Aliens could spot humans on Earth by clocking 12 signs – and top of the list exposes us to E.T 12,000 lightyears away

ALIENS could discover humans on Earth by spotting one of 12 signs, scientists say. Topping the list is a clue that could be seen by extraterrestrials from a mammoth 12,000 lightyears away. The list was created by alien-hunting scientists at the SETI Institute. SETI stands for "Search for Extraterrestrial Intelligence.". They created a list of "technosignatures", which are signs that could give humans away across the vast distances of space.

Topping the list was a type of radio signal called planetary radar. This is when we send a powerful beam of radio waves out into space – and wait for it to bounce back to Earth from an object, like an alien planet. When we get the reflected radio echo, it can be analysed to find out more about the object that the beam hit. Scientists say that these powerful radio signals would be one of the best signs for aliens to look out for.

That's because planetary radar travels over vast distances – exposing us at far greater distances than, say, city lights on Earth. These are visible at distances of up to 10,000 lightyears away – and potentially even 12,000 lightyears. For context, a single lightyear is equivalent to 5.88 trillion miles. Mars is just 0.00002 lightyears away, on average. "Our goal with this project was to bring SETI back 'down to Earth' for a moment," said study author Macy Huston, of the University of California.

"And think about where we really are today with Earth's technosignatures and detection capabilities. "In SETI, we should never assume other life and technology would be just like ours. "But quantifying what 'ours' means can help put SETI searches into perspective.". Aliens might also be looking out for atmospheric technosignatures. They're clues in Earth's atmosphere that show signs that the planet is occupied by humanity.

Scientists say aliens could spot signs like nitrogen dioxide emissions. The upcoming Habitable Worlds Observatory will be able to spot emissions like these from around 5.7 lightyears away. And scientists say that's just beyond Proxima Centauri – the closest star to Earth after the Sun. Once aliens get very close to Earth, they'd be able to see a lot more of the obvious signs. Here's what you need to know...

The Habitable Worlds Observatory (HWO) is a large space telescope. Its mission is to hunt for – and image – Earth-sized habitable worlds. These "exoplanets" will be outside of our own Solar System. The HWO will be an infrared, optical, and ultraviolet telescope, giving it a a broad view of the universe. It's meant to look for planets in the habitable zones of their stars – where it might be possible for water to exist.

It'll use a special coronagraph attachment that blocks out the light of the stars, to better capture views of the planets. The HWO is expected to launch by May 2027, and hopes to identify and directly image "at least 25 potentially habitable worlds", according to Nasa. "It would then use spectroscopy to search for chemical 'biosignatures' in these planets’ atmospheres," Nasa explained. "Including gasses such as oxygen and methane which could serve as critical evidence for life.".

Picture Credit: Nasa. That might include city lights, or heat islands – the temperature differences you'd see from an urban population. They'd also be able to potentially pick up on objects we've put into space, like orbiting satellites or craft on the Moon and Mars. Part of this project is working out whether aliens might stumble upon humanity's existence. But it can also help scientists know what signs to look out for in their own hunt for alien life.

"One of the most satisfying aspects of this work was getting to use SETI as a cosmic mirror," said Dr Sofia Sheikh, of the SETI Institute. "What does Earth look like to the rest of the galaxy? And how would our current impacts on our planet be perceived?. "While of course, we cannot know the answer, this work allowed us to extrapolate and imagine what we might assume if we ever discover a planet, with, say, high concentrations of pollutants in its atmosphere.".

The idea is that scientists will look for signs of technology specifically. Picture Credit: NASA/JPL-Caltech. These will be clues that couldn't be explained by "natural phenomena" – and show that we might be looking at proof of intelligent life. Scientists are already using radio telescopes to track down aliens. Optical telescopes can also be used to scan for laser pulses, which may be a sign of "communications or propulsion".

"Another approach involves studying the atmospheres of exoplanets in habitable zones around stars to look for chemical signatures that might suggest life or industrial activity," SETI explained. "SETI scientists also consider technologies far beyond those currently invented on Earth, such as Dyson spheres, but these far-future technologies were not considered in this study.". The research was published in The Astronomical Journal.