Will we ever find aliens?

When and where are we most likely to find extraterrestrial life?

Curiosity. It’s why we smear bee vomit on our bread and stir tea with a cow’s breast milk.

It’s why the co-founders of Google have amassed a fortune they cannot count. It’s why we’re still pissing about.

Curiosity lured the tetrapod out of water, the hominid out of the savannah, and the human onto the moon.

And curiosity is driving mankind’s obligation to find out whether we’re alone in the universe.

Around 450 BC, Greek philosophers pondered the existence of other worlds, including Anaxagoras, who thought the Sun was a star like all the others.

In 300 BC, Epicurus the… curious just came out with it and said, “There are infinite worlds both like and unlike this world of ours. We must believe that in all worlds there are living creatures and planets and other things we see in this world.”

Acquiescing to curiosity’s demand to look to the skies, in 2 BC, Babylonian astronomers discovered Mercury, Venus, Mars, Jupiter and Saturn. In the early 15th century, pretty much everyone believed that the Sun orbited around the Earth. But the 16th-century astronomer Nicolaus Copernicus had to tell everyone that that wasn’t true – and that it was actually the opposite. In the same century, Catholic monk Giordano Bruno said “there are countless suns and countless earths all rotating around their suns”, and was accused of heresy.

In the early 17th century, curiosity struck Galileo Galilei, and he pointed his telescope at Jupiter. The planet itself was a sight to behold. A giant caramel trifle with a dried apricot pressed against the bottom of a round glass. But to Galileo’s surprise, he saw four dots orbiting it. Now grouped together as the Galilean moons, those dots were to be called Ganymede, Callisto, Io and Europa.

Curiosity struck! Christiaan Huygens discovered Saturn’s rings and its largest moon Titan. William Herschel discovered Uranus (please) and Saturn’s moon Enceladus. Giuseppe Piazzi discovered dwarf planet Ceres. Johann Galle and Urbain Le Verrier discovered Neptune. William Lassell discovered Neptune’s Triton. Clyde Tombaugh discovered Pluto.

In the early 20th century, Edwin Hubble was hired to work with the largest telescope at the time on top of Mount Wilson. He discovered that the small, faint clouds of light in the sky were actually galaxies, each containing hundreds of billions of stars.

In 1990, Voyager 1, the furthest human object from the Earth, took the most distant photograph of Earth. The astronomer to popularise science, Carl Sagan, described the Earth as just a “pale blue dot”. At the time, we didn’t know whether stars had planets, let alone any like Earth. With this came the question “are we alone?” – and we’ve been asking it ever since.

Life, at least as we know it, needs liquid water, an energy source and six chemical building blocks (carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur). Liquid water on Earth exists because it sits in the Goldilocks zone, where temperatures are not too warm, not too cold, but just right. The study of life on Earth acts as a template we can compare with other planets.

On 6 March, 2009, at precisely 10:46:57pm EST, Nasa’s Kepler mission launched. Little did we know that it was about to completely change our view of the universe, and our place in it.

For a little over four years, the Kepler telescope pointed to a patch of sky in search of distant worlds. It measured the dip of over 150,000 stars’ glow as a planet passed in front. In May 2013, Kepler lost its ability to stay pointed to its target without drifting off course. But with the pressure of sunlight to balance it upright, Kepler was up and running again a year later. Feeling better than ever, the Kepler mission evolved into the K2 mission, which studies a specific portion of the sky every 80-odd days.

What Kepler’s doing isn’t easy. It’s like trying to see a fruit fly pass in front of a car’s headlight trillions of kilometres away, and trying to see if the headlight dims a little. Well, Kepler has so far spotted 4,706 possible exoplanets (planets that orbit a star other than the Sun) and confirmed the existence of 1,041 – and the number keeps piling up.

The Kepler team couldn’t believe with was happening. One of those exoplanets is Kepler-452b, or Earth 2.0, the first near-Earth-sized planet in the Goldilocks zone around a Sun-like star. The catch? It’s 1,400 lightyears away (ie, the earliest you’ll get there is in 1,400 years’ time).

