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| The '''Pioneer anomaly''' or '''Pioneer effect''' is the observed deviation from predicted [[accelerations]] of the [[Pioneer 10]] and [[Pioneer 11]] spacecraft after they passed about {{convert|20|AU|sigfig=1|lk=in}} on their trajectories out of the Solar System. The apparent anomaly was a matter of tremendous interest for many years.
| | Hello. Allow me introduce the author. Her title is Refugia Shryock. Playing baseball is the pastime he will never quit performing. My day occupation is a librarian. Years ago he moved to North Dakota and his family members loves it.<br><br>Have a look at my homepage [https://www.tumblr.com/blog/mmattchuu www.tumblr.com] |
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| Both Pioneer spacecraft are escaping the Solar System, but are slowing under the influence of the [[Sun]]'s gravity. Upon very close examination of navigational data, the spacecraft were found to be slowing slightly more than expected. The effect is an extremely small acceleration towards the Sun, of {{val|8.74|1.33|e=-10|u=m/s2}}, which is equivalent to slowly accelerating to a velocity of one kilometer per hour (0.6 mph) over a period of ten years. The two spacecraft were launched in 1972 and 1973 and the anomalous acceleration was first noticed as early as 1980, but not seriously investigated until 1994.<ref>
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| {{cite journal
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| | last1=Nieto |first=M. M.
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| | last2=Turyshev |first2=S. G.
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| | title=Finding the Origin of the Pioneer Anomaly
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| | year=2004
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| | journal=[[Classical and Quantum Gravity]]
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| | volume=21 | issue=17 | pages=4005–4024
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| | arxiv=gr-qc/0308017
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| | doi=10.1088/0264-9381/21/17/001 | bibcode=2004CQGra..21.4005N
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| }}</ref> The last communication with either spacecraft was in 2003, but analysis of recorded data continues.
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| Various explanations, both of spacecraft behavior and of gravitation itself, were proposed to explain the anomaly. Over the period 1998–2012, one particular explanation became accepted. The spacecraft, which are surrounded by an ultra-high vacuum and are each powered by a [[radioisotope thermoelectric generator]] (RTG), can shed heat only via [[thermal radiation]]. If, due to the design of the spacecraft, more heat is emitted in a particular direction—what is known as a radiative [[anisotropy]]—then the spacecraft would exhibit a small acceleration in the direction opposite that of the excess emitted radiation due to [[radiation pressure]]. Since this force is due to the recoil of thermal [[photon]]s, it is also called the '''thermal recoil force'''. If the excess radiation and attendant radiation pressure were pointed in a general direction opposite the Sun, the spacecrafts’ velocity away from the Sun would be decelerating at very slightly greater rate than could be explained by previously recognized forces such as gravity and trace friction due to the [[interplanetary medium]] (imperfect vacuum).
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| By 2012 several papers by different groups, all reanalyzing the thermal radiation pressure forces inherent in the spacecraft, showed that a careful accounting of this could explain the entire anomaly, and thus the cause was mundane and did not point to any new phenomena or need for a different physical paradigm.<ref name="technologyreview.com">[http://www.technologyreview.com/blog/arxiv/26589/ "Pioneer Anomaly Solved By 1970s Computer Graphics Technique"] (March 2011)</ref><ref name="Rievers 2011 439">{{cite journal
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| |last=Rievers |first=B.
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| |last2=Lämmerzahl |first2=C.
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| |year=2011
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| |title=High precision thermal modeling of complex systems with application to the flyby and Pioneer anomaly
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| |journal=[[Annalen der Physik]]
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| |volume=523 |issue=6 |page=439
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| |arxiv=1104.3985
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| |bibcode=2011AnP...523..439R
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| |doi=10.1002/andp.201100081
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| }}</ref> The most detailed analysis to date, by some of the original investigators, explicitly looks at two methods of estimating thermal forces, then states "We find no statistically significant difference between the two estimates and conclude that once the thermal recoil force is properly accounted for, no anomalous acceleration remains."<ref name="thermal">{{cite journal|doi=10.1103/PhysRevLett.108.241101|title=Support for the Thermal Origin of the Pioneer Anomaly|year=2012|last1=Turyshev|first1=Slava G.|last2=Toth|first2=Viktor T.|last3=Kinsella|first3=Gary|last4=Lee|first4=Siu-Chun|last5=Lok|first5=Shing M.|last6=Ellis|first6=Jordan|journal=Physical Review Letters|volume=108|issue=24|arxiv = 1204.2507 |bibcode = 2012PhRvL.108x1101T }}</ref>
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| == Description ==
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| Pioneer 10 and 11 were sent on missions to [[Jupiter]] and Jupiter/Saturn respectively. Each spacecraft was [[spin-stabilisation|spin-stabilised]] in order to keep its [[high-gain antenna]] pointed towards [[Earth]] using [[gyroscope|gyroscopic forces]]. Although the spacecraft included thrusters, after the planetary encounters they were used only for semiannual [[conical scanning]] maneuvers to track Earth in its orbit,<ref>{{cite web| title = Weebau Spaceflight Encyclopedia| date = 9 November 2010| url = http://weebau.com/satplan/pioneer%2010.htm| accessdate = 11 January 2012}}</ref> leaving them on a long "cruise" phase through the outer solar system. During this period, both spacecraft were repeatedly contacted to obtain various measurements on their [[outer space|physical environment]], providing valuable information long after their initial missions were complete.
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| Since the spacecraft were flying with almost no additional stabilization thrusts during their "cruise", it is possible to characterize the [[density]] of the solar medium by its effect on the spacecraft's motion. In the outer solar system this effect would be easily calculable, based on ground-based measurements of the [[Outer space|deep space]] environment. When these effects were taken into account, along with all other known effects, the calculated position of the Pioneers did not agree with measurements based on timing the return of the [[Radio signal#Processes|radio signals]] being sent back from the spacecraft. These consistently showed that both spacecraft were closer to the inner solar system than they should be, by thousands of [[kilometre]]s—small compared to their distance from the Sun, but still statistically significant. This apparent discrepancy grew over time as the measurements were repeated, suggesting that whatever was causing the anomaly was still acting on the spacecraft.
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| As the anomaly was growing, it appeared that the spacecraft were moving more slowly than expected. Measurements of the spacecraft's speed using the [[Doppler effect]] demonstrated the same thing: the observed [[redshift]] was less than expected, which meant that the Pioneers had slowed down more than expected.
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| When all known forces acting on the spacecraft were taken into consideration, a very small but unexplained force remained. It appeared to cause an approximately constant [[sun]]ward acceleration of {{val|8.74|1.33|e=-10|ul=m/s2}} for both spacecraft. If the positions of the spacecraft were predicted one year in advance based on measured velocity and known forces (mostly gravity), they were actually found to be some 400 km closer to the sun at the end of the year.<!-- Δx = 1/2 a t<sup>2</sup> = 0.5 × 8.74 × 10<sup>−10</sup> m/s<sup>2</sup> × (365.25 × 24 × 60 × 60 s)<sup>2</sup> ≈ 435.2 km --> This anomaly is now believed to be accounted for by thermal recoil forces.
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| == Explanation: thermal recoil force ==
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| Starting in 1998, there were suggestions that the thermal recoil force was under-estimated,<ref>{{cite web
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| |title=A Prosaic explanation for the anomalous accelerations seen in distant spacecraft
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| |url=http://arxiv.org/pdf/gr-qc/9810015.pdf
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| |author=Murphy, E.M.
