In this section we explore the possibilities of life on icy worlds. Seraf 9 is an icy world that is cold and barren at first
sight, since its surface is completely frozen. However, beneath its thick icy crust is an ocean of liquid water. In this
respects it is thought to be similar to Europa in the Sol system. However, although little is know about Europa,
Seraf 9 has been studied and is known to contain a rich variety of life forms in its ocean. On this page we shall
discuss the problems facing these life forms in their dark sub-surface ocean and see how they have overcome
Left: a cut-away showing the structure of
Seraf 9. Beneath the thick icey crust is a
vast liquid ocean surrounding the small
terrestrial rocky planet at the centre, which
has a molten mantle and a metallic core.
Radius: 1.36 times that of the Earth
Mass: 1.61 Earth masses
Thickness of icy crust: up to 800 km
Depth of liquid ocean: 2 800 km
So what problems do living things on Seraf-9 face and how do they overcome them?
Source of heat and free energy
Life is energetic! Living things need energy to grow, move and reproduce. Energy is a prime requirement for life, and it must
be energy that can do work. There are several sources of energy available to life on Seraf-9. The first of these, essential to
all life, is heat. Heat energy is needed for chemicals to react inside living things. Reptiles will sun themselves on a cool
morning to absorb the heat that they need to 'power' their chemical engines. Thus, all organisms use heat to some extent,
humans generate their own heat from the food that they eat. Heat has another vital function - it keeps certain materials liquid.
For example, life on Earth is absolutely dependent upon the presence of liquid water. If the Earth gets so hot that all of its
water evaporates then life will perish, and likewise if all the Earth's water freezes.
Seraf-9 is quite a large planet, its rocky core is about 0.5 times the mass of the Earth. Planets form by a process of accretion
- smaller objects mass together into a larger objects as gravity pulls smaller objects toward bigger ones. Imagine a disc of
dust, gas and icy and rocky debris orbiting a newly formed star. Over time some of these icy rocks will clump together, now
the bigger clumps have a stronger gravitational field which draws still more small clumps toward them. Thus a kind of positive
feedback (like a positive spiral) occurs - bigger lumps grow bigger and bigger, faster and faster. Eventually a few lumps will
dominate and sweep out orbits around the star and become planets. Smaller lumps will continue to collide with these objects
as meteors. Early on in a planet's history it is typically subjected to an intense meteoritic bombardment. The point is this:
planet formation generates a lot of heat and newly formed planets are hot and the larger the planet the hotter it will be when
newly born. This is the heat of formation.
Very small planets cool quicker than bigger planets. A large planet like the Earth still has a very hot core and mantle. A
smaller body, such as the Moon, however, is expected to have a much cooler mantle, perhaps a solid one. Seraf-9 is a
medium-sized terrestrial planet and so would become more or less solid depending upon what other sources of heat it had.
For example, a planet closer to its parent star would clearly cool more slowly and may even heat up. There are other
processes that generate heat however. Radiogenic heating is the process by which heat produced by radioactive decay of
minerals like uranium inside a planet heats it up. The larger the planet the more radioactive material it has and the more heat
it can produce for longer. The Earth's large size, combined with its safe distance from its parent star, has kept it warm by solar
heating, radiogenic heating and it has also lost its heat of formation slowly. Seraf-9 is large enough to generate quite a lot of
heat by radiogenic heating, however, it is so far from its parent star that its surface has frozen solid, forming the thick
ice-crust. It accumulated a large ocean of water during its formation, however, which has insulated its core. Indeed, ice is quite
a good thermal insulator. Thus, Seraf-9 has enough heat to prevent its deep ocean from freezing solid, whilst its outer layers
are frozen. Compare this with Europa in the Sol system. Europa is a much smaller body than Seraf-9 and so has less heat of
formation and less radiogenic heating and is also far from the Sun such that its outer layers are frozen solid. However, it is
thought that Europa maintains a liquid ocean beneath the ice because it is subject to appreciable tidal heating.
Volcanic sources of energy
On the ocean bed of Seraf-9 volcanic vents vent off heat, magma and gases from the planet's hot interior. Similar volcanic
vents occur on the Earth's ocean floor. These vents release potential chemical energy that living organisms utilise, for
example hydrogen and carbon dioxide gases can be burned for fuel, rather like oxygen and petrol in a car engine.
Tidal and convective forces
Tidal forces result when one body distorts another, for example the moon pulls at the Earth with its gravity and this stretches
and pulls the Earth in one direction then another as the Moon orbits the Earth. This significantly heats the Earth. Europa is
kept warm by moderately strong tidal heating. Tidal currents are a potential source of energy. Seraf-9 has strong currents in
its oceans, driven by three sources of energy: 1) the planet's rotation, 2) tidal heating and 3) pressure driven convection. The
third of these results from uneven heating of the ocean beneath the thick ice crust of seraf-9. If an icy crust is thin enough
(say less than 40 km thick or so) then convection will occur within the ice itself as well as in the water.
