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Extraterrestrial life

Does life exist outside our Earth on the other planets in our solar system and does life exist on other planets circling distant stars if such planets actually exist?

The search for planets orbiting other stars

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.

At present astronomers believe that they have discovered between 150 and 160 planets orbiting other stars in our galaxy. Three of the earliest discovered extra- solar planets are those orbiting 51 Pegasi, 70 Virginis and 47 Ursae Majoris

An excellent table of planets orbiting other stars is given in the following website and I have printed an extract below with permission of the author.

Star Number of
known planets
(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

Other useful websites containing data about extraterrestrial planets are:

California & Carnegie Planet Search

A very comprehensive account with a table (2001)

A planet orbiting 51 Pegasi

Extrasolar planets encyclopedia data on extrasolar planets recently updated. This is an excellent resource which you can sort by discovery date, mass etc.

Life on other planets

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:

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.


© Keith Gibbs 2020