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| |journal=arXiv preprint gr-qc/9810015
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| |year=1998}}</ref><ref>{{cite journal
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| |title=Comment on "Indication, from Pioneer 10/11, Galileo, and Ulysses data, of an apparent anomalous, weak, long-range acceleration"
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| |author=Katz, J.I.
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| |journal=Physical review letters
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| |volume=83
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| |issue=9
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| |pages=1892--1892
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| |year=1999
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| |publisher=|arxiv = gr-qc/9809070 |bibcode = 1999PhRvL..83.1892K |doi = 10.1103/PhysRevLett.83.1892 }}</ref>
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| and perhaps could account for the entire anomaly.<ref>{{cite journal
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| |last1=Scheffer |first1=L.
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| |year=2003
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| |title=Conventional forces can explain the anomalous acceleration of Pioneer 10
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| |journal=[[Physical Review D]]
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| |volume=67|issue= 8|page=084021
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| |doi=10.1103/PhysRevD.67.084021
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| |arxiv=gr-qc/0107092
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| |bibcode = 2003PhRvD..67h4021S }}</ref> However, accurately accounting for thermal forces was hard, since it needed telemetry records of the spacecraft temperatures and a detailed thermal model, neither of which was available at the time. Furthermore, all thermal models predicted a decrease in the effect with time, which did not appear in the initial analysis.
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| One by one these objections were addressed. Many of the old telemetry records were found, and converted to modern formats.<ref>{{cite journal |title=A study of the pioneer anomaly: new data and objectives for new investigation
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| |author=Turyshev, S.G and Toth, V. and Kellogg, L. and Lau E. and Lee, K.
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| |journal=International Journal of Modern Physics D
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| |url=http://arxiv.org/pdf/gr-qc/0512121.pdf
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| |volume=15
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| |issue=01
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| |pages=1–55
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| |year=2006
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| |publisher=World Scientific|arxiv = gr-qc/0512121 |bibcode = 2006IJMPD..15....1T |doi = 10.1142/S0218271806008218 }}, pages 10-15.</ref> This gave power consumption figures and some temperatures for parts of the spacecraft. Several groups built detailed thermal models,<ref name="Rievers 2011 439"/><ref name="Bertolami">
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| {{cite journal
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| |last=Bertolami |first=O.
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| |last2=Francisco |first2=F.
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| |last3=Gil |first3=P. J. S.
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| |last4=Páramos |first4=J.
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| |year=2008
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| |title=Thermal analysis of the Pioneer anomaly: A method to estimate radiative momentum transfer
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| |journal=[[Physical Review D]]
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| |volume=78 |issue= 10 |page=103001
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| |bibcode = 2008PhRvD..78j3001B
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| |doi=10.1103/PhysRevD.78.103001
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| |arxiv = 0807.0041 }}</ref><ref>{{cite journal |title=Thermal recoil force, telemetry, and the Pioneer anomaly
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| |author=Toth, V.T. and Turyshev, S.G.
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| |journal=Physical Review D
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| |volume=79
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| |issue=4
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| |pages=043011
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| |year=2009
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| |publisher=APS
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| |arxiv=0901.4597|bibcode = 2009PhRvD..79d3011T |doi = 10.1103/PhysRevD.79.043011 }}</ref> which could be checked against the known temperatures and powers, and allowed a quantitative calculation of the recoil force. The longer span of navigational records showed the acceleration was in fact decreasing.<ref>{{cite journal
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| |title=Support for temporally varying behavior of the Pioneer anomaly from the extended Pioneer 10 and 11 Doppler data sets
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| |author=Turyshev, S.G. and Toth, V.T. and Ellis, J. and Markwardt, C.B.
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| |journal=Physical Review Letters
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| |volume=107
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| |issue=8
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| |pages=81103
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| |year=2011
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| |publisher={APS}
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| |url=http://arxiv.org/pdf/1107.2886.pdf
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| |doi=10.1103/PhysRevLett.107.081103}}</ref>
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| In July 2012, [[Slava Turyshev]] ''et al'' published a paper in [[Physical Review Letters]] that explained the anomaly (abstract) ('''emphasis''' added):
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| <blockquote>"We investigate the possibility that the anomalous acceleration of the Pioneer 10 and 11 spacecraft is due to the recoil force associated with an anisotropic emission of thermal radiation off the vehicles. To this end, relying on the project and spacecraft design documentation, we constructed a comprehensive finite-element thermal model of the two spacecraft. Then, we numerically solve thermal conduction and radiation equations using the actual flight telemetry as boundary conditions. We use the results of this model to evaluate the effect of the '''thermal recoil force''' on the Pioneer 10 spacecraft at various heliocentric distances. We found that the magnitude, temporal behavior, and direction of the resulting thermal acceleration are all similar to the properties of the observed anomaly. As a novel element of our investigation, we develop a parameterized model for the thermal recoil force and estimate the coefficients of this model independently from navigational Doppler data. We find no statistically significant difference between the two estimates and conclude that '''once the thermal recoil force is properly accounted for, no anomalous acceleration remains.'''"<ref>[http://prl.aps.org/accepted/L/18074Y63D061333c20be85947af34735e069bf54c Support for the thermal origin of the Pioneer anomaly], Slava G. Turyshev et al, [[Physical Review Letters]], accepted 11 April 2012, accessed 19 July 2012</ref></blockquote>
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| Although the above reference has the most detailed analysis to date, the explanation based on thermal recoil force has the support of other independent research groups, using a variety of computational techniques. Examples include "thermal recoil pressure is not the cause of the Rosetta flyby anomaly but likely resolves
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| the anomalous acceleration observed for Pioneer 10."<ref name="Rievers 2011 439"/> and
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| "It is shown that the whole anomalous acceleration can be explained by thermal effects".<ref>{{cite web |url=http://arxiv.org/pdf/1107.2886.pdf
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| |title=The Contribution of Thermal Effects to the Acceleration of the Deep-Space Pioneer Spacecraft
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| |author=Orfeu Bertolami, Frederico Francisco, Paulo J. S. Gil and Jorge P´aramos
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| |date=29 Nov 2012}}</ref>
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| ==Previously proposed causes==
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| Before the thermal recoil explanation became accepted, other proposed explanations fell into two classes — "mundane causes" or "new physics". Mundane causes include conventional effects that were overlooked or mis-modeled in the initial analysis, such as measurement error, thrust from gas leakage, or uneven heat radiation. The "new physics" explanations proposed revision of our understanding of [[gravitational physics]].
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| If the Pioneer anomaly had been a gravitational effect due to some long-range modifications of the known laws of gravity, it did not affect the orbital motions of the major natural bodies in the same way (in particular those moving in the regions in which the Pioneer anomaly manifested itself in its presently known form). Hence a gravitational explanation would need to
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| violate the [[equivalence principle]], which states that all objects are affected the same way by gravity. It was therefore argued<ref>
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| {{cite journal
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| |last=Tangen |first= K.
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| |year=2007
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| |title=Could the Pioneer anomaly have a gravitational origin?
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| |journal=[[Physical Review D]]
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| |volume=76 |issue=4 |page=042005
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| |arxiv = gr-qc/0602089
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| |bibcode = 2007PhRvD..76d2005T
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| |doi=10.1103/PhysRevD.76.042005
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| }}</ref><ref name="Iorio and Giudice 2006 600–607">
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| {{cite journal
| |
| |last=Iorio |first=L.
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| |last2=Giudice |first2=G.
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| |year=2006
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| |title=What do the orbital motions of the outer planets of the Solar System tell us about the Pioneer anomaly?