The biggest and hottest opportunities of other life are found orbiting the smallest and coolest stars. Astronomers call these stars M dwarfs. Using Kepler’s data, David Charbonneau and Courtney Dressing of Harvard University estimated that there is approximately one Earth-sized planet orbiting in the Goldilocks zone for every four M dwarfs. Astronomers estimate that there are 200bn M dwarfs in our galaxy alone. So if we do the maths, there could be up to 50bn Earths. Life in the universe may be plentiful.

The closest Earth-like planet to us is the unconfirmed Tau Ceti e, which, at around 12 light years away, is just around the corner, astronomically speaking. So we could, at best, get there in about 12 years. But I wouldn’t pack your bags anytime soon – humans so far have only been able to travel as far as the moon, which is 400,000km away. Tau Ceti e is 112,600,000,000,000km away (or 3.65 parsecs in Star Wars talk). If we’re to find aliens, we’ll first need probes, telescopes and satellites.

Unless, of course, they find us first.

In 1984, radio astronomer Frank Drake founded the Search for Extraterrestrial Intelligence (Seti) Institute, which tries to detect light and radio signals left behind by aliens. So far they’ve found nothing. But during a talk at Nasa’s 2014 Innovative Advanced Concepts event, Seti’s senior astronomer Seth Shostak said that by around 2040, astronomers will have scanned enough stars to give Seti a chance to discover alien-produced signals. Maybe what’s needed isn’t necessarily patience but money.

Drake had come up with an equation, now called the Drake Equation, in 1961, to estimate the number of technological civilisations that may exist in our galaxy. There isn’t an answer but scientists still examine the factors. The original estimation says there are almost 19m alien civilisations. Today’s optimistic estimate says there are 72,800 alien civilisations. Today’s sceptical estimation says there is…one.

Stephen Hawking and Russian billionaire Yuri Milner have recently announced a $100m initiative, called Breakthrough Listen, to speed up the alien-finding process. The ten-year project aims to use the world’s two biggest telescopes and will give $1m to anyone who can find aliens first. Breakthrough Listen will widen the search by using open data and open source software. This search is said to be 50 to 100 times more powerful than Seti’s and anyone else’s attempts.

“We believe that life arose spontaneously on Earth, so in an infinite universe there must be other occurrences of life . . . [Breakthrough Listen] is sure to bear fruit,” said Hawking at the Breakthrough Listen launch. “If a search of this scale and sophistication finds no evidence of intelligence out there it will be a very interesting result. It will not prove that we are alone, but it will narrow the possibilities.”

This is a big gamble but it could have a massive payoff. “Buying more telescope time, increasing the range of wavelengths being scanned, enhancing detector sensitivity and extending sky coverage have been argued as prerequisites if a breakthrough within a decade is to be achieved,” astronomer and astrobiologist Chandra Wickramasinghe of Buckingham University tells me.

A planet needs more than just liquid water to support life. Its atmosphere has a lot to do with it, too. Take Venus: named after the Roman goddess of love and beauty because of its benign and ethereal appearance, it is far from cute. It has a surface temperature of almost 500oC – hot enough to melt lead. Early Venus apparently had plenty of liquid water, which was lost due to its thick atmosphere that trapped heat from the Sun in what’s called a runaway greenhouse effect, scorching Venus to oblivion. So a planet’s atmosphere is vital.

Astronomers use computer models to calculate the kind of atmosphere a planet would need for liquid water to exist. In our attempts to get better at these predications, Nasa plans to launch the Transiting Exoplanet Survey Satellite (Tess) in August 2017. It will work on finding planets around the nearest stars in the solar neighbourhood, so that detailed characterisations of their atmospheres can be conducted with the next generation of spectroscopic missions, such as Nasa’s James Webb Space Telescope – Hubble’s successor, scheduled to launch in October 2018.

“The Tess mission will find many planets, and these will be much closer to us than those found by Kepler, so these will be easier to follow up on to try to measure gases in the planets' atmospheres that only life can produce,” says astronomer and actor Aomawa Shields.

