Mystery of the Flyby Anomaly Endures

Article written: 23 Nov , 2009
Updated: 26 Apr , 2016

The weird mystery of the flyby anomaly just got even weirder. Since the early 1990’s scientists and mission controllers have noticed that some spacecraft experience unexpected changes in speed during Earth-flybys. The unexplained variation is extremely small and has occurred as either speed gained or lost, but this variant is not predicted by fundamental physics. The anomaly doesn’t happen to every spacecraft but scientists were hoping to gain more insight into the anomaly when the Rosetta spacecraft swung by Earth on Nov. 13 to pick up a gravitational boost for its journey to rendezvous with a comet in 2014. However, in a major disappointment – which had deepened the mystery — the Rosetta spacecraft did not experience the flyby anomaly during this swingby of Earth, even though the same spacecraft did experience the anomaly when it flew by Earth 2005, but didn’t in 2007.

“It’s a mystery as to what is happening with these gravity events,” said Trevor Morley, lead flight dynamics specialist working on Rosetta. “Some studies have looked for answers in new interpretations of current physics. If this proves correct, it would be absolutely ground-breaking news.”

For the Earth swingbys where the anomaly has been detected, Morley said the main manifestation has been “the inability to get anything like a reasonable fit of an orbit to an arc of radiometric data that encompasses both the pre- and post-perigee (closest to the Earth) intervals.”

For those cases when an anomaly has been seen, the change has been very slight, but noticeable. “In every case, a reasonable data fit could be established only by inserting an artificial velocity change along the direction of the orbital velocity in the vicinity of perigee,” Morley said.

Earth as seen by the Osiris camera on Rosetta. Credit: ESA

Earth as seen by the Osiris camera on Rosetta. Credit: ESA

For this flyby, the team made allowances for the software to estimate an impulsive maneuver at perigee, aligned along the orbital velocity. But after analyzing the radiometric data gathered by ESA and NASA ground stations, nothing anomalous was seen.

“The difference in the quality of the data fit was absolutely negligible,” Morley said. “For Rosetta’s third and final Earth swingby, there was no anomaly.”

Several ideas have been tossed around in an attempt to explain why the anomaly occurs, but no one has been able to pin the cause down as of yet.

Ideas range from tidal effects of the near-Earth environment, atmospheric drag, or the pressure of radiation emitted or reflected by the Earth, to much more extreme possibilities, such as dark matter, dark energy or previously unseen variations in General Relativity.

One American research team, led by ex-NASA scientist John Anderson, is even looking at the possibility that Earth’s rotation may be distorting space-time – the fundamental fabric of our Universe – more than expected, and affecting nearby spacecraft. But there is as yet no explanation how this could happen.

Plus no one can explain why some flybys experience the anomaly and others don’t.

The mystery continues!

Source: Rosetta Blog

20 Responses

  1. Kevin says

    Maybe the planet’s core is a little lumpy, pulling on the spacecraft differently depending on the earths point in its daily rotation?

  2. Sili says

    Didn’t you recently post about it being a case of failing to correct for special relativity? Whatever happened to that?

    I’m not gonna hold my breath for this being new physics. Certainly not when it’s as temperamental as this. Atmosphere and tides sound far more reasonable. The new and improved geode’ll presumably help with the latter.

  3. Astrofiend says

    I’m sure one of the many variants of EU has an explanation that post-predicts this effect perfectly.

    Anyway, it would be great to see new physics or an esoteric explanation such as clouds of DM or something doing their thing, but if I were a betting man I’d have my money on something far more mundane. Obviously I haven’t seen the flight data and know next to nothing about spacecraft navigation, but it seems to me that an unaccounted-for known effect is a far more likely option than an unaccounted for unknown effect.

  4. Sili says

    DM is far too sparse to exert any effects on this scale. We’d have seen it long ago with all the satellite we have up, if that could be a cause.

    I’m actually hoping anaconda will spout nonsense on this entry:

    only by inserting an artificial velocity change along the direction of the orbital velocity in the vicinity of perigee”

  5. Lawrence B. Crowell says

    I suspect these are material effects. Of course this might not explain why the velocity would be larger. This might of course explain the so called Pioneer anomaly, which does not effect the Voyagers. The pioneers are interacting with gas in some way that has a local occurrence or higher density.

    As for lumpiness, various geodetic craft have been set up to measure the gravitational distribution of matter. I would imagine this has been benchmarked against this flyby anomaly.


  6. Dark Gnat says

    I wonder if a computer simulation of all the affected spacecraft could be compiled.

    The position of the Earth, Moon, and Sun may have something to do with it – possible tidal effects?

  7. Well I once spoke with someone who was deeply into this, and I ran through all the usual suspects, and the bottom line is that they’ve been investigated and dismissed.

    Whatever it is, it is hiding very well. Everyone is sure it has GOT to be a mundane explanation, but they just can’t catch it. Makes me smile every time I read about another flyby.