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| |journal=[[New Astronomy (journal)|New Astronomy]]
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| |volume=11 |issue=8 |pages= 600–607
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| |arxiv = gr-qc/0601055
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| |bibcode = 2006NewA...11..600I
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| |doi=10.1016/j.newast.2006.04.001
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| }}</ref><ref name="Iorio 2007 897–918">
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| {{cite journal
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| |last=Iorio |first=L.
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| |year=2007
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| |title= Can the Pioneer anomaly be of gravitational origin? A phenomenological answer
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| |journal=[[Foundations of Physics]]
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| |volume=37 |issue=6 |pages=897–918
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| |arxiv = gr-qc/0610050
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| |bibcode = 2007FoPh...37..897I
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| |doi=10.1007/s10701-007-9132-x
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| }}</ref><ref name="Iorio 2007b 5-8">
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| {{cite journal
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| |last=Iorio |first=L.
| |
| |year=2007
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| |title= Jupiter, Saturn and the Pioneer anomaly: a planetary-based independent test
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| |journal=[[Journal of Gravitational Physics]]
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| |volume=1 |issue=1 |pages=5–8
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| |url=http://journalgp.awardspace.com/journal/0101/010101.pdf
| |
| |bibcode = 2007JGrPh...1....5I
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| |arxiv = 0712.1273 }}</ref><ref>
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| {{cite journal
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| | last1 = Standish | first1 = E. M.
| |
| | year = 2008
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| | title = Planetary and Lunar Ephemerides: testing alternate gravitational theories
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| | journal = [[AIP Conference Proceedings]]
| |
| | volume = 977 | pages = 254–263
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| | doi = 10.1063/1.2902789
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| }}</ref><ref>
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| {{cite journal
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| | last1 = Iorio| first1 = L.
| |
| | year = 2008
| |
| | title = The Lense–Thirring Effect and the Pioneer Anomaly: Solar System Tests
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| | journal = [[Proceedings of the Marcel Grossmann Meeting]]
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| | volume = 11 | pages = 2558–2560
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| | doi = 10.1142/9789812834300_0458
| |
| |arxiv = gr-qc/0608105 }}</ref><ref name="Iorio 2009 947-958 ">
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| {{cite journal
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| |last=Iorio |first=L.
| |
| |year=2009
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| |title=Can the Pioneer Anomaly be Induced by Velocity-Dependant Forces? Tests in the Outer Regions of the Solar System with Planetary Dynamics
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| |journal=[[International Journal of Modern Physics D]]
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| |volume=18 |issue=6 |pages=947–958
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| |bibcode = 2009IJMPD..18..947I
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| |doi=10.1142/S0218271809014856
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| |arxiv = 0806.3011 }}</ref><ref>
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| {{cite book
| |
| | last1 = Fienga | first1 = A.
| |
| | coauthors = ''et al.''
| |
| | year = 2009
| |
| | title = Gravity tests with INPOP planetary ephemerides
| |
| | url = http://sf2a.cesr.fr/2009/2009sf2a.conf..0105F.pdf
| |
| | journal = [[Proceedings of the Annual Meeting of the French Society of Astronomy and Astrophysics]]
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| | volume = | pages = 105–109
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| | arxiv =
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| | bibcode =2009sf2a.conf..105F
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| | doi =
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| }} Also published in ''[[Proceedings of the International Astronomical Union]]'' (2010) '''5''':159–169 {{arxiv|0906.3962}} {{bibcode|2010IAUS..261..159F}} {{doi|10.1017/S1743921309990330}}</ref><ref name="Iorio 2010 2615–2622">
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| {{cite journal
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| |last=Iorio |first=L.
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| |year= 2010
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| |title=Does the Neptunian system of satellites challenge a gravitational origin for the Pioneer anomaly?
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| |journal=[[Monthly Notices of the Royal Astronomical Society]]
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| |volume=405 |issue=4 |pages= 2615–2622
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| |bibcode=2010MNRAS.405.2615I
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| |doi=10.1111/j.1365-2966.2010.16637.x
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| |arxiv = 0912.2947 }}</ref><ref>{{cite book
| |
| | last1 = Pitjeva | first1 = E. V.
| |
| | year = 2010
| |
| | title = EPM ephemerides and relativity
| |
| | journal = [[Proceedings of the International Astronomical Union]]
| |
| | volume = 5 | pages = 170–178
| |
| | bibcode =2010IAUS..261..170P
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| | doi = 10.1017/S1743921309990342
| |
| }}</ref> that increasingly accurate measurements and [[ephemeris#Scientific ephemeris|modelling of the motions of the outer planets]] and their satellites undermined the possibility that the Pioneer anomaly is a phenomenon of gravitational origin. However, others believed that our knowledge of the motions of the outer planets and dwarf planet [[Pluto]] was still insufficient to disprove the gravitational nature of the Pioneer anomaly.<ref>
| |
| {{cite journal
| |
| |last1=Page |first1 = G. L.
| |
| |last2 = Wallin |first2 = J. F.
| |
| |last3 = Dixon |first3 = D. S.
| |
| |year=2009
| |
| |title= How Well do We Know the Orbits of the Outer Planets?
| |
| |journal=[[The Astrophysical Journal]]
| |
| |volume=697 |issue=2 |pages=1226–1241
| |
| |bibcode=2009ApJ...697.1226P
| |
| |doi=10.1088/0004-637X/697/2/1226
| |
| |arxiv = 0905.0030 }}</ref> The same authors ruled out the existence of a gravitational Pioneer-type extra-acceleration in the outskirts of the [[Solar System]] by using a sample of [[Trans-Neptunian object]]s.<ref>
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| {{cite journal
| |
| |last1=Page |first1=G. L.
| |
| |last2 = Dixon |first2 = D. S.
| |
| |last3 = Wallin |first3 = J. F.
| |
| |year=2006
| |
| |title= Can Minor Planets Be Used to Assess Gravity in the Outer Solar System?
| |
| |journal=[[The Astrophysical Journal]]
| |
| |volume=642 |issue=1 |pages=606–614
| |
| |arxiv = astro-ph/0504367
| |
| |bibcode=2006ApJ...642..606P
| |
| |doi=10.1086/500796
| |
| }}</ref><ref>
| |
| {{cite journal
| |
| |last1 = Wallin |first1 = J. F.
| |
| |last2 = Dixon |first2 = D. S.
| |
| |last3=Page |first3=G. L.
| |
| |year=2007
| |
| |title= Testing Gravity in the Outer Solar System: Results from Trans-Neptunian Objects
| |
| |journal=[[The Astrophysical Journal]]
| |
| |volume=666 |issue=2 |pages=1296–1302
| |
| |bibcode=2007ApJ...666.1296W
| |
| |doi=10.1086/520528
| |
| |arxiv = 0705.3408 }}</ref>
| |
| | |
| The magnitude of the Pioneer effect <math>a_p</math> is numerically quite close to the product of the [[speed of light]] <math>c</math> and the [[Hubble constant]] <math>H_0</math>, hinting at a [[Physical cosmology|cosmological]] connection, but this is now believed to be of no particular significance.
