Other
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....5289j&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #5289
Other
Scientific paper
On top of Mercury's continuous rotation which is in a 3:2 resonance with Mercury's orbital period, there is a libration motion which can be roughly described by a single sine function. However, such a simple representation places the maxima 10 degrees (in true anomaly) away from the correct position and also the values of the maxima are 2% lower. It is shown that the libration can be well approximated by Φ_0 sin M + Φ_0 / K sin 2M where Φ_0 is the unknown libration amplitude, M is Mercury's mean anomaly and K = 9.483. K is independent of Φ_0 and can be analytically determined from the eccentricity functions Glpq. Φ_0, the amplitude of Mercury's libration, can be determined by comparing images of the same landmark at different positions of Mercury in its orbit. This is actually planned to be done by BepiColombo, ESA's mission to Mercury which includes an orbiter in a 400 × 1500 km polar orbit. Taking into account errors in the orbital position, errors in the attitude of the camera and errors in the pattern matching techniques, the estimated error in a single landmark displacement determination is 1.6 arcsec at the equator. If the angle between the orbit plane and Mercury's line of periapsis (β-angle) is well chosen there will be many opportunities to acquire images of independent landmarks. On the other hand for unfavourable β-angles there are no opportunities at all. It is shown that if β is between -60^o and +60^o the amplitude of Mercury's libration can be determined with an accuracy below 1 arcsec. For β = 0^o an accuracy of even 0.3 arcsec can be achieved if pattern matching techniques are applied to 20 independent pairs of surface images which will be available in 2 Mercury years (176 days).
Corral Carlos
Jehn Rüdiger
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