Washington, June 28: The sun, a star at the centre
of the solar system, is known to provide ideal conditions for
life to thrive on Earth. But, astronomers have claimed that it
also leaves the planet wide open to harmful cosmic rays.
A joint team from University of Arizona and University
of Texas in the US has found that the sun periodically leaves
Earth open to assaults from interstellar nasties in a way that
most stars do not, the 'New Scientist' reported.
The sun protects humans from cosmic rays and dust from
beyond the solar system by enveloping in the heliosphere -- a
bubble of solar wind that extends past Pluto. These rays would
damage the ozone layer and interstellar dust can 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. So, in their research, the
team, led by David Smith, has calculated the squeezing of
various stars' protective "astrospheres".
The astronomers found Earth is exposed to between one
and 10 interstellar assaults every billion years. Habitable
planets around a red dwarf, which account for three of every
four stars, are never exposed.
That's because they need to be close to these dim
stars to be warm enough to be habitable, they said.
"The bottom line is that habitable planets around
red dwarfs are better protected from climate catastrophes than
Earth is," Smith of the University of Arizona in Tucson was
quoted as saying.
The findings are to appear in 'Astrobiology' journal.
Bureau Report
First Published: Sunday, June 28, 2009, 11:20