I've been fascinated with the sky since I was a ten year old boy and in that time I've seen some truly amazing sights from glittering star forming regions and strange distant galaxies to dying stars and alien worlds, and all with my own eyes.
My passion for all things in the sky led me to study the daytime sky and our own local star the Sun and even learn to fly aircraft so that I can get up into it too. Yet during all these activities I have never seen anything that I have been unable to explain. On occasions a strange weather phenomenon or astronomical object has caught my eye but nothing 'unusual'. I think that's why I find the idea of UFOs (Unidentified Flying Objects) fascinating. I must have clocked up several thousand hours, if not more, looking at the sky – and yet nothing. Moreover, none of my astronomical chums have spotted anything that defies explanation, but it doesn't change the fact that many strange sightings are reported all over the world, so what's going on?
Lets just clarify what we are talking about, UFOs. Unidentified Flying Objects! The key word is 'unidentified' so if you were a cave man plopped into the 21st century and saw me buzzing along in an aircraft then you might consider it a UFO, simply because you wouldn't know what it was. What I am referring to are the UFOs which are supposedly sightings of alien aircraft visiting the Earth and its unsuspecting inhabitants. So let’s explore the idea of whether aliens even exist.
The idea of a Universe swarming with aliens goes back centuries, there is even a tribe called the Dropa who allegedly have alien ancestors that came from a planet around the star Sirius. There are many, many stories and reports of alien visitations like this, some peaceful, others not so, but all lacking the crucial bit of evidence that would once and for all confirm that we are not alone. Studies of nearby star systems show that planetary systems seem common with over 700 exoplanets having been identified. In fact there are thousands of ‘candidate’ planets where scientists are wading through the data to confirm them. Even more impressive is a recent analysis estimates there are 100 billion planets in our Galaxy alone. The idea that Earth is the only one of these planets with inhabitants seems highly unlikely to me yet so far there is still no proof.
If we look at our own galaxy and system of planets and draw on what little facts we do have for life in the Universe we might apply a best guess figure to the number of possible civilisations. The first to try and tackle this was Dr Frank Drake who was preparing for a meeting for the National Academy of Sciences in 1961 when he came across a series of factors to be considered in estimating the number of possible civilisations in our Galaxy. The equation considers such things as the rate of star formation in our galaxy, the fraction of those stars which have planets, the fraction of those which could support life all the way through to the length of time those civilisations might transmit the signals into space.
The equation is usually written: N = R* • fp • ne • fl • fi • fc • L where,
N = The number of civilizations in The Milky Way Galaxy whose electromagnetic emissions are detectable.
R* =The rate of formation of stars suitable for the development of intelligent life.
fp = The fraction of those stars with planetary systems.
ne = The number of planets, per solar system, with an environment suitable for life.
fl = The fraction of suitable planets on which life actually appears.
fi = The fraction of life bearing planets on which intelligent life emerges.
fc = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
L = The length of time such civilizations release detectable signals into space.
Although there is no unique solution to this equation, it is a generally accepted tool used by the SETI (Search for Extra Terrestrial Intelligence) community to assess the factors to be used in estimating the number of technological civilizations that may exist in our Galaxy. Dr Drake is still based at the SETI Institute, an organisation set up to explore, understand and explain the origin, nature and prevalence of life in the universe.
Founded in 1984 the SETI Institute is a private, non-profit organisation. The institute’s Director of SETI Research, Dr Jill Tarter, explained to Sen
"The Drake Equation remains a very useful tool for organising our ignorance. Some terms are unknown and others are unknowable until SETI succeeds or completes a comprehensive enough search to yield a statistically significant negative result."
The SETI Institute reason that any reasonably advanced civilisation will be producing a significant amount of radio signals in the same way our radio, television and electronic signals are broadcast into space. Artificial radio noise would be distinct from naturally produced background radio noise and the SETI Institute are looking for signals that are unnatural.
The SETI Institute's listening tool is the Allen Telescope Array at the University of California, an array of a large number of small dishes that scans the universe for radio noise. The array is named after one of the leading funders, Microsoft co-founder and billionaire Paul Allen.
The SETI Institute recently announced a crowd sourcing initiative, SETI Live, to get volunteers to help look for patterns in the data recorded by the Allen Telescope Array. "I'm hoping that an army of volunteers can help us deal with these crowded frequency bands that confuse our machines" explained Dr Jill Tarter.
