Where are all of the aliens? As President Obama guidelines out Area 51, scientists reveal the very best candidates for extraterrestrials – together with inside our personal photo voltaic system

The hunt for life beyond Earth has taken an unexpected twist as President Barack Obama claims that aliens are real, but that he doesn’t know where they are.

The former president said in an interview that extraterrestrials were ‘not being kept’ in Area 51, a US Air Force base that has long featured in alien theories.

Obama told interviewer Brian Tyler Cohen: ‘There’s no underground facility unless there’s this enormous conspiracy and they hid it from the president of the United States.’

So, with conspiracy theorists’ favourite choice ruled out, where might aliens really be hiding?

Scientists generally believe that the best candidates for alien life are ‘Earth–like’ worlds orbiting distant stars in other parts of the galaxy.

One such contender is the Earth–sized planet TRAPPIST–1e, located just 40 light–years from Earth, which is located safely within its star’s habitable ‘Goldilocks zone’.

But astronomers also believe we don’t need to look so far from home to hunt for alien life.

Even in our own solar system, Saturn’s moons Enceladus and Titan could have the right conditions for life to emerge and thrive.

In a statement on his official Instagram account, Obama clarified his points about aliens, writing: ‘Statistically, the universe is so vast that the odds are good there’s life out there. 

‘But the distances between solar systems are so great that the chances we’ve been visited by aliens is low, and I saw no evidence during my presidency that extraterrestrials have made contact with us. Really!’

Obama’s argument is a variation of a principle which actually plays a key role in the search for alien life.

Professor Mark Burchell, of the University of Kent, told the Daily Mail: ‘The idea is there are so many stars, so many have planets, so many planets are in the habitable zone where the solar heating is enough to permit liquid water on the surface, that something magic happens in a certain per cent of the time and life emerges.’

This is why astronomers focus on looking for solar systems that have worlds with water, since there is a small chance of life emerging on any world where it is present. 

TRAPPIST–1e 

One of the best examples is TRAPPIST–1, an extremely small and cool red dwarf star, with a diameter of just 52,300 miles (84,180 kilometres) and a surface temperature less than half that of the sun’s.

Three of the solar system’s closely orbiting planets fit within the star’s Goldilocks zone – so called because the temperature is just right for liquid water to exist.

Of those, the most promising is TRAPPIST–1e, the fourth planet from the star, which has a mass of 0.692 Earths.

TRAPPIST–1e sits extremely close to its star, but TRAPPIST–1 is so cool that liquid water could still exist on the planet’s surface – making it a great candidate for life.

In a recent study, scientists used the James Webb Space Telescope to measure light filtering through the planet’s atmosphere.

This revealed that TRAPPIST–1e likely has an atmosphere similar to that of Earth, making it more likely that it has managed to hold on to liquid water.

K2–18b

One of the most promising candidates for alien life is the planet K2–18b, which some studies suggest could be teeming with life.

Located 124 light–years from Earth in the constellation of Leo, K2–18b is a giant world covered entirely by oceans – making it what scientists call a ‘Hycean world’.

The planet orbits its cool red dwarf star closely, completing an orbit in 33 Earth days, placing it squarely within the Goldilocks zone.

Most importantly, scientists have used the JWST to detect huge quantities of chemicals that are made by living organisms on Earth.

The researchers picked up the chemical fingerprints of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) – chemicals usually made by microscopic life, like marine phytoplankton.

Speaking at the time of the discovery, lead researcher Professor Nikku Madhusudhan, of Cambridge’s Institute of Astronomy, said: ‘Given everything we know about this planet, a Hycean world with an ocean that is teeming with life is the scenario that best fits the data we have.’

Unfortunately, scientists have since cast some doubt over these exciting claims.

Dr David Armstrong, an expert on exoplanet detection from the University of Warwick, told the Daily Mail: ‘The evidence for life on K2–18b is weak and disputed by a lot of scientists.

‘That’s not to say it’s impossible, but K2–18b is a ‘sub–Neptune’, a planet unlike the Earth, and we still have a lot to learn about even the fundamentals of planets like that before we could confidently claim a detection of life.’

Kepler–62e and Kepler–62f

The twin worlds Kepler–62e and Kepler–62f are another example of astronomers following the water to find alien life.

Located about 1,200 light–years from Earth, Kepler–62 is a seven–billion–year–old dwarf star around two–thirds the size of the sun.

Kepler–62f orbits the star every 267 days and is only 40 per cent larger than Earth, while Kepler–62e orbits every 122 days and is about 60 per cent larger than Earth.

Since both sit inside their stars’ habitable zone, there is a good chance that they are home to liquid water and, therefore, have a chance of hosting life.

In 2015, a NASA research document called Kepler–62f one of the ”most promising planets discovered’ for supporting alien life.

Enceladus

Although it might come as a surprise, scientists actually believe some of the most likely places to find alien life are in our own solar system.

Dr Armstrong says: ‘On Earth, we find life almost everywhere there is liquid water, so the easiest place to look for extraterrestrial life is the same.

‘The most likely place to find it would be in the subsurface oceans of some of the moons orbiting Saturn and Jupiter.’

Saturn’s moon Enceladus is seen as a particularly promising candidate to look for extraterrestrial life because of plumes of liquid water constantly spewing from its South Pole.

With a diameter of 310 miles (500 km) – about as wide as Arizona – Enceladus is Saturn’s sixth–largest moon.

On the surface, conditions are exceptionally cold with temperatures as low as –201°C (–330°F).

However, beneath the frozen surface, there is a vast ocean of liquid water that could provide a home for life.

In 2008, NASA’s Cassini spacecraft flew directly through Enceladus’ icy polar spray and collected samples of ice crystals.

New analysis has shown that these crystals are packed with complex molecules that could be part of the chain of reactions that ultimately lead to life.

Based on these findings, researchers have suggested that the moon now ‘ticks all the boxes’ to be a candidate for supporting alien life.

Titan

Titan, another of Saturn’s icy moons, has also been put forward as a strong candidate in the search for extraterrestrial life.

Scientists used to think that Titan had a wide, open ocean beneath its surface ice, which would mean that heat and nutrients were spread out over the whole planet.

However, recent studies have shown that this is not the entire story.

Using data collected by the Cassini spacecraft, scientists have revealed that Titan has ‘slushy tunnels’ beneath the surface.

This ‘slushy high–pressure ice layer’ is similar to the melting Arctic with a network of aquifers and sea ice.

Lead author Professor Baptiste Journaux, of the University of Washington, told Daily Mail at the time: ‘[This] has implications for what type of life we might find, the availability of nutrients, energy and so on.’

Analyses indicate that the pockets of freshwater on Titan could reach 68°F (20°C) – which is the optimal temperature for life on Earth to thrive.

Any available nutrients would be more concentrated in a small volume of water, compared to an open ocean, which could facilitate the growth of simple organisms.