Mercury is the first planet from the Sun and the smallest in the Solar System. In English, it is named after the Roman god Mercurius (Mercury), god of commerce and communication, and the messenger of the gods. Mercury is classified as a terrestrial planet, with roughly the same surface gravity as Mars. The surface of Mercury is heavily cratered, as a result of countless impact events that have accumulated over billions of years. Its largest crater, Caloris Planitia, has a diameter of 1,550 km (960 mi) and one-third the diameter of the planet. Similarly to the Earth's Moon, Mercury's surface displays an expansive rupes system generated from thrust faults and bright ray systems formed by impact event remnants.
Chao Meng-Fu is a 167 km (104 mi) diameter crater on Mercury named after the Chinese painter and calligrapher Zhao Mengfu (1254–1322). Due to its location near Mercury's south pole and the planet's small axial tilt, an estimated 40% of the crater lies in permanent shadow. This combined with bright radar echoes from the location of the crater leads scientists to suspect that it may shelter large quantities of ice protected against sublimation into the near-vacuum by the constant −171 °C (−276 °F) temperatures.
Scalloped topography is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is particularly prominent in the region of Utopia Planitia, in the northern hemisphere, and in the region of Peneus and Amphitrites Paterae in the southern hemisphere. Such topography consists of shallow, rimless depressions with scalloped edges, commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. A typical scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp. This topographic asymmetry is probably due to differences in insolation. Scalloped depressions are believed to form from the removal of subsurface material, possibly interstitial ice, by sublimation. This process may still be happening at present. This topography may be of great importance for future colonization of Mars because it may point to deposits of pure ice.
Hokusai is a rayed impact crater on Mercury, which was discovered in 1991 by ground-based radar observations conducted at Goldstone Observatory. The crater was initially known as feature B. Its appearance was so dissimilar to other impact craters that it was once thought to be a shield volcano. However improved radar images by the Arecibo Observatory obtained later in 2000–2005 clearly showed that feature B is an impact crater with an extensive ray system. The bright appearance of rays in the radio images indicates that the crater is geologically young; fresh impact ejecta has a rough surface, which leads to strong scattering of radio waves.
Protonilus Mensae is an area of Mars in the Ismenius Lacus quadrangle. It is centered on the coordinates of 43.86° N and 49.4° E. Its western and eastern longitudes are 37° E and 59.7° E. North and south latitudes are 47.06° N and 39.87° N. Protonilus Mensae is between Deuteronilus Mensae and Nilosyrtis Mensae; all lie along the Martian dichotomy boundary. Its name was adapted by the IAU in 1973.
Nilosyrtis Mensae is an area of Mars in the Casius quadrangle. It is centered on the coordinates of 36.87° N and 67.9° E. Its western and eastern longitudes are 51.1° E and 74.4° E. North and south latitudes are 36.87° N and 29.61° N. Nilosyrtis Mensae is just to the east of Protonilus Mensae and both lie along the Martian dichotomy boundary. Its name was adapted by the IAU in 1973. It was named after a classical albedo feature, and it is 705 km (438 mi) across.
The planet Mars has two permanent polar ice caps. During a pole's winter, it lies in continuous darkness, chilling the surface and causing the deposition of 25–30% of the atmosphere into slabs of CO2 ice (dry ice). When the poles are again exposed to sunlight, the frozen CO2 sublimes. These seasonal actions transport large amounts of dust and water vapor, giving rise to Earth-like frost and large cirrus clouds.
Despréz is a crater on Mercury with a diameter of 47.05 kilometers. Its name was adopted by the International Astronomical Union (IAU) in 1979. Despréz is named for the French composer Josquin des Prez, who lived from 1440 to 1521.
A permanently shadowed crater is a depression on a body in the Solar System within which lies a point that is always in darkness.
Planetary oceanography also called astro-oceanography or exo-oceanography is the study of oceans on planets and moons other than Earth. Unlike other planetary sciences like astrobiology, astrochemistry and planetary geology, it only began after the discovery of underground oceans in Saturn's moon Titan and Jupiter's moon Europa. This field remains speculative until further missions reach the oceans beneath the rock or ice layer of the moons. There are many theories about oceans or even ocean worlds of celestial bodies in the Solar System, from oceans made of diamond in Neptune to a gigantic ocean of liquid hydrogen that may exist underneath Jupiter's surface.
Tolkien is one of the northernmost craters on Mercury, located in the Borealis quadrangle at 88.82 N, 211.08 W. It is 50 km in diameter. It was named after the South African born British writer J. R. R. Tolkien. The name was approved by IAU's Working Group for Planetary System Nomenclature on August 6, 2012. Since Tolkien is very close to the north pole, and Mercury has almost no axial tilt, Tolkien receives very little sunlight. S band radar data from the Arecibo Observatory collected between 1999 and 2005 indicates a radar-bright area covers the entire floor of Tolkien, which is probably indicative of a water ice deposit.
Carolan is a crater on Mercury. Its name was suggested by an Irishman, Fergal Donnelly, and two Americans, Joseph Brusseau and Deane Morrison, in a naming contest which was eventually adopted by the International Astronomical Union (IAU) on 2015. Carolan is named for the Irish composer and performer Turlough O'Carolan, who lived from 1670 to 1738 C.E. The craters Kulthum, Enheduanna, Karsh, and Rivera were also named as part of the contest.
Vonnegut is a crater on Mercury, near the north pole. It was named by the IAU in 2017 after the American author Kurt Vonnegut. Part of Vonnegut's 1959 novel The Sirens of Titan takes place on Mercury. The crater was referred to as e5 in scientific literature prior to naming.
Yoshikawa is a crater on Mercury, near the north pole. It was named by the IAU in 2012 after the Japanese novelist Eiji Yoshikawa.
Tryggvadóttir is a crater on Mercury. The north pole of Mercury is located next to its northern rim. It was named by the IAU in 2012 after the Icelandic artist Nína Tryggvadóttir.
Chesterton is a crater on Mercury, near the north pole. Its name was adopted by the International Astronomical Union in 2012, after the English author G. K. Chesterton.
Gordimer is a crater on Mercury, near the north pole. Its name was adopted by the International Astronomical Union (IAU) in 2019, after the South African writer Nadine Gordimer.
Remarque is a crater on Mercury. Its name was adopted by the International Astronomical Union (IAU) on December 16, 2013. Remarque is named for the German author Erich Maria Remarque.
Petronius is a crater on Mercury. It has a diameter of 36 kilometres. Its name was adopted by the International Astronomical Union (IAU) on the August 6, 2012. Petronius is named for the Roman author Petronius.
Morrison is a crater on Mercury. Its name was adopted by the International Astronomical Union in September 2022. Morrison is named for the American author Toni Morrison, who lived from 1931 to 2019.