Given the sheer scale of the Universe it seems the chances of extra terrestrial life are greater than zero so if they are out there, where should we look and is there a chance of finding life in our Solar System? As far as the Solar System is concerned its probably safe to say that, other than us here on Earth, there are no advanced civilisations lurking round the corner. We can certainly discount Mars although throughout history it has been at the centre of controversies from the strange linear features seen by Italian astronomer Giovanni Schiaparelli in 1877 to the haunting 'Face on Mars' seen in the Cydonia region of the red planet. Some hope remains though as a martian meteorite found in the Allan Hills meteorite fields of Antarctica had what some scientists consider evidence for byproducts of extremely primitive life called Polycyclic Aromatic Hydrocarbons or PAHs for short. Its likely that the primitive life that caused it will be extinct now but recent reviews of information from the early Viking martian landers suggest maybe some further evidence of primitive life may have been found. At best its a controversial report but one to watch.
The search for ET in our Solar System is really for “microbial” life forms. Amongst the rest of the Solar System, its the moons of giant planets we need to look at for signs of life. Europa, one of the Galilean satellites of Jupiter, is one of the favourites for finding signs of life as there is a tantalising possibility that microbial life may exist in subsurface oceans. Other Jovian moons including its largest moon Ganymede and the moon Callisto are also believed to have subsurface oceans. On Earth, entire eco-systems are found thriving around hypothermal vents deep in the oceans where no sunlight penetrates. Its thought that maybe life like this may have evolved on the Jovian moons. The European Space Agency is due to announce this week that its next large mission, JUICE – Jupiter Icy Moons Explorer – will focus on the conditions that may have led to the emergence of habitable environments among the Jovian icy satellites, with special emphasis on the three ocean-bearing worlds, Ganymede, Europa, and Callisto.
Other possible candidate moons for life are Saturn’s moons Titan and Enceladus. Titan, Saturn’s largest moon, has a thick atmosphere composed of hydrogen and other gasses. When the Cassini mission deployed the Huygens lander it found an absence of hydrogen at the surface suggesting that maybe something was consuming it.
Saturn's sixth largest moon Enceladus is a further possibility as water rich plumes were discovered by the Cassini spacecraft as it performed several flybys in 2005. Further studies of these icy geysers has shown the jets of all sizes near Enceladus's south pole are spraying water vapor, icy particles, and organic compounds all over the place. Cassini has flown several times now through this spray and has tasted it.
“We have found that aside from water and organic material, there is salt in the icy particles. The salinity is the same as that of Earth's oceans," said Carolyn Porco, leader of the Imaging Science team for Cassini, talking about the flyby in April 2012.
Porco believes Enceladus is the most promising place in the solar system for a "flagship-scale" astrobiology mission to search for microbial life. In an interview with NASA Science she reasoned: "The kind of ecologies Enceladus might harbor could be like those deep within our own planet. Abundant heat and liquid water are found in Earth's subterranean volcanic rocks. Organisms in those rocks thrive on hydrogen (produced by reactions between liquid water and hot rocks) and available carbon dioxide and make methane, which gets recycled back into hydrogen. And it's all done entirely in the absence of sunlight or anything produced by sunlight."
A closer examination of the jets from Enceladus is planned by Cassini for October 2015 and that may gather further insightful data.
Beyond our Solar System, with hundreds of planets discovered and the possibility of there being billions of planets, one wonders how these can be studied for signs of life. Using remote techniques it’s possible to estimate the mass of the planets and their distances from the parent star, yet so far we are unable to directly observe any which are Earth sized. We can infer whether the conditions might be right for life but new technologies will be needed to take this further and identify any possible biological activity.
Even if life does exist elsewhere in the Universe, I think its unlikely to be the cause of the many UFO sightings since even the fastest manmade object, the Helios space probe, would take tens of thousands of years to reach the nearest star system. The distances in space seem just too great, but still, the prospect of finding life is tantalising. Even writing this article I find myself daring to imagine a day when news breaks that we have finally found un-refutable evidence that we are not alone and it sends an excited shiver down my spine. I genuinely do believe that such a day will come, but for now we just have to sit, wait and listen for that faint signal coming from an alien world. As Tarter reminds us, “quoting Morrison and Cocconi's 1959 paper on the search for interstellar communication, ‘The probability of success is difficult to estimate, but if we never search the chance of success is zero' we're searching".