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A Mundane Cause for the Pioneer Anomaly?

Everybody loves a mystery, and the one surrounding Pioneer has everything going for it, an unusual effect observed via two of the most distant spacecraft ever launched. Both Pioneer 10 and 11 are slowing a bit more than expected as they move through the outer reaches of the Solar System. Explanations range from a variety of on-board causes to suggestions that our understanding of gravity itself needs an upgrade.

NASA’s Slava Turyshev, as noted in this New Scientist story, is compiling data from the spacecraft that had previously been inaccessible due to data formats and media incompatible with modern equipment. Turyshev’s work may take a year to complete, but it holds the promise of nailing what many think to be the probable cause of the anomaly: heat from the RTGs (radioisotope thermoelectric generators) that provide power for the probes. Asymmetrical radiation of that heat just might do the trick.

Meanwhile, New Scientist also gets into far more exotic possibilities, noting that ways of ‘tweaking’ gravity to account for the Pioneer anomaly don’t gibe with the observed orbits of the outer planets:

If you allow violations of [Einstein’s] equivalence principle, modifying the laws of physics can explain the Pioneer anomaly without messing up the orbits of the outer planets, says Robert Sanders of the University of Groningen in the Netherlands.

A theory called modified inertia, proposed by Mordehai Milgrom of the Weizmann Institute of Science in Rehovot, Israel, does just this. It says the way objects accelerate under gravity depends on their past trajectories – a breach of the equivalence principle. In this scenario, the Pioneer spacecraft, whose trajectories are taking them out of the solar system, experience an anomaly, while the outer planets, whose orbits keep them bound to the Sun, do not.

Fascinating stuff, but is there any need to invoke it? The odds on a more mundane explanation are enhanced by Norwegian physicist Kjell Tangen, who leaves the equivalence principle alone and finds no explanation for the Pioneer anomaly in disruptive revisions to the law of gravity. With Turyshev hot on the case, smart money will probably ride on the RTGs for now, but we have no conclusive evidence at this point, so for at least a year the odd journeys of these spacecraft will still inspire controversy.

Comments on this entry are closed.

  • Brian Swiderski June 30, 2007, 23:54

    Wasn’t it reported at some point that the anomalous acceleration is expressible as a proportion of physical constants? If I recall it correctly, that wouldn’t be likely to occur if the explanation were heating. Unless the Pioneers are oriented the same relative to the Sun, it also doesn’t seem likely that asymmetrical heating could produce a similar (identical?) acceleration toward the Sun. Just my $.03 worth.

  • Hans Bausewein July 1, 2007, 7:10

    At least the antenna was oriented the same relative to the Earth, that’s not very far from the Sun (seen from the Pioneer).

  • ljk July 2, 2007, 11:46

    Maybe something attached itself to the Pioneers….

  • Dan Williams July 8, 2007, 11:59

    I bet it’s really Larry Niven’s “Outsiders”.

  • ljk August 9, 2007, 1:20

    Resolving Pioneers’ anomaly

    Authors: Qasem Exirifard

    (Submitted on 6 Aug 2007)

    Abstract: The Pioneers 10 and 11, spacecrafts deployed to explore the outer solar system, are reported to have experienced a constant anomalous acceleration toward the Sun. I contend that a generally covariant correction is the cause of the observed Pioneers’ anomaly. I include the dominant generic corrections of the pure gravity before computing their corrections to the space-time geometry around the Sun. Afterwards I will find the correction describing the Pioneers’ anomaly. I observe that the covariant resolution of the Pioneers’ anomaly challenges the common sense to the gravitational interactions among the elementary particles. I then notice that it predicts an anomaly for satellites orbiting the earth.

