The Dark Star: The Planet X Evidence (2 page)

5. The Extended Habitation Zone

Our investigation starts with a look at our current understanding
of where life can be found in the solar system. In years gone by, scientists
and fictional writers speculated that life was common on other planets and that
alien civilizations existed on Venus and Mars, our nearest neighbours. When Humanity
began to explore the planetary environments in more detail with space probes,
it became apparent that life was a rare commodity in the solar system, and
perhaps throughout the galaxy as well.

Life needs liquid water, and water takes its liquid form through a
relatively small range of temperatures. Most of the planetary environments in
the solar system have more extreme environments than we enjoy here on Earth.
Mercury, the sun’s closest planet, is hard-boiled and baked, its surface
blasted by the heat of the sun.

Venus, planet number 2, maintains a thick atmosphere which has
been made highly acidic by what is thought to be a runaway greenhouse gas
effect. Temperatures on the surface of the planet are extremely high, air
pressures intolerable, and the combination of these factors means that lead
melts on the ground there. Not very promising for the search for life, although
it may still be found high in the atmosphere.

The Earth, however, is just the right distance away from the sun,
and basks in the sort of medium-range temperatures that allow liquid water to
exist across most of the surface of the planet. This has been the case for
billions of years, and life has had a firm foothold here for most of that time.
Earth is in the sun’s ‘habitation zone’. If the sun was bigger and hotter then
that habitation zone might have been on the next planet, Mars.

If the sun was smaller and cooler, then Venus might have enjoyed a
more profitable relationship with life. But only Earth enjoys that exalted, and
possibly unique position. The discovery of life further out in the planetary
solar system remains one of the great unanswered questions in science.

Is There Life on Mars?

We still don’t know for sure whether there is life on Mars, and by
implication whether there is life elsewhere in the solar system, or Universe
beyond. The Viking landers searched for signs of life in the 1970s, but the
results of the experiments on soil samples on the Martian surface were said to
be ‘inconclusive’.
¹
The famous meteorite ALH 84001, discovered in
the Allan Hills of Antarctica in 1984, seemed to contain evidence that life
once existed on Mars.
²
These findings remain controversial, and
provide the merest threads of proof of extraterrestrial life. But those strands
of hope are enough for many people to maintain their hopes that the rest of the
solar system is not barren.

Confirmation of the existence of alien life has been inextricably
entwined with the search for life on Mars, mainly because it seems to offer the
second most hospitable environment in our solar system. Its atmospheric
conditions are certainly deadly for most life-forms currently dwelling on
Earth, but under the regolith of its barren plains may lie lakes and even seas
of frozen water. Surface features of the red planet tantalizingly suggest the
movement of liquid water during the distant past, or possibly more recently.

Thousands of enthusiasts scour over detailed images of Martian
terrain sent back by NASA probes hoping to find conclusive proof that the
surface of the red planet plays host to life. Others are intrigued by the trace
amounts of methane detected in the Martian atmosphere, which may allude to
micro-biological activity occurring under suspected ice packs. Their
motivations may be driven by the fear that Mars is the last hope; that beyond
this cold world the solar system may be truly devoid of life.

But
there are other possibilities elsewhere, much further from the sun. This is
where the conventional notion of the ‘habitation zone’ starts to break down,
and new possibilities open up.

The
asteroid belt beyond Mars is simply a collection of orbiting rocks, devoid of
life like our Moon. Scientists have been able to rule out life on the gas
giants, Jupiter and Saturn, and the frigid outer giants Uranus and Neptune.
These huge worlds have no detectable solid surfaces below their immense
pressurized atmospheres, and even if they did the internal pressures would
surely rule out the emergence of life in any recognizable form. Pluto, at the
far reaches of the planetary zone, is a frigid Moon-like world far too bleak
to harbour the chrysalis of life.

So,
by a process of elimination we are left with just two candidates among the
recognized worlds orbiting our sun: Mars, and the Earth. This is the classic
argument supported by the notion of the ‘habitation zone’. But there may be
nooks and crannies on other planetary bodies that could hold liquid water. As
implausible as this may first seem, we must consider the moons of the outer
planets.

The
vast majority of these distant moons orbiting the gas giants are barren rocks.
However, we now know that several of them have features suggestive of frozen
oceans. This has provided an extension of the solar system’s ‘habitation zone’
to the realm of the gas giants Jupiter and Saturn. Life could readily await
discovery on one or more of their numerous moons.

The
chances for future discoveries of life have increased because biologists have
been able to show that life is able to withstand extreme conditions with
unexpected ease in parts of the Earth once deemed "uninhabitable".
³
The discovery of veritable ‘oases’ of water scattered widely through the solar
system has increased the potentialities further: where there is liquid water,
there is the potential for life.

The
4 major ‘Galilean’ moons of Jupiter are ‘warmed’ by the gravitational influence
of the gas giant itself, and, among them, Europa almost certainly boasts a
liquid water ocean below its icy crust.
⁴
The tidal effect produced
by the parent planet internally warms Europa and shows that our traditional
assumptions about what is thought to constitute the habitable zone around a
given star have been ‘oversimplified’.
⁵
Distance from the sun is not
the only factor at play, even if it remains the most important.

Moons of Life?

