Radio signals sent to NASA spacecraft could have already reached four neighbouring star systems, and if any aliens tried to respond, we might hear from them within a few years from now.
If aliens are nearby and listening in on our spacecraft command signals, we could hear back from them as early as 2029.
 |
| A radio antenna at the Deep Space Network’s Canberra facility in Australia NASA/Canberra Deep Space Communication Complex |
Since 1972, NASA has used a system of radio antennae called the Deep Space Network (DSN) to track spacecraft and send powerful radio signals towards them.
Howard Isaacson at the University of California, Berkeley, and Reilly Derrick at the University of California, Los Angeles, worked out which stars these radio signals may have reached and when the earliest responses could be received on Earth.
“In the search for extraterrestrial intelligence, we’re always thinking about the best places to look because we can’t look at every single place at once,” says Isaacson.
To do this, Isaacson and Derrick mapped out the paths of five spacecraft – Voyager 1 and Voyager 2, which have left our solar system, and Pioneer 10, Pioneer 11 and New Horizons, which are heading that way – and the radio signals sent to those spacecraft during their travels. They then used the comprehensive Gaia catalogue of stars in our local neighbourhood to see which star systems those signals would reach and when.
They found that the DSN signals have already reached four stars. Aliens living near one of them, which lay in the path of Pioneer 10’s received signals, could theoretically have sent a response that would reach Earth by 2029. Replies from aliens near two more star systems, reached by Voyager 2’s signals, could reach us in 2031 and 2033.
We know little about whether these stars have planets around them or if they could be hospitable for life because they are much fainter than our own sun, says Isaacson, so any exoplanets would be difficult to detect. But statistically planets appear to be relatively common and there should still be many undiscovered planets, he says.
“It’s hard to know whether any given strategy is the one that will ultimately lead to contact with our counterparts on another planet, but Derrick and Isaacson have provided another valuable tool in our collection of methods to refine the search,” says Steve Croft at the University of California, Berkeley.
Reference:
Publications of the Astronomical Society of the PacificDOI: 10.1088/1538-3873/acc1a1