Astronomers have made very detailed searches for planets around other
stars. One telescope used for this research is the Lick observatory's 2.4 m diameter Rocky
Planet Finder Telescope on Mount Hamilton in the USA. If there was a large planet orbiting a
star the gravitational attraction between the star and the planet would make the star wobble
as it moved around the galaxy. This is rather like a hammer thrower walking across a field
while swing the 7.5 kg hammer round their body on the end of a wire. They would stagger as
the ball went round and round.
In our galaxy there are some 100 000 million stars
and there are millions of galaxies in the rest of the Universe. This means that there are at
least a 100 000 million million stars in the Universe and it seems quite likely that at least one
of these has a system of planets revolving round it.
| Star | Number of known planets |
Distance (light years) |
Name of discoverer | Announcement date |
| 51 Pegasi | 1 | 50 | M.Mayor & D.Queloz | 6th October 1995 |
| 70 Virginis | 1 | 59 | G.Marcy & R.P.Butler | 17th January 1996 |
| 47 Ursa Majoris | 2 | 46 | G.Marcy & R.P.Butler | 6th October 1995 |
| 55 Rho Cancri | 4 | 45 | G.Marcy & R.P.Butler | 17th January 1996 |
| 16 Cygni B | 1 | 85 | G.Marcy & R.P.Butler B.Cochran & A.Hatzes |
22nd October 1996 |
| 79 Ceti | 1 | 117 | G.Marcy et al | 29th March 2000 |
| g Cephei | 1 | 38.5 | W.Cochran et al | 13th September 2002 |
| HD 118213 | 4 | 45 | R.da Silva et alr | 22nd August 2005 |
| HD 10295 | 4 | 45 | J.Ge et al | 12th January 2006 |
| Gliese 581 Libra | 6 | 20.3 | Not known | 29th September 2010 |
As far as we know life does not exist on any other of the planets
orbiting our sun but what about life somewhere else in the Universe?
The question
is what kind of 'life' are we looking for? We will only look at the possibility of finding life as we
know it – that is a form of life based on carbon and breathing air as we do. Plant
life.
For life as we know it to develop there would have to be a planet with the same
atmosphere as ours at just the right distance from a star. The temperature of the planet
would have to be just right and the planet's atmosphere would need to be of similar
composition to our own.
Even if an alien race does exist how can we get in touch?
Would we be afraid of them and would they be afraid of us? Would we find them repellent
and would they find us unpleasant to look at?
Another problem is the vastness of
space. This affects the time for radio signals to travel across the space between our Earth
and another planet circling a distant star. For example it would take a radio signal over four
years to reach the nearest star – a signal sent out now (2006) would not return until
2014!
On the other hand it is possible that even before I have finished writing this
someone on this planet may receive a signal from another intelligent race far off in the galaxy
– a signal that was transmitted many years ago.
The signal would be very weak as it
spreads out over the vastness of space. Are we likely to ever hear from our near neighbours
in the galaxy? What about a visit from an alien race – how would we on Earth receive the.
Earth inhabitants – small metal box like creatures rushing along hard roads. From them
come even smaller soft like things that disappear into solid boxes that don't move. Would an
alien recognise that the intelligent life form is the soft objects (humans) and not the metal
boxes (cars)?
Even if we could make contact with an alien race how would we talk
to them? It is hard enough speaking to someone from another country whose language and
alphabet we do not understand. How much more difficult to communicate with an alien who
might 'speak' in a totally different way to us.
In 1961 Frank Drake, a Professor at
Cornell University in the USA, proposed a formula that would tell you how many intelligent
civilisations might exist in our galaxy. It involves some intelligent guess work about things like
the number of stars in our galaxy, the number of them that might have planets, the number of
planets that might be able to support life, the time a civilisation might last and so on.
Depending on our guesses for these numbers the number of intelligent civilisations
in our galaxy varies between 1 and one million! Hardly an accurate prediction.
You
can work this out for yourself by logging onto the following web site:
http://www.activemind.com/Mysterious/Topics/SETI/drake_equation.html
In his
book Bill Bryson "A short History of Everything" uses the formula to work out the average
distance between intelligent life forms in our galaxy and this turns out to be about 200 light
years.