The fly-by anomaly returns with Juno

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The uncertainty of science: An orbital discrepancy between where engineers predict where Juno should be and where it actually is suggests it represents the recurrence of an anomaly that has been seen with numerous past planetary spacecraft.

During the 1970s when the Pioneer 10 and 11 probes were launched, visiting Jupiter and Saturn before heading off towards the edge of the Solar System, these probes both experienced something strange as they passed between 20 to 70 AU (Uranus to the Kuiper Belt) from the Sun.

Basically, the probes were both 386,000 km (240,000 mi) farther from where existing models predicted they would be. This came to be known as the “Pioneer anomaly“, which became common lore within the space physics community. While the Pioneer anomaly was resolved, the same phenomena has occurred many times since then with subsequent missions.

…Another mystery is that while in some cases the anomaly was clear, in others it was on the threshold of detectability or simply absent – as was the case with Juno‘s flyby of Earth in October of 2013. The absence of any convincing explanation has led to a number of explanations, ranging from the influence or dark matter and tidal effects to extensions of General Relativity and the existence of new physics.

However, none of these have produced a substantive explanation that could account for flyby anomalies.

The article describes in detail an effort to pin down the extent of Juno’s orbital anomaly, and to use that information to develop a model that would explain the phenomenon. Not surprisingly, they have not really come up with a comprehensive explanation. To me, the variability of the phenomenon suggests that it isn’t real, that it is either an unmeasured instrument effect or an ordinary component of solar system travel and orbital mechanics that programmers have not yet pinned down. For example, the gravitational effect of every planet and rock in the solar system will influence the path of a spacecraft, though with most that influence will be very small. It would not surprise me if this anomaly is simply the consequence of missing some of this influence.



  • wayne

    “A Possible Flyby Anomaly for Juno at Jupiter”

  • eddie willers

    For example, the gravitational effect of every planet and rock in the solar system will influence the path of a spacecraft, though with most that influence will be very small. It would not surprise me if this anomaly is simply the consequence of missing some of this influence.

    Just one of the reasons I am a climate “skeptic”. Talk about variables and chaos! Anyone that thinks they have climate figured out is talking out of their hat.

  • Darwin Teague

    I listen to your interviews with John Batchelor, and your segments are my favorite part of his show.

    Might I suggest a topic for a future show?

    How do space scientists determine locations in the solar system and beyond? Do they use something similar to latitude and longitude or something different?

    What is the center of their model, if there is one? EVERYTHING is moving!

    Thanks a lot.

    I can’t wrap myself around the concept at all.

  • wayne

    I find it hard to conceptualize as well, but it is fascinating and we do know a lot, (but not everything…)

    There is no ‘center’ as such ,(and we aren’t it) but yes, there is a standardized coordinate system. It doesn’t matter where you start at, as long as you’re consistent throughout.
    There is an entire branch of Astronomy dedicated to ‘where-stuff-is.’ Just look up “celestial mechanics.”
    (tangentially– check out the ‘3 body problem,’ as it relates to orbits & gravity. Calculating correct orbits escalates to an extremely difficult problem when you start factoring in ‘everything.’)

    For a visualization of how our ‘local group’ of galaxies would appear if we had an omniscient viewpoint.

    For making star-maps for use on Earth, they do factor in relative motion, and maps are tied into a specific date-period that has to be referenced. (I believe they are called epochs. I have older star maps tied to 1950.)

    And, the expansion of space itself, between galaxies, is also factored in when trying to determine distance and location.
    (our galaxy & solar system are internally gravitationally bound, although remain in motion.)

  • LocalFluff

    A paper that is about to be published has used pulsar timing to extremely precisely measure the Sun’s movement around the barycenter of the Solar system. Each planet has its clear component in the moment. It shows that there does not exist a planet nine or any sizable planet out there. Thanks to Cassini’s gravity measurements, Saturn’s center of mass has been located to one mile in precision! Out of a distance of a billion miles. Astronomers are pretty good at ephemeris, knowing what will be where when.

  • Edward

    I wonder how would such an anomaly affect the results of the Ebb and Flow (GRAIL) mission to map the Moon’s gravitational field and localized densities. Once they have this figured out, I wonder how much data collected over the past few decades will have to be revisited.

  • While a 240,000 mile discrepancy could be ‘instrumentation’, it’s not nothing. Maybe spacetime is slightly ‘lumpy’ on a scale we can notice.

  • Pioneer anomaly has been solved:

    It’s non-isotropic radiation of spacecraft heat.

    The science is settled. Duh!

  • Max

    John L,
    Good find! This makes sense. The plutonium battery waste heat is being emitted in such a way that it causes thrust. Like proof of concept of a weak ion engine. The same thing that makes a radiometer spin. This is probably why they have a hard time keeping the dish & antennas pointing towards earth. Other satellites not experiencing this effect because they emit their heat evenly out in all directions.
    I’ve often wondered if a solar sail catching the solar wind would have much thrust, I bet a black sail of the same size aborbing energy and emitting heat would work much better in a comparison race. This may change our understanding of why a comets tail always points away from the sun, the particles could be driven by heat more than solar wind.
    I have experimented with my radiometer. In front of LED lights (4- 100 W equivalent) it does not spin. When placed in front of the heat dish, it spins very slowly (the heat being reflected off the outside of the glass). But when placed in front of bright halogen lights, it spins like crazy.

  • wayne

    (have my radiometer somewhere in the house, purchased from the Adler Planetarium gift-shop in the late 1960’s. Spent many hours watching it…)
    Interesting take.
    this sentence caught my eye– “Other satellites not experiencing this effect because they emit their heat evenly out in all directions.” Which is the one I would quibble about… I’m seriously doubting it’s ‘evenly out in all directions.’
    It’s my understanding, (and correct me if I’m mistaken) all these probes are not stabilized in flight by the same method, some are spun-up and some aren’t.

    Tangentially– whatever happened to the Messenger Probe??

  • Wayne: Messenger was sent crashing into Mercury when its fuel ran out.

  • Edward

    John L,
    I am a bit skeptical that the solution that you pointed to applies to Juno. The December 2017 “Juno” article notes that several other factors are included in this recent Juno analysis. I doubt that they would be doing this analysis if the mystery had been solved already.

    Both articles talk about analyses, but it appears that so far no spacecraft mission has confirmed the 2012 “Case Closed” article’s analysis of 2004.

  • John L

    Well, you know, I think maybe the science isn’t settled. :(

    I think we’re talking different anomalies- flyby and pioneer.

    My understanding is the paper thinks the Jovian flyby anomaly is a small, mostly radial, occurring at two peaks that occur at either side of the closest approach to the planet. The pioneer anomaly is really, really small sunward direction far out in space. So I guess the radiant heat effect that supposedly explains pioneer, is not applicable to Juno.

    Who knows, maybe the textbook analysis in the computer model doesn’t precisely fit real life. Maybe there’s something near that planet that we don’t yet know about.

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