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EVOLUTION OF THE SOLAR ACTIVITY OVER TIME AND EFFECTS ON PLANETARY ATMOSPHERES. I. HIGH-ENERGY IRRADIANCES (11700 8)
 

Summary: EVOLUTION OF THE SOLAR ACTIVITY OVER TIME AND EFFECTS ON PLANETARY
ATMOSPHERES. I. HIGH-ENERGY IRRADIANCES (1­1700 8)
Ignasi Ribas,1
Edward F. Guinan,2
Manuel Gu¨del,3
and Marc Audard4
Receivved 2004 October 7; accepted 2004 December 9
ABSTRACT
We report on the results of the Sun in Time multiwavelength program (X-rays to UV) of solar analogs with ages
covering $0.1­7 Gyr. The chief science goals are to study the solar magnetic dynamo and to determine the radiative
and magnetic properties of the Sun during its evolution across the main sequence. The present paper focuses on the
latter goal, which has the ultimate purpose of providing the spectral irradiance evolution of solar-type stars to be
used in the study and modeling of planetary atmospheres. The results from the Sun in Time program suggest that
the coronal X-ray­EUV emissions of the young main-sequence Sun were $100­1000 times stronger than those
of the present Sun. Similarly, the transition region and chromospheric FUV­UV emissions of the young Sun are
expected to be 20­60 and 10­20 times stronger, respectively, than at present. When we consider the integrated
high-energy emission from 1 to 1200 8, the resulting relationship indicates that about 2.5 Gyr ago the solar high-
energy flux was about 2.5 times the present value and about 3.5 Gyr ago was about 6 times the present value (when
life supposedly arose on Earth). The strong radiation emissions inferred should have had major influences on the
thermal structure, photochemistry, and photoionization of planetary atmospheres and have played an important

  

Source: Audard, Marc - INTEGRAL Science Data Centre & Observatory of Geneva, Université de Genève

 

Collections: Physics