The planetary systems so far discovered around other stars have generally been dominated by huge, gas giant worlds, many with so-called ‘hot Jupiters’ that orbit extremely close to their parent star. And that makes sense, given that a major method used for detecting exoplanets relies upon the star’s ‘wobble’ as it is influenced by such high-mass objects. We’re not yet at the point where Earth-sized planets can be found, although we’ve reduced the detection size down to Neptune-class objects, with better things to come.
But don’t assume that even the systems discovered so far are without terrestrial planets. As many as half of them may harbor habitable worlds, according to work by Barrie Jones, Nick Sleep, and David Underwood at the Open University in Milton Keynes (UK), which was presented today at the Royal Astronomical Society National Astronomy Meeting in Birmingham. The team used computer models to analyze the gravitational effects of known exoplanets on other, undiscovered worlds in their solar systems. They then inserted an Earth-like planet into the mix to see if it survived in the star’s habitable zone, where water can exist at the surface.
The results showed the location of two ‘disaster zones’ where the gas giant planet would cause the terrestrial world either to collide with it or the parent star, or be ejected from the planetary system altogether. With these rules in hand, the model was then run against all known exoplanetary systems. The result:
They discovered that about half of the known exoplanetary systems offer a safe haven for a period extending from the present into the past that is at least long enough for life to have developed on any such planets. This assumes that “Earths” could have formed in the first place, which seems quite likely.
You can read more in this Royal Astronomical Society press release. Interestingly, these numbers go up if you take into advantage the changes to the habitable zone as the star ages, allowing outer planets a chance to develop life (as recently discussed in Centauri Dreams).
Again from the press release:
These scenarios of past extinction and future birth increase to about two-thirds the proportion of the known exoplanetary systems that are potentially habitable at some time during the main-sequence lifetime of their central star.
The paper in which this work will be presented is Barrie W. Jones, David R. Underwood, and P. Nick Sleep, “Prospects for habitable ‘Earths’,” which is scheduled to appear in the 1 April 2005 issue of The Astrophysical Journal. The RAS meeting Web site is here.