Until fairly recently, it was generally thought (and taught) that the planets in our solar system were formed more or less where they currently reside on their solar orbits. Within the the last few decades, planetary scientists have had to re-think this theory.
Once we’d all got used to the idea, proposed by Copernicus in 1514, that the Solar System planets orbited the Sun (rather than the geocentric idea with the Earth at the centre), we had no reason to believe that our home grown planetary system had ever looked different than it does today. All that changed when NASA’s Kepler Mission was launched in 2009. The mission’s objective was to search for new habitable worlds orbiting distant stars within the Milky Way.
The Kepler space telescope – a 0.95m photometer, or light meter – uses the ‘transit method’ to find new worlds. It looks for tiny dips in the luminosity of stars, which could indicate transiting planets. Since its launch, data from Kepler has hinted that most evolved stars beyond our Sun could have their own unique planetary systems. Thousands of planet candidates have so far been discovered using Kepler, with 966 confirmed new worlds to date [15th May 2014]. And that’s just within our neighbourhood of the Milky Way.
The search for planets beyond our Solar System goes further back than the Kepler Mission though. The first exciting discoveries were made in 1992 using ground-based telescopes. Back then, it was thought that most, if not all, extra solar planets – these days just called ‘exoplanets’ – would be similar to those we’re so familiar with. But no! What astronomers have found are unimaginably strange worlds – mostly gas planets of giant proportions, orbiting their suns furiously fast and dangerously close. These radiation lovers, or ‘hot Jupiters’, are much easier to spot than relatively tiny worlds like Earth. Planets with tight orbits that whizz around their stars are also easier to detect, but only if they transit from our line of sight.
Sadly, the Kepler space telescope encountered problems with its pointing system in 2013. Plans are now afoot to overcome the problem using solar energy as a method of propulsion, and to re-name the mission ‘K2’. In the meantime though, data already captured will keep astronomers busy for the next few years. Using these data, over 700 newly confirmed exoplanets were announced by NASA in February this year, more than doubling the Kepler database previously confirmed. Almost all of these are multiple planet systems – just like ours.
The first exoplanets were discovered using the ‘radial velocity method’: a way of detecting planets by studying stellar movements. By measuring the amount that a star appears to ‘wobble’, it is possible to deduce whether the movement is due to the gravitational dance between star and planet. Over 500 new worlds have been discovered using this and other techniques, bringing the total number of confirmed discoveries to over 1500 and rising.
Amongst the strange new worlds so far discovered are sterile exoplanets, bathing in the radiation of pulsars; lifeless orbs circling white dwarf stars; planets being ripped apart by stellar plasma; and fated worlds being swallowed by black holes.
But the most exciting discovery yet came earlier this year: a world a lot like Earth. This new planet, with the catchy name of Kepler-186f, is part of a five planet system, and orbits within an area known as the ‘Goldilocks zone’ – an area around a star, not too cold and not too hot – where water can exist at the surface. This is likely to be the first of many Earth-like discoveries; dispelling all ideas that our familiar world is unique.
If, based on scientific discoveries, we can change our minds on such huge astronomical concepts within 500 years; just imagine the discoveries and possibilities yet to come, and contemplate how these discoveries might change our long-cherished theories.
Why are hot Jupiters so close to their suns? And why are our gas giants so far from ours? Could it be that our octet of planets have drifted from their original orbits? These questions are what makes space science so exciting. If you want to learn more about space science, there are lots of courses available, from GCSE Astronomy to Bachelor’s and Master’s degrees. Some universities offer distance learning in astronomy, cosmology, and planetary science; from free taster courses, right through to degree level study.
© Melanie Davies 2014