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| In fact the latest [[Jet Propulsion Laboratory]] review (2010) undertaken by [[Slava Turyshev|Turyshev]] and Toth<ref name="TuryshevToth">
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| {{cite journal
| |
| |last=Turyshev |first=S. G.
| |
| |last2=Toth |first2=V. T.
| |
| |year=2010
| |
| |title=The Pioneer Anomaly
| |
| |url=http://www.livingreviews.org/lrr-2010-4
| |
| |journal=[[Living Reviews in Relativity]]
| |
| |volume=13 |page=4
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| |bibcode=2010LRR....13....4T
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| |doi= 10.12942/lrr-2010-4
| |
| |arxiv = 1001.3686 }}</ref> claims to rule out the cosmological connection by considering rather conventional sources while other scientists provided a disproof based on the physical implications of cosmological models themselves.<ref>
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| {{cite journal
| |
| |last1 = Mizony |first1= M.
| |
| |last2=Lachièze-Rey |first2=M.
| |
| |year=2005
| |
| |title=Cosmological effects in the local static frame
| |
| |journal=[[Astronomy and Astrophysics]]
| |
| |volume=434 |issue=1 |pages=45–52
| |
| |arxiv = gr-qc/0412084
| |
| |bibcode=2005A&A...434...45M
| |
| |doi=10.1051/0004-6361:20042195
| |
| }}</ref><ref>
| |
| {{cite journal
| |
| |last=Lachièze-Rey |first=M.
| |
| |year=2007
| |
| |title=Cosmology in the solar system: the Pioneer effect is not cosmological
| |
| |journal=[[Classical and Quantum Gravity]]
| |
| |volume=24 |issue =10 |pages= 2735–2742
| |
| |arxiv = gr-qc/0701021
| |
| |bibcode = 2007CQGra..24.2735L
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| |doi=10.1088/0264-9381/24/10/016
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| }}</ref>
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| | |
| Gravitationally bound objects such as the solar system, or even the galaxy, are not supposed to partake of the [[Metric expansion of space|expansion of the universe]]—this is known both from conventional theory<ref>
| |
| {{cite journal
| |
| |last=Noerdlinger |first=P. D.
| |
| |last2=Petrosian |first2=V.
| |
| |year=1971
| |
| |title=The Effect of Cosmological Expansion on Self-Gravitating Ensembles of Particles
| |
| |journal=[[Astrophysical Journal]]
| |
| |volume=168 |page=1
| |
| |bibcode=1971ApJ...168....1N
| |
| |doi=10.1086/151054
| |
| }}</ref> and by direct measurement.<ref>
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| {{cite journal
| |
| |last=Williams |first=J. G.
| |
| |last2=Turyshev |first2=S. G.
| |
| |last3=Boggs |first3=D. H.
| |
| |year=2004
| |
| |title=Progress in Lunar Laser Ranging Tests of Relativistic Gravity,
| |
| |url=http://iau-comm4.jpl.nasa.gov/JGWSGTDHB.pdf
| |
| |journal=[[Physical Review Letters]]
| |
| |volume=93 |issue=26 |page=261101
| |
| |arxiv = gr-qc/0411113
| |
| |bibcode=2004PhRvL..93z1101W
| |
| |doi=10.1103/PhysRevLett.93.261101
| |
| }}</ref> This does not necessarily interfere with paths new physics can take with [[Drag (physics)|drag effects]] from [[Secular phenomena|planetary secular accelerations]] of possible cosmological origin.
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| ==Indications from other missions==
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| The Pioneers were uniquely suited to discover the effect because they have been flying for long periods of time without additional course corrections. Most deep-space probes launched after the Pioneers either stopped at one of the planets, or used thrusting throughout their mission.
| |
| | |
| The [[Voyager program|Voyagers]] flew a mission profile similar to the Pioneers, but were not spin stabilized. Instead, they required frequent firings of their [[Monopropellant rocket|thrusters]] for [[attitude control]] to stay aligned with Earth. Spacecraft like the Voyagers acquire small and unpredictable changes in speed as a side effect of the frequent attitude control firings. This 'noise' makes it impractical to measure small accelerations such as the Pioneer effect; accelerations as large as 10<sup>−9</sup> m/s<sup>2</sup> would be undetectable.<ref name="TuryshevToth"/>
| |
| | |
| Newer spacecraft have used spin stabilization for some or all of their mission, including both [[Galileo spacecraft|Galileo]] and [[Ulysses (spacecraft)|Ulysses]]. These spacecraft indicate a similar effect, although for various reasons (such as their relative proximity to the Sun) firm conclusions cannot be drawn from these sources.
| |
| | |
| The [[Cassini–Huygens|Cassini]] mission has [[reaction wheel]]s as well as thrusters for attitude control, and during cruise could rely for long periods on the reaction wheels alone, thus enabling precision measurements. It also had [[radioisotope thermoelectric generators]] (RTGs) mounted close to the spacecraft body, radiating kilowatts of heat in hard-to-predict directions. The measured value of unmodelled acceleration for Cassini is {{val|26.7|1.1|e=-10|u=m/s2}}, roughly three times as large as the Pioneer acceleration. The measured value is the sum of the uncertain thermal effects and the possible anomaly. Therefore, the Cassini cruise measurements neither conclusively confirm nor refute the existence of the anomaly.<ref>
| |
| {{cite journal
| |
| |last=Anderson |first=J. D.
| |
| |last2=Lau |first2=E. L.
| |
| |last3=Giampieri |first3=G.
| |
| |year=2003
| |
| |title=Improved Test of General Relativity with Radio Doppler Data from the Cassini Spacecraft
| |
| |url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/37309/1/03-2152.pdf
| |
| |journal=[[Physical Review Letters]]
| |
| |bibcode=2003gr.qc.....8010A
| |
| |arxiv=gr-qc/0308010
| |
| |page=8010
| |
| }}
| |
| :''Note:'' The arXiv preprint was withdrawn at the recommendation of the Cassini Radio Science Team.</ref>
| |
| | |
| After Cassini arrived at Saturn, it shed a large fraction of its mass from the fuel used in the insertion burn and the release of the [[Huygens probe]]. This increases the acceleration caused by the radiation forces, since they are acting on less mass. This change in acceleration allows the radiation forces to be measured independently of any gravitational acceleration.<ref>
| |
| {{cite web
| |
| |last1=Di Benedetto |first1=M.
| |
| |last2=Iess |first2=L.
| |
| |last3=Roth |first3=D. C.
| |
| |date=
| |
| |title=The non-gravitational accelerations of the Cassini spacecraft
| |
| |url=http://www.mediatec-dif.com/issfd/OrbitdI/IESS.pdf
| |
| |work=
| |
| |publisher=
| |
| }}</ref> Comparing cruise and Saturn-orbit results shows that for Cassini, almost all the unmodelled acceleration was due to radiation forces, with only a small residual acceleration, much smaller than the Pioneer acceleration, and with opposite sign.<ref>
| |
| {{cite web
| |
| |last1=Iess |first=L.
| |
| |date=January 2011
| |
| |title=Deep-Space Navigation: a Tool to Investigate the Laws of Gravity
| |
| |url=http://www.ihes.fr/~vanhove/Slides/iess-IHES-jan2011.pdf
| |
| |work=
| |
| |publisher=
| |
| }}</ref>
| |
| | |
| == Proposed explanations ==
| |
| A number of proposed explanations for acceleration towards the sun have been pursued. These are categorized under the following: ''an unaccounted for real deceleration'', ''observational errors'', and explanations that would essentially be ''New Physics''.
| |
| During March 2011, experts proposed new calculations which seem to confirm that heat is the cause of the spacecraft slowing down.<ref>[http://www.technologyreview.com/blog/arxiv/26589/ Pioneer Anomaly solved], March 2011</ref>
| |
| | |
| ===The deceleration model===
| |
| It has been viewed as possible that a real [[deceleration]] is not accounted for in the current model for several reasons.