    Comments: 7 pages

    Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph); High Energy Physics – Phenomenology (hep-ph)

    Report number: IPM/P-2007/028

    Cite as: arXiv:0708.0662v1 [gr-qc]

    Submission history

    From: Qasem Exirifard [view email]

    [v1] Mon, 6 Aug 2007 09:27:02 GMT (8kb)


  • ljk September 25, 2007, 23:02

    Pioneer anomaly: a drift in the proper time of the spacecraft

    Authors: Vikram H. Zaveri

    (Submitted on 24 Sep 2007)

    Abstract: A relativistic theory is proposed to explain the anomalous accelerations of Pioneer 10/11, Galileo and Ulysses spacecrafts. The theory points out at the limitations of the weak field approximation and proposes a drift in the proper time of the spacecraft outside the framework of general relativity. In this theory the proper time of a body is associated with the gravitational frequency shift of the constituent fundamental particles of the body. The frequency shift changes the energy level of the body which gets reflected in its motion. This change in energy level causes the time like geodesics to deviate from that of the standard theoretical models. We introduce proper time in the line element of a metric theory according to a fixed set of rules laid down by general relativity for introducing deviation in the flat Minkowski metric. The frequency shift for bodies of different composition traversing different trajectories however, is not the same and this gets reflected in its motion as an unmodeled anomalous effect. This association of proper time with the gravitational frequency shift of the body requires the flat Minkowski metric to deviate in different ways for different two body systems. This solves the problem of anomalous acceleration in a very simple way. Gravitational redshift of light, bending of light and perihelic precession of planets are within the permissible limits.

    Comments: 4 pages

    Subjects: Mathematical Physics (math-ph); Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc)

    Cite as: arXiv:0709.3690v1 [math-ph]

    Submission history

    From: Vikram Zaveri [view email]

    [v1] Mon, 24 Sep 2007 05:52:25 GMT (9kb)


  • Qasem Exirifard December 2, 2007, 5:22

    Thanks to Peter Bender, I realised that there exists a strong evidence against the covariant resolution of the Pioneer anomaly from the Earth’s GM measured by the Lunar Laser Ranging and LAGEOS satellite orbiting the Earth, I thus modified my work accordingly.

    Please counsel the details in the revised paper

  • ljk December 11, 2007, 10:05

    What’s Slowing the Pioneer Spacecraft? – Pondering a Mysterious Force

    What goes up must come down – unless you throw it hard enough. That’s the lesson learned by four man-made objects to date, the Pioneer and Voyager space probes flung into the heavens to go where no man has gone before.

    These grandfathers of gadgetry could still kick your iPhones whippersnapper of an ass with both high-gain antennae tied behind their back – they’ve gone above and beyond their functions in ways that make John McClain look like a wimpy quitter.

    Pioneer 10 and 11 were launched in the early seventies. They carried scientific instruments deep into the solar system, probing the asteroid belt , giving us our first close looks at Jupiter and Saturn and blazing a trail that the Voyager probes would follow.

    These enduring explorers couldn’t be returned to the store for repairs and were McGyvered together by remote control for years of their operation, rerouting power and running backup components while the only special sensor your new phone has triggers a self-destruct the instant it detects your warranty has expired.

    Now, long after completing their intended missions these astronomical adventurers are giving scientists plenty to think about with the “Pioneer Anomaly”.

    Full article here:


  • ljk December 12, 2007, 11:36

    Jupiter, Saturn and the Pioneer anomaly: a planetary-based independent test

    Authors: Lorenzo Iorio

    (Submitted on 8 Dec 2007)

    Abstract: In this paper we use the ratio of the corrections to the standard Newtonian/Einsteinian secular precessions of the longitudes of perihelia of Jupiter and Saturn, recently estimated by the Russian astronomer E.V. Pitjeva by fitting almost one century of data with the EPM ephemerides, to make an independent, planetary-based test of the hypothesis that the Pioneer anomaly (PA), as it is presently known in the 5-10 AU region, is of gravitational origin. Accounting for the errors in the determined apsidal extra-rates and in the values of the PA acceleration at the orbits of Jupiter and Saturn the answer is negative.

    If and when the re-analysis of the entire Pioneer 10/11 will be completed more firm conclusions could be reached. Moreover, it would also be important that other teams of astronomers estimate independently their own corrections to the perihelion precessions.

    Comments: Latex, 6 pages, no figures, no tables, 22 references. To appear in JGP (Journal of Gravitational Physics)

    Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph); High Energy Physics – Phenomenology (hep-ph); Space Physics (physics.space-ph)

    Cite as: arXiv:0712.1273v1 [gr-qc]

    Submission history

    From: Lorenzo Iorio [view email]

    [v1] Sat, 8 Dec 2007 10:31:43 GMT (6kb)


  • ljk January 22, 2008, 8:27

    The puzzle of flyby anomolies

    January 8th, 2008 by KFC

    On 8 December 1990, something strange happened to the Galileo spacecraft as it flew past Earth on its way to Jupiter. As the mission team watched, the spacecraft’s speed suddenly jumped by 4 mm per second. Nobody took much notice — a few mm/s is neither here or there to mission planners.

