Doubts about hyped-up planet
Does Gliese 581g exist at all?
Published: 24 November 2011 (GMT+10)
Zina Deretsky, National Science Foundation
The planetary orbits in the Gliese 581 system compared to those of our own solar system. However, latest studies cast doubt on the existence of Gliese 581g.
Remember the claims of ET life on an extrasolar planet last year? Readers may recall the outstanding claims and the hype, if only from our article on the subject, in which one researcher was cited as being “100%” sure that it had life on it.1
But it’s likely that not many have heard that the existence of Gliese 581g, the planet where this ET life was so certain to exist, has now itself been called into serious question.
A number of studies and re-analyses have been conducted since the ‘discovery’ of Gliese 581g that have cast significant doubt on Vogt et al.’s interpretation of their data.
A Swiss team presented evidence that suggested Gliese 581g may not even exist.2 Despite finding that the probability for the non-existence of Gliese 581g was small, statistically, the measurements on which it was based were still not significantly different to the background noise in those same measurements. This is enough to cast reasonable doubt on the existence of Gliese 581g, at least for now. The major reason for this uncertainty is that our current technology is at this point stretched to its limit looking for exoplanets the purported size of Gliese 581g. Therefore the Swiss team came to the correct conclusion based on their data. The existence of Gliese 581g will most likely only be confirmed (or not) with more sensitive detection equipment.
A re-analysis of Vogt et al.’s data by using a complex form of statistics called Bayesian inference also added further doubt to the original conclusions of Vogt et al.3 This study concluded that Gliese 581g had a 99.9978% chance of being a false positive result based on the current data, thus the existence of Gliese 581g is highly doubtful at the moment.
Nevertheless, Vogt and his fellow researchers stand by their data and remain unconvinced that these studies have falsified their claims.4 A number of other studies have been written that either support5 or deny6 the existence of Gliese 581g.
So where does this leave us? At the moment, the debate about the existence of Gliese 581g seems to be at a stalemate. It seems that only new and higher resolution data will be able to definitively solve the matter. But this is the nature of science: tentative, open to revision based on new data, and open to reinterpretation using different analytical techniques. It provides a sober warning about trusting hyped-up, evolution-supporting claims in the media as soon as they break. There is no scientific reason to suspect that anything other than Earth-based life exists in the universe. So far from being ‘100% certain’ that life exists on this alleged planet, we don’t even know if Gliese 581g exists at all.
- Vogt, S.S., Butler, R.P., Rivera, E.J., et al., The Lick-Carnegie Exoplanet Survey: A 3.1 M_Earth Planet in the Habitable Zone of the Nearby M3V Star Gliese 581, Astrophysical Journal, (in press), 2010. www.arxiv.org/abs/1009.5733. Return to text.
- Mullen, L., Doubt cast on existence of possibly habitable alien planet, MSNBC.com, 12 October 2010. www.msnbc.msn.com/id/39640401/ns/technology_and_science-space/. Return to text.
- Gregory P.C., Bayesian Re-analysis of the Gliese 581 Exoplanet System. arXiv: 1101.0800, 5 January 2011. www.arxiv.org/abs/1101.0800. Return to text.
- Osbourne, D., Goldilocks planet lost in translation, 14 January 2011, www.abc.net.au/science/articles/2011/01/14/3113180.htm; Plait, P., Does Gliese 581g exist? Discover, 18 January 2011. www.blogs.discovermagazine.com/badastronomy/2011/01/18/does-gliese-581g-exist/. Return to text.
- E.g. Anglada-Escudé, G. and Dawson, R.I., Aliases of the first eccentric harmonic : Is GJ 581g a genuine planet candidate? arXiv: 1011.0186, 29 April 2011. www.arxiv.org/abs/1011.0186. Return to text.
- E.g. Andrae, R., Schulze-Hartung, T. and Melchior, P., Dos and don’ts of reduced chi-squared, arXiv: 1012.3754, 16 December 2010. arxiv.org/abs/1012.3754. Return to text.