For centuries it has been one of the most vexing mysteries for mankind: are we, the seven billion inhabitants of this wondrous blue planet really alone, or is there life somewhere out there in the universe?
Yesterday, we came a step closer to answering that tantalising question with the landmark announcement by nasa scientists of the discovery of a new solar system that has at least three Earth-like planets — with climates that just might support life.
The kind of planets that a certain ET might have called home.
The discovery by an international team using advanced telescopes in space and at far-flung locations around the world has caused a frenzy of excitement among astronomers who, as a breed, are not given to hyperbole.
However, it is being described as the ‘holy grail’ for researchers.
The intriguing new planets are comparatively near neighbours, too, at just 39 light years from Earth. Granted, 39 light years (234 trillion miles) is hardly a short hop.
But that relative proximity will enable astronomers with ultra-sophisticated telescopes and scanners to focus on the planets and confirm if there is water and the benign atmosphere needed for life to thrive.
Thomas Zurbuchen, associate administrator of Nasa’s Science Mission Directorate in Washington DC, said yesterday: ‘These questions about “are we alone” are being answered as we speak, in this decade and the next decades. This story gives us a hint that finding a second Earth is not just a matter of if, but when.’
Scientists have long speculated that life-supporting planets must exist somewhere in the universe, but none has ever yet been confirmed as potentially life-sustaining.
Now astronomers say they have detected no less than seven Earth-sized worlds orbiting a red dwarf star — the equivalent of our sun — called TRAPPIST-1.
The seven planets are believed to be at least a billion years old and, in theory, all could have lakes and oceans. But three are too close to the star and, therefore, likely to be too hot to have water, while the furthermost planet is too cold.
It is the three planets in the middle (named TRAPPIST-1 ‘e’, ‘f’ and ‘g’) that are generating the most interest as they lie in what is known as the habitable ‘Goldilocks Zone’ — neither too hot nor too cold for life to thrive.
The surface temperatures range from zero to 100c, so water won’t boil off as vapour.
In addition, planet ‘e’ is very close in size to Earth and receives about the same level of light from its star.
The Trappist-1 star, an ultra-cool dwarf, has seven Earth-size planets orbiting it. This graphic shows how the outer orbiting 1h is an icy planet, while inner orbiting 1b, 1c and 1d are likely to be hot and dry. Though the researchers claim that all seven planets could feasibly have water at their surface, it is planets 1e, 1f, and 1g that are most likely to have water oceans
This chart shows, on the top row, artist impressions of the seven planets of Trappist-1 with their orbital periods, distances from their star, radii and masses as compared to those of Earth. The bottom row shows data about Mercury, Venus, Earth and Mars. The seven planets’ orbits are closer to their star than Venus, Earth or Mars, and are therefore significantly shorter
HOW MIGHT HUMANS EXPLORE THE NEW PLANETS?
Solar sails use the radiation of stars to propel spacecraft forward without conventional fuel. An artist’s impression of solar sails is shown here
Engineers have been developing new space travel technologies to reach exoplanets outside of the solar system for a decade.
Travel between star systems is difficult because storing enough conventional fuel to travel interstellar distances without heavily weighing down the spacecraft is near impossible.
To travel light years in a lifetime would require spacecraft that can travel far faster than current technology allows.
But some scientists have proposed new methods of transport that do not use conventional rocket fuel.
A soap-sized probe was developed earlier this month that uses photon sails driven by radiation from stars to propel it through space at 14million metres per second (46million feet per second).
The probe weighs 100 grams (0.2lbs) and measures only a few inches. It was designed to investigate nearby exoplanet Proxima b located around four light years from Earth.
But whether this model could ever scale up to carry humans is debatable.
Another option put forward by researchers is to use nuclear detonations in space to propel a spacecraft forward on the shock waves at rapid speeds.
‘Nuclear Pulse Propulsion’ would not involve detonating nuclear weapons on the spacecraft – a long ship would be fitted with a larger pusher plate.
Weapons could be detonated a safe distance behind the craft so that the pusher plate could catch the shock wave.
Planet ‘f’ is potentially water-rich and gets about the same amount of light as Mars. Planet ‘g’ is the largest: its radius is about 13 per cent larger than Earth’s.
Measurements of the planets’ density suggest the innermost six are rocky, too, just like Earth.
No other known star system contains such a large number of Earth-sized and probably rocky planets, another factor in encouraging life to form.
The research, published in the journal Nature, was led by the STAR Institute at the University of Liege in Belgium.
