Fr.: élément orbital
Any of the six parameters needed to specify the → orbit of an object around a → primary body (such as a planet around the Sun or a satellite around the Earth) and give its position at any instant. Two of them define the size and the form of the orbit: → semi-major axis (a) and → eccentricity (e). Three angular values determine the orbit position in space: the → inclination (i) of the object's → orbital plane to the reference plane (such as the → ecliptic), the → longitude of ascending node (Ω), and the → argument of periapsis (ω). And finally the sixth element is the → time of periapsis passage which allows calculating the body's position along the orbit at any instant.
Fr.: éléments orbitaux osculateurs
The orbital elements of an osculating orbit.
→ osculating; → element.
Fr.: élément parent
A radioactive element that spontaneously decays into a new substance. The product of this decay is known as a "daughter" element.
platinum group element (PGE)
bonpâr-e goruh-e pelâtin
Fr.: élément du groupe du platine
One of the six metals → platinum (Pt), → iridium (Ir), → osmium (Os), → palladium (Pd), → rhenium (Rh), and → ruthenium (Ru) that are grouped together in the → periodic table. They are relatively hard and resistant to corrosion and are used in jewellery and in some industrial applications. All are resistant to chemical attack.
An element, such as uranium, whose isotopes are all radioactive.
rare earth element
bonpâr-e xâki-ye kamyâb, xâk-e kamyâb
Fr.: terre rare
Any of the group of metallic → chemical elements with → atomic numbers between 57 and 71 inclusive. The name is an inappropriate terminology, since they are neither rare nor earth; preferred name → lanthanide.
Fr.: élément sidérophile
In the → Goldschmidt classification, any → chemical element that has an → affinity to combine with → iron rather than some other element. These elements are concentrated in the → Earth's core. The group includes → iron (Fe), → nickle (Ni), → cobalt (Co), → platinum (Pt), → gold (Au), → tin (Zn), and → tantalum (Ta). The siderophile elements include → highly siderophile element (HSE).
→ siderophile; → element.
Fr.: élément trace, oligo-élément
Any → chemical element that is found in extremely small amounts, especially one used by organisms and held essential to maintain proper physical functioning.
Fr.: élément transuranien
An element beyond uranium in the periodic table, with atomic number greater than 92. Such elements do not occur in nature, but may be obtained by suitable nuclear reactions. They are all radioactive and members of the actinide group.
Fr.: élément volatile
In → planetary science, any of a group of → chemical elements and → chemical compounds with relatively low → boiling points that are associated with a planet's or moon's → crust and/or → atmosphere. For example, H, He, C, N, O are underabundant (relative to the solar → photospheric values) in all types of → meteorites, including the C1 → carbonaceous chondrites. Any heating of the meteorite parent body subsequent to its formation would tend to drive the volatile elements out of the rock, whence it sublimated into → interplanetary medium.