Deep space gravity tests
Deep space gravity tests
in the solar system
in the solar system
CNRS, ENS, UPMC (Paris) Laboratoire Kastler Brossel
Serge REYNAUD
Discussions and collaborations with persons quoted below and several collaborations “Deep Space Gravity Explorer”, Hansjörg
Dittus (ZARM) et al; “Solar System
ODYSSEY”, Bruno Christophe (ONERA)
et al; “SAGAS”, Peter Wolf (SYRTE) et al;
“ZACUTO”, Orfeu Bertolami (ISTL) et al “Investigation of the Pioneer Anomaly” @ ISSI,
Experimental tests of gravity show a good agreement with
General Relativity (GR)
But GR is a classical theory which show inconsistencies
with quantum field theory ; unification models predict
(small) deviations of gravity laws from GR
The scientific context
“Dark matter” and “dark energy” are seen as gravitational
anomalies; as long as they are not also observed
through independent means, they may also be
interpreted as modifications of gravity laws at large
(galactic and cosmic) scales
A few measurements in the solar system show deviations
from the predictions of GR
GR usually tested against the family of PPN metrics
¾
Courtesy : Cassini @ NASA
Tests select GR out of the PPN family
Bertotti, Iess, Tortora Nature 425 (2003)
Using also Lunar Laser Ranging The best test to date : tracking of
Cassini during its cruise from Jupiter to Saturn
Courtesy : J. Coy, E. Fischbach, R. Hellings, C. Talmadge, and E. M. Standish (2003)
log
10
α
log10λ (m)
Windows remain open for deviations at short ranges or long ranges Satellites Laboratory Geophysical LLR Planetary
The Search for Non-Newtonian Gravity, E. Fischbach & C. Talmadge (1998)
“Fifth-force” tests of the Newton law
Are GR predictions valid at all scales ?
Search for a deviation
in particular under the form of a Yukawa correction
Exclusion domain in the plane (λ,α)
Strong constraint now at sub-mm distances
¾ A Yukawa interaction with Newton strength (α=1) must have a range smaller than λ<56µm D.J. Kapner et al PRL 98 (2007)
FIG. 6: Constraints on Yukawa violations of the gravitational 1/r2law. The shaded region is
excluded at the 95% confidence level. Heavy lines labeled Eöt-Wash 2006, Eöt-Wash 2004, Irvine, Colorado and Stanford show experimental constraints from this work, Refs. [11], [14], [15] and [16, 17], respectively. Lighter lines show various theoretical expectations (Ref. [9]).
Exclusion domain in the plane (λ,α)
E.G. Adelberger et al, arXiv:hep-ph/0611223
Searches in the short-range window
At shorter ranges, tests consist in comparisons of Casimir force measurements with theory …
A large-scaled test of gravity was performed by Pioneer 10 & 11 probes during their extended missions decided by NASA after their primary planetary objectives have been met
Searches in the long-range window
Pioneer 10: pre-launch testing
Pioneer 10/11 as precisely navigated deep-space vehicles :
– Spin-stabilization and design permitted acceleration sensitivity ~10- 10m/s2,
unlike a Voyager-type 3-axis stabilization that were almost 50 times worse
Courtesy : JPL @ NASA S. Turyshev
The largest scaled gravity test ever carried out…
The observable is the frequency ratio, interpreted as a Doppler velocity υ. It depends on the motion of
probes while including
relativistic and gravitational effects
It must also be corrected for propagation effects, station motions….
The Doppler observable
A radio signal is sent from a station on Earth to the probe, sent back
(transponded) by the probe, and finally received by a station on Earth :
the same for 2-way tracking; another one for 3-way tracking.
THE DEEP SPACE GRAVITY PROBE SCIENCE TEAM
THE DEEP SPACE GRAVITY PROBE SCIENCE TEAM
Deviation of the observed Doppler velocity
from the modeled one varying ~ linearly with time
Interpreted as an anomalous acceleration
Anomalous acceleration
1987 1998.8
1 Hz is equivalent to 65 mm/s velocity
It is unlikely that the equivalence principle be violated at the level of the Pioneer anomaly
We keep the description of gravitation as a Riemannian metric theory with motions identified as geodesics
But the metric in the solar system could differ from GR solution, leading to modifications of geodesic motions of probes or of propagation of radio-links
This defines a phenomenology larger than the PPN framework
Modifications producing the anomaly should not affect the agreement of other tests with GR but it could produce correlated anomalies to be looked for on other signals…
Can the PA be a metric anomaly ?
