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Could Aliens really exist?
For many years scientists have been trying to find life in outer space, especially in our solar
system. On Earth there is a large range of both physical and chemical conditions which has
allowed complex life to evolve. As well as harbouring life such as humans, plants and
animals Earth also has a range of extremophiles which exist in the most extreme conditions
on Earth. If there is life surviving in the extreme conditions on Earth then it may be possible
for simple life to also exist on a range of other planets and moons which meet the
requirements to harbour simple life. Jupiter’s moon Europa, Saturn’s moon Titan and the
planet Mars are the most likely places for life to exist in our solar system.
Although complex life might not exist anywhere other than Earth in our solar system, it
could be possible that simple life such as bacteria and Archaea (which are a very primitive
form of bacteria) are living on other planets and moons in our solar system. The
requirements for simple life are much more basic than those for complex life. The three
essential requirements are liquid water, a carbon source, and an energy source. Liquid
water is one of the most important factors for life as it acts as a medium for nutrients to
diffuse into cells, and for wastes to exit the cell. Water is also a solvent (a liquid, solid or
gas, which dissolves another liquid, solid or gas), which many chemical substances can
dissolve into. This is essential for life as it allows important metabolic reactions to take
place. These reactions are essential as they allow organisms to survive, maintain their
structures, grow and reproduce.
A Carbon source is another requirement which is important for the most basic forms of life.
Carbon is important to life as it can chemically bond with up to four other atoms to create a
range of organic molecules such as lipids, carbohydrates, proteins, and nucleic acids.
Because carbon is the building block for all forms of life on Earth, it is likely that any life in
our Solar System would also be carbon-based.
Another requirement for life is that there must be an energy source. Energy is an essential
for all life as it fuels chemical reactions which must be carried out in order for any life to be
able to exist. For many years it was believed that life was dependant on solar energy from
the Sun, which made the presence of life on other planets and moons seem less likely,
however on Earth microbes have been discovered who gain energy from minerals such as
sulphates and nitrates. Therefore organisms could exist on other planets or moons such as
Europa where life would have to exist under the surface where no sunlight would reach.
When we search for life on other planets the organisms which are living in extreme
environments on Earth gives us an idea on what environments we might find life in and
what form they may be in. Earth has a range of extreme environments ranging from being
extremely hot, extremely cold, very acidic, very alkaline, salty, and there are even places
with intense radiation. These environments are the ones likely to be common-place on other
planets and moons so by being able to find life in these conditions in the form of
extremophiles (microbes which can survive in extreme environments) it means that it is
definitely possible for this type of life to be able to exist elsewhere in our solar system.
Biologists have discovered a wide range of extremophiles on Earth, mostly bacteria and
Archaea, such as Thermophiles, Psychrophiles, Halophiles, Acidophiles, Alkaliphiles ,
Xerophiles, radiation resistant microbes and many others surviving under extreme
conditions.
When searching for life in our solar system the most likely places where we are going to find
it are on Jupiter’s moon Europa, Saturn’s moon Titan and on Mars.
Europa is slightly smaller than our moon, and it is thought to have a rocky mantle, iron core,
and a liquid ocean of salty water which covers the whole surface of Europa, and is
completely frozen over. The temperature on Europa is roughly -220 degrees Celsius at the
poles, and around -160 degrees Celsius on the rest of the moon. These temperatures are
due to the tidal forces, caused by Jupiter’s gravity, which makes the sea below the surface
rise and fall. The friction caused from the motion of the tides has resulted in Europa being
warmer than it would be without the tidal heating. This motion is also likely to have caused
the cracks which can be seen in images of Europa. Life being under the surface of Europa
would protect organisms from radiation, as Europa has a very weak atmosphere.
Titan which is a moon of Saturn’s is another place in our solar system where it may be
possible for simple life to exist. Titan resembles Earth in many ways as a space probe has
shown it to have mountains, dunes, lakes and possibly volcanoes. As well as this the
weather on Titan appears to have erased most of its meteorite craters, which is what the
weather on Earth has done as well. Another similarity between Titan and Earth is that they
both have an atmosphere consisting of mainly nitrogen, Earth is 78% whilst Titan’s is 90%.
Titan’s thick atmosphere would protect organisms living on the moon from the harmful
ultraviolent radiation rays of the Sun. On Titan there is very little oxygen in the atmosphere,
meaning that any life living there would not be breathing oxygen or using it as part of their
feeding process.