# Is the Pioneer Anomaly really directed towards the Sun ?

1. Sep 1, 2008

### Bjarne

Is the Pioneer Anomaly really directed towards the Sun ?
How sure are we ?

Why not directed around the Sun ?

2. Sep 2, 2008

### Garth

This is a good question that is being actively researched.

The anomaly is a Doppler time drift in the signals being received from the spacecraft.

This is normally interpreted as an unexpected acceleration, initially towards the Earth because we are receiving the signals on the Earth.

However it seems there is no reason why the spacecraft should accelerate towards the Earth, so as the Earth and Sun are very close from the spacecrafts' perspective, it is normally interpreted as an actual acceleration towards the Sun. (But note not "around the Sun".)

If the anomalous acceleration can be resolved sufficiently accurately to distinguish whether the 'acceleration' is towards the Sun or the Earth then that would help to identify its cause.

If the PA is towards the Sun it could be due to a modification of the Solar gravitational potential (new physics), or to an imbalance of the spacecrafts' solar radiation absorption/radiation budget.

If the PA is towards the Earth it could be due to a clock drift between ephemeris and atomic clocks (new physics), or to an unmodeled radio transmission radiation budget (as the transmitters are pointing towards the Earth).

If you want to read more about the PA I have posted before, such as here, with links to eprint articles about it.

But first the effect has to be verified as real by other experiments....

Garth

3. Sep 2, 2008

### kmarinas86

Maybe it is because the conservation of angular momentum law does not require a inverse square relationship for force between moving bodies when a craft's main velocity component in the radial direction.

L=mvrsin(theta)

If you take the derivatives (product rule), you get:

dL=(dm)vrsin(theta)+m(dv)rsin(theta)+mv(dr)sin(theta)+mvrcos(theta)

You have several derivatives in the equation each weighted differently.

An excessive dr might prevent dv from following what is expected in the usual trajectory (it would decrease more than expected). With a somewhat straight trajectory out of the solarsystem, I would expect changes theta to be minimal. m hardly changes here and r increases, requiring v to drop (as is already known).

Last edited: Sep 2, 2008
4. Sep 4, 2008

### Bjarne

( Sorry if this is not perfect English)

1.
The 8 of December 1992 Pioneer 10 was suddenly changing course.
Do somebody know, to which directed it changed course, - and how much

2.
Several probes in gravity assist manoeuvre were gaining between 4 and 13 mm per second.
But Pioneer 10 was loosing an average of 400 mm per second right?
So the unknown force seems to be between 40 to 80 times stronger in the outer solar system, compared to the inner, right?

5. Sep 4, 2008

### Garth

Bjarne you need to read a decent paper on the subject such as this one: The Study of the Pioneer Anomaly: New Data and Objectives for New Investigation by Turyshev at the JPL et al.
So Pioneer 10 did not change course in 1992, that was when the effect was first noticed and mentioned in a JPL Interoffice Memorandum, 8 July 1992.

The PA effect wasn't detected in the inner solar system because it was swamped by other effects, such as perturbation by Jupiter and Saturn and scheduled course corrections.

Garth

6. Sep 5, 2008

### Bjarne

Thank you for the advice Garth.

1.
I am reading it now and wonder:

Pioneer 10 have lost totally 400.000 km travelling about 30 years.

How can I calculate how much the probe was loosing, - for instance every month, - by using the information that it lost about >> 8 .74 × 10−10 m/s^2 (per second).

What confuse me is that seconds here is m/s^2

When I want to calculate how much the probe is loosing, let say in 10.000 second, how can I do this?

2.
Pioneer 10 was really changing course, http://science.nasa.gov/headlines/y2001/ast03may_1.htm
On December 8, 1992, when Pioneer 10 was "only" 5.2 billion miles away, the craft experienced an unexpected course change.
Astronomers think it was diverted slightly by the gravitational pull of a Kuiper Belt Object.

I wonder to which direction did it change course ?

KR
Bjarne
KR
Bjarne

Last edited: Sep 5, 2008
7. Sep 5, 2008

### Bjarne

sorry this was double

8. Sep 5, 2008

### Garth

If the PA is an actual unmodeled acceleration, and not a clock drift, then the distance traveled away from the predicted position, as the acceleration has been more or less constant, over a period of 30 years i.e. 109seconds, is simply given by

$$d = \frac{1}{2}at^2 \sim \frac{1}{2}10^{-9} \times 10^{18} m \sim 5 \times 10^5 km$$

Thank you, I hadn't realised that it had this slight diversion, which would be most probably a perturbation by a body out there. Discovered by a team at my old Alma Mater, Queen Mary College, London, no less!But I wonder how robust that observation actually is? Discovered by a team at my old Alma Mater, Queen Mary College, London, no less!

Garth

Last edited: Sep 5, 2008
9. Sep 7, 2008

### Bjarne

I have now read the article
Several facts have brought me to the conclusion that a space probe is only affected by the strange force so soon it is released from the gravitational force of the Sun ( the equivalence principle ).
So long a space probe is bound to the gravitational force of the Sun, it seems that the force is to weak to to make any difference. .
I also think that when a probe is bounded by the gravitational force of a planet, the anomaly will not occur. But we properly have to poor date to confirm or dismiss this right now.
This thought could very well be the first little step that can help to solve this mystery.
KR
Bjarne Lorenzen

10. Sep 7, 2008

### Garth

Now I see that my last post duplicated a sentence! Too late to edit...

You seem to be a little confused. The space probes are still under the gravitational influence of the Sun and the planets, and will remain so for all time, the force from them just decreases as r-2.

The anomalous acceleration (or clock drift) is simply too small to be seen in the inner solar system and is swamped by noise. It may be there within the orbit of Saturn or it may not, we just cannot tell with the present data.

It is also interesting to note that when spacecraft are close to planets another anomaly reveals itself, the Flyby Anomaly. But because the two anomalies are so different in behaviour I personally do not think they can be the same effect, or maybe not even related.

Garth

11. Sep 7, 2008

### Bjarne

Garth

I agree that a space probe would still is under "influence" of gravity as you wrote.
I mean still you need power to lift up a probe, - I haven't misunderstood that.

What I mean, imaging a weak force in space trying to push the moon away.
It would not be possible because of gravity always binds the moon to the earth.

But when the moon had "lift up" and the gravity force between the earth and moon was equalized, even the magnetic field of earth could push the moon, - right? – Nothing would keep the moon here.

In the same way, it seems that we have no Pioneer Anomaly or other anomaly in our Solar system so long Space Probes are bound by the Sun (or planet) gravity.

Just think about why we have no anomaly when space probes are moving in weak ellipse orbits or circular orbits around the Sun, - but only when the orbits are very elliptical, or when probes moves directly out of the solar system. ( same is the case with sattelites around the earth, we will have no anomalies here too)

KR
Bjarne

Last edited: Sep 7, 2008