Washington
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.

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.