| |
| | |
| ====Thermal radiation pressure====
| |
| | |
| A real deceleration not accounted for in the model could result from asymmetrical [[thermal radiation]] pressure of the heat from the spacecraft (the effect cannot be from the radiation pressure of sunlight or the spacecraft's radio emissions as it is too small at this distance, and points in the wrong direction).
| |
| | |
| Possibilities include the asymmetrical radiation of heat from the RTGs (See [[Radioisotope rocket]]) or the spacecraft electronics. Even if the RTGs themselves radiate symmetrically, some of their radiation will reflect from the back of the spacecraft's dish-like main antenna, causing a recoil like sunlight striking a solar sail.
| |
| | |
| The asymmetrical radiation of heat remains a prime suspect, as presented at the second ISSI meeting in Bern, February 2007. A presentation at the [[American Physical Society|APS]] April 2008 meeting suggests that differential heating may account for as much as one third of the observed acceleration.<ref>{{cite news |url=http://www.symmetrymagazine.org/breaking/2008/04/13/pioneer-spacecraft-a-step-closer-to-being-boring/ |title=Pioneer spacecraft a step closer to being boring |journal=SymmetryMagazine.org |first=David |last=Harris |date=April 13, 2008 |accessdate=February 12, 2011}}</ref>
| |
| | |
| A research team from Portugal has proposed that previous modelling used to predict the directions of radiation pressures was incorrect. By using the [[Phong reflection model]] to model [[Diffuse reflection|diffusive]] and [[specular reflection]]s they believe that the observed and theoretical results no longer diverge. This proposed explanation finds most of the diverging thrust in the heat from the main equipment compartment reflecting off the back of the main antenna, which would tend to produce a thrust in the direction of the sun.<ref name="PortugeseThermal">{{cite arxiv |title=Modelling the reflective thermal contribution to the acceleration of the Pioneer spacecraft |eprint=1103.5222 |class=physics.space-ph |last1=Francisco |first1=F|last2=Bertolami |first2=O |last3=Gil |first3=P J S |last4=Páramos |first4=J |year=2011 |version=v1}}</ref> The Jet Propulsion Laboratory is currently attempting to confirm this explanation by studying their own thermal data.<ref name="JPLThermal">{{cite web|url=http://www.technologyreview.com/blog/arxiv/26589/ |title=Pioneer Anomaly Solved By 1970s Computer Graphics Technique|work=Technology Review: The Physics arXiv Blog |author=KFC |date=March 31, 2011 |accessdate=April 3, 2011}}</ref>
| |
| | |
| According to [[Slava Turyshev]] of JPL in the paper "Support for temporally varying behavior of the Pioneer anomaly from the extended Pioneer 10 and 11 data sets," published in ''Physical Review Letters'' in 2011, the anomaly has a temporally-decaying (not constant as previously thought) nature and points towards Earth. This strengthens the case for on-board generated recoil forces as the reason behind the anomaly.<ref>{{cite journal
| |
| |title=Support for temporally varying behavior of the Pioneer anomaly from the extended Pioneer 10 and 11 Doppler data sets
| |
| |author1=Turyshev, S.G. |author2=Toth, V.T. |author3=Ellis, J. |author4=Markwardt, C.B.
| |
| |journal=Physical Review Letters
| |
| |volume=107
| |
| |issue=8
| |
| |pages=81103
| |
| |year=2011
| |
| |publisher=[[American Physical Society|APS]]
| |
| |url=http://link.aps.org/doi/10.1103/PhysRevLett.107.081103
| |
| |doi=10.1103/PhysRevLett.107.081103 |bibcode = 2011PhRvL.107h1103T |arxiv = 1107.2886 }}</ref> A more recent 2012 analysis by the same group concludes that thermal forces can explain all the anomalous acceleration.<ref name="thermal"/>
| |
| | |
| ====Gravity====
| |
| It is possible that deceleration is caused by [[gravitational]] forces from unidentified sources such as the [[Kuiper belt]] or [[dark matter]]. However, this acceleration does not show up in the orbits of the outer planets, so any generic gravitational answer would need to violate the [[equivalence principle]] (see modified inertia below). Likewise, the anomaly does not appear in the orbits of Neptune's moons, challenging the possibility that the Pioneer anomaly may be an unconventional gravitational phenomenon based on range from the Sun.<ref name="Iorio 2010 2615–2622"/>
| |
| | |
| ====Drag====
| |
| The cause could be [[drag (physics)|drag]] from the [[interplanetary medium]], including [[dust]], [[solar wind]] and [[cosmic rays]]. However, the measured densities are too small to cause the effect.
| |
| | |
| ====Gas leaks====
| |
| [[Gas]] leaks, including [[helium]] from the spacecrafts' [[radioisotope thermoelectric generator]]s (RTGs) have been viewed as possible causes.{{Citation needed|date=July 2011}}
| |
| | |
| === Observational or recording errors ===
| |
| The possibility of observational errors, which include measurement and computational errors, has been advanced as a reason for interpreting the data as an anomaly. Hence, this would result in approximation and statistical errors. However, further analysis has determined that significant errors are not likely because seven independent analyses have shown the existence of the Pioneer anomaly as of March 2010.<ref>
| |
| {{cite web
| |
| |last=Turyshev |first=S. G.
| |
| |date=March 28, 2007
| |
| |title=Pioneer Anomaly Project Update: A Letter From the Project Director
| |
| |url=http://www.planetary.org/programs/projects/innovative_technologies/pioneer_anomaly/update_20070328.html
| |
| |publisher=[[The Planetary Society]]
| |
| |accessdate=2011-02-12
| |
| }}</ref>
| |
| | |
| The effect is so small that it could be a statistical anomaly caused by differences in the way data were collected over the lifetime of the probes. Numerous changes were made over this period, including changes in the receiving instruments, reception sites, data recording systems and recording formats.
| |
| | |
| ===New physics===
| |
| Because the "Pioneer anomaly" does not show up as an effect on the planets, Anderson ''et al.'' speculated that this would be interesting if this was ''new physics''. Later, with the Doppler shifted signal confirmed, the team again speculated that one explanation may lie with new physics, if not some unknown systemic explanation.<ref name=clock-accel/>
| |
| | |
| ====Clock acceleration====
| |
| Clock acceleration is an alternate explanation to anomalous acceleration of the spacecraft towards the Sun. This theory takes notice of an [[expanding universe]], which creates an ''increasing'' background 'gravitational potential'. The increased gravitational potential then accelerates cosmological time. It is proposed that this particular effect causes the observed deviation from predicted trajectories and velocities of [[Pioneer 10]] and [[Pioneer 11]].<ref name=clock-accel/>
| |
| | |
| From their data, Anderson's team deduced a steady frequency drift of 1.5 Hz over 8 years. This could be mapped on to a clock acceleration theory, which means all clocks would be changing in relation to a constant acceleration. In other words, that there would be a non-uniformity of time. Moreover, for such a distortion related to time, Anderson's team reviewed several models in which time distortion as a phenomenon is considered. They arrived at the "clock acceleration" model after completion of the review. Although the best model adds a quadratic term to defined [[International Atomic Time]], the team encountered problems with this theory. This then led to ''non-uniform time in relation to a constant acceleration'' as the most likely theory.<ref group=note>''non-uniform time in relation to a constant acceleration'' is a summarized term derived from the source or sources used for this sub-section.</ref><ref name=clock-accel>
| |
| {{cite journal
| |
| |last=Rañada |first=A. F.
