How Red Dwarfs Protect Their Planets

By Ken Croswell

Published in New Scientist (June 27, 2009)

The Sun provides ideal conditions for life to thrive, right? In fact, it periodically leaves Earth open to assaults from interstellar nasties in a way that most stars do not.

The Sun protects us from cosmic rays and dust from beyond the solar system by enveloping us in the heliosphere--a bubble of solar wind that extends past Pluto. These cosmic rays would damage the ozone layer, and interstellar dust could dim sunlight and trigger an ice age. However, when the solar system passes through very dense gas and dust clouds, the heliosphere can shrink until its edge is inside Earth's orbit.

In a paper to appear in Astrobiology, David S. Smith at the University of Arizona in Tucson and John Scalo at the University of Texas, Austin, calculated how often and by how much the protective �astrospheres� of various stars were squeezed.

They found that Earth is exposed to between 1 and 10 interstellar assaults every billion years. In contrast, habitable planets around a red dwarf, which account for three of every four stars, are never exposed. That�s because habitable planets have to huddle close to these dim red suns to stay warm. �The bottom line is that habitable planets around red dwarfs are better protected from climate catastrophes than Earth is,� says Smith.

Ken Croswell is an astronomer and the author of Magnificent Universe and Ten Worlds.

"Magnificent Universe by Ken Croswell is elegant and eloquent."--Washington Post. See all reviews of Magnificent Universe here.

"On the basis of its striking design and photographs, this handsome, large-format volume is well worthy of praise. And astronomer Croswell's concise yet conversational, information-packed text wins it sky-high accolades in the narrative sphere as well."--Publishers Weekly, starred review. See all reviews of Ten Worlds here.

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