    Then on 23 January 1998, the same thing happened to NASA’s Near spacecraft as it swung past Earth. This time its speed jumped by 13 mm/s.

    The following year, Cassini’s speed was boosted by 0.11mm/s during its Earth fly-by.

    And people finally began to ask questions when the Rosetta spacecraft’s speed also jumped by 2 mm/s during its 2005 close approach.

    Nobody knows what causes these jumps but Magic McCulloch, an unaffiliated astrothinker from the UK has an interesting proposal. He suggests that a sudden change in inertia might occur when objects experience very low accelerations.

    The thinking goes like this: inertia is the result of pressure from so-called Unruh radiation which objects experience only when they accelerate. At very low accelerations, the wavelength of this radiation is so large that it does not fit within the universe (ie it is greater than the Hubble distance). As the acceleration increases, the wavelength drops to less than the Hubble distance and the spacecraft appears to receive a kick. (A similar wavelength related phenomenon happens with the Casimir force.)

    McCulloch says his idea could be tested in low acceleration experiments using an invisibility cloak designed to make an object invisible to Unruh radiation (although it’s a big jump from making these cloaks for microwave radiation and visible light to making them for Unruh raditation). So it wouldn’t experiecne inertia in the same way.

    Interesting idea.

    Ref: arxiv.org/abs/0712.3022: Can the Flyby Anomalies be Explained by a Modification of Inertia?


  • ljk February 6, 2008, 23:52

    Astrodynamical Space Test of Relativity using Optical Devices I (ASTROD I) – A class-M fundamental physics mission proposal for Cosmic Vision 2015-2025

    Authors: Thierry Appourchaux, Raymond Burston, Yanbei Chen, Michael Cruise, Hansjoerg Dittus, Bernard Foulon, Patrick Gill, Laurent Gizon, Hugh Klein, Sergei Klioner, Sergei Kopeikin, Hans Krueger, Claus Laemmerzahl, Alberto Lobo, Xinlian Luo, Helen Margolis, Wei-Tou Ni, Antonio Pulido Paton, Qiuhe Peng, Achim Peters, Ernst Rasel, Albrecht Ruediger, Etienne Samain, Hanns Selig, Diana Shaul, Timothy Sumner, Stephan Theil, Pierre Touboul, Slava Turyshev, Haitao Wang, Li Wang, Linqing Wen, Andreas Wicht, Ji Wu, Xiaomin Zhang, Cheng Zhao

    (Submitted on 5 Feb 2008)

    Abstract: ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test General Relativity with an improvement in sensitivity of over 3 orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of the solar system and to measure the time rate of change of the gravitational constant with an order of magnitude improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is an international project, with major contributions from Europe and China and is envisaged as the first in a series of ASTROD missions.

    ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way, two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth, to achieve the ASTROD I goals. A second mission,

    ASTROD II is envisaged as a three-spacecraft mission which would test General Relativity to one part per billion, enable detection of solar g-modes, measure the solar Lense-Thirring effect to 10 parts per million, and probe gravitational waves at frequencies below the LISA bandwidth. In the third phase (ASTROD III or Super-ASTROD), larger orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below the ASTROD II bandwidth.

    Comments: 26 pages, 11 figures, shortened from the original cosmic vision proposal, submitted to Experimental Astronomy

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0802.0582v1 [astro-ph]

    Submission history

    From: Wei-Tou Ni [view email]

    [v1] Tue, 5 Feb 2008 10:22:20 GMT (749kb)