  8. Lawrence B. Crowell says

    These events are scatter-shot. They don’t exhibit a consistent trend. This goes for the Pioneer anomaly as well. So it is then suspected these are the result of transient conditions. These might be localized gas clouds, atmospheric heating that generates plumes, solar flaring and … .


  9. Member
    Aqua says

    I’d like to see the data comparing solar flux index’ and the geomagnetic reflex and/or aurora activity on the dates of the anomoly(s).vs dates where that effect did not occur… just for grins. Also any radio freq activity increase from Jupiter.

  10. Member
    Aqua says

    Ion flux tubes or tribo-electric tornado’s anyone? How might those accelerate or decelerate an ionized body? Surely not by chirality or even monopole repulsions, but perhaps … too simple, an unexpected magnetic field generation?

  11. Member
    Aqua says

    P.S. What was the cosmic ray count looking like?

  12. DrFlimmer says

    It is a quantum mechanical effect. It only happens, when nobody’s watching 😉

    Or it is dark energy. I once attended a talk where someone claimed that the Pioneer anomaly could be explained with it…..

    But most obviously it is an effect that can be explained with plasmas and currents…

    Sorry, I have no real contribution to the discussion..

  13. Olaf says

    EU proponents will explain it all perfectly, even predict it when the next spacecraft will have it an how big this effect will be. So I would say EU proponents, here is your chance you have finally a way to proof EU by predicting all next satellite anomalies.

    But real scientists will say, we don’t know since we do not have enough data to understand it at this moment. We have many idea’s but none fit the anomaly yet or even predict it.

  14. Olaf says

    Two questions comes to mind.
    Does it also happens on the other planets?
    And could it have a human cause? For example switching on a LHC at the moment the satellite happens to be near and the magnets of the LHC slows the satellite? LOL Just kidding, but could it have some human cause?

    Also the complete solar system is flying through space, could this be cause of some combined effect like deep space gravity wave in combination with Moon-Earth position?

  15. Torbjorn Larsson OM says

    I don’t know the probe height or atmosphere height, but it has come to my attention that not only is atmospheric density fluctuating a lot high up, there is a large discrepancy between measurement types. (For example, drag vs ion to neutral flow measurements.)

    So I wouldn’t worry too much about the cause, until we know for certain that drag isn’t the cause.

  16. Olaf says

    It can’t be drag since the report alo shows speeding up along the direction of the mouvement.

    I am also wondering if more than one satellites are influenced at the same moment and how much.

    Too bad the EU proponents are awfully quite since they could finally prove that EU models can predict this behavior since it explains it all. They could for example show this model that if this satellite is influenced then all these
    other satellites will be influenced with this rate according to this formula with this time lag. I mean if this plasma coming from the Sun is doing this Z-pinch back flip in front of the incoming satellite then it will also influence other nearby satellites with predictable speed change. You would probably even measure the effect of the z-pinch back flip in the satellite electronics that has an increased current and thus. detectable. LOL

  17. Sili says


    I’m not so sure drag can’t be invoked. I vaguely recall there being a ‘famous’ paradox that is you’re orbiting high in the atmosphere you can actually speed up by increasing your drag. If I recall correctly it’s to do with the drag initially lowering your orbit.

    It would seem to fit the bill perfectly. Assuming of course that the spacecraft affected passes through the exosphere at the time.

    I’d still like to hear what happened to last year’s suggestion about Special Relativity having been uncorrected for.

  18. Olaf says

    I don’t know if drag is speeding up, but I found this: Oberth effect which says that in a dense gravitational field you have more speed gain with the same fuel than outside a gravitational field.

    It is some trick that it feeds on the energy of the exhaust. If I understand correctly, you have the action = reaction of the speed of the exhaust, but somehow this exhaust also transfers it’s energy to the rocket speed.

    I am wondering if this is real science of pseudoscience. First time I hear about this, but does not acount for this anomaly.

  19. Lawrence B. Crowell says

    It is true that drag can cause an increase in velocity. The retro rockets on a spacecraft change the orbit so it is more elliptical and brings the craft into the Earth’s atmosphere. The potential energy begins to decline and kinetic energy K = mv^2/2 increases. So the velocity of the craft does actually increase. Then once the craft hits the atmosphere the kinetic energy decreses further. This could increase the velocity further. In an uncontrolled reentry this can continue until the craft experiences extreme friction with the air and burns up. Drag decreases the total energy E = K + U, where U is the gravitational potential energy. If U decreases fast enough the K an increase even though E is also decreasing due to drag. This is why there is a window for a proper reentry of a craft.


  20. mikemcjimsey says

    As Sili mentioned above, last year, Universe Today covered a paper that purported to explain all of these anomalies using Special Relativity ( But today’s article doesn’t even mention SR as a possible explanation. Has the paper been discredited? If not, then it seems to me to be the perfect kind of explanation for these so-called anomalies – simple and without the need to introduce new physics of any kind. I wish I were good enough at relativistic mathematics and orbital mechanics to determine the validity of the paper on my own, but I’ll have to rely on others to vet it.

Comments are closed.