Until now, astronomers believed that only five to 15 per cent of Sun-like stars had orbiting planets, but Lineweaver and Grether’s work shows that previous estimates under-reported the proportion of so-called extrasolar planets. The Astrophysical Journal, the world’s leading journal of astrophysics, has accepted their research for publication.
Astronomers have been carefully monitoring 2,000 nearby stars for the presence of orbiting extrasolar planets. “To date, they’ve detected a hundred or so, meaning the fraction of stars with extrasolar planets was around five per cent,” says Dr Lineweaver. “But most planets are too small or take too long to orbit their host stars to be detected. For example, if the Sun were one of the stars being monitored, we still wouldn’t have detected any planets around it.
“Using a new method to correct for this incompleteness, we found that at least 25 per cent of Sun-like stars have planets.”
Dr Lineweaver believes that the figure of at least 100 billion stars with orbiting planets could be on the low side when it comes to cosmic counting. It could be that close to 100 per cent of stars have planets. “Given that there are about 400 billion stars in our Galaxy alone, it means there could be up to 400 billion stars with planets,” he says. “With about 100 billion galaxies in the observable universe, our result suggests that there are at least 10 trillion planetary systems in the Universe.”
‘What Fraction of Sun-like Stars have Planets?‘ by Charles H Lineweaver and Daniel Grether will be published later this year. It is available online.
Dr Lineweaver is an ARC Senior Research Fellow and Senior Lecturer, School of Physics, UNSW. Daniel Grether is working on a PhD.
By coincidence, Ricky happened to mention this book just at the time I had decided to put the historical portion of it online at my website. The “modern” part of the book, which was published in 1974, is of course very outdated, so it’s not a candidate for reprinting. But the historical section–more than half the book–is still of interest, and it includes facts that most people aren’t aware of. How many realize that in the 17th and 18th centuries and most of the 19th, almost all educated people believed that the planets of other suns are inhabited, and that many famous people mentioned this in their writing? Because the idea dropped out of favor among scientists until the 1970s, it came to be assumed that such belief is recent and originated in science fiction, which is far from the case.
I based all my research for this portion of the book on primary sources from earlier centuries, since there were no secondary sources covering the subject when I wrote it. Since then, some have been published, so I no longer plan to write a scholarly book from my xeroxed source material as I once did. (The Planet-Girded Suns was published as a teen book, so couldn’t be as detailed as I’d have liked to make it.) I want to make the information available, though, so I’m scanning it and within a few weeks I hope to have it at my site.