Milky, Not Dusty

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Science  01 Oct 2010:
Vol. 330, Issue 6000, pp. 13
DOI: 10.1126/science.330.6000.13-b

As many of us now learn at a young age, our solar system hosts small planets close to the Sun and giant planets farther out. What do the first planetary systems that formed in our Galaxy look like? Sheehan et al. used the Spitzer Space Telescope to search for dust around stars that formed early in the Milky Way's history. The stars they observed are twice the age of our Sun. Detection of discs of dust and debris around these stars would be a sign that at least small planetary bodies formed around them, because these discs are generated and maintained through collisions between comets and asteroids. Of the total of 11 stars observed by the authors and 11 others observed by other groups, none showed signs of dust. This does not necessarily imply that these stars do not host planetary systems; some of them are known to be orbited by giant planets. The lack of dust implies that some of these systems did not stop at planetesimal growth but proceeded to giant planet formation. They could be analogues of our solar system, where there is very little cometary dust left after the formation and evolution of the gas giant planets.

Mon. Not. R. Astron. Soc. 10.1111/j.1745-3933.2010.00936.x (2010).

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