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Friday, April 2, 2010

Wonk On, Oh Hard Scientist, Wonk On

If the Young Sun was 75% fainter than the present sun, as usually thought, how did life ever get started?  Earth should have iced over.  One possible answer comes from study of κ Ceti, which is very like the sun is thought to have been in its early life.  Apparently, its greater activity makes up for its dimness and throws a protective magnetic blanket over any prospective planets there.  If the same is true of Young Sol, it would shield the earth from galactic cosmic rays, preventing the formation of albedo-enhancing cloud cover, thus keeping prospective planets warmer than they would otherwise be from radiative effects alone. 

How did the Sun affect the climate when life evolved on the Earth?

Abstract: Using kappa Ceti as a proxy for the young Sun we show that not only was the young Sun much more effective in protecting the Earth environment from galactic cosmic rays than the present day Sun; it also had flare and corona mass ejection rates up to three orders of magnitude larger than the present day Sun. The reduction in the galactic cosmic ray influx caused by the young Sun's enhanced shielding capability has been suggested as a solution to what is known as the faint young Sun paradox, i.e. the fact that the luminosity of the young Sun was only around 75% of its present value when life started to evolve on our planet around four billion years ago. This suggestion relies on the hypothesis that the changing solar activity results in a changing influx of galactic cosmic rays to the Earth, which results in a changing low-altitude cloud coverage and thus a changing climate. Here we show how the larger corona mass ejection rates of the young Sun would have had an effect on the climate with a magnitude similar to the enhanced shielding capability of the young Sun.
Comments: 5 pages, 1 figure, submitted to Astronomische Nachrichten
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:1003.6043v1 [astro-ph.SR]

1 comment:

  1. 1) Not 75% fainter, Mike, but 75% as luminous as the sun is now.

    2) Amazing how one can get a paper out of this many ifs, ands, and buts.


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