Astronomers have decided to make another pre-emptive move in contacting alien life, beaming out a welcome message to a neighbouring star system. By their calculations, we could get a message back within 25 years.

The target of the message is Luyten's star, or GJ 273; a red dwarf some 12.4 light-years away in the Canis Minor constellation. One of its orbiting planets, GJ 273b, is currently one of the best candidates we have for a system containing habitable planets.

According to the Messaging Extraterrestrial Intelligence (METI) International organisation, which is behind the broadcast, the odds are against a reply coming back from outer space, but you never know.

"I think that's an unlikely outcome, but it would be a welcome outcome," METI president Douglas Vakoch told Dan Falk at New Scientist.

The transmission sent out from the radio telescope in Tromsø in Norway last month included information about our maths and geometry, as well as a description of how radio waves work, and a tutorial about how we keep time here on Earth.

Everything was packed together in a binary system of two alternating frequencies, pulsing at 125 times per second. In total, it took around eight hours to send across three days.

"It's like creating a puzzle," one of the team, cognitive scientist Mike Matessa, told Emma Grey Ellis at Wired. "We tried to make it as easy as possible, but it's really challenging when you can't refer to anything in your culture, only science."

The message was sent almost exactly 43 years after the Arecibo message, humankind's first attempt to strike up a conversation with life elsewhere in the Universe, and named after the telescope in Puerto Rico that it was sent from.

Not everyone agrees that this kind of reaching out into the cosmos is such a good idea, though.

Stephen Hawking has been among those to argue that we're just inviting trouble on ourselves, and it's a view shared by many at the SETI (Search for Extraterrestrial Intelligence) Institute, the organisation that METI emerged from.

"Ninety-eight percent of astronomers and SETI researchers, including myself, think that METI is potentially dangerous, and not a good idea," Dan Werthimer, a chief scientist at SETI, told New Scientist.

"It's like shouting in a forest before you know if there are tigers, lions, and bears or other dangerous animals there."

For their part, Vakoch and his colleagues at METI say that even passively listening out for alien life is going to reveal our existence anyway, so there's little point in trying to hide.

"Any civilisation that could travel to Earth to do us harm could already pick up our leakage television and radio signals," Vakoch told Hannah Osborne at Newsweek. "So there's no increased risk of alerting them of our existence."

"Earth's atmosphere has been giving off evidence of life's existence for two and a half billion years, thanks to the oxygen in our air."

Whatever you think about METI's approach, chances are we won't have to worry about anyone or anything getting back to us for a few decades yet, but a more advanced message is already being proposed for 2018.

Included in the broadcasts is a date – a date when METI astronomers will be listening out for a response. It might just be worth circling 21 June 2043 in your diary.

"The only way we'll get a reply back from GJ273b is if the entire galaxy is filled with life," Vakoch told Newsweek. "It's certainly possible we'll get a reply, but more likely we'll need to ping many, many more stars before we get a response."