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 are baffled at what could be causing the barrier to shrink in this way and are launching a mission today to study the heliosphere.
The Interstellar Boundary Explorer, or Ibex, is being launched from an aircraft on a Pegasus rocket into an orbit 150,000 miles above the Earth where it will "listen" for the shock wave that forms as our solar system meets the interstellar radiation.
The heliosphere is created by the solar wind -- a combination of electrically charged particles and magnetic fields that emanate at more than a million miles an hour from the sun -- which meets the intergalactic gas that fills the gaps in space between solar systems.
At the boundary where they meet, a shock wave is formed that deflects interstellar radiation away from the solar system.
The scientists are hoping that the Ibex mission will help them to predict what protection it will offer in the future.
If the heliosphere continues to weaken, it is feared that the amount of harmful cosmic radiation reaching Earth will increase, disrupting electrical equipment and satellites and potentially harming life.
If the heliosphere disappeared, the cosmic radiation would make life on Earth almost impossible by destroying DNA and leaving the climate uninhabitable.
David McComas, the principal investigator on the Ibex mission, said: "There is no imminent danger, but it is hard to know what the future holds.
"It is likely that there are natural variations in solar wind pressure and over time it will either stabilise or start going back up."