| |
| |year=2004
| |
| |title=The Pioneer anomaly as acceleration of the clocks
| |
| |journal=[[Foundations of Physics]]
| |
| |volume=34 |issue=12 |page=1955
| |
| |doi=10.1007/s10701-004-1629-y
| |
| |arxiv=gr-qc/0410084
| |
| |bibcode = 2004FoPh...34.1955R }}</ref>
| |
| | |
| ====Definition of gravity modified====
| |
| {{disputed-section|date=January 2014}}
| |
| The [[Modified Newtonian dynamics]] or MOND [[hypothesis]] proposes that the force of gravity deviates from the traditional Newtonian value to a very different force law at very low accelerations on the order of 10<sup>−10</sup> m/s<sup>2</sup>.<ref name=MOND>
| |
| {{cite journal
| |
| |last=Bekenstein |first=Jacob D.
| |
| |year=2006
| |
| |title=The modified Newtonian dynamics (MOND) and its implications for new physics
| |
| |journal=[[Contemporary Physics]]
| |
| |volume=47
| |
| |issue=6 |page=387
| |
| |bibcode= 2006ConPh..47..387B
| |
| |doi=10.1080/00107510701244055
| |
| |arxiv=astro-ph/0701848
| |
| }}</ref> Given the low accelerations placed on the spacecraft while in the outer solar system, MOND may be in effect, modifying the normal gravitational equations. The [[Lunar Laser Ranging experiment]] combined with data of [[LAGEOS]] satellites refutes that simple gravity modification is the cause of the Pioneer anomaly.<ref>
| |
| {{cite journal
| |
| |last=Exirifard |first=Q.
| |
| |year=2010
| |
| |title=Constraints on ''f''(''R''<sub>''ijkl''</sub>''R''<sup>''ijkl''</sup>) gravity: Evidence against the co-variant resolution of the Pioneer anomaly
| |
| |journal=[[Classical and Quantum Gravity]]
| |
| |volume=26 |issue=2 |page=025001
| |
| |doi=10.1088/0264-9381/26/2/025001
| |
| |bibcode = 2009CQGra..26b5001E |arxiv = 0708.0662 }}</ref> The precession of the longitudes of perihelia of the solar planets<ref name="Iorio 2007 897–918"/> or the trajectories of long-period comets<ref>
| |
| {{cite journal
| |
| |last=Nieto |first=M. M.
| |
| |last2=Turyshev |first2=S. G.
| |
| |last3=Anderson |first3=J. D.
| |
| |year=2005
| |
| |title=Directly measured limit on the interplanetary matter density from Pioneer 10 and 11
| |
| |volume=613
| |
| |issue=1–2 |page=11
| |
| |journal=[[Physics Letters B]]
| |
| |doi=10.1016/j.physletb.2005.03.035
| |
| |arxiv = astro-ph/0501626 |bibcode = 2005PhLB..613...11N }}</ref> have not been reported to experience an anomalous gravitational field toward the Sun of the magnitude capable of describing the Pioneer anomaly.
| |
| | |
| ====Definition of inertia modified====
| |
| [[Modified Newtonian dynamics|MOND]] can also be interpreted as a modification of inertia, perhaps due to an interaction with [[vacuum energy]], and such a trajectory-dependent theory could account for the different accelerations apparently acting on the orbiting planets and the Pioneer craft on their escape trajectories.<ref name=VACUUM>
| |
| {{cite journal
| |
| |last=Milgrom |first=M.
| |
| |year=1999
| |
| |title=The Modified Dynamics as a vacuum effect
| |
| |journal=[[Physics Letters A]]
| |
| |volume=253 |issue= 5–6|page=273
| |
| |doi=10.1016/S0375-9601(99)00077-8
| |
| |arxiv=astro-ph/9805346
| |
| |bibcode = 1999PhLA..253..273M }}</ref> A model of inertia using [[Unruh effect|Unruh radiation]] and a Hubble-scale [[Casimir effect]], which, unlike MOND, has no adjustable parameters, has been proposed to explain the Pioneer anomaly and the [[flyby anomaly]].<ref name=MIHCE>
| |
| {{cite journal
| |
| |last=McCulloch |first=M. E.
| |
| |year=2007
| |
| |title=Modelling the Pioneer anomaly as modified inertia
| |
| |journal=[[Monthly Notices of the Royal Astronomical Society]]
| |
| |volume=376
| |
| |issue=1 |pages=338–342
| |
| |bibcode=2007MNRAS.376..338M
| |
| |doi=10.1111/j.1365-2966.2007.11433.x
| |
| |arxiv=astro-ph/0612599
| |
| }}</ref><ref name=MiHsC>
| |
| {{cite journal
| |
| |last=McCulloch
| |
| |first=M. E.
| |
| |year=2008|title=Modelling the flyby anomalies using a modification of inertia
| |
| |journal=[[Monthly Notices of the Royal Astronomical Society Letters]]
| |
| |volume=389 |issue=1 |pages=L57–60
| |
| |bibcode= 2008MNRAS.389L..57M
| |
| |doi=10.1111/j.1745-3933.2008.00523.x
| |
| |arxiv=0806.4159
| |
| }}</ref> A possible terrestrial test for evidence of a different model of modified inertia has also been proposed.<ref name=SHLEM>
| |
| {{cite journal
| |
| |last=Ignatiev |first=A. Yu.
| |
| |year=2007
| |
| |title=Is violation of Newton's second law possible?
| |
| |journal=[[Physical Review Letters]]
| |
| |volume=98
| |
| |issue=10 |page=101101
| |
| |doi=10.1103/PhysRevLett.98.101101
| |
| |arxiv=gr-qc/0612159
| |
| |bibcode=2007PhRvL..98j1101I
| |
| }}</ref>
| |
| ====Parametric time====
| |
| Another theoretical explanation is based on a possible non-equivalence of the atomic time and the astronomical time, which can give the same observational fingerprint as the anomaly.<ref>{{cite journal|author=Rañada, Antonio F.|author2=Tiemblo, A.|year=2012|title=Parametric invariance and the Pioneer anomaly|journal=Canadian Journal of Physics|volume=90|pages=931–937|doi=10.1139/p2012-086|url=http://arxiv.org/pdf/1106.4400v2.pdf}} Antonio Fernández-Rañada and Alfredo Tiemblo-Ramos propose "an explanation of the Pioneer anomaly that is a refinement of a previous one and is fully compatible with the cartography of the solar system. It is based on the non-equivalence of the atomic time and the astronomical time which happens to have the same observational fingerprint as the anomaly."</ref>
| |
| | |
| == Further research avenues ==
| |
| It is possible, but not proven, that this anomaly is linked to the [[flyby anomaly]], which has been observed in other spacecraft.<ref>
| |
| {{cite web
| |
| |last=Choi |first=C. Q.
| |
| |date=March 3, 2008
| |
| |title=NASA Baffled by Unexplained Force Acting on Space Probes
| |
| |url=http://www.space.com/scienceastronomy/080229-spacecraft-anomaly.html
| |
| |publisher=[[Space.com]]
| |
| |accessdate=2011-02-12
| |
| }}</ref> Although the circumstances are very different (planet flyby vs. deep space cruise), the overall effect is similar—a small but unexplained velocity change is observed on top of a much larger conventional gravitational acceleration.
