Why Is Earth So Special?
By Steve Johnson
The planet upon which we live is a truly remarkable place. The odds are that there is no other planet in the galaxy quite like it. Compare the Earth with all the other planets in our Solar System:
Mercury (right) is a blistering rock only a little larger than our own Moon. When the sun is at its zenith, the surface attains a temperature hot enough to melt lead. A most unsavoury place.
LIFE? Not a chance.
Our 'sister' world, Venus (radar map left), is even more inhospitable than Mercury. Its dense carbon-dioxide atmosphere has perpetuated a runaway greenhouse effect and the surface pressure is 92 times that of Earth's. Sulphuric acid clouds rain lethal fire onto a boiling, rocky landscape.
LIFE? No - unless it is very, very hardy. Although it has recently been suggested that microbes could thrive in the uppermost regions of the Venusian atmosphere
The romantic planet of Mars (right) is, even today, the best bet for life to have evolved independently of the Earth. Dry river beds and ancient flood plains clearly show that liquid water once cascaded across the Martian surface. Unfortunately, something happened in the distant past and much of the atmosphere leaked away into space. The surface pressure is now so slight that liquid water cannot exist, however, violent winds recently destroyed a Russian probe on the Red Planet's rugged surface.
Some have suggested that the structures at Cydonia are artificial. If this is the case, then they are massive creations. You could argue that Mars' lower gravity would facilitate the construction of gargantuan edifices. If they are not the products of natural forces, then they were not built recently. The structures are probably hundreds of thousands (if not millions) of years old.
Today, the climate of Mars is very unstable, with violent temperature and pressure variations over relatively small geographical areas.
LIFE? Probably not any more - but we keep our hopes up!
Between Mars and Jupiter lies the main asteroid belt. Some of these chunks of space rock are quite large - Ceres, the largest, is 600 miles in diameter. All of the bodies here are too small to cling on to an atmosphere. Several years ago, however, there were theories bandied about that alien space probes could have been secreted within the belt, there orbits obscured amongst the myriad of planetoids surrounding them. Most unlikely in my opinion. Unlike the densely-packed field in The Empire Strikes Back, our asteroids are very diffusely spread, millions of miles separating many of the rocks.
LIFE? No, unless alien probes do exist there and are a strain of artificial life-form.
Jupiter (right, with it's moon Ganymede), the largest planet in the Solar System, is so enormous that its mass is greater than all the other planets combined. It is a gas giant i.e. it has no solid surface. This means that life, as we know it, cannot exist there. Bacterial organisms could, possibly, float around the warmer regions deep within the atmosphere, but the chances of this being the case are slim.
Jupiter has 16 moons. One in particular has come under extreme scrutiny recently. Europa, it seems, could have liquid water flowing beneath its fractured, icy surface. Could life have evolved in this distant ocean, far from the sun's warmth? Sulphur-eating life-forms do exist on our own sea floor, where the sun's rays cannot penetrate, so it is possible that similar organisms could have evolved on that Jovian satellite. Unlikely as it may seem, Europa has one of the best chances for extra-terrestrial life in our Solar System.
LIFE? Very possibly. Organic compounds ’have“ been detected on this remote moon, however, Jupiter's vast and deadly magnetosphere may be a deciding, negative factor.
With its magnificent system of rings, Saturn (left) is, without doubt, the most beautiful of Sol's planets. Like Jupiter it is a gas giant with its own complement of moons - 22 at the last count and the Cassini probe will probably discover more.
Of these known satellites, Titan is by far the largest. In fact, it is a planet in its own right, with a dense nitrogen/methane atmosphere. Many scientists have described Titan as a primordial Earth in deep-freeze. Life is unlikely, though, due to the extremely low temperatures in that distant region of the Solar System. Most of Saturn's other moons are more traditional rocky, cratered bodies, especially Mimas, which, with its enormous impact crater, resembles the ’Death Star“ from Star Wars.
LIFE? Doubtful, unless the hidden surface of Titan is beyond our wildest expectations
Nearly three billion kilometers from the sun orbits the third gas giant, Uranus (right). It, like Saturn has an extensive ring system. Uranus is peculiar in that its axial tilt is 98 degrees. This means that its polar regions receive more energy from the sun than does its equator. Due to some unknown factor, though, the equatorial region is hotter than the poles. This huge, blue planet has 15 satellites; 10 small, dark moons and 5 larger ones orbiting farther out from Uranus.
LIFE? Not likely.
The last real planet in the Solar System is Neptune (left), the outermost gas giant. It is similar in size and colour to Uranus and is orbited by at least 8 moons and four faint rings. Until 1999, Neptune is the most distant planetary body from the sun and is therefore a very cold, inhospitable place.