The Galilean moons of Jupiter offer good conditions for the
emergence for life because the vast bodies of water under their surfaces are
warmed by gravitational and tidal effects induced by their massive parent. Io
is the closest moon to Jupiter, and the effect is extreme enough to make this
moon highly active volcanically. Europa is the best candidate for life, and a
deep ocean seems to lie below its frozen surface which may contain twice as
much water as all the oceans of Earth combined!

Europa looks like a scratched and colourful billiard ball from
space, and NASA plans to explore the geography of this moon by radar and
probes.
⁴
The two further Galilean moons, Callisto and Ganymede, may
also be hiding secret oceans below their frozen surfaces. Yet these worlds are
five times further away from the sun as the Earth.

Is it possible to move even further away from the sun and apply
the same principles to moons of the more distant, and colder, planets?

The main moon of the beautiful ringed planet Saturn is Titan, a
smoggy, cold world covered in hydrocarbons. We now know that Titan has oceans
of liquid hydrocarbons on its surface, mostly consisting of methane. It also
has landmasses and coastlines, familiar features to us on Earth. Liquid methane
goes through a similar dynamic process there as water does here; evaporation,
precipitation, run-off and drainage occurring below Titan’s surface.
⁶
Scientists speculate that there may be water buried beneath the surface of
Titan, warmed by Saturn’s tidal forces. It’s perfectly possible that water
might ‘geyser’ up into the organic molecule-rich oceans, and allow the building
blocks of life to emerge.
⁷

One day, when the sun begins to wind down and expands to a red
giant, Titan will become the most valuable real estate in the solar system. For
a short time Titan will become the new Earth, warmed by a massive red sun that
has already driven off all of the waters of the Earth.
⁸
We have 4
billion years to wait before that happens, though.

But
at the present time, Titan seems too inhospitable a climate for complex life,
despite the presence of liquid water. The dark atmospheric smog and great
distance from the sun will stop photosynthetic reactions taking place,
preventing a meaningful ecosystem from developing on the surface of Titan. But
there may be the presence of ‘extremeophiles’: Life that can evolve and exist
at the limits of environmental conditions. After all, the building blocks for
the formation of life exist on Titan, and a dynamic environment may have
already created the spark that is needed for life to begin.

The
major moon of the very distant planet Neptune is called Triton. It has no
atmosphere to speak of, and lies at the edge of the planetary zone around our
sun. Its surface is laden with dark organic materials and nitrogen ices, some
of which appear to have occurred as snowfall near the equator. It is simply too
frigid at this distance for Triton to hold onto an atmosphere, despite tidal
warming by Neptune.

Any
atmosphere it might once have, had precipitated out onto the surface as ice.
⁹
At this distance there is simply too little heat to create the conditions for
life, even with the tidal warming effects by Neptune. Liquid water is not
available out here, and even the most optimistic commentator must doubt whether
the extended habitation zone goes as far as Neptune, some 30 times the distance
of Earth from the sun (known as 30 Astronomical Units).

This
seems to mark the boundary for the potential for life in the solar system.
Beyond Neptune and Jupiter lie two collections of comets. The first is a belt
very similar to the asteroid belt between Mars and Jupiter, which surrounds the
planetary zone. It is known as the ‘Edgeworth-Kuiper Belt’, and the discoveries
that are taking place about its nature will form the basis for some of this
book.

The
second collection of comets is a far more distant one which surrounds the solar
system. This ‘Oort Cloud’ is a deep spherical layer of comets which are finely
distributed, some of which occasionally fall back towards the sun as
long-period comets. There appears to be a substantial gap between the
Edgeworth-Kuiper Belt and the inner Oort Cloud, where few comets trespass.
Again, an explanation for this can be found in this book.

It has been argued that comets carry with them the seeds of life,
and this may well be so. Such ideas form the basis for Panspermia, a theory
that involves the universal spread of life via such intra-and interstellar
travelers. But even if comets hold onto bacterial spores, they do not provide conditions
for that life to actually get started. Instead, ‘life’ rests here in a state of
suspended animation.

Our knowledge about what celestial bodies might lurk beyond the
orbits of Neptune and Pluto is still in its infancy. As the distances from the
sun become ever greater, our ability to detect dark bodies ‘out there’
diminishes rapidly. The Harvard astrophysicist Matthew Holman recently noted
that a Mars-sized planetary body could easily have escaped detection even if it
was located as close as 200AU away.
¹⁰
Given that one Astronomical
Unit (A.U.) is the distance between the sun and the Earth, then this is a
considerable distance indeed. An undiscovered planet could be orbiting the sun
beyond this point and we could still be none the wiser, despite the advances in
detection methods.

This is because the brightness of an object depends on its
distance from the sun to the fourth power.
¹¹
The luminosity of an
object rapidly falls away with distance. This is why the immense planets Uranus
and Neptune cannot be seen in the night sky with the naked eye. As the
distances increase further, into the Edgeworth-Kuiper Belt and beyond, the
potential for a substantial undiscovered planet increases with it.

The reason why this is an important question is that there is a
possibility that our extended habitation zone could find itself out among the
comets. If something is out there and is significantly massive, then it may
generate its own heat. A planet that size would have to be more massive than
Jupiter.

Common sense would lead us to believe that scientists should
surely have discovered such a world by now. But that is not necessarily the
case. Remember, luminosity drops off sharply with distance, and finding
anything ‘dark’ among the comets is a real challenge for astronomers, even with
the largest telescopes.

Such a massive planet has been proposed before by various
scientists, and their ideas considered seriously by the scientific community.
It is not the realm of the fantastic at all.