| |
| | |
| The Pioneer spacecraft are no longer providing new data (the last contact having been on 23 January 2003)<ref>
| |
| {{cite web
| |
| |last= |first=
| |
| |date=July 26, 2003
| |
| |title=The Pioneer Missions
| |
| |url=http://www.nasa.gov/centers/ames/missions/archive/pioneer.html
| |
| |publisher=[[NASA]]
| |
| |accessdate=2011-02-12
| |
| }}</ref> and [[Galileo spacecraft|Galileo]] was deliberately burned up in Jupiter's atmosphere at the end of its mission. So far, attempts to use data from current missions such as [[Cassini-Huygens|Cassini]] have not yielded any conclusive results. There are several remaining options for further research:
| |
| | |
| * Further analysis of the retrieved Pioneer data. This includes not only the data that was first used to detect the anomaly, but additional data that until recently was saved only in older, inaccessible computer formats and media. This data was recovered in 2006, converted to more modern formats, and is now available for analysis.<ref>{{cite web |url=http://planetary.org/programs/projects/pioneer_anomaly/update_20060601.html |title=Projects: Pioneer Anomaly - Data Saved! |publisher=Planetary Society |date=1 June 2006}}</ref>
| |
| * The ''[[New Horizons]]'' spacecraft to Pluto is spin-stabilised for much of its cruise, and there is a possibility that it can be used to investigate the anomaly. ''New Horizons'' may have the same problem that precluded good data from the ''Cassini'' mission—its RTG is mounted close to the spacecraft body, so thermal radiation from it, bouncing off the spacecraft, may produce a systematic thrust of a not-easily predicted magnitude, several times as large as the Pioneer effect. Nevertheless efforts are underway to study the non-gravimetric accelerations on the spacecraft, in the hopes of having them well modeled for the long cruise to Pluto after the Jupiter fly-by that occurred in February 2007. In particular, despite any large systematic bias from the RTG, the 'onset' of the anomaly at or near the orbit of Saturn might be observed.<ref>
| |
| {{cite journal
| |
| |last= Nieto |first=M. M.
| |
| |year=2008
| |
| |title=New Horizons and the Onset of the Pioneer Anomaly
| |
| |journal=[[Physics Letters B]]
| |
| |volume=659 |issue=3 |page=483
| |
| |doi=10.1016/j.physletb.2007.11.067
| |
| |arxiv=0710.5135
| |
| |bibcode = 2008PhLB..659..483N }}</ref>
| |
| * A dedicated mission has also been proposed.<ref>
| |
| {{cite web
| |
| |last= |first=
| |
| |date=September 1, 2004
| |
| |title=Pioneer anomaly put to the test
| |
| |url=http://physicsworld.com/cws/article/print/20123
| |
| |work=[[Physics World]]
| |
| |accessdate=2009-05-17
| |
| }}</ref> Such a mission would probably need to surpass 200 [[Astronomical Unit|AU]] from the Sun in a [[Hyperbolic trajectory|hyperbolic escape orbit]].
| |
| * Observations of [[asteroid]]s around 20 AU may provide insights if the anomaly's cause is gravitational.<ref>
| |
| {{cite web
| |
| |last=Clark |first=S.
| |
| |date=10 May 2005
| |
| |title=Lost asteroid clue to Pioneer puzzle
| |
| |url=http://www.newscientist.com/article.ns?id=mg18624984.700
| |
| |work=[[New Scientist]]
| |
| |accessdate=2009-01-10
| |
| }}</ref><ref>
| |
| {{cite journal
| |
| |last=Page |first=G. L.
| |
| |last2=Dixon |first2=D. S
| |
| |last3=Wallin |first3=J. F.
| |
| |year=2006
| |
| |title=Can Minor Planets be Used to Assess Gravity in the Outer Solar System?
| |
| |doi=10.1086/500796
| |
| |journal=The Astrophysical Journal
| |
| |volume=642
| |
| |page=606
| |
| |arxiv=astro-ph/0504367
| |
| |bibcode=2006ApJ...642..606P
| |
| }}</ref>
| |
| | |
| ==Meetings and conferences about the anomaly==
| |
| | |
| A meeting was held at the [[University of Bremen]] in 2004 to discuss the Pioneer anomaly.<ref>
| |
| {{cite web
| |
| |title=Conference on The Pioneer Anomaly - Observations, Attempts at Explanation, Further Exploration
| |
| |url=http://www.zarm.uni-bremen.de/Pioneer/Participants.htm
| |
| |publisher=[[Center of Applied Space Technology and Microgravity|ZARM]]
| |
| |accessdate=2012-02-12
| |
| }}</ref>
| |
| | |
| The [[Pioneer Explorer Collaboration]] was formed to study the Pioneer Anomaly and has hosted three meetings (2005, 2007, and 2008) at [[International Space Science Institute]] in [[Bern]], [[Switzerland]] to discuss the anomaly, and discuss possible means for resolving the source.<ref name=PECmain>
| |
| {{cite web
| |
| |date=February 18, 2008
| |
| |title=The Pioneer Explorer Collaboration: Investigation of the Pioneer Anomaly at ISSI
| |
| |url=http://www.issi.unibe.ch/teams/Pioneer/
| |
| |publisher=[[International Space Science Institute]]
| |
| |accessdate=2009-01-10
| |
| }}</ref>
| |
| | |
| == See also ==
| |
| * [[Flyby anomaly]]
| |
| * [[Galaxy rotation problem]]
| |
| * [[STVG]]
| |
| * [[Modified Newtonian dynamics]]
| |
| * [[General relativity]]
| |
| * [[Unsolved problems in physics]]
| |
| | |
| ==Notes==
| |
| {{reflist|group=note}}
| |
| | |
| ==References==
| |
| {{reflist|colwidth=30em}}
| |
| | |
| ==Further reading==
| |
| | |
| *{{Cite journal
| |
| |last=Anderson |first=J D.
| |
| |last2=Laing |first2=P. A.
| |
| |last3=Lau |first3=E. L.
| |
| |last4=Liu |first4=A. S.
| |
| |last5=Nieto |first5=M. M.
| |
| |last6=Turyshev |first6=S. G.
| |
| |year=1998
| |
| |title=Indication, from Pioneer 10/11, Galileo, and Ulysses Data, of an Apparent Anomalous, Weak, Long-Range Acceleration
| |
| |journal=[[Physical Review Letters]]
| |
| |volume=81
| |
| |issue=14 |pages=2858–2861
| |
| |doi=10.1103/PhysRevLett.81.2858
| |
| |arxiv=gr-qc/9808081 |bibcode=1998PhRvL..81.2858A
| |
| }}
| |
| : The original paper describing the anomaly
| |
| *{{cite journal
| |
| |last=Anderson |first=J D.
| |
| |last2=Laing |first2=P. A.
| |
| |last3=Lau |first3=E. L.
| |
| |last4=Liu |first4=A. S.
| |
| |last5=Nieto |first5=M. M.
| |
| |last6=Turyshev |first6=S. G.
| |
| |year=2002
| |
| |title=Study of the anomalous acceleration of Pioneer 10 and 11
| |
| |journal=[[Physical Review D]]
| |
| |volume=65
| |
| |issue=8 |page=082004
| |
| |doi=10.1103/PhysRevD.65.082004
| |
| |arxiv=gr-qc/0104064
| |
| |bibcode = 2002PhRvD..65h2004A }}
| |
| :A lengthy survey of several years of debate by the authors of the original 1998 paper documenting the anomaly. The authors conclude, "Until more is known, we must admit that the most likely cause of this effect is an unknown systematic. (We ourselves are divided as to whether 'gas leaks' or 'heat' is this 'most likely cause.')"
