Astronomy Without A Telescope – Is An Anomalous Anomaly A Normality?

Article written: 3 Apr , 2010
Updated: 24 Dec , 2015

The lack of any flyby anomaly effect when the Rosetta spacecraft passed Earth in November 2009 is what, an anomaly? No. Anomalies arise when there is a mismatch between a predicted and an observed value. When it happens our first thought shouldn’t be that OMG there’s something wrong with physics! We should probably start by reviewing whether we really got the math right.

The flyby anomaly story starts with the Galileo spacecraft‘s flyby of Earth in December 1990 – where it was measured to have gained a speed increase (at least, an increase over the predicted value) of 2.5 millimeters per second at perigee. In its second pass in December 1992, the predicted value was the same as the observed value, although it has been suggested that atmospheric drag effects confound any analysis of this particular flyby.

The next, and biggest anomaly so far detected, was the NEAR spacecraft‘s flyby in 1998 (a whopping 7.2 millimeters per second at perigee increase over the predicted value). After that you have Rosetta showing an anomaly on its first flyby in 2005. Then a quantitative formula which aimed to model the various flybys to date was developed by Anderson et al in 2007 – predicting a small but detectable speed increase would be found in Rosetta’s second fly-by of 13 November 2007. However (or should I say anomalously), no such increase was detected in this, or in Rosetta’s third (2009), pass.

So, on balance, our spacecraft (and often the same spacecraft) are more likely to behave as predicted than to behave anomalously. This reduces (though not negates) the likelihood of the anomaly being anything of substance. One might sagely state that the intermittent absence of an anomaly is not in itself anomalous.

More recently, Mbelek in 2009 has proposed that the anomalous flyby data (including Anderson et al’s formula) can be explained by a more rigorous application of special relativity principles, concluding that ‘spacecraft flybys of heavenly bodies may be viewed as a new test of SR which has proven to be successful near the Earth’. If such recalculated predicted values match observed values in future flybys, that would seem to be that.

Pioneer 10 - launched in 1972 and now making its way out towards the star Aldebaran, which it should pass in about 2 million years. Credit: NASA

Then there’s the Pioneer anomaly. This has no obvious connection with the flyby anomaly, apart from a common use of the word anomaly, which gives us another epistemological maxim – two unrelated anomalies do not one bigger anomaly make.

Between around 20 and 70 AU out from Earth, Pioneer 10 and 11 both showed tiny but unexpected decelerations of around 0.8 nanometers per second2 – although again we are just talking about an observed value that differed from a predicted value.

Some key variables not considered in calculating the original predicted value are radiation pressure from sunlight-heated surfaces, as well as internal radiation generated from the spacecrafts’ own (RTG) power source. A Planetary Society update of an ongoing review of the Pioneer data indicated that revised predicted values now show less discrepancy from the observed values. Again, this doesn’t yet negate the anomaly – but given the trend for more scrutiny equals less discrepancy, it’s fair to say that this anomaly is also becoming less substantial.

Don’t get me wrong, this is all very useful science, teaching us more about how our spacecraft operate out there in the field. I am just suggesting that when faced with a data anomaly perhaps our first reaction should be Doh! rather than OMG!


10 Responses

  1. Member
    Aqua says

    Hmm… the story that just wouldn’t go away? was first reported here at ‘Universe Today’ on April 16th, 2008 in “The Pioneer Anomaly: A Deviation from Einstein Gravity?” And on September 18th, 2008 as “Flyby Anomalies Explained?” and now today’s entry… (I probably missed one or more similar stories?)

    I went back and read the comments made in both articles and found a couple interesting “anomaly’s” there!

    1) The ‘regulars’ here today are not the same as the regulars back then.

    2) Any story reported by this page is fodder for all kindsa quirky indulgences from all kinds of quirky readers – myself included!

    3) Personal theories are as numerous as the stars, but make for interesting reading? Especially the personal attacks in rigorous defense of nonsense by the ‘Trolls’? LOL!

    I like what # alphonso richardson said on April 17th, 2008 at 7:51 am – “That should keep the guys busy for a LOONG time…………………..” He was right!

  2. Member
    Aqua says

    I may have been wrong stating ‘…was first reported on…”? Because I really didn’t look that deep – I was actually looking for what I may have posted? so I could ‘cover my 6’…[email protected]; )

  3. Member

    Umm… OK. I just thought it was a new angle on an old chestnut. I did mass extinctions last week, which was not exactly breaking news either. Thanks for reading.

  4. Member
    Aqua says

    @Steve Nerlich – Don’t get me wrong sir! The story was appreciated as I wondered after that effect and the closure you’ve provided seamlessly seals the deal~ I like!

  5. Lawrence B. Crowell says

    This illustrates the apparent device and condition dependencies of these orbital anomalies. That they appear and disappear, or appear with certain spacecraft and not others strongly suggests they are not a signature of any consistent physics.


  6. Jesper says

    I’m a software developer. The story, especially the “OMG there’s something wrong with physics!” reminds me of a mistake that beginning programmers sometimes make: they don’t understand some aspect of the programming language and then say “OMG, I found this enormous bug in the compiler!”.

  7. Duncan Ivry says

    A refreshing normal approach to these anomalies. Thanks go to Steve Nerlich.

    Things like these happen every day, when you drive a car, a boat, a computer, a spacecraft, your body, a large hadron collider, or what else.

    One point catches my eye: The anomalies the article talks about are, as far as I can see, rare events, some even singular ones, like single measurements here and there in different physical experiments. No wonder it’s difficult catching them all in one theory (here e.g. one of those notorious alternative theories of gravitation).

  8. Torbjorn Larsson OM says

    Right. Except that the use of common sense doesn’t make sense in science.

    Here, the absence of anomalies made any real anomaly a priori harder to predict. Likewise, the two different kinds of anomalies were related by the use of the same theory (GR).

    As for the flybys, Mbelek claims that the discrepancies can be explained by SR not being fully accounted for in previous timing analysis. If that indeed wasn’t done, you don’t need “extraordinary evidence” to back up these seemingly “extraordinary observations” because they were in fact not. These “observations” were errors.

    [“Extraordinary claims need extraordinary evidence” sounds like common sense, but I would argue it is not. Here “extraordinary claim” means either hard to explain observations, or observations that seem to conflict with previous theory.

    The former need testable evidence in the form of parsimonious theory, not complicated ad hocs, which is in itself “extraordinary evidence” in comparison as ad hocs are numerous as rain drops compared to oceans of theory.

    The later _can_ point to new theory replacing old rather than new theory supplementing old. That is again asking for testable “extraordinary evidence”, when those oceans of theory swell out of former bounds.]

    As for the Pioneer anomalies, it turns out in closer analysis that here again there are errors but that those discovered in fact have nothing to do with the underlying theory of GR. So the connection with the other anomaly is (again) aposterori severed.

    That two rather unrelated anomalies turns out to be completely unrelated by theory (but completely related as errors :-o) is mundane and to be expected. Nothing anomalous here. 😀

    Oh, and “when faced with a data anomaly perhaps our first reaction should be Doh! rather than OMG!” is eminent common sense!

  9. Torbjorn Larsson OM says

    Ups! My HTML ran amok. …is eminent common sense!

  10. singaraju babu says

    it real or grphics

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