It used Nasa’s orbiting Spitzer Space Telescope in addition to ground-based facilities, including the Liverpool Telescope, operated by the Liverpool John Moores University (LJMU) Astrophysics Research Institute (ARI).
Dr Chris Copperwheat, an astronomer from LJMU, who co-led the international team, says: ‘The discovery of multiple rocky planets with surface temperatures that allow for liquid water make this amazing system an exciting future target in the search for life.’
In fact, it was the robotic telescope operated by LJMU that played a major role in the discovery.
Located on La Palma in the Canary Islands, it detects planets using the ‘transit’ method.
It monitors dips in the light output of a star — in this case TRAPPIST-1 — caused by planets passing, or transiting, in front of it and allows astronomers to infer information about size, composition and orbits.
TRAPPIST-1 is in the constellation of Aquarius: perhaps appropriately, the ‘water carrier’.
An artist’s conception showing what the Trappist-1 planetary system may look like based on data about their diameters, masses and distances from the host star. The planets are labelled 1b-1h and each could have water on its surface given the right atmospheric conditions, meaning that all could potentially host alien life
Comparing the Trappist-1 system with the solar system. The left image compares the sizes of the main objects of the solar system with the planets of Trappist-1. The Trappist-1 star is small, barely bigger than Jupiter. The planets of Trappist-1 are comparable to Earth. The right image shows the amount of energy received from the star (vertical axis), which for Earth = 1. Numbers indicate how much flux (2 = twice more, ½ = half) a certain distance corresponds. Sizes of the planets are relative
View of the Trappist planetary system from above. The star is at the centre and the planets are in orbit around it. Their relative position corresponds to what the system would have looked like when the researchers saw the first planet pass in front of the star. The relative sizes of the planets are correct, but on a different scale to their distance to the star
|Name||Orbit (days)||Mass (where 1.0 = mass of Earth)||Distance to star (millions of miles)||Distance to star (millions of km)||Possibility of hosting alien life|
|1b||1.5||0.85||1.02||1.64||Less likely – too hot|
|1c||2.4||1.38||1.39||2.24||Less likely – too hot|
|1d||4||0.41||1.95||3.14||Less likely – too hot|
|1h||20||unknown||5.58||8.97||Less likely – too cold|
It is very small for a star — its mass is less than a tenth of our Sun’s and only marginally bigger than Jupiter.
It is described as a ‘quiet’ star, emitting some solar flares, but not strong enough to wipe out life. It is because the star is so dim that the planets orbiting it are warmed gently, despite having orbits that are much smaller than that of Mercury, the planet closest to the Sun in our solar system.
The three most promising planets receive similar amounts of solar energy to Venus, Earth and Mars, and Nasa’s Hubble Space Telescope is already searching for atmospheres around them. Some scientists are predicting we will know within a decade if any of the planets harbour life.
And if there are life forms, they will have had much longer to evolve than we have on Earth — thanks to their relatively low temperature, dwarf stars such as TRAPPIST-1 burn through their supply of hydrogen less rapidly than stars such as the Sun. While the Sun has an estimated lifetime of ten billion years, dwarf stars may exist for trillions.
As well as focusing on the new solar system, the international team of astronomers will go on to search 1,000 of the nearest ultra-cool dwarf stars to Earth in the hope of identifying more Earth-like planets in new solar systems.
Indeed, experts at Nasa’s Science Mission directorate say the project is in the ‘gold rush’ phase. Dr Emmanuel Jehin, another member of the Liege team, says: ‘With the upcoming generation of telescopes, such as the European Extremely Large Telescope and Nasa’s James Webb Space Telescope, we will soon be able to search for water, and perhaps even evidence of life on these worlds.’
The announcement yesterday prompts another intriguing and much debated question: if there is intelligent alien life on a planet orbiting TRAPPIST-1, why hasn’t it made the effort to get in touch with us or even come visiting?
This is especially pertinent if the aliens there have had an evolutionary head start on us lasting billions of years.
This is the famous conundrum dubbed the ‘Fermi Paradox’. Back in the Forties, the renowned Italian physicist Enrico Fermi suggested that, with 100 billion stars in our galaxy, it was logically inevitable that intelligent life should have evolved elsewhere in the universe.
What’s more, he added, a highly evolved extra-terrestrial life-form should surely have colonised the galaxy by now.
So, Fermi asked, where are all the aliens?
The paradox has become more ever more baffling as our knowledge of the universe grows.
As well as the newly found planets orbiting TRAPPIST-1, deep space scans performed by Nasa have discovered a further nine potentially life-supporting planets farther away.
