Another Earth?

The systematic scientific search for extra terrestrial intelligence, which began as Project Ozma back in 1960, has continued for over sixty years with no positive result.  The best possibility of an alien message – the famous “Wow” signal in 1977 – remains highly disputed and was almost certainly of terrestrial origin.

The logic behind the search is impeccable – there are around 100 billion stars stars in our galaxy, the Milky Way, and scientists now agree that many of these suns have planets orbiting around them. Some of these planets are in the so-called “Goldilocks” zone where water exists in a liquid state throughout the planet’s year and therefore it can be assumed that life could potentially come into existence.

The Origins of Life

Life emerged relatively early in our own planet’s history, but took billions of years to evolve into its current state.  Life as we know it cannot develop beyond microbe-like forms without oxygen, for example, and the oxygen we breathe is itself is a product of early life on this planet.

Around 3.4 million years ago, simple lifeforms evolved which relied on a form of photosynthesis to absorb sunlight and carbon dioxide to generate energy. However, this was not photosynthesis as we know it today, because these bacteria did not release oxygen as a waste product. Single celled life relying on this anoxygenic form of photosynthesis remained the dominant form of life for a billion years but around 2.5 to 2.2 billion years ago, the Great Oxidation Event occurred after some cyanobacteria evolved a new form of photosynthesis that released oxygen.

This oxygen was toxic waste in view of existing life on the planet, but it began to build up in the seas and atmosphere – though concentrations remain below modern levels for over a billion years. Once oxygen became widespread, it caused drove a mass extinction event among the archaic microbes that were unable to cope with it, but it also drove the evolutionary innovations responsible for the dazzling diversity of life today.

The Earth’s moon – probably formed when a proto-planet smashed into our planet early in the solar system’s history – may also have played a vital part in the development of life. That early, devastating collision increased the size of Earth’s molten core, strengthening the magnetic fields which protect life from the constant bombardment of heavy particles from the sun, and the formation of the moon later encouraged this mixing of oceanic oxygen with the atmosphere.

Several moons in our own solar system not only harbour water but are wracked by gravitational forces from their host planets which maintain liquid oceans under a thick carapace of ice.  However, any life on these moons of Jupiter and Saturn will have to rely on energy from thermal vents, as their distance from the sun and multi-mile thick ice pack thwarts any possibility photosynthesis.

Once the ancient seas of Earth became saturated with oxygen, living cells began to combine as algae and sponges. Life diversified in these ever-more oxygenated oceans, with more sophisticated species developing sexual reproduction, a range of senses and larger brains.  Eventually sea-creatures began to venture out onto dry land, helped again by the tides created by our large and powerful moon.

While life elsewhere may have evolved in very different ways, it is likely to require a similar combination of carbon, water and oxygen to develop. Due to the large numbers of planets involved, it is logical to assume that some small, rocky planets in the Goldilocks zone do, in fact possess these necessary elements, up to and perhaps including a large moon like our own.

There may not be many ‘new Earths’ precisely like our own, however. We would need to discover a planet large enough to retain its atmosphere, but not generate a runaway greenhouse effect like Venus.  A planet with an active core able to generate a protective magnetic field but not so active as to be covered with lava.  It must also have a large amount of water, as well as an orbit that allows it to stay liquid, rather than boil or freeze as ice.

Furthermore, given the current capability of even our most sophisticated space-based telescopes, it would have to cross the plane of its sun at precisely the right angle for us to detect its presence and analyse its atmosphere, while being relatively close to us in cosmic terms.

Are they here yet?

So, given the numbers of planets involved, we may be confident that some have the right conditions to generate simple forms of life, even if we may be less certain of discovering one ‘close’ to us.  The more interesting question is how many of these ‘alternate Earths’ have produced intelligent, technology using species?  Furthermore, have any of these potential civilisations not only mastered intersteller travel in ways beyond our foreseeable capabilities, but visited Earth, a planet would no doubt find intriguing?

Sightings of unidentified flying objects, and mythical creatures which modern eyes might perceive as aliens, have occurred throughout history but the vast majority can be understood as myths or misapprehensions of natural phenomena.  The planet Venus is bright in the morning or evening sky, while lenticular clouds can look like flying saucers and electrical discharges like St Elmo’s fire fool many observers to this day.

Furthermore, countless planes, helicopters, balloons, drones and other man-made paraphernalia now clog our skies, prompting over-eager observers to see any set of landing lights in the sky as irrefutable evidence of imminent alien visitation.  Though everyone now carries a sophisticated camera in their pocket, those cameras can themselves create misleading artifacts, and even seasoned observers are wont to interpret snippets of film or military heat signature data as UFOs. Every picture is taken from just too far away to properly identify it because if it were any closer, a more prosaic explanation would be clear.

As our technology and understanding of the universe improves, the perhaps depressing lack of evidence for life on other planets or alien visits to our world must be balanced by the increasing certainty that the elements required for life, and planets capable of hosting life, are common throughout our galaxy.  While there’s no sign of a flying saucer landing on the White House lawn – though if it happened to any President, it would surely be Donald Trump – the potential for signs of life to be discovered through our space-based and radio-telescopes can only grow stronger.