The New Worlds
Submitted: Monday, 25th June 2007 by Trevor Hand
We all wish we could turn our telescopes on to a star and see a family of planets dancing around it, alas the laws of mathematics and physics make this, for the moment at least, a dream. However, by applying a number of observational techniques and statistical analyses we have been able to detect more than 200 planets outside our solar system (exo planets). In one transiting planet is detectable by amateurs with only moderate size telescopes and suitable electronic photometric measuring equipment.
Books on the subject are pretty lean on the ground at the moment, there are perhaps half a dozen currently in print. I found this book on Amazon and decided to give it a try.
Originally published in France in 2005, this translation was published in 2007. Other than a few minor translation or printing errors (I am sure Jupiter weighs more than 19x1024 kg and in the accompanying table of planets I don’t think a planet at a distance of 0.05AU will take in excess of 4 years to complete one orbit) this book is crammed full of data. If I were to use one word to describe it, “fascinating” would be a suitable choice.
The book begins with a brief history of the first discovery, 51 Pegasi. A comparison of the difficulty seeing a planet the size of Jupiter sets the stage for the difficulty of the discovery (this would be like seeing a candle next to a lighthouse from a distance of hundreds of kilometres). We are then transported back in time to the “plurality of worlds” theory, canals on Mars and false planetary alarms with Barnard’s Star, 61 Cygni and 70 Ophiuchi. The discoveries start to come thick and fast with a planet of 1.6 Moon masses found orbiting a pulsar, whilst another of Uranus size was soon discovered orbiting another pulsar 30,000 light years away, subsequently shown to be in error.
Then we are introduced to the most successful detection method so far, velocimetric measurement. Essentially this measures the wobble of the target star as the planet orbits. As a comparison, Jupiter produces an effect of 12.5 m/sec in the normal movement of the Sun around the Milky Way. By measuring the shift in spectral lines, this wobble can be detected. Other methods such as transits and even gravitational lensing are also explained. Comparisons with the effects caused by our own solar system are also given; it is interesting to note that with our current techniques we would be unable to detect Jupiter orbiting our own Sun!
If you are put off by complex equations and detailed statistics, this is the book for you. The authors manage to cover a lot of information about some very complex procedures without the need to quote sophisticated mathematical analyses. The book is littered with tables, graphs and pictures that help the reader to understand, at least at an introductory level, the multitude of detection methods used.
Other chapters investigate the various planetary formation theories, correlation between star metalicity and incidence of planets, comparison between various planetary systems and their parent stars, protoplanetary disks and the use of spectra to determine the compositions of disks and even planets themselves.
The final few chapters concern the possibility of life on other planets and some of the criteria required such as orbital distance, chemical composition, organic molecules etc. The book concludes with future projects like COROT, TPF and interferometry that promises resolution down to milliarcseconds. A table of statistics of the first 200 exo planets is printed in the appendix.
If you have an interest in exo planets and the methods used to detect them, this book provides an excellent introduction to the fundamentals of a complex subject. Over the years you may accumulate a number of books on this subject, but this will make an excellent first choice.