No molecular gas around nearby solar-type stars     

J. S. Greaves  I. M. Coulson  W. S. Holland 《Monthly notices of the Royal Astronomical Society》2000,312(1):L1-L3

Molecular gas around main-sequence stars is thought to disperse in only a few million years, constraining the time-scale for giant planets to form. However, this hypothesis has never been fully tested, as many of the search targets have been A-type stars, where the primary gas tracer, carbon monoxide, is readily photodissociated. A survey has been made of 14 nearby F and G stars with known circumstellar dust – no CO is detected, and a mean upper limit for all the stars implies less than 0.015 Uranus masses of H₂. Since these solar-like stars have negligible dissociating UV radiation, this indicates that the lack of gas detections is not an observational bias, and also that theories with formation of the outer gas giants at late times are not supported.  相似文献