Is there life beyond our solar system? Expert verdict The detection of life beyond our solar system would be the most profound scientific discovery in history. DR PAUL ELLIOTT, a lecturer in the School of Applied Sciences at the University of Huddersfield, looks at how close we are to such a discovery.
HOW many planets are there?
Your instant answer might be nine, the familiar family of planets that circle our Sun; fiery Mercury, hellish Venus, our home Earth, chilly Mars, the giant Jupiter, majestic Saturn, the other mysterious giants Neptune and Uranus and tiny little Pluto. Simple, right?
But how many planets there are is a hotly debated matter. The official ruling from the International Astronomical Union (IAU) is eight after Pluto was demoted from having planet status in 2006.
The main reasons for Pluto's demotion were its small size (smaller in fact than our own Moon!) and the discovery of several other objects of similar size. So where do you stop? They can't all be called planets.
If we accepted all of these small objects we'd end up with a list of hundreds of planets in our solar system! Rather than 'true' planets these have been called 'dwarf planets'. In reality it's simply a matter of opinion but one on which opinions have been very strongly argued.
So it's sorted, there are eight planets, right? Well no, there's actually a lot more. The thing is, the others don't orbit our star, the Sun.
These are extrasolar planets or exoplanets, planets that orbit other stars in our galaxy.
As of December 2008, there have been some 333 planets detected that orbit other stars and the number keeps rising.
Recently, astronomers from the University of California announced very important results, publishing grainy pictures in the journal Science of four large planets that circle nearby stars called Fomalhaut and HR 8799.
So what was so important about their work after the discovery of so many other planets? It's important because no one had been able to take direct images of exoplanets before.
Direct imaging of exoplanets is incredibly difficult because any light coming from them is swamped by the light of its parent star. Imagine trying to distinguish the light reflected off a moth while it is buzzing around a flood light from a distance of a mile and you'll get an idea of the problem facing astronomers.
So how do we know that all these other exoplanets are there if we can't see them?
There are two main ways in which exoplanets have been discovered. If we look at all the stars in our galaxy, we can imagine that for at least some of them we are looking at their solar systems from the side.
If this is the case, planets travelling in their orbit might pass in front of their parent star and block out a little of its light.
Many exoplanets have been detected through the continual monitoring of the amount of light that we can see coming from a large range of stars. For some we see a periodic drop in the amount of light and if this happens on a regular predictable basis, this is a clear marker for the existence of an exoplanet.
The second method relies on the effect of an orbiting planet on the star's motion. The planet orbits the star because the star is very much heavier and exerts a big gravitational pull on it. The star is also attracted toward the planet but to a much smaller degree. So if a planet is orbiting a star, it will cause a tiny but measurable 'wobble'.
This wobble measured over time then allows astronomers to estimate the size of the planet and how far it orbits from its star.
For the moment, the only planets that we can detect are very big, Jupiter sized or larger. The ultimate goal would be the detection of Earth sized planets and we would hope to see the tell tale chemical signs of extraterrestrial life. For that we need to image exoplanets directly and to examine the light bouncing off them. This is why our Californian astronomers' work is very important. They achieved this by high tech methods that selectively ignore the light coming from the star in order to see the light coming from a planet.
We are still a long way from being able to detect Earth sized planets however, but with future planned telescopes this could soon become a reality.
The detection of life beyond our solar system would be the most profound scientific discovery in history, proof that we are not alone and that the universe perhaps isn't such a big place.
Professor John Brown, the Astronomer Royal of Scotland and Regius Professor of Astronomy at the University of Glasgow, will be giving a public lecture on January 9 at the University of Huddersfield, organised jointly with the Huddersfield Astronomical and Philosophical Society, to celebrate the launch of the International Year of Astronomy. Professor Brown's lecture, entitled Our Magical Cosmos and How We Reveal its Tricks - From Freddy Flintstone to the Hubble Telescope and Beyond, promises to be both very informative and very entertaining.
Professor Brown's lecture will be given in the Canalside West Lecture Theatre (room CWS/10) Firth Street, Huddersfield at 7pm on Friday, January 9 2009. Free refreshments will be served from 6:30pm in room CWG/01
'Proof that we are not alone and that the universe perhaps isn't such a big place'
NEW DISCOVERIES: As of December 2008, there have been some 333 planets detected that orbit other stars and the number is rising