Recent Attempts to Measure the General Relativistic Lense-Thirring Effect with Natural and Artifical Bodies in the Solar System

Abstract

According to general relativity, a spinning body of mass M and angular momentum~S, like a star or a planet, generates a gravitomagnetic field which induces , among other phenomena, also the Lense-Thirring effect, i.e. secular precessions of the pat h of a test particle orbiting it. Direct and indisputable tests of such a relativistic prediction are st ill missing. We discuss some performed attempts to measure it in the gravitational fields of several bodies in the Solar System with natural and artificial objects. The focus is on the realistic evaluat ion of the impact of some competing classical forces regarded as sources of systematic uncerta inties degrading the total accuracy obtainable. In the case of the test performed with the LAGEOS and LAGEOS II Earth’s satellites one of the major sources of systematic uncertainty is the imperfect knowledge of the even zonal harmonic coefficients of the multipolar expansion of the New tonian part of the terrestrial gravitational potential. The lingering uncertainty in some of them makes the total error in such a test as large as 15 − 30%, contrary to more optimistic evaluations (≈ 5 − 10%). Some different strategies to extract the relativistic signature from the data of the LAGEOS satellites which may complement and robustly corroborate the so far implemented tests are suggested. We critically discuss the possibilities that the LARES satellite, to be launched a t the end of 2009, will realistically allow to measure the Lense-Thirring effect with a ≈ 1% accuracy. Since it will orbit at much lower altitude than LAGEOS and LAGEOS II, much more even zonals will have to be accounted for; according to the present-day uncertainty in them, calculations performed with standard geodetic techniques show that their impact may be orders of magnitude larger than the expected accuracy level. Recent progresses in the planetary orbit determinat ion make the perspective of reliably measuring the Sun’s Lense-Thirring effect a realistic poss ibility. Presently, the magnitude of the gravitomagnetic perihelion precessions of the inner planets is about of the same order of magnitude of the present-day uncertainties in determining the se cular perihelion precessions from the observations of the rocky planets. Moreover, the predicted Lense-Thirring effect for all of them are in agreement with the estimated corrections to the standard Newtonian/Einsteinian perihelion precessions. Finally, we discuss a recent interpretation o f some orbital data of the Mars Global Surveyor spacecraft in terms of the gravitomagnetic field of Mars which recently raised a debate. 5th International School on Field Theory and Gravitation,