Forg
et about little green men, ET or Alien – they don’t exist. Or at least we don’t have any proof that they do. Despite this, the search for extra terrestrial life is now as lively as ever : from the discoveries of planets orbiting other stars in our galaxy to the SETI (Search for Extra Terrestrial Intelligence) project, scientists are scrambling to find a glimpse of life away from our own home planet.
Exoplanets and the Goldilocks principle
Exoplanets are planets that orbit stars other than the Sun. For decades astronomers had suspected that other stars in our galaxy might have planets orbiting them ( just like the Sun has Mercury , Venus, Earth, and so on… ) Like all the other scientific predictions, you can only confirm it if you have enough evidence to back it up. Guess what – for the last ten years or so, astronomers have found evidence that in fact there are planets orbiting stars in our galaxy.
Planet in transit across the star disc: Picture: ESO/L. Calçada
The problem with seeing planets orbiting stars so far away from us is that the brightness of the star outshines the tiny amount of light reflected by the planet. Only very recently , with developments in image processing software and improvements in CCD technology have scientists been able to detect planets. But this doesn’t even mean that we can actually “see” the planets – we can’t , at least not directly. We must look for clues in how the light from these stars reaches us.
One way of telling if a star has planets orbiting it is called the “Planetary transit” method. Whenever a planet is placed between us and the star, we can detect a small decrease in the brightness of the star. Imagine a mosquito flying in front of a lamp – whenever it flies between us and the lamp, we can see that the lamp seems to get dimmer because the mosquito blocks a tiny bit of its light. The same happens with a planet that orbits around a far away star. Every so often the planet blocks some of the star’s light and the star appears to have dimmed by a little amount. Scientists look out for these tiny changes in the brightness of stars and use their data to compare the size of the planet with the size of the star.
This is all fine, there are more planets in the Universe than those we have learnt about in Miss Gileece’s lesson…. My Very Easy Method Just Speeds Up Naming Planets… But is there life living on them? Do they have BBM?
The answer is….. we can’t tell if there is life on any of the exoplanets that were found, let alone whether or not they have BBM. One thing we know is that life as we know it has first appeared in liquid water – right here on Earth, millions of years ago. So, we can be certain that planets where liquid water exists are more likely to have life. The planets that obey this condition must be at the right distance from their star for the temperature to be just right for liquid water to exist. Depending on the kind of star , and on the size and composition of the planet, the temperature is just right for liquid water if the planet orbits the star at a range of distances often called “the Goldilocks region”.
This raises the question: how do we know if these exoplanets have liquid water? And if they do have liquid water does that definitely mean that they have some kind of life? Life on Earth evolved in water , but there are so many variables to take into account that it is currently impossible to prove that there is indeed other life forms in the Universe.
So, if you were expecting a YES or NO answer to the question you may now be disappointed (or not!). All we can say is that most probably there is life somewhere in the Universe, possibly in a planet orbiting one of the hundreds of million stars in our own galaxy, the Milky Way.
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Jupiter and Jupiter’s Moon Io by Robert Altenburg (left)
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