- Apocentre:This is the point of an elliptical orbit, which is the furthest from the parent body.
- Ascending node: This is an intersection between the orbit and the reference plane.
- AU: Stands for Astronomical Unit. This is the mean distance between the Sun and the Earth, i.e. 149,597,870.700 km
- Chaos: A trajectory is chaotic when, at some point, you cannot accurately predict it.
- Circulation: An angle is circulating when it can take any number between 0° and 360°.
- Eccentricity: This parameter characterizes the elongation of a trajectory. Eccentricity e = 0 means that the trajectory is circular. Elliptical orbits have always e < 1.
- Hamiltonian: Total energy of a dynamical systems, expressed with convenient (canonical) variables, which mathematical properties permit an in-depth analysis of the dynamics. In the absence of dissipation, the Hamiltonian is constant.
- Kozai-Lidov mechanism: Dynamical mechanism raising the inclination of a body, when eccentric enough. This results in the libration of the difference between its pericentre and its ascending node.
- Longitude (orbital): It is an angle determining the emplacement of a body on its orbit.
- Mass wasting: Bulk movement of rock debris and / or soil down slope due to gravity.
- Orbit: Trajectory of a body.
- Parent body: The body around which a given body moves. The parent body of the Earth is the Sun, the parnt body of the Moon is the Earth.
- Pericentre: This is the point of an elliptical orbit, which is the closest from the parent body.
- Resonance: Equality between two independent frequencies of a given dynamical system. This results in a raise of the response, pushing a dynamical parameter like the eccentricity, the inclination…
- Three-body problem: The motion of 3 bodies, interacting with each other. When one of these bodies is so small that it is assumed to not affect the other ones, we speak of the restricted 3-body problem.
- Tides: Differential gravitational action of an outer body on another one, with a finite size. This results in stress and strains which alter the shape of the body, and energy dissipation, which also affects its rotation and its orbit.
New results in planetary sciences in 1,000 words