‘Impatience asks for the impossible, wants to reach the goal without the means of getting there.’ –Hegel
In the early 1970s, NASA sent two spacecraft on a roller coaster ride towards the outer Solar System. Pioneer 10 and 11 travelled past Jupiter (and Saturn in Pioneer 11’s case) and are now heading out into interstellar space.
But in 2002, physicists at NASA’s Jet Propulsion Laboratory in Pasadena, noticed a puzzling phenomenon. The spacecraft are slowing down. Nobody knows why but NASA analysed 11 years of tracking data for Pioneer 10 and 3 years for Pioneer 11 to prove it.
This deceleration, called “the Pioneer anomaly,” has become one of the biggest problems in astrophysics. One idea is that gravity is different at theses distances (Pioneers 10 and 11 are now at 30 and 70 AU [Astronomical Units]). That would be the most exciting conclusion.
But before astrophysicists can accept this, other more mundane explanations have to be ruled out. Chief among these is the possibility that the deceleration is caused by heat from the spacecraft’s radioactive batteries, which may radiate more in one direction than another.
