intents and purposes, then, we may really be alone.