  • ljk February 28, 2008, 15:04


    The American Institute of Physics Bulletin of Physics News

    Number 857 February 28, 2008 http://www.aip.org/pnu

    by Phillip F. Schewe and Jason S. Bardi

    MORE SPACECRAFT VELOCITY ANOMALIES. A new look at the trajectories
    for various spacecraft as they fly past the Earth finds in each case
    a tiny amount of surplus velocity. For craft that pursue a path
    mostly symmetrical with respect to the equator, the effect is
    minimal. For craft that pursue a more unsymmetrical path, the
    effect is larger. In the case of the NEAR asteroid rendevous craft
    (http://near.jhuapl.edu/), for instance, the velocity anomaly
    amounts to 13 mm/sec. Although this is only one-millionth of the
    total velocity, the precision of the velocity measurements, carried
    out by looking at the Doppler shift in radio waves bounced off the
    craft, is 0.1 mm/sec, and this suggests that the anomaly represents
    a real effect, one needing an explanation. Some ten years ago
    another anomaly was identified for the Pioneer 10 spacecraft (see
    http://www.aip.org/pnu/1998/split/pnu391-1.htm) and a certain amount
    of controversy has clung to the subject since then.

    One of the researchers on that earlier measurement is part of the
    new study, conducted by Jet Propulsion Lab scientists. John D.
    Anderson (jdandy@earthlink.net, 626-449-0102) says that the JPL
    scientists are now working with German colleagues to search for
    possible velocity anomalies in the recent flyby of the Rosetta
    spacecraft. (Anderson et al., Physical Review Letters, upcoming
    article; designated as an editor*s suggested article)


    PHYSICS NEWS UPDATE is a digest of physics news items arising
    from physics meetings, physics journals, newspapers and
    magazines, and other news sources. It is provided free of charge
    as a way of broadly disseminating information about physics and
    physicists. For that reason, you are free to post it, if you like,
    where others can read it, providing only that you credit AIP.
    Physics News Update appears approximately once a week.

  • ljk March 5, 2008, 10:46

    Earth’s rotation may account for wayward spacecraft

    New Scientist news service Mar. 4, 2008

    A mysterious phenomenon causing
    small, unexpected deviations in
    robotic spacecraft trajectories near
    Earth may be a step closer to an
    explanation. Scientists at NASA’s
    Jet Propulsion Laboratory have come
    up with a mathematical formula that
    successfully reproduces all the
    known occurrences of the effect, and
    they suspect the Earth’s rotation…


  • ljk April 21, 2008, 10:24

    The Pioneer Anomaly: A Deviation from Einstein Gravity?

    Written by Ian O’Neill

    Both Pioneer probes are approximately 240,000 miles (386,000 km)
    closer to the Sun than predicted by calculation. Scientists have been
    arguing over the cause of this mysterious force for a decade and
    reasons for the Pioneer anomaly range from the bizarre to the sublime.

    Is it a simple fuel leak, pushing the probes of course? Is it phantom
    dark matter dragging them down? Or do the gravity textbooks need
    to be re-written? Unfortunately there’s still no one answer, but some
    researchers believe there might be a small deviation in the large-
    scale space-time Einstein described in his famous theory of general
    relativity. See, I knew there would be a simple explanation…

    Full article here:


  • ljk April 22, 2008, 11:41

    To quote from The Planetary Society blog:

    The Pioneer Anomaly: April 13, 2008 presentation

    Slava Turyshev reported on the progress of thermal modeling
    of the Pioneer 10 spacecraft at the American Physical Society
    Meeting in St. Louis, Missouri on April 13, 2008. The complete
    presentation may be downloaded here (PDF format, 7.2 MB).


  • ljk April 23, 2008, 11:16

    In case anyone wonders what might happen some day
    to the Pioneer 10 probe, in the event that it is found in
    a galaxy full of post Singularity civilizations, see here:


    An even more unusual fate awaits Voyager 1:


  • James M. Essig April 24, 2008, 21:59

    Hi ljk;

    I have read from experts of the interstellar medium that the probe may pretty much just float around the galaxy for many trilllions of year before being destroyed by a collision with interstellar debris. It is really awesome that we have added some technical artifact to what is essentially interstellar space. It is so small compared to the zillions of much larger objects in the galaxy that its presence just might be missed by those venturing among the stars within the Milky Way Galaxy over the comming eons.



  • ljk May 20, 2008, 12:04

    Can the flyby anomaly be attributed to earth-bound dark matter?

    Authors: Stephen L. Adler

    (Submitted on 19 May 2008)

    Abstract: We make preliminary estimates to assess whether the recently reported flyby anomaly could be attributed to dark matter interactions. We consider both elastic and exothermic inelastic scattering from dark matter constituents; for isotropic dark matter velocity distributions, the former decrease, while the latter increase, the final flyby velocity.

