122 research outputs found
The Determination of Jupiter’s Angular Momentum from the Lense-Thirring Precession of the Juno Spacecraft
No full textJupiter spin-pole precession rate and moment of inertia from Juno radio-science observations
No full textThrough detailed and realistic numerical simulations, the present paper assesses the precision with which the Juno spacecraft can measure the normalized polar moment of inertia (MOI) of Jupiter. Based on Ka-band Earth-based Doppler data, created with realistic 10 Î1⁄4m/s of white noise at 60 s of integration, this analysis shows that the determination of the precession rate of Jupiter is by far more efficient than the Lense-Thirring effect previously proposed to determine the moment of inertia and therefore to constrain the internal structure of the giant planet with Juno. We show that the Juno mission will allow the estimation of the precession rate of Jupiters pole with an accuracy better than 0.1%. We provide an equation relating the pole precession rate and the normalized polar moment of inertia of Jupiter. Accounting for the uncertainty in the parameters affecting precession, we show that the accuracy of the MOI inferred from the precession rate is also better than 0.1%, and at least 50 times better than inferred from the Lense-Thirring acceleration undergone by Juno. This accuracy of the MOI determination should provide tight constraints on the interior structure of Jupiter, especially the core size and mass, helping to distinguish among competing scenarios of formation and evolution of the giant planet. In addition, though the Juno mission operations are already defined, the exact duration of the tracking and its occurrence with respect to the spacecraft pericenter pass are not definitely scheduled. The simulations performed here quantify the impact of this aspect of the mission on the Juno sensitivity to (in particular) the spin-pole precession rate of Jupiter. Finally, additional simulations have been performed to test the usefulness of combining Doppler data with VLBI data, showing the latter measurements to be 104-105 times less sensitive than the former to our parameters of interest and therefore, obviously, totally needless
Mary Jo Shotts Collection
No full textPhotograph of the Woodmen of the World, Caddo, Indian Territory. L to R: UNIDENTIFIED, UNIDENTIFIED, D. B. Williams, A. R. Easeley, N. Miller, A. W. Cole, T. M. Vaughan, W. Fergo, UNIDENTIFIED, UNIDENTIFIED, C. A. Skein, Ben Self, UNIDENTIFIED, Charles Stephens, F. W. Harvey, UNIDENTIFIED, C. N. Craighead, UNIDENTIFIED, UNIDENTIFIED, W. J. Melton, M.D., W. F. Dodd, Mr. Hogue, E. I. Harris, J. J. Reeder, W. T. Keath, C. A. Bilbo, J. A. Frickey, O. E. Smith, D. O. Beard, A. B. McCoy, UNIDENTIFIED, C. C. Brauham, UNIDENTIFIED, UNIDENTIFIED, UNIDENTIFIED, UNIDENTIFIED, J. N. Mullens, UNIDENTIFIED, UNIDENTIFIED, W. F. Russell, N. A. Shelby, W. Folkner, J. F. Lamb, Jim A. Beaird, Gene Sargents, Ernest Bass, and D. Craighead. Photo by W. W. Clinkscales, Caddo, Indian Territory
The gravity field of Jupiter after the first three orbits of Juno
No full textIn 2016 the spacecraft Juno completed its first three perijove passes, respectively on Aug. 27 (PJ-1), Oct. 19 (PJ-2), and Dec. 11 (PJ-3), at an altitude of about 4000 km above the cloud level. Measurements of the spacecraft range rate were carried out across closest approach in all three passes, thanks to a coherent, two-way tracking at X band (7.2-8.4 GHz) from the antennas of the Deep Space Network. In PJ-1 a second downlink frequency at Ka band (32.5 GHz) allowed a good calibration of the path delay variations due to the Io plasma torus. During PJ-3, dedicated to radio science and Jupiter gravity determination, the full onboard Ka band system was activated, enabling a coherent radio link at 32.5-34 GHz and high accuracy range rate measurements. After removal of media effects (earth troposphere and Io plasma torus), tracking data from all three passes were combined to obtain a first cut determination of Jupiter gravity field. We report on this preliminary solution, and compare it with the theoretical expectations available in the literature
Jupiter gravity field estimated from the first two Juno orbits
No full textThe combination of the Doppler data from the first two Juno science orbits provide an improved
estimate of the gravity field of Jupiter, crucial for interior modeling of giant planets. The low-degree spherical harmonic coefficients, especially J4 and J6, are determined with accuracies
better than previously published [Anderson et al., 1974; Null et al., 1975; Campbell and Synnott,1985] by a factor of 5 or more. In addition, the independent estimates of the Jovian gravity field, obtained by the orbits separately agree within uncertainties, pointing to a good stability of the
solution. The degree 2 sectoral and tesseral coefficients, C2,1, S2,1, C2,2, and S2,2 were determined to be statistically zero as expected for a fluid planet in equilibrium
The depth of Jupiter’s great red spot constrained by Juno gravity overflights
No full textJupiter’s Great Red Spot (GRS) is the largest atmospheric vortex in the Solar System and has been observed for at least two centuries. It has been unclear how deep the vortex extends beneath its visible cloud tops. We examined the gravity signature of the GRS using data from 12 encounters of the Juno spacecraft with the planet, including two direct overflights of the vortex. Localized density anomalies due to the presence of the GRS caused a shift in the spacecraft line-of-sight velocity. Using two different approaches to infer the GRS depth, which yielded consistent results, we conclude that the GRS is contained within the upper 500 kilometers of Jupiter’s atmosphere
Jupiter's Gravity Field Halfway Through the Juno Mission
No full textThe Juno spacecraft reached the mid‐point of its nominal mission in December 2018, after completing 17 perijove passes. Ten of these were dedicated to the determination of the gravity field of the planet, with the aim of constraining its interior structure. We provide an update on Jupiter's gravity field, its tidal response and spin axis motion over time. The analysis of the Doppler data collected during the perijove passes hints to a non‐static and/or non‐axially symmetric field, possibly related to several different physical mechanisms, such as normal modes or localized atmospheric or deeply‐rooted dynamics
Navigational utility of high-precision radio interferometer for Galileo's approach to Jupiter
No full textThe effect of very long baseline interferometry (VLBI) measurements of 2-nanoradian (nrad) accuracy has been studied for use in Galileo's approach to Jupiter's moon Io. Of particular interest is reducing the error in the minimum altitude above Io's surface. The nominal tracking strategy includes Doppler, range, and onboard optical data, in addition to VLBI data with 25-nrad accuracy. For nominal data, the altitude error is approximately 250 km with a data cutoff of 19 days before closest approach to Io. A limited number (two to four) of 2-nrad VLBI measurements, simulating a demonstration of improved VLBI data, were found to reduce the altitude error by 10 to 40 percent. Improving the accuracy of the VLBI measurements of the nominal tracking strategy to 2 nrads, to simulate the results from an operational few-nrad VLBI capability, was found to reduce the altitude error by an approximate factor of four. This reduction in altitude error is attributed to the ability that VLBI data give to help determine the along-track component of Jupiter's ephemeris. This capability complements the ability of the onboard optical data to determine the radial and cross-track components of Jupiter's ephemeris
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