title: The faint young Sun paradox: an observational test of an alternative solar model.
abstract: We report the results of deep observations at radio (3.6 cm) wavelengths of the nearby solar-type star pi 01 Ursa Majoris with the Very Large Array (VLA) intended to test an alternative theory of solar luminosity evolution. The standard model predicts a solar luminosity only 75% of the present value and surface temperatures below freezing on Earth and Mars at 4 Ga, seemingly in conflict with geologic evidence for liquid water on these planets. An alternative model invokes a compensatory mass loss through a declining solar wind that results in a more consistent early luminosity. The free-free emission from an enhanced wind around nearby young Sun-like stars should be detectable at microwave frequencies. Our observations of pi 01 UMa, a 300 million year-old solar-mass star, place an upper limit on the mass loss rate of 4-5 x 10(-11) M(solar) yr-1. Total mass loss from such a star over 4 Gyr would be less than 6%. If this star is indeed an analog of the early Sun, it casts doubt on the alternative model as a solution to the faint young Sun paradox, particularly for Mars.
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA. gaidos@gps.caltech.edu
authors.forename: E J
authors.initials: EJ
authors.lastname: Gaidos
authors.forename: M
authors.initials: M
authors.lastname: Gudel
authors.forename: G A
authors.initials: GA
authors.lastname: Blake
mesh_terms: D001256:Astronomy / Q000379:methods*; D018559:Exobiology; D005118:Extraterrestrial Environment; D007091:Image Processing, Computer-Assisted; D055585:Physical Phenomena; D010825:Physics; D011846:Radio Waves; D019445:Solar Activity; D016082:Solar System