Earth might have inadvertently sent messages to alien civilisations – and we could get a reply from aliens before the end of this century, a new study has shown.
A paper uploaded to the pre-print server Arxiv highlights that five planets could receive signals sent to various spacecraft launched from Earth in previous decades.
By 2100, any hypothetical alien civilisations in the right places could have sent a reply to Earth, the researchers say.
The researchers write in their paper, after having left the heliosphere, Voyager 1 and Voyager 2 continue to travel through interstellar space. The Pioneer 10, Pioneer 11, and New Horizons spacecraft are also on paths to pass the heliopause, which is the sun's protective bubble.
“These spacecraft have communicated with the Deep Station Network (DSN) radio antennas in order to download scientific data and telemetry data. Outward transmissions from DSN travel to the spacecraft and beyond into interstellar space.’
The Voyager 2 probe which blasted off from Earth on August 20, 1977 became the second man-made object to leave the solar system in 2018.
The probe blasted off from Earth some 16 days before its twin spacecraft, Voyager 1, but entered the interstellar medium six years after Voyager 1 due to its slower trajectory.
It crossed the outer edge of the sun's heliopause on November 5 2018.
The new study shows that signals sent to probes including Voyager 1 and 2 will travel in the direction of nearby stars – and could in theory be intercepted by alien civilisations.
Reilly Derrick, a student at University of California, Los Angeles' Samueli School of Engineering told Universe Today that the new study was inspired by a 2019 paper which examined what stars the spacecraft would travel past.
Derrick says, "Our paper expands upon this idea by identifying which stars the terrestrial transmissions to interstellar spacecraft will encounter. These transmissions cover a wider volume of the surrounding Universe, meaning they will encounter more stars.
"Additionally, the transmissions from Earth travel much faster than the spacecraft themselves, so we would expect potential intelligent life to notice and return transmissions much sooner."
"Our results include five total stars for which we could expect returned transmissions within the 21st century, and seven total stars for which we could expect returned transmissions within the next 100 years.”
"Although this is obviously a very small number compared to all the stars in the surrounding Universe, the fact that there is even a small chance intelligent life surrounding these stars could recognise human transmissions and communicate back to us within our lifetimes is very exciting."
The researchers add, “These transmissions have encountered and will encounter other stars, introducing the possibility that intelligent life in other solar systems will encounter our terrestrial transmissions.
"We use the beamwidth of the transmissions between DSN and interstellar spacecraft to perform a search around the past and future positions of each spacecraft obtained from the JPL Horizons System.”
Watch: What happens when we find aliens?