Long range gravity testsLong range gravity testsand the Pioneer anomalyand the Pioneer anomaly

CNRS, ENS, UPMC (Paris)

Laboratoire Kastler Brossel

Serge REYNAUD

Thanks to Marc-Thierry Jaekel (LPT ENS, CNRS, Paris)

Pierre Touboul et al (ONERA, Chatillon)

members of “Investigation of the Pioneer Anomaly” Team (ISSI)Slava G. Turyshev et al, www.issi.unibe.ch/teams/Pioneer

and of “Deep Space Gravity Probe” Team (ESA/NASA)Hansjörg Dittus et al, arXiv.org/abs/gr-qc/0506139

Gravitational field ≡ metric in Riemann space-time• ideal (atomic) clocks measure the

proper time along their trajectory• freely falling probes (masses and

light rays) follow geodesics

Equation tested by comparing predicted geodesics with observations/experiments

General Relativity (in one slide !)

Einstein equation– one curvature tensor

has a null divergence (Bianchi identities)like the stress tensor (conservation laws)

– in General Relativity, the 2 tensors are simply proportional to each other

One of the most accurately tested principles of physics

Solution of GR in the solar system– with the Sun treated as a

point-like motionless source

– using spatially isotropic coordinates

– with the Newton potential

Tests of General Relativity (GR)

GR usually tested through its confrontation with the larger family of PPN metrics

Motions predicted as the geodesics of this metric

Comparisons between observations and predictions expressed in terms of anomalies of the PPN parameters

1

0.998 10.999 1.001 1.002

1.002

1.001

0.999

0.998

β

γ

Cassini ‘03

Mercury Ranging ‘93

LLR ’02

General Relativity

Ranging on planetsLunar Laser Ranging

(LLR)Astrometry and VLBIDoppler velocimetry

on probes

Mars Ranging ‘76

Astrometric VLBI ‘97

Courtesy : Slava Turyshev JPL NASA

30 years of tests of General Relativity

Living Reviews in Relativity, C.F. Will (2001)

Tests consistent with GR

(accuracy lesser than for EP)

Courtesy : J. Coy, E. Fischbach, R. Hellings, C. Talmadge, and E. M. Standish (2003)

log 1

0αlog10λ (m)

Windows remain open for deviations at shortranges

or longrangesanges

Satellites

Laboratory

Geophysical

LLR Planetary

The Search for Non-Newtonian Gravity, E. Fischbach & C. Talmadge (1998)

“Fifth-force” tests of the Newton lawScale dependent tests of GR

Search for a deviation

in particular under the form of a Yukawa correction

Gravity measurements at short distances (λ > ~ 30µm)

At shorter ranges, searches involve comparisons of Casimirforce measurements with theoretical predictions (QED)

Aim : to bridge the gap with galactic and cosmic scales

Method : perform gravity tests at as large distances as possible

Best example : NASA approved to extend Pioneer 10/11 missions after Jupiter/Saturn flybies with the aim (among other) of testing Celestial Mechanics at large heliocentric distancesThis led to the observation of the Pioneer anomaly

A. Lambrecht et al, in Séminaire Poincaré (2002) quant-ph/0302073

Eric Adelberger’s talk, yesterday

No deviations recorded to date in the short-range window

Searches in the short-range window

Searches in the long-range window

The Pioneer “gravity test”:the largest scaled test ever carried out…

…and it failed to confirm the known laws of gravity !

THE DEEP SPACE GRAVITY PROBE SCIENCE TEAMTHE DEEP SPACE GRAVITY PROBE SCIENCE TEAM

Two way Doppler measurement

1987 1998.81 H

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ival

ent t

o 65

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/s v

eloc

ity

Courtesy : Slava Turyshev JPL NASA

Doppler observable → relative velocityDeviation of the observed velocity from the modelled one varying ~ linearly with time

J. Anderson et al, Phys. Rev. D 65 (2002) 082004

The anomaly has been registered on the two deep space probes with the best navigation accuracy

The two probes were identical and had similar trajectories : one experiment performed twice with the same result.

Might be an artefact ?Satisfactory explanation has been looked for, not yet found !

Data re-analysis soon performed …

A key question : is the Pioneer anomaly compatible with other gravity tests ?The equivalence principle (EP) cannot be violated at the

level of the Pioneer anomaly

→we preserve the geometrical interpretation of Einstein theorygravitation described as a Riemannian metric theory

motions identified with geodesics

But the Einstein-Hilbert equation can be modified→modifications studied thereafter are naturally induced by

“radiative corrections” to GR due to its coupling with quantum fields

→ they lead to modifications of the metric in the solar systemand then to modifications of geodesic motions

→ they define a phenomenological framework larger than PPN

A general linear expression between the Einstein tensor and the stress tensor may thus be given in terms of two running constants, which depend on momentum and differ in the two sectors

Extending GR : two argumentsIn the linearized theory, equations may be written in Fourier

space: it turns out that the Einstein tensor contains two independent divergence-free components, one related to the trace, the other one traceless

The general isotropic and stationary metric is written in terms of two potentials (they are related to thetwo running constants)