But what if the answer is right under our noses, in our solar system? Jupiter’s moon, Europa, is thought to be the place in our solar system most likely to harbour aliens.

Europa is a ball of ice. But scientists believe there is a very active ocean beneath its icy surface. In Arthur C Clarke’s science fiction novel 2010: Odyssey Two, Europa is discovered by the crew of a doomed Chinese spacecraft Tsien, who reported that there was life underneath the ice, living in a sub-surface ocean.

You’ll have to get through about 20km of Europa’s ice to get to an ocean 150km deep – over ten times deeper than Earth’s oceans. Photosynthesis wouldn’t work in an ocean so dark. But tidal heating could be warming the ocean. Tidal heating is caused when the energy of moons and planets dissipate as heat in their crust, warming what’s their insides and driving plate tectonics. This idea is proving to be more believable since the 2014 discovery of plate tectonics on Europa.

Plate tectonics are important because they can deliver organic material left behind by comets to an underworld for life to form and eat. Europa also a thin of oxygen atmosphere which can penetrate through its layer. Now, don’t expect Europa’s aliens to look like something out a Ridley Scott movie – they’ll probably be microbes called extremophiles. Extremophiles on Earth are badass, but even the most hardened critters cannot survive temperatures as low as -30oC. Europa’s water temperature may be -50oC.

Jupiter’s other icy moons, Ganymede and Callisto, are probably neck-and-neck candidates for biology. Like Europa, they may have oceans around 100km deep. But you’d have to get through 150km of ice and rock to get to it.

In 2009, Nasa and Esa announced plans for a joined mission called the Europa Jupiter System Mission (EJSM-Laplace). It was expected to launch around 2020 with a focus on mainly Europa and Ganymede. But in 2011, Nasa pulled out until it could get its funding issue sorted out.

In 2012, Esa decided to go it alone and announced the Jupiter Ice Moon Explorer (Juice) mission. Juice hopes to freshly squeeze out signs of life in the 2030s by flying past Callisto, Europa and Ganymede. With Juice’s help, the Russian Space Research Institute hopes to land a probe on Ganymede called Laplace-P. They’ve opted for Ganymede because the radiation there is less extreme than Europa’s.

Nasa will be contributing to Juice but announced last year that it will be launching its own $2bn flyby mission to Europa in the 2020s called the Europa Multiple Flyby Mission, possibly with a lander that will drill through the ice and collect some samples. Esa wants to throw in an extra €500m to the mission because it believes the Americans can’t travel to Europa without the Europeans.

I understand Nasa wants to see its name in lights if the news of life on Europa arrives, and know Nasa can get things done, but I think Nasa should leave Esa to focus on Jupiter’s moons and turn its attention to Saturn’s moons Titan and Enceladus. They, too, are possible places for life.

The icy moon Enceladus is small but could be hiding a huge number of things – an ocean 10km deep for one. In 2005, Nasa’s Cassini spacecraft took a photo of geysers of frozen water, salts and organic material shooting out of its southern hemisphere. This hints towards some kind of hydrothermal activity. The great thing about Enceladus is that if it does have life, it’ll be fairly easy to find as bits of what’s in it always gets thrown out, just waiting for us to grab.

The German Aerospace Centre sponsored mission Enceladus Explorer mission hopes to land a probe on Enceladus that will melt through the ice to see the ocean. Moreover, as part of Nasa’s Discovery Programme, several Enceladus-related missions have been proposed. The Enceladus Life Finer and Journey to Enceladus and Titan (Jet) will assess the habitability of Enceladus and Titan. The Life Investigation for Enceladus (Life) will capture icy particles from Enceladus and return it to Earth for study. The winner of the competition will have Nasa fund its development for launch by the end of 2021. Place your bets.