What is convection: convection is the bulk movement of a fluid driven by uneven heating. For example, heat a saucepan of
water and the water gets hotter quicker toward the bottom of the pan. The hot water at the bottom is compelled to transfer its
heat to the water above and it does this by rising upwards (as warm water is less dense than cold water) heating the water
beside it as it rises. Denser cooler water at the top of the pan sinks. This causes local circuits of fluid flow, called convection
cells, to be established - you can see this by the shadows that each cell of water forms on the saucepan bottom. Convection
occurs in Seraf-9's ocean, however, its icy crust is too thick to undergo substantial convection. This convection generates
strong ocean currents.
The icy crust imposes another problem for Seraf-9. When the Earth's oceans heat up they expand and the sea level rises.
The extremely thick icy crust of Seraf-9 restricts the water beneath it so that it can not freely expand. This sets up strong
pressure-driven flow in the ocean as warm water, heated by a local volcanic event on the ocean floor, wants to expands, but it
can't as the water is confined. This generates an area of high pressure which pushes water outwards to a cooler area of lower
pressure - this sets up strong 'winds' within the oceans of Seraf-9. Combined with moderate tidal forces, this creates some jet
streams of high speed water flow.
These currents are utilised as a source of energy by living things on Seraf-9. For example, one organism forms hollow
cone-like structures born on a robust stalk. The stalk keeps these structures facing the oncoming currents, which are
funneled into the cones, increasing the shearing force of the water against the inner walls of the cones which bear
projections. As these projections are distorted by the flowing water, they generate electricity by a piezoelectric effect. This
electricity is used to establish a voltage gradient which drives nano-scale molecular motors within the organisms tissues.
These motors then convert their rotational energy into chemical energy (much like the ATPase motors inside the mitochondria
in human cells).
Finally, some organisms on Seraf-9 utilise infrared radiation, not that which comes from the parent star as this is mostly
absorbed by the thick icy crust, but from the hot rifts and volcanic events that release heat and infrared radiation on the
ocean floor. This light has sufficient energy to trigger infrared photosynthesis in some organisms.
The (hydrostatic) pressure at the depth of the 2 800 km ocean is immense, about 280 000 atmospheres. This compares to
the pressure at the bottom of the deepest Hadal trench on Earth's ocean bed, at about 1100 atmospheres of pressure. At
these depths on Earth, the biochemistry of is affected by the high pressure. Since many chemical reactions involve an
increase in volume (even if gases are not involved slight volume changes can occur) then these reactions become inhibited
at great pressure, but even at much lower pressures the behaviour of proteins and enzymes changes. Creatures living at
these immense pressures require very different biochemistry specialised to function at high pressure.
Life on Seraf-9
The picture above shows one of the more sophisticated life-forms on Seraf-9. It is a type of Seravian worm which lives at the
very bottom of Seraf-9's extremely deep ocean, click the image to enlarge it. These worms spend the first part of their lives
burrowed into the bottom ooze, with only there tentacles and mouths showing above the surface. These worms grow in places
where sea mounts shelter the local vicinity from the fierce tidal currents that occur on Seraf-9. Organic debris collects in these
relatively stagnant regions which also teem with organisms that thrive on the slowly rising nutrients that get carried upwards
by convecting warm water rising from below. As organic material accumulates within these convecting cells of nutrient-rich
water, organic debris eventually leaves the convective zone and sinks in the stagnant water column to the ocean bed. Thus,
there is a constant snow of organic debris down to the ocean floor in these regions. This debris is gathered by the worm's
tentacles and transported to the mouth, which is in the middle of the tentacle ring. Living this way for many years, these
worms can reach large proportions, up to 4 metres in length, though this depends upon their exact location and the nutrients
available, with some growing no more than a few centimetres in length.
At this point the worms enter another stage of their life cycle. The worms pull themselves from their burrows and turn
upside-down and begin to scavenge the ocean floor by crawling about on their tentacles. Living in local regions of dense
nutrient availability, these Seravians form what appear to be social groups, though very little is known about the nature of
their social interactions, but they do exhibit signs of high intelligence.
Living deep down in a very deep ocean beneath a thick layer of ice, these worms live in total darkness, apart from the small
lights produced by certain other organisms. However, they appear to sense their environment by electrolocation. They
generate waves and pulses of electrical currents. Any object in the vicinity of the Seravian will distort the electrical field that
the worm generates and this distortion is detected by electro-sensors. There is evidence that these creatures also use these
electrical signals as a mode of communication. Their long and highly extensible tentacles are also equipped with very
sensitive vibration and pressure sensors that can detect nearby objects and movements. It would appear that these worms
can also generate sizeable electric voltages for self-defense, or possibly to stun fast-moving prey creatures. Since the oceans
of Searf-9 are poor in oxygen, but rich in sulphur, it would appear that these worms respire sulphates instead of oxygen as an
oxidising agent to burn their chemical fuel which they obtain from their food.
Coming soon - more creatures from the oceans of Seraf-9.