by Andy Lloyd
If correct, then the primordial Earth must have been a very significant planet indeed, such that major impacts upon it created the asteroid belt, the Moon and possibly some of the comets. Furthermore, such a wide scattering of water into the solar system may explain the relative high content of water on other planets, which we discussed in the last chapter. The implication would be, then, that the Earth was once a much larger world, the excess made up to a great degree by water.
Such a massive terrestrial planet could have readily held onto a vast amount of volatiles at the original distance of 4 astronomical units; its greater gravity alone could have meant a greater retention of water and other volatiles. It also would not be so incongruous that the larger primordial Earth would have brought into being and then successfully held onto such a massive satellite as our Moon. In other words, our Moon is colossal because at one point the Earth was much bigger relative to how it is now.
The migration of the Earth into the inner solar system would then have driven off much of that water, as predicted by theory. Also, the scientific discovery of the 'late, great bombardment' upon the Earth/Moon system 3.9 billion years ago brings a further insight into how successive massive bombardments of the Earth might have caused more oceanic water to be suddenly lost.10 Even so, because we started from a much higher threshold of domestic water, we now enjoy oceans and seas and lakes.
Our aqueous environment is due to our planetary origins lying near to Jupiter, not to cometary bombardment. This migration might make the Earth a rather special place. After all, without it a reasonably sized planet would not enjoy such abundant water so close to the sun. Earth might just have a unique signature; a planet in the habitable zone that somehow managed to retain its early water resources.
However, before we become too wrapped up in this idea, we must look at a vital point about the heat output of the sun over time.
The Cold Sun
When discussing the conditions that existed on the primitive Earth, it is important to note that different conditions existed in the solar system at the time. The sun was probably one of many thousands of stars in a cluster or star nursery. It's possible that the Dark Star was a wide binary companion to the sun, and that the system was disrupted early on, causing dramatic changes.
Examples of other young star systems present us with evidence of such binaries, where spiral structure has appeared in the proto-planetary discs, implying either massive distant stellar companions, or close stellar encounters.11,12,13 These findings imply that the stellar environment surrounding the early solar system was certainly busier than was previously thought. We should not infer from the stable, rustic charm of the present formation of planets that things were always this way.
The other thing to bear in mind is that the early sun emitted less light than it does now, and this may have contributed to a cooler primitive Earth. The sun's nuclear fires were concentrated in a relatively small sphere near its centre early on. This means that the Earth received about 70% of the sunlight it enjoys today.14 However, such considerations should already have been taken into account by scientists looking at the isotopic balance of oxygen in terrestrial and extraterrestrial water. Nevertheless, it's worth bearing in mind that the sun's own activity levels may have played a part.
Earth's Special Character
So, was the formation of the Earth a rather special, possibly unique phenomenon? If the Earth should not be nearly as wet as it is, being so close to the sun, then it is perfectly possible that the Earth is actually a rather special place. Without the action of a passing intruder planet of vast proportions, or the shunting effect of a significant impact, the Earth would be a much colder place than it is now. It would be more like the so-called "Snowball Earth", a condition that applied to our world some 600 million years ago.15
Life relies upon liquid water...would the current bio-diversity on this planet have arisen if Earth was still residing in the Asteroid Belt?
If a newly forming planet is close to a star - like Earth is to the sun - and thus warmed by it sufficiently to maintain liquid water later in its history, then these exact same conditions should preclude the inclusion of water on that world in the first place. The presence of abundant liquid water on the cooled planet becomes a paradox, because heat and water do not appear to mix when terrestrial planets form. So, this paradoxical situation we currently find on Earth is solved either by considering the possibility that the Earth has moved significantly closer to the sun since its formation, or by rethinking how planets form.
Whatever caused our world to have so much water so close to the sun, it may be unusual, possibly even unique. The Earth's abundance of liquid water may be very rare, if the action of an intruder planet is required to explain its shunting into a closer inner orbit. Saying that, some of the extrasolar planets found so far have distinctly odd orbits; particularly gas giants that swing wildly around the parent stars at very close proximity.16
Why were the constituent volatile gases of these planets not blown away by the star before the planet got a chance to form? Does this imply that planetary orbits can change radically, possibly as a result of outside interference?
The sheer variety of the extrasolar planets seems to mitigate against our conclusion of uniqueness for the planet Earth. If this 'Great Water Conundrum' helps us to understand anything it is that planets can migrate around - and end up enjoying orbits that seem, on the face of it, to be docile and placid. This overturns our previous assumptions that the observed planets in their nice quiet circular orbits must have always been that way. It opens the door for other possibilities further out into the colder regions of the solar system as well. Because if planets can migrate inwards, they can also migrate out.