Imagine a world that sports lakes, rivers, oceans, rain, snow in the form of liquid methane. That’s Titan. Titan, with the exception of Earth, is the only place in the solar system with a nitrogen-rich atmosphere. The nitrogen atmosphere causes a greenhouse effect so any bit energy from the Sun could be trapped for life to use. Titan has no oxygen so creatures there would have to find some other way to breathe.

Titan has made astronomers think outside the box. What if the formation of life doesn’t require the same chemistry as life on Earth? Life could demonstrate a different type of origin – a second genesis. The closest thing Earth has to a Titan-type critter are extremophiles Hesiocaeca methanicola. They colonise methane ice and can survive in an anoxic environment for almost 100 hours. Titan is a manifestation that every world is unique and we must welcome the possibility of life on non-Earth-like worlds, too.

Nasa and Esa has plans for a $2.5bn Titan Saturn System Mission (TSSM) to Titan and Enceladus. It includes a hot-air balloon floating in Titan’s atmosphere, conducting research for six months. TSSM was expected to launch in 2020, but its competition was lost in 2009 to EJSM-Laplace. TSSM will hopefully launch at a later date.

Along with the possibility of the Jet mission, Nasa would like to launch the Titan Mare Explorer (Time) mission. The mission would involve a relatively cheap lander splashing down in a lake in Titan’s northern hemisphere and floating on the surface for a few months.

The mission was cancelled in 2012 in favour of the InSight lander which was set to launch to Mars in March 2016 but has since has hardware problems and will, if costs are decent, launch at a later date. If the Time mission does reopen then a logical follow-up would be to dive into Titan’s lakes. In 2015, Nasa awarded a grant to the Titan Submarine mission.

A project known as the Titan Lake In-situ Sampling Propelled Explorer (Talise) was proposed in 2012 by Spanish-based firm Sener and the Centro de Astrobiología in Madrid. Talise is different from Time because it includes a propulsion system so it wouldn’t just drift once it falls into the lake.

The Aerial Vehicle for In-situ and Airborne Titan Reconnaissance mission was proposed in 2012 by James Barnes of the University of Idaho and hopes to fly through Titan’s atmosphere and take HD photos. Nasa rejected its $715 million request so the project might not happen. So, all in all, there could be plenty of Titan projects underway.

But what about life on Mars?

We have synonymised Mars with life. But let’s face it, Mars isn’t much to look at – there’s almost nothing but miles and miles and dust and rubble. But back in the day, Mars had an atmosphere thick enough to support liquid water. In September 2015, Nasa confirmed that liquid water intermittently flows on Mars.

Nasa’s rover Curiosity landed on Mars soil on August 6, 2012. Two weeks later, it spun its wheels on Martian soil in search of evidence of ancient microbial life. In December 2014, Curiosity recorded “burps” of methane – perhaps the burps of living organisms? So Mars has water and methane? Astronomers are intrigued.

Since the UK’s Beagle 2 disappearance, which, after 12 years, was found surprisingly intact near its original touchdown point, Europe is making another attempt at landing on Mars. Esa’s ExoMars mission blasted off from Kazakhstan on 14 March and is the first mission to specifically focus on whether there is or has ever been life on Mars. Esa hopes this mission also will pave the way for a future Mars sample return mission in the 2020s.

Other potentially life friendly candidates include dwarf planet Ceres and Neptune’s largest moon Triton. Ceres is the largest object in the asteroid belt. It has the second largest reservoir of water to Earth in the inner solar system and gets a decent amount of heat from the Sun. In 2014, the Herschel Space Observatory announced evidence of water-vapour emissions from Ceres, thus the possibility of a subsurface ocean. Nasa’s Dawn mission launched in 2007 is currently and studying orbiting Ceres.

Using restored data from Voyager 2’s 1989 encounter with Neptune, Nasa released a detailed map of Triton in 2014. The icy moon could be using Neptune’s orbit to create tidal heating, melting areas of the subsurface into an ocean. Nasa thinks Triton it’s a prime target but there’s been no aims to land on Triton any time soon as all the money has gone to Jupiter and Saturn projects. This is a shame because, in my opinion, Ceres and Triton are just as much candidates for life as the other bigshots.

