In 2002, NASA sent radio signals to the Pioneer 12 probe in a routine protocol to send data and ensure communication was established.

This signal also reached a star about 27 light-years from our planet as the transmission spreads out when they come into contact with an object. UC researchers hope that this signal was intercepted by aliens and returned to Earth.

“This is a famous idea from Carl Sagan, who used it as a plot point in the movie Contact,” Howard Isaacson, an astronomer and co-author at the University of California, Berkeley, told Popular Science Homepage (PopSci).

The 1997 film Contact, based on the story by Carl Sagan, tells the story of a SETI scientist who finds evidence of aliens on a distant planet 26 light-years from Earth and chooses to make first contact by sending out radio wave signals.

In this case, the study used signals sent from Earth to Voyager 1, Voyager 2, Pioneer 10, Pioneer 11, and New Horizons, mapping where the signals may have spread when they were sent out into the universe.

These spacecraft have communicated with the Deep Station Network (DSN) radio antennas to download scientific data and telemetry data, according to the study published in the journal of the Astronomical Society Publications.

The Deep Station Network is NASA’s international array of giant radio antennas that support interplanetary spacecraft missions, as well as some that orbit the Earth.

The team determined that transmissions to Voyager 2, Pioneer 10 and Pioneer 11 have already found at least one star.

Pioneer 10 transmissions found a white dwarf star in 2002. Pioneer 10 transmissions will find 222 stars in 2313. “The earliest we can expect a returned transmission is 2029,” the team shared in the study.

Signals for Voyager 1 and New Horizons will find their first stars in the near future. The team calculated the data that nearby stars would be hit with transmissions by considering the rate at which the speed of light covers one parsec every 3.26 years.

This allowed them to determine the time in years for the transmissions to reach each star, as the transmissions to Voyager 1 have yet to reach any.

The signals are predicted to reach one in 2044, and all their transmissions will reach 277 stars in 2341.

“The earliest we can expect to receive a return transmission of potential intelligent extraterrestrial life found by Voyager 1 transmissions is 2109,” the study says.

Transmissions from Voyager 2 have found two objects, which were hit in 2007. By 2336, all 272 nearby stars will have been hit, and experts expect the aliens to return their call by 2033.

Signals set at Pioneer reached a dwarf star in 2018, but scientists said all 386 stars will receive a signal by 2317. And they are looking for a return transmission in 2058.

Transmissions from ‘New Horizons’ have yet to find a star, but will contact one in 2119 and encounter 139 stars in 2338.

“The earliest we can expect to receive a returned transmission is 2232,” the study reveals. “Transmissions to New Horizons will not find a star for up to 75 years after transmissions from any other spacecraft.”

“This difference is mainly due to New Horizons having a later release date and spending less time inside the heliosphere.”

This work gives Search for Extraterrestrial Intelligence researchers a narrower group of stars to focus on, said lead author Reilly Derrick, an engineering student at the University of California, Los Angeles.