    Since the observed flyby velocity anomaly shows examples with both positive and negative signs, a two-component model is indicated, involving both elastic and inelastic scatterers with differing spatial distributions. The magnitude of the observed anomalies requires dark matter densities many orders of magnitude greater than the galactic halo density. Such a large density could result from an accumulation cascade, in which the solar system-bound dark matter density is much higher than the galactic halo density, and the earth-bound density is much higher than the solar system-bound density.
    Constraints on this picture are discussed.

    Comments: Latex, 7 pages. Comments welcome

    Subjects: Astrophysics (astro-ph); High Energy Physics – Phenomenology (hep-ph); High Energy Physics – Theory (hep-th)

    Cite as: arXiv:0805.2895v1 [astro-ph]

    Submission history

    From: Stephen Adler [view email]

    [v1] Mon, 19 May 2008 16:11:47 GMT (8kb)


  • ljk June 24, 2008, 11:23

    Can the Pioneer anomaly be induced by velocity-dependent forces? Tests in the outer regions of solar system with planetary dynamics

    Authors: Lorenzo Iorio

    (Submitted on 18 Jun 2008)

    Abstract: In this paper we analyze the impact on the orbital motions of the outer planets of the solar system from Jupiter to Pluto of some velocity-dependent forces recently proposed to phenomenologically explain the Pioneer anomaly, and compare their predictions (secular variations of the longitude of perihelion \varpi or of the semimajor axis a and the eccentricity e) with the latest observational determinations by E.V. Pitjeva with the EPM2006 ephemerides.

    It turns out that while the predicted centennial shifts of a are so huge that they would have been easily detected for all planets with the exception of Neptune, the predicted anomalous precessions of \varpi are too small, with the exception of Jupiter, so that they are still compatible with the estimated corrections to the standard Newton-Einstein perihelion precessions.

    As a consequence, we incline to discard those extra-forces predicting secular variations of a and e, also for some other reasons, and to give a chance, at least observationally, to those models predicting still undetectable perihelion precessions. Of course, adequate theoretical foundations for them should be found.

    Comments: LaTex, WS macros, 12 pages, 4 tables, 4 figures, 30 references

    Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph); Space Physics (physics.space-ph)

    Cite as: arXiv:0806.3011v1 [gr-qc]

    Submission history

    From: Lorenzo Iorio [view email]

    [v1] Wed, 18 Jun 2008 14:21:57 GMT (40kb)


  • ljk July 4, 2008, 13:52

    The Anomalous Acceleration of the Pioneer Spacecrafts

    Authors: Jose A. de Diego

    (Submitted on 3 Jul 2008)

    Abstract: Radiometric data from the Pioneer 10 and 11 spacecrafts have revealed an unexplained constant acceleration of a_A = (8.74 +/- 1.33) x 10^(-10) m s^(-2) towards the Sun, also known as the Pioneer anomaly.

    Different groups have analyzed the Pioneer data and have got the same results, which rules out computer programming and handling errors. Attempts to explain this phenomenon arguing intrinsic causes on-board the spacecrafts failed or have lead to inconclusive results.

    Therefore, the Pioneer anomalous acceleration has motivated the interest of researchers to find out explanations that could bring insight upon the forces acting in the outer Solar Systems or a hint to discover new natural laws.

    Comments: Invited talk in Astronomia Dinamica en Latinoamerica. To be published in Revista Mexicana de Astronomia y Astrofisica, Conference Series

    Subjects: Space Physics (physics.space-ph); Astrophysics (astro-ph)

    Cite as: arXiv:0807.0617v1 [physics.space-ph]

    Submission history

    From: Jose A. de Diego [view email]

    [v1] Thu, 3 Jul 2008 19:07:47 GMT (281kb)


  • ljk August 17, 2008, 23:01

    The Pioneer Anomaly and a Machian Universe

    Authors: Marcelo Samuel Berman

    (Submitted on 13 Jun 2006 (v1), last revised 6 Aug 2008 (this version, v2))

    Abstract: We discuss astronomical and astrophysical evidence, which we relate to the principle of zero-total energy of the Universe, that imply several relations among the mass M, the radius R and the angular momentum L of a “large” sphere representing a Machian Universe.