LIFE? Virtually no chance whatsoever.
Finally, we encounter Pluto. Until recently, this enigmatic body lay inside the orbit of Neptune and its orbital inclination is also much higher than that of the other planets in the Solar System.
Currently, there is a great deal of debate concerning the nature of Pluto and its companion world, Charon (seen right in a Hubble Space Telescope image). Most orthodox astronomers maintain that Pluto is, in fact, a planetary body, while a growing number of scientists are claiming that it is the largest member of a group of objects which inhabit the Kuiper Belt. The Kuiper Belt objects are large asteroidal and cometary bodies that share similar orbits to Pluto. The concensus at the moment, however, is that cold, dark Pluto is, and will likely remain for the foreseeable future, a planet.
LIFE? No, unless the outer reaches of the Solar System are very different to our accepted theories.
So, you can see why the Earth is so special and significant within our sun's family of planets. It is the only world that has an abundance of life. It is warm enough, and stable enough, to allow a multitude of organisms to flourish. It is large enough to hold on to a substantial oxygen atmosphere. Another point of interest concerns our Moon. No other planet (except perhaps Pluto) has a satellite as proportionately large as our Moon is. Every other natural satellite in the Solar System is significantly smaller than its parent.
Pluto and Charon orbit a common centre of gravity and is generally regarded as a twin-planet system. The Earth and Moon also share a common fulcrum, but this centre lies deep within the Earth itself, so it is easier to say that the Moon orbits the Earth.
It is easy to see why alien visitors to our star system would be interested in our planet. With its teeming life-system, it is an exo-biologist's dream. The nearby, larger than is usual satellite (which keeps one hemisphere permanently towards us) is perfectly located for a long-term base of operations. It only took our astronauts three days to get there. A race which has developed interstellar flight could, in all probability, make the same journey in hours or even minutes.
Earth is the only planet from where natural total solar eclipses can be viewed. Peculiar how this occurs on the only life-bearing planet in out tiny portion of the galaxy.
How come the Earth shows only limited signs of meteoric impacts? Scientists tell us that this is due to natural weathering and erosion. Venus has extreme weather conditions, yet its surface is still pockmarked with impact craters. The same can be said of Mars. Dust storms frequently rage across the Red Planet. Even accounting for Mars' lower atmospheric pressure, surely most of the thousands of ancient craters, many of them millions of years old, would have been worn away by now. Faced with this information, geologists fall back on plate tectonics. This is the theory of the movement of the Earth's crust over millions of years.
At the deep ocean faults, magma wells up and solidifies in the cold water, forming new sea-bed material (see diagram below). This new matter pushes the plates on either side of the fault underneath the plates neighbouring them. Over millions of years, this movement can affect landmasses far from the oceanic fault lines.
This may explain why impact craters have been largely erased, but why is the Earth the only planet with plate tectonics in the first place? (*UPDATE* Scientists believe they have found evidence of ancient plate tectonics on Mars. See here.)
If plate tectonics is rare in the universe, then this could explain why extra-terrestrial visitors would come here to study it. It could also be the reason why UFOs are frequently sighted entering the Atlantic Ocean off the Icelandic coast. Iceland rests on the Mid-Atlantic Ridge - an area of high tectonic activity.
So, it is possible to deduce why Earth is such a fascinating world for alien scientists: The vast numbers of wildly differing species (botanical and biological) are being studied by ET naturalists; their geologists are probably fascinated by the Earth's fluid and constantly evolving crust; and finally, our large and conveniently placed neighbour, the Moon, is unlike any other satellite in this star system. Alien astronomers can study the solar corona during our frequent total eclipses. Perhaps this is what happened when large numbers of UFOs were sighted during the Mexican eclipse of 11 July 1991.
The abduction phenomenon is the most sinister of UFO legends. Is mankind part of some vast, alien genetic experiment? Are the so-called ’Greys“ creating human/alien hybrids? If so, then is our planet being prepared for a gradual invasion?
Earth is being closely scrutinized, of that there is no doubt, as is its ecology. Perhaps the Greys are a dying race. Could it be possible that they are ensuring their continued genetic existence by creating human/alien hybrids which can infiltrate our society and pass on Grey DNA through natural procreation? If the hybrids were carefully placed around the globe, then, within a few generations, alien genetic material would be present in all the peoples of the world.
Many say that this is a disturbing scenario ( and I would be the first to agree), but if this is a kind of quiet invasion, by gradually altering the genetic make-up of man, isn't it better than the Greys charging in with guns blazing?
Independence Day it may not be, but at least nobody gets seriously hurt in the process. Collaborator! Yellow belly! I hear you cry.
But do you think that there is anything we can do about it anyway?
© 1998 Steve Johnson
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Updated 16th August, 2012