Life Around Cool Stars
We always assume that our average boring old sun is the blueprint for other star systems that might harbour the conditions for life. Perhaps this assumption is correct, and the search for ExtraTerrestrial Intelligence should remain targeted at similar stars to our own sun. But, if Earth's acquisition of abundant water is truly an anomaly given the local heat generated by our sun upon its formation, then perhaps we should be looking for life on star systems whose primordial fires aren't so hot. After all, the spectrum of stellar characteristics does not begin with our own sun.
Red, or dare I say, even brown dwarfs would have formed without the same water-purging enthusiasm as our own yellow star. In fact, brown dwarfs themselves contain large quantities of water within their fiery atmospheres. They also have been seen to have their own planetary systems, even the smallest of the brown dwarfs.17
Perhaps that means that we should direct our attention to the less bright members of the celestial family; even those who remain hidden entirely. These relatively cool stars might have allowed watery worlds to form more readily around them, but bombard them with less harmful radiation than our own overenthusiastic sun.
Ironically, SETI may have been searching in the wrong place all this time.
Water Worlds
The concept of 'migration' of planets has becoming increasingly acceptable of late. It was not so long ago that Tom van Flandern heavily criticized Zecharia Sitchin's "12th Planet Theory" on the basis that Earth could not have migrated into the inner solar system from the asteroid belt. Van Flandern argued that Earth's orbit should still be highly elliptical if that was the case, and that the orbit should still cross through the asteroid belt. These arguments were partly sufficient to swing the author Alan Alford away from the idea of the existence of a substantial Planet X body.18
But science has moved on in recent years, and is now generally more open to new possibilities about undiscovered planets in our solar system.19 This is not only partly due to discoveries about our own outer solar system, but also because of the data which has accumulated about extrasolar planets.
Many of these "exoplanets" have anomalous orbits. Some of them are orbiting their stars at very small distances, and are known as "Hot Jupiters". These bizarre giant
planets are too close to their stars to have formed where they currently lie (according to existing theoretical models of planet formation), so the concept of 'migration' is increasingly mooted to help planetary scientists sleep at night. If such a model can be widely applied elsewhere, then surely it could have happened in our solar system too?
The science writer Andrew Pike once described a possible new class of planets that sound remarkably similar to the large, watery primordial Earth we have been thinking about here. This class of planets, called the "Water Worlds", is still theoretical. The idea was suggested by Alain Leger of the Institut d'Astrophysique Spatiale, France.
He wondered whether worlds twice as large as the Earth might exist with a super-abundance of water. This aqueous environment would take the form of a planet-wide ocean many kilometers deep, along with a gaseous atmosphere. He envisioned them beginning life as the extrasolar equivalents of Uranus or Neptune, but then migrating inwards.20
Again, the notion of planetary migration is being used to explain distant anomalies. Other examples of proposed migratory patterns of planets have also been seen in the scientific press lately.21,22 It does not take much imagination to apply the same principles here in our own solar system.
There is so much that we don't understand about the formation of planetary systems. This can be only one of a myriad of possibilities, but its early introduction to scientific speculation would indicate its potential. If such Water Worlds are found to exist, then they would provide a huge lift for the ideas presented here. Our own planet may once have been like this.
Electron Glow
Scientists are now actively discussing how life might emerge on planets orbiting brown dwarfs, or Dark Stars, I have described how an ecosystem might have arisen on a moon orbiting a small brown dwarf, whose light emission is minimal. It can be easily argued that the conditions on that moon would be warm enough for liquid water. But, some commentators have offered a counter-argument that there still would be insufficient light for photosynthesis to take place in the outer solar system. After all, it takes more than just liquid water to create life; light itself is often a useful ally.
Such light as there is would have to come from the Dark Star, a rather old sub-brown dwarf, which belongs to a new class of failed stars about which we have little actual knowledge.
Astronomers argue about whether such bodies can even emit light, but there does seem to be a good possibility that they do - through chemical reactions in the outer layers of atmosphere, driven by extreme magnetic fields and surface gravity. These effects result in 'flaring', but is this enough of a light source to allow photosynthesis to take place on nearby terrestrial worlds?
Uranus exhibits an inexplicable internal lighting effect known as "electron glow". This effect is in addition to Uranus' magnetic aurora. It is thought that the luminous effect, seen on such a 'dead' world, is due to electrons exciting hydrogen in the upper atmosphere, although it is not at all clear where those electrons originate from.23 Perhaps such an effect is possible on a sub-brown dwarf, to a greater extent, supplementing the other light-sources from this failed star that we have already discussed.
So, there are several means by which the Dark Star could be classified as a "light-emitting" planet. Indeed, it could be a highly excitable combination of them all. This is rather like arguing for light-emitting fish in the Deep Sea oceans.
Before their discovery, no one would have expected 'Angler Fish' at the bottom of our oceans. Is the Dark Star the planetary equivalent of a neon red Angler Fish? Is its moon system lit by this little oasis of red light in the deep abyss of the outer solar system? I suspect so.