    By calculating the angular speed, we find a peculiar centripetal acceleration for the Universe. This is an ubiquituous property that relates one observer to any observable. It turns out that this is exactly the anomalous acceleration observed on the Pioneers spaceships.

    We have thus, shown that this anomaly is to be considered a property of the Machian Universe. We discuss several possible arguments against our proposal.

    Comments: 6 pages including front page. Published

    Subjects: General Physics (physics.gen-ph)

    Journal reference: Astrophysics and Space Science, 312, 275 (2007)

    Cite as: arXiv:physics/0606117v2 [physics.gen-ph]

    Submission history

    From: Marcelo S. Berman [view email]

    [v1] Tue, 13 Jun 2006 22:43:04 GMT (4kb)

    [v2] Wed, 6 Aug 2008 23:15:12 GMT (8kb)


  • Bjarne Lorenzen August 26, 2008, 16:22

    The cause of the Pioneer anomaly Solved


    Kind regards

    Bjarne Lorenzen

  • ljk September 19, 2008, 7:19

    Special relativity may account for the spacecraft flyby anomalies

    Authors: Jean Paul Mbelek

    (Submitted on 11 Sep 2008 (v1), last revised 12 Sep 2008 (this version, v2))

    Abstract: Recently, J. D. Anderson et al. [1] have proposed an empirical formula that accurately reproduces all the Earth flyby anomalies observed yet. Here, we show that special relativity (SR) transverse Doppler shift together with the addition of velocities may reproduce that formula.

    Comments: 3 pages, no figure, error corrected and approximation improved in section 2

    Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)

    Cite as: arXiv:0809.1888v2 [gr-qc]

    Submission history

    From: Jean-Paul Mbelek [view email]

    [v1] Thu, 11 Sep 2008 12:51:53 GMT (71kb)

    [v2] Fri, 12 Sep 2008 13:41:55 GMT (72kb)


  • ljk October 7, 2008, 7:37

    Pioneer Doppler data analysis: study of periodic anomalies

    Authors: A. Levy, B. Christophe, P. Berio, G. Metris, J-M. Courty, S. Reynaud

    (Submitted on 16 Sep 2008)

    Abstract: This paper reports the results of an analysis of the Doppler tracking data of Pioneer probes which did show an anomalous behaviour. A software has been developed for the sake of performing a data analysis as independent as possible from that of J. Anderson et al. (Phys. Rev. D65, 082004, 2002), using the same data set.

    A first output of this new analysis is a confirmation of the existence of a secular anomaly with an amplitude about 0.8 nm s$^{-2}$ compatible with that reported by Anderson et al. A second output is the study of periodic variations of the anomaly, which we characterize as functions of the azimuthal angle $\varphi$ defined by the directions Sun-Earth Antenna and Sun-Pioneer.

    An improved fit is obtained with periodic variations written as the sum of a secular acceleration and two sinusoids of the angles $\varphi$ and $2\varphi$. The tests which have been performed for assessing the robustness of these results are presented.

    Comments: 13 pages, 6 figures

    Subjects: General Relativity and Quantum Cosmology (gr-qc); Space Physics (physics.space-ph)

    Cite as: arXiv:0809.2682v1 [gr-qc]

    Submission history

    From: Serge Reynaud [view email]

    [v1] Tue, 16 Sep 2008 11:33:05 GMT (117kb)


  • ljk October 7, 2008, 9:58


    Periodic Pioneer anomaly points to modified general relativity

    September 26th, 2008

    The Pioneer anomaly grows ever more fascinating.

    Here’s the background: Pioneer 10 and 11 were launched in 1972 and 1973 respectively and, after sweeping past a number of the outer gas giants, have been heading out of the solar system ever since.

    NASA has been accurately tracking their position and speed using Doppler tracking measurements of radio signals from the craft. But this data has thrown up a problem. Both probes appear to be decelerating faster than can be explained by the Sun’s gravity. All that has been widely discussed and numerous explanations have been put forward to explain this discrepancy.

    What isn’t so well known is that there is a periodic component to the anomaly. The team at the NASA’s Jet Propulsion Lab who have been collecting the data say that it’s unlikely that this variation is a from the spacecraft. Instead, they think probably the result of something at our end such as a tiny variation in Earth’s orbit.

