An Etymological Dictionary of Astronomy and Astrophysics
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A → European Space Agency (ESA) program to investigate the Martian environment and to demonstrate new technologies paving the way for a future Mars sample return mission in the 2020's. Two missions are foreseen: one consisting of an Orbiter plus an Entry, Descent and Landing Demonstrator Module (EDM), launched in 2016, and the other, featuring a rover, with a launch date of 2018. Both missions will be carried out in cooperation with Russia's Roscosmos space agency. The ExoMars program will demonstrate a number of essential flight and in-situ enabling technologies that are necessary for future exploration missions, such as an international Mars Sample Return mission. At the same time, a number of important scientific investigations will be carried out. The 2016 mission included a Trace Gas Orbiter (TGO) and an EDM. The Orbiter will carry scientific instruments to detect and study atmospheric trace gases, such as methane. The EDM will contain sensors to evaluate the lander's performance as it descends, and additional sensors to study the environment at the landing site. The 2018 mission includes a rover that will carry a drill and a suite of instruments dedicated to exobiology and geochemistry research.

ExoMars, short for "→ exobiology on → Mars."

The first functioning → reflecting telescope with a silvered glass mirror. It was built by Léon Foucault in 1826 for the Marseille Observatory. The mirror of 80-cm in diameter (f/d = 5) had an excellent quality. The telescope was used for a century as a visual instrument. Edouard Stéphan (1837-1923) used it from 1871 to 1884 to find 800 high-brightness galaxies, among which the → Stephan's Quintet. From 1906 to 1962 the telescope was used by Robert Jonckheere (1888-1927) to discover 3,350 new binary stars. In 1873, following an idea of Hippolyte Fizeau (1819-1896), Stéphan attempted to use it as an → interferometer to measure the diameter of a number of stars. In 1914 Charles Fabry (1867-1945) and Henri Buisson (1873-1944) used the telescope to obtain the first astronomical Fabry-Pérot interferogram, on the → Orion Nebula.

After the French physicist and optician Léon Foucault (1819-1868); Marseille (Observatory), the second largest city of France, located on the south east coast of the Mediterranean Sea, from L. Massalia, from Gk. Massalia; → reflector.

Fourth planet from Sun and the seventh largest. Mass 6.42 × 10²⁶ g (0.11 Earth's), radius 3397 km. Mean distance from Sun 1.52 → astronomical units. → Sidereal period 687 days, → synodic period 779.9 days. Surface temperature 248 K., → rotation period, or → sol, 24h37m22s.6. Mars' → obliquity is currently 25.19 degrees, but has changed dramatically over billions of years since solar system formation. Atmosphere more than 90% CO₂, traces of O₂, CO, H₂O. Two tiny satellites (→ Phobos and → Deimos), both of which are locked in → synchronous rotation with Mars.

Late M.E., from L. Mars the Roman god of war, Ares in Gk. mythology.

Bahrâm, from Mid.Pers. Vahrâm, from Vahrân "god of victory," from Av. vərəθraγna- "victory, breaking the defence, the god of victory." The first element vərəθra- "shield, defensive power," cf. Skt. vrtrá- "defence, name of a demon slain by Indra," Arm. vahagan name of a god (loanword from Iranian). The second element γna-, from Av., also O.Pers., jan-, gan- "to strike, hit, smite, kill" (jantar- "smiter"); cf. Mod.Pers. zadan, zan- "to strike, beat;" Mid.Pers. zatan, žatan; Skt. han- "to strike, beat" (hantar- "smiter, killer"); Gk. theinein "to strike," phonos "murder;" L. fendere "to strike, push;" Gmc. *gundjo "war, battle;" PIE *g^when- "to strike, kill."

The → zero point of elevation on Mars. It is the elevation at which the atmosphere pressure is 6.1 millibars, or 610 → Pascals. Atmosphere pressure has to be used because Mars has no ocean, and "sea level" cannot be used like on Earth. More formally, the datum is a fourth-order, fourth-degree surface of equal → gravitational potential (determined from the Viking orbiter spacecraft) such that the pressure of the atmosphere is 6.1 millibars (source: Lunar and Planetary Institute, USRA).

→ Mars; → datum.

A member of the family of → asteroids located at either of the stable → Lagrangian points (L4 or L5) of the orbit of → Mars.

→ Mars; → Trojan asteroid.

A special calendar for time reckoning on Mars in which the year consists of 668 → sols (687 Earth days) and each sol has 24h 39m 35s. For convenience, sols are divided into a 24-hour clock. Each landed Mars mission keeps track of local solar time at its landing site, which depends upon the lander's longitude of Mars. The Martian year begins when Mars arrives at the → vernal point of the orbit in its northward journey; in other words, when the solar longitude Ls is 0°. Mars' other seasons begin when Ls = 90° at → summer solstice, 180° at → autumn equinox, and 270° at → winter solstice. The year counts begin at Mars Year 1, at the northern → vernal equinox of April 11, 1955. The second half of that year was marked by a major dust storm (→ Mars' dust storm). February 7, 2021 marked the start of Year 36 on Mars. Year 37 will start on Dec. 26, 2022, and Year 38 on Nov. 12, 2024. On Earth, spring, summer, autumn, and winter are all similar in length, because Earth's orbit is nearly circular (→ eccentricity = 0.0167), so it moves at nearly constant speed around the Sun. By contrast, Mars' elliptical orbit (→ eccentricity = 0.0934) makes its distance from the Sun change with time, and also makes it speed up and slow down in its orbit. Mars is at → aphelion (249,200,000 km from Sun) at Ls = 70°, near the northern summer solstice, and at → perihelion (206,700,000 km) at Ls = 250°, near the southern summer solstice. The Mars dust storm season begins just after perihelion at around Ls = 260°.

→ Mars; → calendar.

A violent atmospheric disturbance on Mars marked by high amounts of dust, especially during spring and summer seasons of the planet southern hemisphere. The elongated orbit of Mars has several important consequences. During southern spring and summer, Mars travels near its → perihelion, while its southern pole is tilted toward the Sun. Therefore, its surface receives much more heat . The atmosphere's temperature near surface raises and since the upper layers of the atmosphere are cold, warm air moves up and takes dust particles upward. Each several years big storms occur and cover significant portions of the planet such that dust stays in the atmosphere for several weeks or months. See also → Mars' calendar.

→ Mars; → dust; → storm.

A quake on the → planet Mars, probably caused by some phenomena other than → tectonic plate motions. Unlike Earth, Mars seems to lack tectonic plates. Therefore, its quakes are thought to arise from the slow cooling of the planet over time, which causes the → crust to contract and develop fractures. These quakes can also come from the impact of → meteorites and possibly the movement of → magma deep below the surface. On April 6, 2019, the instrument called Seismic Experiment for Interior Structure (SEIS) on NASA's Mars → InSight Mission lander recorded quakes that appear to have come from inside the planet, the first time ever a likely marsquake.

→ Mars; → quake.