Ocean Planets
In this article we are going to explore the possibilities of alien life on ocean planets and discuss what space explorers
may find. Above and below: a species of biosciform, an aquatic organism from the ocean of Undinion. These
organisms have two mouths that are adapted for filter-feeding. Each of the two highly inflatable filter-funnels sieves
out food organisms from the water and periodically contracts to expel the water. Some of the water is moved into a
highly distensible reservoir which pumps it out of the pair of movable exhalent siphons, in a series of spurts, enabling
jet propulsion. The organism is neutrally buoyant and so requires little additional effort to stay afloat. The filters also
act as gills, absorbing oxygen from the water. Filter-feeding is one of the most common feeding mechanisms in
aquatic environments on Earth and we would expect to find it in the life-supporting oceans of other planets. Most of
these organisms are only 10-20 cm long, but some reach over 10 metres in length.
Above: Planet Undinion. Ocean Planets can be divided into classes. The classification we will use is as follows: a class A
ocean planet has its surface entirely covered by liquid ocean; a class B ocean planet has more than half of its surface
covered by ocean and class c include planets with large seas and lakes. Further classification includes the nature of the
liquid: for example, subclass W means that the liquid is predominantly water (water is the main solvent), A for ammonia, H
for hydrocarbons and N for liquid nitrogen and nitrogen compounds other than ammonia. In this classification the Earth
would be a class BW planet. Some planets also have subsurface oceans, sea
ice planets like Europa, for example.

In this article, we will look at aquatic life on the planet Undinion. Undinion orbits a dim red dwarf class M star, which it
orbits at 0.3 AU (this is about as close as Mercury is to the Sun, but the parent star of Undion has only one-tenth the
luminosity of the Sun). Undion is 2.4 times as massive as the Earth and is typically shrouded in a dense cloud-layer.
Photosynthetic organisms in both the surface ocean and in the clouds themselves drive the ecosystem. Red dwarfs are
long-lived and so are good candidates for hosting life-bearing worlds, since life may have a long time to evolve on such
worlds. On Undinion, life is advanced, but still somewhat archaic in its level of sophistication compared to life on Earth.
Study the images of the biosciformes and consider the questions below:
Above: a planet with hydrocarbon
oceans. This world is similar to
in your own Solar System.
Animal or plant? Above - a cell from the tissues of a biosciforme. The cells of these organisms are not quite like
the cells of animals on Earth. They have a flexible cell wall, more like plant cells, and they form a variety of
crystalline and fibrous tissues. The genetic material is not enclosed in a lipid envelope, as it is in both animal
and plant cells, instead the nucleic material is wound onto a protein scaffold, visible as the spirals and rods in
this cell. There are no mitochondria, though there are energy-generating organelles of respiration, they have
not evolved by endosymbiosis as they did in eukaryotes on Earth. These cells are, however, carbon and
The biosciformes sieve tiny organisms from the water such as this single-celled planktonic organism. This cell
Explore life in a sub-surface ocean on
the icy world
The organism above is colonial. The main central individual acts as a pump and jet-propulsion unit, as well as
Left: another colonial organism, consisting of eight individuals
connected in a ring. The diagrams show one cycle in the
feeding-locomotion behaviour of this organism. The organism is
moving vertically upwards in these images and begins by taking in
water into the upper chambers. The inhalent aperture then closes and
water is pumped into the lower chambers which then pump the water
out as exhalent jets. In between the two chambers is a filter which
sieves out food particles and passes to the ring, in which they are
digested and the food disseminated to all parts of the colony. Clearly,
there has to be a valve system between the two chambers of each
pump, to ensure that water flows in the correct direction.

Q. We have seen how such organisms move, feed and respire, but
how might these organisms combat predation pressures? What
defenses might they have?

Another, larger species is shown below, in which the individuals have
more closely merged into a single compound organism.
Oceania beta-4
Left: a view looking directly down on the inhalent

Coming soon - more alien organisms from the ocean of
The organism above is a single cell, a giant cell, typically growing to 10-20 cm in length. It moves along the ocean
Above: another species of biosciform which has appendages rich in photosynthetic symbionts - micro-organisms