    Now Bruno Christophe and pals from the French aerospace lab, ONERA, near Paris and various other French institutions, have carried the most detailed analysis yet on these periodic variations and raise another interesting possibility.

    A number of people have suggested modifications to general relativity that would explain the Pioneer anomaly. But there has never been a way to test these modifications.

    Now Christophe and co say that the periodic variations are compatible with the effects on radio signals that some of these modifications might cause.

    That’s an extraordinary claim. Obviously, more analysis is needed and it always pays to be cautious with these kinds of ideas. But could it really be possible that the Pioneer anomaly is the first evidence of physics beyond Einstein’s version of general relativity?

    Ref: arxiv.org/abs/0809.2682: Pioneer Doppler Data Analysis: Study of Periodic Anomalies

  • ljk May 7, 2009, 12:47


    Is Pluto Being Pulled by the Pioneer Effect?

    If the Pioneer effect is real, then the outer planets ought to be tugged by it too.

    Thursday, May 07, 2009

    Here’s an interesting take on the Pioneer effect–the mysterious deceleration that seems to be afflicting Pioneer 10 and 11 as they head out of the Solar System.

    If the effect is real, it ought to influence the orbits of the outer planets. Pluto, in particular, ought top feel this force if it’s out there. In the last few years, a few astronomers have calculated what sort of influence the Pioneer effect should have on Pluto, concluding that it should produce significant periodic effects. The fact that we don’t see these effects means we can rule out the Pioneer effect as a phenomenon affecting the outer planets, they say. And that means it probably isn’t a fundamental effect but some kind of artifact.

    But now it sees that it’s too early to be making these kinds of assertions. Gary Page from George Mason University in Virginia and a couple of pals say the calculations are less than convincing. They point out that our knowledge of Pluto’s orbit is based entirely on optical observations and so are far less well characterised than the nearer planets.

    In fact, so poor is our knowledge of Pluto’s orbit that it is impossible to say whether it is being pulled by a Pioneer-like force or not.

    Page and pals say:

    “Of course, this does not mean that the Pioneer effect exists. It does mean that we cannot deny the existence of the Pioneer effect on the basis of motions of the Pluto as currently known.”

    Ref: http://arxiv.org/abs/0905.0030: How Well Do We Know The Orbits Of The Outer Planets?

  • ljk July 8, 2009, 17:17


    Wednesday, July 08, 2009

    How F=ma Could Break Down at Low Accelerations

    If Newton’s second law is wrong, we might just be able to see the evidence in the orbital motions of the planets, suggests a new analysis.

    Newton’s second law, F=ma, is one of the bedrocks of modern physics. Or at least it was until the early 1980s, when astronomers noticed that stars orbiting spiral galaxies don’t obey it.

    Here’s the problem. By Newton’s law, more distant objects should orbit a central massive object more slowly. That’s exactly what happens in the solar system. But the stars in spiral galaxies orbit far more quickly than Newton’s law predicts.

    Astronomers have proposed two solutions to this conundrum. Most think that there must be a halo of invisible matter pulling the stars in some unseen way. Others think that Newton’s law must somehow break down for the tiny accelerations that stars feel in galaxies.

    These guys have spent the 20 years since then exploring the implications of Modified Newtonian Dynamics, or MOND, led by Mordehai Milgrom from the Weizmann Institute Center for Astrophysics, in Israel, who dreamed up the idea in 1983.

    The trouble is that MOND only kicks into action when the acceleration is tiny–so small that no experiment on Earth has been able to distinguish its effects from Newton’s law. And measurements on stars in distant galaxies are difficult to make, so it has been hard for astronomers to find evidence for or against it.

    But today, Milgrom says that he has calculated a new effect of MOND that should be measurable for planets and comets in the solar system.

    The new effect is a quadropole force that repels objects in the space above and below the plane of the solar system while attracting objects that lie within the plane. Milgrom says that this should produce an effect on the precession of the perihelion of planets in the solar system.

    He says that the current measurements are not yet precise enough to see or constrain this effect, but the appropriate precision seems to be within reach.

    Interestingly, last year astronomers found that the precession of the perihelion of Saturn does not quite fit with predictions.