The two “sectors”
First possibility : a change of the temporal component of the metric
– It amounts to a modification of Newton law and is constrained by planetary tests
– But the deviation could appear only after Jupiter …
Presentation
John Moffat
Second possibility : a change of the spatial components of the metric
– It induces a modification of light propagation and is equivalent to a parameter γ depending on the heliocentric distance
– It has only a small effect on slow material motions (especially on circular orbits)
– It produces a Pioneer-like anomaly for probes with radial motions in the outer solar system
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 actively looked for, not yet found
Can it be something else ?
A challenge ahead of all of us :
– Will we be able to solve the discrepancy and show that Pioneer gravity test once more confirmed GR ?
– Or to confirm the existence of a gravity anomaly ?
Any of these two conclusions will be of great value for fundamental physics, astrophysics and cosmology
THE DEEP SPACE GRAVITY PROBE SCIENCE TEAM
THE DEEP SPACE GRAVITY PROBE SCIENCE TEAM
V. Toth and S. Turyshev, arXiv:gr-qc/0603016
Recent Pioneer Data Recovery Effort
Ongoing Pioneer data re-analysis is an international effort : teams at work in US, Canada, Germany, France, Italy, Norway…
Data used for the analysis of 1998-2002 (1996-1998) :
Pioneer 10: 11.5 years; distance = 40−70.5 AU Pioneer 11: 3.75 years; distance = 22.4−31.7 AU
Telemetry & Doppler data recovered from launch to the last data point
Pioneer 10:
– 1973-2002: ~ 30 years
– Distance range: 4−87 AU – Jupiter encounter
– ~60,000 data points, ~20GB – Maneuvers, spin, initial cond.
Pioneer 11:
– 1974-1994: ~ 20 years
– Distance range: 4−33 AU – Jupiter & Saturn encounters – ~50,000 data points, ~15GB – Maneuvers, spin, initial cond.
Doppler Data now available :
Pioneer data recently recovered (Planetary Society & JPL, NASA) :
More informations on the website “Investigation of the Pioneer Anomaly” Team @ ISSI
THE STUDY OF THE PIONEER ANOMALY
THE STUDY OF THE PIONEER ANOMALY
New solutions for Pioneer 10 &11 data at JPL
Improvement of solutions (with respect to the analysis published in
PRD 2002)
– Updated Filter strategy
– Improved models and improved consistency of non gravitational effects on Pioneer 10 & 11 probes
– …
Confirms & updates anomaly estimates in Deep Space solutions
Observes variations in stochastic acceleration estimates
Detects anomaly during Saturn approach
More analysis required …
Courtesy : JPL @ NASA S. Turyshev
Groupe Anomalie Pioneer : OCA, ONERA, LKB, IOTA, SYRTE
Independent analysis of Pioneer
data by the French group
Gilles Metris & Philippe Berio (OCA), Agnès Lévy (ONERA), Jean-Michel Courty (LKB)
J. Anderson et al, Phys. Rev. D 65 (2002) 082004
Poster
presentation
Agnès Lévy
The presence of the anomaly is once more confirmed (its interpretation is still unknown) …
Deep Space Gravity Proposals
After the proposal submitted in 2004 to ESA in response to the Cosmic Vision call, the objective of testing Deep
Space Gravity has been recognized by ESA
4 Letters of Intent submitted to ESA on end of March 2007
– Deep Space Gravity Explorer (Hansjorg Dittus, Bremen) – Solar System ODYSSEY (Bruno Christophe, Chatillon) – SAGAS (Peter Wolf, Paris)
– ZACUTO (Orfeu Bertolami, Lisboa)
Presentations
Bruno Christophe
Peter Wolf
Now, a common roadmap for all these LoI’s with 2 proposals to be submitted
on end of June 2007
– One class M proposal – One class L proposal