So, would this be sufficient for photosynthesis to take place out there? We can look to events on our own planet to answer that question, particularly under the Antarctic ice. The scientist Chris McKay has studied ecosystems that depend upon the dimmest of light emerging through the ice to trigger photosynthesis, and has concluded that photosynthesis can be easily supported by just 2 percent of the sun's available light. He argues that there are plants here on Earth that are able to photosynthesize in luminous environments equivalent to 100 Astronomical Units from the sun, which is twice as far as the most distant body in the Edgeworth-Kuiper Belt yet discovered.14
Arguments about photosynthesis are thus rather redundant. I would argue that a Dark Star can supply not just direct and indirect warmth, through gravitational tidal action - but sufficient light as well, to allow photosynthesis to take place on one of its moons.
Life Among The Comets?
Even so, to establish whether life could exist among the comets around an object as exotic as a sub-brown dwarf, we must first establish its presence there. In the next chapter or so, we shall look at recent scientific studies that imply the previous presence of a substantial planet. These anomalous findings in the outer solar system have become central to our hunt for the Dark Star, because they offer indirect evidence for its existence.
Currently, astronomers are considering things they once would never have countenanced. The reason is their new appreciation for how strange the Edgeworth-Kuiper Belt is.
Beyond the orbit of Neptune is a swarm of bodies orbiting the sun, whose individual sizes, and great distances, have prevented their detection until relatively recently. The first Edgeworth-Kuiper Belt Object (EKBO) was discovered in 1992, and since then there have been many more, some of which exhibit very strange orbital properties. One such object, known as 2000 CR105, has an orbit of 3300 years, and behaves in a very odd way, leading some astronomers to suggest that its orbit is being affected by an external influence, such as another planet beyond Pluto.24
This piece of evidence is of some importance to us. The astrophysicists studying the Kuiper Belt Object 2000 CR105 have speculated quite openly about how it could have come to have such a large orbit, one that seems to have developed beyond the scope of Neptune's influence. A massive Perturber causing anomalies in the Kuiper Belt is now considered a very real possibility by many astronomers. Other minor planets, also showing unexpectedly eccentric orbits, are being discovered, including one known to be greater in size than the planet Pluto.
In the next chapter we will begin our crucial exploration of the Edgeworth-Kuiper Belt.
Deep Impact
As this book goes to press, findings are emerging about comets which may vindicate some of the ideas we have discussed in this chapter. NASA created the biggest Independence Day firework in the history of, well, America, on 4th July 2005. This awesome display was the result of the careful steering of a washing machine-sized projectile into the path of the comet Tempel 1. At the time, concerned citizens of the Earth wondered whether this 'Deep Impact', as NASA called it, might cause the comet to fracture, sending fragments hurtling towards our unprotected world. Scientists reassured us that the experiment posed no more danger to the comet's integrity than a gnat would to the windscreen of a car.
The impact was sensational. Though not, perhaps, as sensational as the scientific analysis of the impact might turn out to be. That's because there was more to this colossal firework than just American patriotism. The Deep Impact spacecraft was joined by several other telescopes, each carefully studying the materials that were forcefully expelled from the interior of the Tempel 1 comet. Such studies should give scientists the first real idea of what comets comprise of.
Such information could establish an intrinsic link between the composition of comets and the Earth.
The results of the studies have not been released to the public yet. This is frustrating, but somewhat understandable. It takes time to calibrate the spectra, work through all of the data and write up the scientific papers. However, one of the scientists involved has given some good insights into what we might expect when the complete picture of the composition of Tempel 1 is eventually released.25
The comet is composed mostly of ice: the Deep Impact event releasing large quantities of hot water into space. This much was expected. However, the geology of the co
met is complex, with a cratered landscape suggesting a multi-faceted life. What's more unusual is the composition of the rocks in the comet, which include limestone. This material can form in the presence of water, but it seems unlikely that such a mechanism could take place in the frigidly cold conditions of the outer solar system. It doesn't seem possible that limestone rock ended up as part of a comet. Yet the tell-tale sign of carbonates clearly show up on the spectra.
The comet seems to have all the elements associated with Earth rocks present, but lacks iron. This is also providing scientists with a headache. Iron tends to concentrate in the cores of planets, but in smaller bodies with lesser internal forces at work, iron should be present throughout the comet. So where is it?
These provisional findings suggest to me that the comet is a chunk of watery rock knocked off the surface of a planet whose iron had already sunk into the planetary core. I think that the comet didn't form independently way out in the outer solar system, but was once part of a watery planet. Such a scenario is consistent with the presence of limestone.
Yet Tempel 1 seems to be a regular short range comet. It is not an unusual body. All of this suggests that short range comets may be connected with previous catastrophic events in the solar system. It is very tempting at this early stage to wonder whether Zecharia Sitchin is correct; that the collision between Nibiru and Tiamat not only left a battered Earth spinning into a new orbit closer to the sun, but also spawned a celestial ocean of comets. Those comets should then have a composition broadly in line with that of the Earth.