Observational Constraints on Late Heavy Bombardment Episodes around Young Solar Analogs

Thermal emission from dust is investigated around 36 nearby G and K stars selected as analogs to the young Sun during the period of late heavy bombardment on the Moon (prior to 3.8 Ga). Measurements or upper limits at 12, 25, and 60 μm wavelengths were obtained from observations by the Infrared Astronomical Satellite (IRAS), and photosphere contributions were subtracted using the models of Kurucz and ground-based optical and near-infrared data. A single star, HD 128400, has circumstellar emission that is consistent with a 490 K blackbody with an effective area ~7×10³ times that of the present solar system zodiacal cloud. Emission from 260 K dust at a mean level exceeding 900 times the present zodiacal cloud can be ruled out for the remaining 35 stars. A model of dust production by cometary impactors scaled to the lunar cratering record shows that dust from late heavy bombardment episodes around these stars would fall below IRAS detection levels after 500 Myr (4.1 Ga). The emission from HD 128400 is broadly consistent with the model at the star's 300 Myr age.