The extension can be considered as promoting the Eddingtonparameters to the status of r-dependent functions

The first sector The first anomalous potential modifies the Newton law

and is strongly constrained by planetary tests :– the third Kepler law is verified on the orbital period of Mars

compared to the radius of its orbit (measured independently)

– the perihelion precession of the planets agree with GR

The deviation could in principle appear only after Saturn !To confirm / infirm this possibility, one has to discuss the

ephemeris of outer planets or other objects in the outer solar system (John Moffat’s talk yesterday)

Deviations needed to explain the Pioneer anomaly are too large to remain unnoticed on planetary tests, if they are assumed to have a Yukawa or linear form

The modification of GR producing the Pioneer anomaly should not spoil its agreement with other gravity tests

but it can produce related anomalies to be looked for…

The second potential is equivalent to an Eddington parameter γ depending on the distance to Sun

It produces a Pioneer-like anomaly for probes with escape trajectories in the outer solar system

We evaluate this effect by :– calculating the Doppler velocity taking into account the

perturbation of light propagation to and from the probesas well as the perturbation of the motion of the probes

– writing the derivative of this velocity as an acceleration– subtracting the result of the standard calculation to obtain the

anomalous acceleration

The second sector

The next steps

Recent Pioneer Data Recovery EffortGoal: recover Doppler and telemetry data over the whole

period from launch to the last data point

Recovery now completed at JPL, certification ongoing, upcoming Pioneer data analysis planned as an international effort (contact : Slava Turyshev @ JPL)

Open questions :better control of the systematics !direction of the force ? time variation ? spin contribution ?anomaly arising on Pioneer 11 @ Saturn encounter ?correlation of the signal with theoretical models ?…

Look for a scale dependence in ranging tests (Shapiro time delay) or deflection tests (they depend on γ)

Look for anomalies in the motions of planets or other objects in the solar system

Search for Pioneer-related anomalies which might be scale dependent: if something is present there, is it also here ?

Some ideas which also look promising

Fly dedicated probes or dedicated passenger instruments on planetary missions

Immediately : develop and validate enabling technologies laser ranging between Earth and probes, Earth and landers, probes and probes… accelerometers controlling the deviation from geodesic motionaccurate clocks on board measuring separately

THE DEEP SPACE GRAVITY PROBE SCIENCE TEAMTHE DEEP SPACE GRAVITY PROBE SCIENCE TEAMarXiv:gr-qc/0506139 : ESA “Cosmic Vision”A Mission to Explore the Pioneer Anomaly

The Deep Space Gravity Probe Science Team

The Deep Space Gravity Probe Science Team

H.J. Dittus, C. Laemmerzahl, S. Theil (ZARM, Bremen), B. Dachwald, W. Seboldt (DLR, Köln),W. Ertmer, E. Rasel (U. Hannover), K. Scherer (U. Bonn),R. Förstner, U. Johann (Astrium, Friedrichshafen),H.-J. Blome (FH Aachen), F. Hehl, C. Kiefer (U of Cologne),T.J. Sumner (Imperial College, London), R. Bingham, B. Kent (RAL, Didcot),S. Reynaud (LKB, Paris), A. Brillet, F. Bondu, E. Samain (OCA, Nice),P. Touboul, B. Foulon (ONERA, Châtillon), P. Bouyer (IOTA, Orsay),O. Bertolami (IST, Lisboa), D. Giulini (U of Freiburg, Breisgau), J.L. Rosales (QIG, RSFE, Madrid),C. de Matos (ESA-HQ, Paris), A. Rathke, C. Erd, J. C. Grenouilleau, D. Izzo (ESA/ESTEC), J.D. Anderson, S.W. Asmar, G. Giampieri, S.G. Turyshev (JPL, Caltech, Pasadena),M.M. Nieto (LANL, Los Alamos), B. Mashhoon (U of Missouri, Columbia)

H.J. Dittus, C. Laemmerzahl, S. Theil (ZARM, Bremen), B. Dachwald, W. Seboldt (DLR, Köln),W. Ertmer, E. Rasel (U. Hannover), K. Scherer (U. Bonn),R. Förstner, U. Johann (Astrium, Friedrichshafen),H.-J. Blome (FH Aachen), F. Hehl, C. Kiefer (U of Cologne),T.J. Sumner (Imperial College, London), R. Bingham, B. Kent (RAL, Didcot),S. Reynaud (LKB, Paris), A. Brillet, F. Bondu, E. Samain (OCA, Nice),P. Touboul, B. Foulon (ONERA, Châtillon), P. Bouyer (IOTA, Orsay),O. Bertolami (IST, Lisboa), D. Giulini (U of Freiburg, Breisgau), J.L. Rosales (QIG, RSFE, Madrid),C. de Matos (ESA-HQ, Paris), A. Rathke, C. Erd, J. C. Grenouilleau, D. Izzo (ESA/ESTEC), J.D. Anderson, S.W. Asmar, G. Giampieri, S.G. Turyshev (JPL, Caltech, Pasadena),M.M. Nieto (LANL, Los Alamos), B. Mashhoon (U of Missouri, Columbia)