LONDON: The protective bubble around the sun that helps to shield the Earth from harmful interstellar radiation is shrinking and getting weaker, NASA scientists have discovered.

New data from the Ulysses deep-space probe show that the heliosphere, the protective shield of energy that surrounds our solar system, has weakened by 25 per cent over the past decade and is now at it lowest level since the space race began 50 years ago.

Scientists, baffled at what could be causing the barrier to shrink in this way, were set to launch a mission overnight to study the heliosphere.