Are there planets beyond our solar system?
Extrasolar planets are planets orbiting stars other than our Sun.
Our solar system is neat and orderly.
Orbiting our Sun are four small rocky planets (Mercury, Venus, Earth and Mars), the asteroid belt,
four big gas giant planets (Jupiter, Saturn, Uranus and Neptune) and the belt of icy bodies.
What would you think of a solar system that was completely different?
How about a giant planet, much bigger than Jupiter, orbiting a star so closely that they're practically touching?
What about planets orbiting not one, but two stars in a binary star system?
For a long time, imagining other solar systems was the job of science fiction writers.
Beginning in the mid 1990s, astronomers began finding evidence of planets orbiting stars other than our Sun.
At first, the only planets that could be detected were really big.
However, as telescopes and computers advanced, astronomers began finding smaller and smaller planets.
Since Jupiter is the biggest planet in our solar system,
scientists get really excited when they find planets the size of Jupiter or smaller.
Astronomers have found more than two hundred Extrasolar planets.
The first one was detected in 1995 by the Swiss astronomers Michel Mayor
around the star 51 Pegasi
Since then Extrasolar planet hunting has continued with great excitement.
Most planets discovered early on were large like Jupiter and only take a few days to orbit their star.
Astronomers call them "Hot Jupiters".
Later smaller or distant planets and even some planetary systems with two or more planets were detected.
Using the precise spectrometers and large telescopes scientists have discovered about 13 planets with masses below 20 Earth's masses.
The smallest one, so far, has only 1.5 times larger in diameter
than the Earth.
However, none of these planets has been directly seen.
They all were discovered using the indirect methods.
Astronomers use a number of different ways to detect planets orbiting around other stars.
One way is called the radial velocity technique, where observers look for small wobbles of the stars
which might be caused by planets orbiting them. Most of the known Extrasolar planets were discovered in this way.
However, this works only for Jupiter sized planets and as we know such large planets are likely inhospitable for human life,
unless they have a habitable moon. There is also a photometric technique,
where scientists monitor the brightness of stars to look for slight changes that would be caused
if a planet were to pass in front of the star. Using this technique, we may register not only the Earth size planets,
but also indicate some gases like ozone or water vapor, which may indicate life.
The real challenge in this technique is to distinguish the planet from the star which is approximately the same size.
While detection of Extrasolar planets similar to the Earth seems only matter of time,
searching for traces of life is challenging. Traces of water vapor, oxygen
likely indicators of extraterrestrial life.
According to scientists the relatively large amounts of oxygen and ozone in Earth's atmosphere are a result living organisms.
How does ozone indicate evidence of life?
Without constant reproduction of oxygen by living organisms,
the ozone layer in Earth's atmosphere would quickly vanish because the molecules have a tendency to
combine with other molecules and solar UV
light easily destroys them.
So to find life on other planets scientists are looking for evidence of oxygen or ozone.
The smallest Extrasolar planet found so far orbits the red dwarf Gliese 581
located in constellation Libra
about 20.5 ly
way of from our Sun.
Astronomers, detected the planet using the radial velocity method, which also allows them to estimate the mass.
It is about 5 times the mass of the Earth and orbits around the Gliese for 13 days.
Astronomers are very excited about this planet, because it lies in the habitable zone and may have liquid water.
Since the host star is about 1/3 of the Sun's mass
and 50 times fainter,
its habitable zone is located closer to the star.
With average temperatures between 0° C and 40° C and radius only 1.5 times Earth's radius the planet
should be either rocky or covered with water.
There are two other planets orbiting around the same star.
One is Neptune sized with an orbital period
of 5 days, and other is about 8 Earth masses
and orbits in 84 days.