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| The ISSI meeting above has an excellent [http://www.issi.unibe.ch/teams/Pioneer/pa-literature.htm reference list] divided into sections such as primary references, attempts at explanation, proposals for new physics, possible new missions, popular press, and so on. A sampling of these are shown here:
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| | |
| *{{cite journal
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| |last= |first=
| |
| |date=December 1998
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| |title=
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| |journal=[[Scientific American]]
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| |volume=279 |issue=6 |pages=26–27
| |
| |doi=
| |
| }}
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| * Reardon, A. C. (2011). "Gravitational Analysis of V541 Cygni, DI Herculis, and the Pioneer anomaly". Astrophysics and Space Science, Vol. 336, No. 2 369-377, [http://www.springerlink.com/content/l2328n7528w26202/] Theory establishes a gravitational connection between the unexplained periastron advance observed in two binary star systems and the Pioneer anomaly.
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| | |
| * {{cite journal
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| |last=Anderson |first=J. D.
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| |last2=Turyshev |first2=S. G.
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| |last3=Nieto |first3=M. M.
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| |year=2002
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| |title=A mission to test the Pioneer anomaly
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| |journal=[[International Journal of Modern Physics D]]
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| |volume=11 |issue=10 |page=1545
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| |doi=10.1142/S0218271802002876
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| |arxiv=gr-qc/0205059
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| |bibcode = 2002IJMPD..11.1545A }}
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| *{{cite conference
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| |last=Turyshev |first=S. G.
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| |last2=Nieto |first2=M. M.
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| |last3=Anderson |first3=J. D.
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| |year=2005
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| |title=A Route to Understanding of the Pioneer Anomaly
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| |pages=13–17
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| |volume=2004
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| |issue=752
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| |booktitle=The XXII Texas Symposium on Relativistic Astrophysics
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| |editor1-last=Chen |editor1-first=P.
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| |editor2-last=Bloom |editor2-first=E.
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| |editor3-last=Madejski |editor3-first=G.
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| |editor4-last=Petrosian |editor4-first=V.
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| |arxiv=gr-qc/0503021
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| |bibcode = 2005tsra.conf..121T
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| |id=Stanford e-Conf #C04, paper #0310
| |
| }}
| |
| *{{cite journal
| |
| |last=Dittus |first=H.
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| |year=2005
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| |title=A Mission to Explore the Pioneer Anomaly
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| |pages=3–10
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| |volume=588
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| |journal=ESA Spec.Publ.
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| |arxiv=gr-qc/0506139
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| |author-separator=,
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| |author2=Pioneer Explorer Collaboration
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| |display-authors=1
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| |authorlink2=Pioneer Explorer Collaboration
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| |bibcode = 2005gr.qc.....6139T }}
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| *{{cite journal
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| |last1= Nieto |first1=M. M.
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| |last2=Turyshev |first2=S.G.
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| |year=2004
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| |title=Finding the origin of the Pioneer anomaly
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| |journal=[[Classical and Quantum Gravity]]
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| |volume= 21|issue= 17|page=4005
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| |doi=10.1088/0264-9381/21/17/001
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| |bibcode = 2004CQGra..21.4005N }}
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| : Further elaboration on a dedicated mission plan (restricted access)
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| *{{cite journal
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| |last1= Page |first1=J. F.
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| |last2= Dixon
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| |last3= Wallin
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| |year=2005
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| |title=Can Minor Planets be Used to Assess Gravity in the Outer Solar System?
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| |first2= David S.
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| |first3= John F.
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| |doi= 10.1086/500796
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| |journal= The Astrophysical Journal
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| |volume= 642
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| |page= 606
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| |arxiv=astro-ph/0504367
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| |bibcode=2006ApJ...642..606P
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| }}
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| *{{cite web
| |
| |last=Johnson |first=J.
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| |date=January 2, 2005
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| |url=http://seattletimes.nwsource.com/html/nationworld/2002138196_pioneer02.html
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| |title=Opening New Doors in Space
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| |work=[[The Seattle Times|Seattle Times]]
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| |accessdate=2012-01-12
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| }}
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| *{{cite journal
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| |last1=Nieto |first1=M. M.
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| |last2=Anderson |first2=J. D.
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| |year=2005
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| |title=Using Early Data to Illuminate the Pioneer Anomaly
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| |doi=10.1088/0264-9381/22/24/008
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| |journal=Classical and Quantum Gravity
| |
| |volume=22
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| |issue=24
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| |pages=5343–5354
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| |arxiv=gr-qc/0507052
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| |bibcode = 2005CQGra..22.5343N }}
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| *{{cite journal
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| |last= |first=
| |
| |date=October 2005
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| |title=
| |
| |journal=[[Scientific American]]
| |
| |volume=293 |issue=4 |pages=24–25
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| |doi=
| |
| |author1= <Please add first missing authors to populate metadata.>
| |
| }}
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| * {{cite journal
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| |last=Brownstein |first=J. R.
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| |last2=Moffat |first2=J. W.
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| |year=2006
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| |title=Gravitational solution to the Pioneer 10/11 anomaly
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| |journal=[[Classical and Quantum Gravity]]
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| |volume=23
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| |issue=10 | pages=3427–3436
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| |doi=10.1088/0264-9381/23/10/013
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| |arxiv=gr-qc/0511026
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| |bibcode = 2006CQGra..23.3427B }}
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| *{{cite journal
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| |last=Anderson |first=J.
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| |date=January 28, 2009
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| |title=March 2009: Is there something we don't know about gravity?
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| |url=http://www.astronomy.com/en/sitecore/content/Home/Press%20Room/Press%20Releases/2009/01/March%202009%20Is%20there%20something%20we%20dont%20know%20about%20gravity.aspx
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| |journal=[[Astronomy Magazine]]
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| |volume=37 |issue=3 |pages=22–27
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| |doi=
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| }}
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| == External links ==
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| * [http://www.technologyreview.com/blog/arxiv/26589/ "Pioneer Anomaly Solved By 1970s Computer Graphics Technique"] (March 2011)
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| * [http://www.sciamdigital.com/index.cfm?fa=Products.ViewIssuePreview&ARTICLEID_CHAR=AF24384E-BA31-411E-9296-B8E04C67159 "Pioneering Gas Leak? The strange motions of two space probes have mundane explanations--probably"] ''[[Scientific American]]'' (December 1998)
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| * [http://www.sciam.com/article.cfm?chanID=sa004&articleID=000BB6BE-A7BA-1330-A54583414B7F0000 "A Force to Reckon With: What applied the brakes on Pioneer 10 and 11?"] ''[[Scientific American]]'' (October 2005)
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| * [http://www.newscientistspace.com/article/dn8631 "Gravity theory dispenses with dark matter"] - STVG ([[Scalar-tensor-vector gravity]]) theory claims to predict Pioneer anomaly
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| * [http://www.spacedaily.com/reports/TPS_Enables_Study_Of_Mysterious_Pioneer_Anomaly.html Planetary Society data recovery effort enables study]
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| * [http://xstructure.inr.ac.ru/x-bin/theme3.py?level=1&index1=256123 Shows number of publications about the Pioneer anomaly on arXiv.org, by year.]
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| * [http://www.space.com/scienceastronomy/mystery_monday_041018.html Space.com: The Problem with Gravity: New Mission Would Probe Strange Puzzle]
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| * [http://www.economist.com/science/displaystory.cfm?story_id=10804075 "Wanted - Einstein Junior"] ''[[the Economist]]'' (March 2008)
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| * [http://www.popsci.com/pioneeranomaly?page=1 The Pioneer Anomaly, a 30-Year-Old Cosmic Mystery, May Be Resolved At Last] - Popular Science (December 2010)
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| {{Pioneer program}}
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| {{DEFAULTSORT:Pioneer Anomaly}}
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| [[Category:Pioneer program]]
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| [[Category:Gravitation]]
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| [[Category:Unsolved problems in physics]]
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