Radio telescopes have monitored thousands of distant star systems in the hope of detecting intelligent life – and have so far been met with silence.
NASA and other space scientists believe that aliens might be lurking out of sight in our own solar system – either buried or deliberately concealed.
Here’s the most likely places that we could find alien life a stone’s throw from Earth.
Saturn’s moon Enceladus
Saturn’s icy moon Enceladus ‘has all the ingredients for alien life,’ scientists say
Geyser-like plumes of ice which erupt from the surface of Saturn’s moon Enceladus have offered a new hint that life could lurk in the moon’s subsurface ocean.
Scientists found large carbon-rich organic molecules emanating from a liquid water ocean beneath the moon’s surface.
That makes Enceladus the only other place apart from Earth in the solar system which satisfies all the basic requirements for life.
NASA’s Cassini probe sampled a plume of material erupting from Enceladus’s surface.
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Scientists believe that the complex carbon molecules are linked to chemical reactions between the moon’s rocky core and warm water from an ocean under the surface.
Christopher Glein of the Southwest Research Institute said, ‘Previously we’d only identified the simplest organic molecules containing a few carbon atoms.
‘Now we’ve found organic molecules with masses above 200 atomic mass units. That’s over ten times heavier than methane.’
Under the surface of Pluto
When NASA’s New Horizons probe flew past Pluto, it beamed back quite a few surprises to observers here on Earth.
The early results showed water ice mountains – and hints of possible organics and even a liquid water ocean beneath the surface.
Michael Summers, a planetary scientist on the New Horizons team said, ‘”The connection with astrobiology is immediate—it’s right there in front of your face. You see organic materials, water and energy.
Seth Shostak of the SETI (Search for Extraterrestrial Intelligence) Project says, ‘Under the surface of Pluto there could be pockets of liquid water. Any place you have liquid water -liquid of any kind -maybe have microbes.’
Hidden in our asteroid belt
Fleets of robotic space probes from alien civilisations could already have arrived in our solar systems, a mathematical study found.
Scientists have warned that we may not be able to detect them with our technology – the probes may also be so hi-tech they can “conceal” themselves – perhaps as asteroids among the millions in the asteroid belt.
Earth’s own Voyager probe has only just reached the edge or our solar system – but older alien civilisations could have launched probes long ago, using knowledge far beyond ours, according to a paper in the International Journal of Astrobiology.
The probes would only need to travel around 10% of light speed to explore our whole galaxy within 10 million years.
Duncan Forgan of the University of Edinburgh said, ‘We can conclude that that a fleet of self-replicating probes can indeed explore the Galaxy in a sufficiently short time.. orders of magnitude less than the age of the Earth.’
Under the surface of Mars
The reason NASA’s Rovers haven’t found signs of life on Mars so far could be simple – it’s buried beneath the surface.
That’s not to say the little green men have cities under there – but microbes could cling on underneath the surface.
Future missions will look for geothermal energy sources which could provide lifeforms with the heat they need to survive, NASA says.
NASA says, ‘Here on Earth, we find life in many places where sunlight never reaches–at dark ocean depths, inside rocks, and deep below the surface. Chemical and geothermal energy, for example, are also energy sources used by life forms on Earth. Perhaps tiny, subsurface microbes on Mars could use such energy sources too.’
But Mars is thought to have had an ocean – and, possibly, life – 3.4 billion years ago, just when life was starting to form on Earth, so if we want to find signs of ancient life on Mars, we might need to dig.
On Saturn’s icy moon, Titan
Titan, a moon of Saturn where 300-foot dunes of frozen chemicals roll across the surface could offer a better chance of finding the origins of life than Mars, scientists have previously suggested.
Studies have suggested that liquid water may exist deep under Titan’s surface.
Other data suggest that areas of Titan’s seafloor may be similar to areas of Earth’s seafloors where hydrothermal vents exist.
These passageways into Earth’s interior spout hot, mineral-rich water – and could offer a place for life to thrive.
NASA says, ‘In many respects, Saturn’s largest moon, Titan, is one of the most Earth-like worlds we have found to date.’