Why are there no aliens near Earth?
Firstly there’s a line to be drawn between the make believe of popular Science Fiction, and fact. Science Fiction shows demonstrate made up technologies. Background explanations are used to pad these ideas out with back stories, to help give an air of plausibility. Viewer buy-in propels these concepts into the public domain. In such shows it is commonplace to journey from one alien encounter to another in a matter of days, or even hours. We understand terms such as phaser beams, teleportation, hyperspace and warp drive, even though these are made up. We also understand alien though, as yet, we haven’t encountered any. Our expectations are led by popular, made up shows. The reality is we are a long way off phaser beams, we haven’t mastered teleportation, the best place to find hyperspace is on TV shows and our technology can’t get to other star systems in a matter of days. Taking that last point as an example; it would take us centuries to get to the nearest star, to get there in days we would need to be 100,000 times faster. This is a bit like the difference between travelling by car and walking on foot – the next town is only minutes away by car – virtually next door – but on foot it could take you hours.
There is a difference between make believe and reality, in Science Fiction that difference is so big that the hard facts can come as a shock. To bring expectations down to earth, it’s worth running through what we know.
What it takes to survive as a species.
Man is a competitive, destructive species. This is one of the prerequisites of survival. Any non-human intelligence on this planet would either have been eliminated by man, or have exterminated us in turn; whimsical accounts of man’s history might conceal our predatory nature but does not change our nature. This leaves the Earth dominated by the predator at the top of its food chain, us.
Can life as we know it live anywhere?
What we know about the universe is governed by our perceptions of it – the background phenomena of space, galaxies, stars, planets and moons is deduced by studying the electromagnetic spectrum, making assumptions and developing theoretical models. We continue to make discoveries relevant to the question of alien existence, for example, it wasn’t until 1995 that scientists could be sure that there were planets circling other stars; i.e. exoplanets. Ten years back exoplanet discovery began to accelerate. Many of these are giants – that is they are Jupiter class and some mass much larger. Taking Jupiter, the fifth planet from the Sun as an example, its atmosphere is a turbulent, raging storm complex composed of a Hydrogen – Helium mix; it may have a rocky core but scientists aren’t sure; it’s a gas giant with a diameter over 10 times that of Earth’s. Jupiter and the other gas giants, Saturn, Uranus and Neptune are many times larger than Earth and are inhospitable. Gravity on Jupiter is a punishing 2.4 times Earth normal. It radiates more heat than it gets from the Sun – it isn’t large enough to fuse hydrogen (and thus become a star) but plainly something is going on down there under the storms – it is estimated to have a core temperature of 36,000ºC. This is an example of a planet where life as we know it would have difficulty establishing itself and evolving.
The Solar system
Our solar system has a good selection of planetary types – Jupiter is important because if it were much more massive, its gravity would be very disruptive – it makes for a good cradle for humankind. It’s possible to conjecture life under different chemical bases than that of our Earth: carbon-oxygen-hydrogen-nitrogen, and Science Fiction writers often make play on this (including this writer e.g. halogen based intelligences ¹) however the number of alien civilisations in the Solar system is none. A quick survey of the Solar system gives an indication of where life can develop:
- Of the inner planets Venus is the second closest to the Sun, and is only fractionally smaller than Earth. It has a carbon dioxide atmosphere and the air pressure at the surface is over 90 times that of Earth’s. Surface temperatures at around 450ºC, ranks it higher than Mercury (which is the closest planet to the Sun) and unlike Earth it doesn’t have a planetary magnetic field.
- Mercury has no atmosphere, long days and nights (each day lasts two years) and its temperatures range from –173ºC to 425ºC. It is the smallest planet with a diameter of 3,000 miles (4,800 km)
- The third planet from the Sun is Earth. Think we don’t expect a lot? Imagine fixing up a planet to match this wish list: not too close to sister planets as to cause orbital perturbations, temperate heat, moderate and regulated levels of radiation, ample supply of water, a moon to effect tidal activity, a standard atmosphere, tectonic activity to ensure planetary features are renewed, an extensive but balanced biosphere. Earth has a diameter of 8,000 miles (12,750 km). We live there and take it for granted.
- Mars, the fourth planet from the Sun, is an airless planet. It has a diameter of 4,200 miles (6,800 km) and is much smaller than Earth. Temperatures range from -140ºC to as high as 30ºC in the equator area during the Martian summer. Although its gravity is only 40% of Earth normal and it is too cold for life, it is the closest planet to our needs.
- The Asteroid Belt that lies between Mars and Jupiter has rocks of all shapes and sizes, up to planetoid size. Current thinking on its origin isn’t yet settled however in 2006 it was announced that a population of comets (beyond the ‘snow line’ of 2.7 AUs) were discovered to have accumulated ice and that they may explain the source of Earth’s water. Some theories explain the belt as the remnants of planetary mass that never formed a planet due to Jupiter’s mass. The largest is Ceres at 600 miles (950 km) diameter. It contains one third of the mass of the entire Asteroid Belt, has no atmosphere and is very cold, never getting warmer than -38ºC; its surface is composed of icy carbonates and clay minerals.
- Although Jupiter has already been mentioned, it has 69 moons. Most are small but four range from Moon sized up to nearly the size of Mercury; these have thin atmospheres. Jupiter emits a lot of radiation and has a strong magnetic field; because of this, scientists suspect that the safest one to examine, and to establish a base for human exploration of the Jupiter system, would be Callisto which is the furthest of the four from Jupiter. The diameter of Callisto is 3,000 miles (4,800 km). Although its surface temperatures are 100ºC and more below freezing, it could have sub-surface oceans of water.