I ask Professor Andrew Knoll of Harvard University what the chances are of finding alien life in our lifetimes are: “I think it’s a long shot, although not impossible. I doubt that we’ll find evidence of life on Mars or elsewhere in our solar system but would happily be proven wrong! I’d place my bets on the characterisation of exoplanets,” he says.

Ok, so maybe we shouldn’t expect too much from our solar system. But with respect to Fermi’s Paradox, if the number of Earth-like exoplanets is apparently high, why aren’t aliens obvious?

“Being the same size and temperature as the Earth doesn't guarantee the presence of life. It could be that the events that led to life gaining foothold on the Earth were so rare that we are effectively alone,” Charbonneau tells me.

Life, let alone intelligent life, may well be the rarest phenomenon in the entire universe. A phenomenon that only the “pale blue dot” has the privilege of looking after. Life is still a mystery to us. We’ve tried to simulate the conditions of Earth when life first emerged but, at best, it’s only produced complex organic molecules. If we have no explanation for life and its ability to reproduce, are we really prepared to explain the commonness of aliens?

Earth is 4.6bn years old. That’s unfathomably old. We’re Earth’s last second phenomenon. In 500m years, the Sun will make Earth too hot for us to live on. But Earth has fought a good fight. It has had its atmospheric composition repeatedly changed while its ability to absorb heat has fluctuated as the amounts of water, clouds, rock and land have changed in response to geological and biological evolution. And all while the Sun gets hotter.

But for some weird reason, these fluctuations have cancelled each other out. The Earth’s has stayed warm and wet for most of its life. It wasn’t an inevitability but it was certainly essential for the continuation of life. So why did it happen?

Did an anthropomorphic, English-speaking, Anglo-Saxon, pro-American Time Lord do it? Well, at this point, I wouldn’t completely rule it out right. Maybe Gaia? Gaia proposes that a complex biosphere evolves to maintain or enhance the stability of the Earth’s climate. Some scientists disagree with this and say a complex biosphere is the consequence of stable climate, not the cause.

Even if Gaia were true, some of Earth’s events would have to have been by sheer luck. 66m years ago, an asteroid impact wiped out the dinosaurs. There’s no reason why it couldn’t have been big enough to wipe out all other living things indefinitely.

In a universe with 1,000,000,000,000,000,000,000,000 planets, statistics make it so that fortuitous cancellations maintain life-friendly conditions. And if you believe in multiverses then the chances are even greater.

Geophysicist David Waltham writes in his book Lucky Planet:

“We are most likely living on a second-best planet in a second-best universe . . . advanced civilisations elsewhere are inevitable – but they will also be so far away that we will never be able to communicate with them or even observe influences they may have on their galactic neighbourhoods.”

The universe is a dangerous place; objects are constantly colliding with others and things are constantly being thrust across space. Early Earth had its fair share of beatings. So it should come as no surprise when I say that life may be one of those “things”. If life is a cosmic phenomenon and its genetic components are in the form of viruses and bacteria, then they can be continually exchanged over a cosmic scale. So you would expect life to be everywhere. And if the cosmic process, like on Earth, leads to smart things like us, then that same process would take billions of years to evolve on other worlds.

“The requirement, however, is that we establish firmly that life is a cosmic phenomenon, and that can be done with much more modest levels of investment than has been doled out for revamping Seti-type projects,” says Wickramasinghe. “That would be the first step in establishing that we are not alone in the universe.”

Charbonneau adds:

“Data tells us that planets are exceedingly common, but as for life we must remain open-minded about whether we live in a Star Trek universe (with inhabited worlds around every star), or whether we are a cosmic rarity. What is exciting is that, for the first time in human history, we don't have to limit ourselves to speculation. Instead, we can reasonably aspire to build the telescopes that will look for the chemical signatures of life on planets circling distant stars.”

Aliens, we’re coming for you.

Tosin Thompson writes about science and was the New Statesman's 2015 Wellcome Trust Scholar.