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Venus currently rotates slowly, with its spin controlled by solid-body and atmospheric thermal tides. However, conditions may have been far different 4 billion years ago, when the Sun was fainter and most of the carbon within Venus could…

Saturn's largest satellite, Titan, has stratospheric wind speeds that may be up to ~210 m/sec [1], circling Titan in about a day compared to Titan's slow 16-day rotation. Theoretical models to explain such super-rotating winds are not well…

The local curvature of the space produced by the Sun causes not only the perihelion precession of Mercury's elliptical orbit, but also the variations of the whole orbit, in comparison with those predicted by the Newtonian theory of…

The origin of Mars's small moons, Phobos and Deimos, remains unknown. They are typically thought either to be captured asteroids or to have accreted from a debris disk produced by a giant impact. Here, we present an alternative scenario…

Prevailing models for the formation of the Moon invoke a giant impact between a planetary embryo and the proto-Earth \citep{Canup_2004, Cuk_Stewart_2012}. Despite similarities in the isotopic and chemical abundances of refractory elements…

For a hypothetical planet on a highly eccentric orbit, we have calculated the osculating orbital parameters and its closest approaches to Earth and Moon over a period of 750 kyr. The approaches which are close enough to influence the…

Stars are not perfectly spherically symmetric. They are deformed by rotation and magnetic fields. Until now, the study of stellar shapes has only been possible with optical interferometry for a few of the fastest-rotating nearby stars. We…

Gravitational and electronic forces produce a correlation between the mass and shape of objects in the universe. For example, at an average radius of ~ 200 km - 300 km, the icy moons and rocky asteroids of our Solar System transition from a…

% context heading (optional) {Thanks to the Venus Express Mission, new data on the properties of Venus could be obtained in particular concerning its rotation.} % aims heading (mandatory) {In view of these upcoming results, the purpose of…

We point out that by comparing the total mass (in gravitational units) of the earth-moon system, as determined by lunar laser ranging, with the sum of the lunar mass as independently determined by its gravitational action on satellites or…

A time-dependent gravitational constant or mass would correctly describe the suspected increasing of both: the Astronomical unit and the eccentricity of the Lunar orbit around the Earth.

The evolution of the orbits of bodies ejected from the Earth, Moon, Mercury and Mars was studied. At ejection velocities about 12-14 km/s, the fraction of bodies ejected from the Earth that fall back onto the Earth was about 0.15-0.25. The…

Planet migration is the process by which a planet's orbital radius changes in time. The main agent for causing gas giant planet migration is the gravitational interaction of the young planet with the gaseous disk from which it forms. We…

Several mechanisms have been proposed to explain the formation process of satellite systems, and relatively large moons are thought to be born in circumplanetary disks. Making a single-moon system is known to be more difficult than…

The physical state of the lunar soil in the permanently shadowed craters of the moon is inferred from experimental investigation. The permanently shadowed craters do not undergo the same thermal cycling experienced by other parts of the…

A long-term numerical integration of the classical Newtonian approximation to the planetary orbital motions of the full Solar System (sun + 8 planets), spanning 20 Gyr, was performed. The results showed no severe instability arising over…

Moons orbiting extrasolar planets are the next class of object to be observed and characterized for possible habitability. Like the host-planets to their host-star, exomoons have a limiting radius at which they may be gravitationally bound,…

The orbital displacement of the Moon is known to a precision on the order of centimeters from the lunar laser ranging data, while the lunar profile's confidence level is still only about 200 m. The lunar motion is used to measure the solar…

Lunar occultation can be used to measure the proper motions of some of the long time scale microlensing events, $t_{e} \gsim 70$ days, now being detected toward the Galactic bulge. The long events are difficult to explain within the context…

The (yet-to-be confirmed) discovery of a Neptune-sized moon around the ~3.2 Jupiter-mass planet in Kepler 1625 puts interesting constraints on the formation of the system. In particular, the relatively wide orbit of the moon around the…