- Saturn is further out. It’s the sixth planet from the Sun and is like Jupiter in several ways, a gas giant; an atmosphere composed of Helium and Hydrogen, a lot of moons – over 60 – and is also conjectured to have a solid core. Its largest moon is Titan with a diameter of 3,200 miles (5,150 km) making it considerably bigger than our Moon and ranking it the second largest in the Solar system (after Jupiter’s Ganymede). It is composed mostly of outer layers of water ice and ammonia with a core of rocky material. Unusually for a moon, it has a dense atmosphere – largely nitrogen. The surface has planetary features similar to Earth’s but its temperatures hover around -180ºC – that’s 200 degrees lower than here.
- The seventh planet from the Sun is Uranus. Like Jupiter and Saturn, it is a gas giant with an atmosphere of Hydrogen + Helium; it also has traces of water ices such as ammonia and methane along with other hydrocarbons. It has nearly 30 moons; the largest of these is Titania with a diameter of just under 500 miles (800 km).
- The eighth planet from the Sun is Neptune. Its atmosphere is similar to that of Uranus: Hydrogen, helium, water ices and other hydrocarbons. It has 14 known moons and the largest of these is Triton. Unlike other planetary moons, Triton has a retrograde orbit indicating it was captured rather than forming in place. Its origin may have been as a dwarf, rogue planet, from the Kuiper belt. So far, Triton is the coldest object in the Solar system – it is the second moon discovered to have a substantial atmosphere. Its diameter is 1,680 miles (2,700 km).
- Pluto no longer counts as a planet but it too is extremely cold and inhospitable.
Each of these planets and moons poses substantial and sometimes unique challenges to life, whereas Earth is hospitable to life as we know it. In all, the Solar system gives an idea of the likelihood of encountering worlds where we might find aliens, and presents us with a number of challenges to master if we are to have any success in exploring, establishing bases and settling beyond the reach of Sol.
What we know about places beyond the Solar system
Like most galaxies, the Milky Way is spiral galaxy. The Solar system is in a minor arm known as the Orion Arm; it is about half way between the galactic core and the edge of the galaxy. Stars in the core are more densely packed than out in the spiral arms. An alien in the galactic core would notice that stars are 4 times closer than here. The chance that gravity from a nearby star would interfere with the orbits of planets in nearby systems would greatly increase. A change in Earth’s orbit could cause an ice age, or mass floods as the polar caps melted; it might drag Earth away from the Sun, sending us into the bleak emptiness of interstellar space, or even send the Moon crashing into us. The core is probably a great deal more exciting than out here in the Orion Arm; however out here, things are relatively stable which gives evolution the chance to deliver intelligence, leading to civilisation.
Out there are all kinds of systems; where there are exoplanets, there is a chance some could support life. There is an inner and outer planetary orbit a rocky planet needs to occupy, in order to support life. This is known as the Goldilocks zone. In our system, the Goldilocks zone lies somewhere between Venus and Mars.
The Sun (or Sol) is a G-class star, as are 7.5% of stars in our galaxy; 1 in 5 of these will have an Earth like planet in the Goldilocks zone. Most planets are discovered by indirect detection, in particular, radial velocity measurements and transit monitoring techniques. Planets are a tiny proportion of observable matter, this being: black holes, stars, nebulae and other cosmic dust. Scientists believe dark matter exists. Without dark matter, their models of the universe don’t make sense. Dark matter makes up 90% of galactic mass; observable matter makes up the remaining 10%.
Scientists continue to look into the universe: many planets in the Goldilocks zone may be unsuitable and lack the things we take for granted (see earlier: third planet from the Sun). We are carbon based life forms. If life could evolve in an environment based on a different group of elements, which would be favourite? Halogens have been proposed: that’s elements such as chlorine, bromine, fluorine. There’s no example of that kind of environment in the Solar system and it’s hard to imagine how that chemistry of life would work. ¹ That kind of life could be much rarer than carbon based life.
How about in interstellar space? Space is vast, cold and bleak, there’s plenty of room to conceal things out there. The most important things are in short supply: heat, light, radiation, matter… just about everything except the will to live. ²
Trace organic compounds are out there in space, sometimes they fall to earth. ³ Where do they originate? Were they originally part of something larger? Could they be the remnants of a planet, or even alien beings murdered long, long ago? Here Science merges with Science Fiction – science proposes mechanisms and hypotheses, Science Fiction takes you there and tells a story. For example, if they’re out there, why don’t they communicate? An answer to that could be: they are communicating but we’re not advanced enough to understand them; another answer could be: they do not broadcast their presence because if they did, something devastatingly awful that lurks, waiting for signs of intelligence, would track their signal down and exterminate them. Either answer would make a Science Fiction story.
Science Fiction is primarily a self-congratulatory genre with the message: our side wins again. It can also explore thoughts such as: what’s possible when we go out there? and would we rather not know?
Terence Park is a Science Fiction writer. His latest novel, The Tau Device, is from a series called The Dark Matter War. He has used concepts from the above article as noted below:
¹ In The Tau Device, the alien t’negi, originate from a halogen environment. They have been genetically re-engineered to live in a carbon based environment because this allows them better commerce and trade with most intelligent species and they feel less isolated.
² In Dragon Shard, both Heb and his enemies, the Zhun-yini, inhabit the empty wastes of interstellar space, living low mass, low energy lives.
³ A Guide to First Contact. Earth is managed by powerful alien entities that periodically bombard the planet with additional organic compounds which provoke wild bursts of evolution. These compounds come from rocky animites; the harvested remnants of ancient creatures kept in suspended animation since before the Big Bang.