Some scientists go so far as to speculate that there may be around 60 billion planets capable of supporting life in the Milky Way alone.
Yet 40 years of intensive searching for extra-terrestrial intelligence has yielded nothing. No radio signals, no credible spacecraft sightings, no close encounters of any kind.
IS THERE LIFE IN THE TRAPPIST-1 SYSTEM?
Though all seven planets could have liquid water, three of them – 1e, 1f, 1g – have the right atmospheric conditions to hold oceans of water at their surface.
These oceans may have already evolved life, though co-author Dr Amaury Triaud told MailOnline that the researchers cannot possibly know at what stage this life might be.
‘We only know the star is older than half a billion years and likely the planets are too, so far we do not know if there is liquid water and even less if there is life,’ he said.
The team have already begun using larger telescopes positioned across the globe to search the atmospheres of the planets for signs of life.
‘Several different molecules and relative make-ups of atmosphere will allow us to conclude that there is biological life present,’ lead-author Dr Michael Gillon said.
‘The presence of methane, water, oxygen, and carbon dioxide are all strong indicators.’
The team say that they will know if biological life exists on the planet within a decade.
While the Trappist-1 star is not young at half a billion years old, the system is burning through its hydrogen reserves at a slow pace.
Astronomer Professor Ignas Snellen of the Netherlands’s Leiden University, not involved in the study, claims that the system has great potential for evolving life in the future.
‘In a few billion years, when the sun has run out of fuel and the solar system has ceased to exist, Trappist-1 will still be only an infant star,’ she writes in a Natrure News and Views article.
‘It burns hydrogen so slowly that it will live for another 10 trillion years, more than 700 times longer than the universe has existed so far, which is arguably enough time for life to evolve.’
The astronomers used a series of both ground-based and space telescopes to find the new planets. They measured the dimming of light of the system’s star Trappist-1 as each planet orbited in front of it. This image shows the Nasa Spitzer Space Telescope used by the team, which takes stellar light readings from Earth’s orbit
Artist’s concept of what Trappist-1 planet 1f could look like. 1f has been listed by the researchers as the most likely planet to host alien life. Dr Amaury Triaud told MailOnline: ‘Planet F is a similar size to Earth but is a bit cooler, and the temperature is about right. ‘The planet is very similar to Earth in size, and it receives just a little less energy from its star than Earth does’
HOW WERE THE PLANETS FOUND?
Artist’s impression of a Trappist-1 star transit. The telescopes made readings as each planet transited the system’s star, passing in front of it and causing its brightness to dip
Each planet, labelled 1b-1h, was found via telescopes using the ‘tranit’ method, in which the orbit and other properties of planets is measured as they pass in front of their star, causing it to briefly dim.
An international group of researchers used a series of space and ground telescopes to find the seven planets in the Trappist-1 system, which sits 39 light years away from Earth.
Thousands of exoplanets have been discovered before, but this system has more Earth-sized planets orbiting its star than any planetary system seen before.
The researchers measured the ‘transits’ of planets by reading dips in the star’s brightness with each passing planet.
They could then make estimates about the features of each planet based on their orbits and the time taken for each transit.
Using these transits they discovered seven planets whose orbit is close enough to to the Trappist-1 star that they could have water at their surface.
The astronomers plan to use larger telescopes to take readings of the planets’ atmospheres in future to determine if they host alien life.
Geoffrey Miller, an evolutionary psychologist at the University of New Mexico, has proposed a disturbing answer. Perhaps there is a limit to how sophisticated a species can become.
We become smart enough to make nuclear bombs — and dumb enough to use them, he says. Or perhaps we just get addicted to social media and computer games, Miller suggests facetiously.
‘The aliens may forget to send radio signals or colonise space because they are too busy with runaway consumerism and virtual reality narcissism . . . just as we are doing today,’ he says.
With the discovery of TRAPPIST-1’s Earth-like planets, we have a chance to find out whether current theories about alien life hold any truth.
But less we expect too much, a word of caution from Astronomer Royal, Lord Rees: ‘Even if conditions are close to Earth-like, the mysteries of biology remain.
‘We know how simple life evolved into our present biosphere. But we don’t know how the first life was generated from a “soup” of chemicals.
‘It might have involved a fluke so rare that it happened only once in the entire galaxy — like shuffling a whole pack of cards into a perfect order.’
On the other hand, this crucial transition might have been almost inevitable given the ‘right’ environment.’ Watch this space.