In the 1970s, Nasa sent maps revealing Earth's location into space on board four craft, in the hope of communicating with aliens.

But Dr Frank Drake, who designed the maps, has now spoken out about the potentially "dangerous" decision to send the charts over 40 years ago.

All four crafts have now left the solar system and are speeding into deep space with Earth's co-ordinates on board, according to the Daily Mail.

Dr Drake worked with Nasa to design charts placed aboard Pioneer 10 and 11, launched in 1972 and 1973.

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And similar maps were placed on Nasa's 1977 probes Voyager 1 and Voyager 2.

In a new interview, Dr Drake spoke about the maps he helped design.

"In those days, all the people I dealt with were optimists, and they thought the ETs would be friendly,' he told his daughter, Nadia Drake, who writes for National Geographic.

"Nobody thought, even for a few seconds, about whether this might be a dangerous thing to do."

Plaques placed inside the Pioneer craft show a man and a woman alongside a basic map of Earth which plots its position in relation to distant pulsar stars.

Each record was etched with a map similar to those placed on the Pioneer craft. Photo / Nasa
Each record was etched with a map similar to those placed on the Pioneer craft. Photo / Nasa

These stars are long-lasting and bright so could still point aliens in the right direction if they are found millions of years from now.

The Voyager probes launched into space with golden records on board etched with similar pulsar maps to our planet.

The goal was to put something on the Voyager that said where it came from, and how long it was travelling.

The records contain sounds from nature, such as volcanoes and thunder, as well as noises linked with humanity including a train, a horse and cart, and even a kiss between a mother and child.

Despite the potential dangers the interstellar maps pose, Dr Drake said that the chances of aliens picking up the messages are "very small".

A gold record in its cover, attached to a Voyager space probe, USA, circa 1977. Photo / Getty Images
A gold record in its cover, attached to a Voyager space probe, USA, circa 1977. Photo / Getty Images

He added: "The thing is going something like 10 kilometres [6.2 miles] per second, at which speed it takes - for the typical separation of stars - about half a million years to go from one star to another."

The astronomer is not the first expert to warn of the risks of contacting aliens.

Renowned physicist Professor Stephen Hawking suggested last year that meeting beings from another planet could lead to humans being wiped out.

Hawking said it could be similar to when the Native Americans first encountered Christopher Columbus - and "that didn't turn out so well".

The physicist believes if aliens discovered Earth, they are likely to want to conquer and colonise our planet.