NASA scientists say they may have discovered a new force of nature, after research showed two of their deep space probes were being inexplicably pulled off course. Pioneer 10 and Pioneer 11, which have been in space for over 40 years, are being steadily pulled towards the sun by an unknown power, according to London’s Telegraph newspaper, The scientists said it could not be gravity or solar radiation, as they decreased over distance. They have also discounted gas leaks and nuclear heat leaks from the satellites. Although the force is relatively weak — around 10 billion times weaker than gravity — the satellites are travelling at around 43,000km/h on a journey expected to last several million years. Two other satellites in the solar system, Galileo and Ulysses, are also being affected by a similar force.