Juno, the angular momentum of Jupiter and the LenseThirring effect
Abstract
The recently approved Juno mission will orbit Jupiter for 1 year in a highly eccentric (r=1.06R,r=39R) polar orbit (i=90°) to accurately map, among other things, the jovian magnetic and gravitational fields. Such an orbital configuration yields an ideal situation, in principle, to attempt a measurement of the general relativistic LenseThirring effect through the Juno's node Ω which would be displaced by about 570 m over the mission's duration. Conversely, by assuming the validity of general relativity, the proposed test can be viewed as a direct, dynamical measurement of the Jupiter's angular momentum S which would give important information concerning the internal structure and formation of the giant planet. The longperiod orbital perturbations due to the zonal harmonic coefficients J_{ℓ},ℓ=2,3,4,6 of the multipolar expansion of the jovian gravitational potential accounting for its departures from spherical symmetry are, in principle, a major source of systematic bias. While the LenseThirring node rate is independent of the inclination i, the node zonal perturbations vanish for i=90. In reality, the orbit injection errors will induce departures δi from the ideal polar geometry, so that, according to a conservative analytical analysis, the zonal perturbations may come into play at an unacceptably high level, in spite of the expected improvements in the lowdegree zonals by Juno. A linear combination of Ω, the periJove ω and the mean anomaly M cancels out the impact of J_{2} and J_{6}. A two orders of magnitude improvement in the uncanceled J_{3} and J_{4} would be needed to reduce their bias on the relativistic signal to the percent level; it does not seem unrealistic because the expected level of improvement in such zonals is three orders of magnitude. More favorable conclusions are obtained by looking at single Doppler rangerate measurements taken around the closest approaches to Jupiter; numerical simulations of the classical and gravitomagnetic signals for this kind of observable show that a 0.25% accuracy would be a realistic goal.
 Publication:

New Astronomy
 Pub Date:
 August 2010
 DOI:
 10.1016/j.newast.2010.01.004
 arXiv:
 arXiv:0812.1485
 Bibcode:
 2010NewA...15..554I
 Keywords:

 General Relativity and Quantum Cosmology;
 Astrophysics;
 Physics  Space Physics
 EPrint:
 LaTex, 28 pages, 3 figures, 2 tables. To appear in New Astronomy (NA)