    Could this be the smoking gun that Milgrom is looking for?

    Ref: http://arxiv.org/abs/0906.4817: MOND effects in the inner solar system

  • ljk July 31, 2009, 10:45


    Wednesday, July 29, 2009

    The Puzzle of Astronomy’s Unexplained Anomalies

    A series of mysterious observations of objects within the solar system could indicate the existence of exotic new physics.

    At the end of the 19th century, astronomers discovered that the perihelion of Mercury (its closest point to the sun during its orbit) was slowly advancing in a way that could not be explained by Newtonian physics. The anomaly was small, so tiny that most believed that a simple explanation would soon be found. It turned out, of course, that Mercury’s orbit was a clue to the existence of an entirely new physics concept, called general relativity, which fundamentally changed our understanding of the universe.

    If there’s a lesson there, it is to pay attention to small anomalies.

    Which is why a list prepared by John Anderson at the Jet Propulsion Laboratory in California and Michael Nieto at Los Alamos National Laboratory in New Mexico makes for interesting reading. The two scientists have compiled details on four unexplained anomalies that astronomers are currently scratching their heads over (I’ve added a fifth). Let’s take a look.

    1. First up is the flyby anomaly, which we’ve discussed on the arxivblog here, here, and here. This is the discovery that spacecraft flying past Earth experience a small but significant change in acceleration, an effect that has been studied in detail by Anderson and shown to be real rather than an artifact of some kind.

    2. Next is the slow but sure increase in the length of the astronomical unit (AU), a unit of measure roughly equal to the mean distance from Earth to the sun. This has been calculated as 149,597,870,700 meters, plus or minus three meters, and it is by far the most accurately determined constant in astronomy, the data coming from distance measurements between Earth and various Mars orbiters and landers dating from 1976 to the present. However, these data indicate that the AU is increasing by about 15 centimeters per year.

    One explanation is that the mass of the sun is increasing (there is a mathematical relationship linking the AU to the mass of the sun). In fact, the mass of the sun ought to be decreasing because of mass loss to solar radiation and the solar wind. To explain the increase in the AU, the sun would have to be increasing its mass by 10^18 kilograms per year. That’s equivalent to swallowing a good-sized planetary moon or about 40,000 comets per year. Surely we’d have noticed that.

    3. Then there is the Pioneer anomaly, the small but steady slowing of the Pioneer spacecraft as they move out of the solar system. Nobody has been able to satisfactorily explain what’s pulling them back, although there has been no shortage of attempts.

    4. Finally, Anderson and Nieto point to the increase in eccentricity of the moon’s orbit, as measured by laser-ranging measurements between 1970 and 2008. These data show that the moon’s apogee and perigee have increased in distance by about 3.5 millimeters per year.

    5. Anderson and Nieto could add a fifth puzzle to their list: the recent anomalies measured in Saturn’s orbit.

    Does that add up to evidence for new physics, or just a poor application of the physics we do know? Whatever the answer, these are problems worth watching.

    Ref: http://arxiv.org/abs/0907.2469: Astrometric Solar-System Anomalies

  • Bjarne Lorenzen September 27, 2009, 10:11

    The space probes anomalies reveal much more than only small and insignificant forces / anomalies.

    The decelerating force that affected the Pioneer probes and the accelerating force that had caused many Fly-by anomalies:

    1.) Both affect the Earth (and the planets) as well, – and with full force.
    2.) Automatically equalize each other (when affecting the planets in our solar system).

    Its 2 fundamental forces responsible for much more than we so fare have imaging.

    These to opposite forces in reality also express the law of nature responsible for the following mysteries:

    1.) Why gas-planets can be found very closed to starts (with their atmosphere intact)
    2.) Why huge planets can be found more as 15 billion km. from their mother stars.
    3.) How Jupiter’s was created (longer away from the Sun) and what brought closer to the Sun.
    4.) How water came to earth.
    5.) How solar systems was created.
    6.) The connection between matter and space.
    7.) Why WASP-18b had surveyed so many million years..
    8.) Why stars in the inner galaxy are too slow, and in the periphery too fast.

    http://www.science27.com – read especially the chapter: The Pioneer Anomaly, but start with the chapter “Abstract”