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Stars and the Universe

The Universe - Life on Other Planets.

People have wondered for a long time
about the possibility of extraterrestrial life.
"Extraterrestrial" means "beyond the Earth".

Scientists use three approaches
to look for life on other planets (or moons).

1.  The direct observation of life or fossils from samples or pictures.
People have been to the moon and collected samples of rock
and dust which have been brought back to Earth for analysis.
Robots can land on planets and send pictures back to the Earth.
This has been done on Mars and Europa (a moon of Jupiter).

Material from space also arrives on the Earth when meteorites land.
Some of these may contain fossils of extraterrestrial life.
If you are not sure what a fossil is, see the GCSE Chemistry site.

2.  Living organisms change the chemical composition of a planet
(see how the evolution of life
has changed the Earth on the GCSE Chemistry site).
Scientists using telescopes can tell about the composition of
other planets by looking at the wavelengths of light which
are reflected from them.
A large amount of oxygen in the atmosphere of a planet
would indicate that life (photosynthesis) was present.

3.  Scientists look at radio signals from space.
There is a project called SETI which stands for
the 'search for extraterrestrial intelligence' that looks for
meaningful signals within a narrow band of wavelengths.
SETI has been running for 50 years
but has not found signs of life on other planets yet.

So far, there is no hard evidence that life exists outside of the Earth
from any of the methods listed above.

In view of the fact that there are a huge number of stars and planets
and that many of these planets may be suitable for life,
it seems highly likely that some forms
of life exist somewhere else in the Universe.

Given the size and the age of the Universe, it seems
unlikely that people on Earth will ever contact other life forms.
Still, who knows? By the time
you are reading this the aliens might already have landed!

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