2 April 2009

The Curious Case of Pioneer 10

Posted by Dan Satterfield

Dr. John Anderson of the Jet Propulsion Laboratory has discovered something very weird. Two other colleagues have been working on it as well. As of now, there is no explanation. Safe to say it’s likely keeping them up at night!

Not that they haven’t tried to figure it out!

Sherlock Holmes said, that once you rule out the impossible, then what remains, however improbable, must be the truth.

The truth, in this case is that the laws of gravity, might not be right.

Pioneer 10 was launched in 1972, and along with Pioneer 11, and the two Voyager spacecraft, is now speeding along well out of our solar system. We lost contact with Pioneer 11, but scientists were able to get some data back from Pioneer 10 in 2000. It was twice as far from the sun, as very distant Pluto. Well over 80 times, the distance from the Earth to the Sun.

This Earth-Sun distance is called an Astronomical Unit. Earth is therefore 1 AU from the sun. Pluto is about 40. Pioneer 10 is over 100AU. The last contact with it was in 2003. It’s now well over 24 light hours from Earth! (The sun is 8 light minutes!)

Pioneer 10 from NASA JPL

Pioneer 10 from NASA JPL

The problem here is that Pioneer 10 is not where it should be. It’s a bit behind schedule. Not a big deal, since it will not likely run into anything for awhile. The star Aldebaran (53 light years away) is expecting a visit….in about 1,700,000 years. Plenty of time to kick the cat out, and clean the rugs.

Paths of Pioneer 10/11 Ctsy: NASA JPL

Paths of Pioneer 10/11 Ctsy: NASA JPL

Pioneer 10 is slowing down though. Something is pulling it back toward the sun. The magnitude of this acceleration is .00000008 cm/sec/sec.(8 x10 -8 cm/sec squared)  Yeah, not much, but when you have traveled over 13 billion kilometers, it adds up!

So what is causing it??

Well, they have ruled out all kind of things. Yes, they added in Einstein’s relativity. They checked the Atomic clocks, and a dozen other things.

They found that Pioneer 11 had the same problem, before radio contact was lost. They have even discovered the same affect, on a couple of other planetary space craft. (The Voyager spacecraft can’t be used, because they make too many position changes with their thrusters).

Could it be the heat given off by the nuclear power system. Nope, checked. How about the radio antenna? Every action gives an equal and opposite reaction, right. So sending those radio waves back to Earth at the speed of light will cause an acceleration, no? Yes, it certainly will!

Not that.

How about a mysterious planet X? Checked, nice try.

Dark matter! That’s it!

NO, they checked.

Gravity from the Galaxy?
No, but two points for thinking of it.

So what’s the answer?

They would really like to know. Could our understanding of the laws of Gravity be missing something? Perhaps. The affect is not seen in the orbits of planets, like Mars. It only seems to affect small space craft.

Someone is going to have to call Aldebaran, and let them know that Pioneer will be late. That’s going to be one heck of a roaming charge.


PS For the super nerds out there- go here.