|390 km (240 mi)
Tolstoj is a large, ancient impact crater on Mercury. It was named after Leo Tolstoy by the IAU in 1976.The albedo feature Solitudo Maiae appears to be associated with this crater.
The impact that produced the Tolstoj Basin occurred very early in the history of Mercury. Two ragged, discontinuous rings approximately 356 km and 510 km in diameter encompass the structure but are poorly developed on its north and northeast sides; a third partial ring with a diameter of 466 km occurs on its southeast side. Diffuse patches of material of dark albedo lie outside the innermost ring. The central part of the basin is covered by a high reflectance smooth plains (HRP) material. The bright interior of the basin is noticeably redder than the surrounding plains, which are made of a bluer low reflectance material (LRM). The dark annulus of ejecta around Tolstoj is one of the darkest places on the surface of Mercury.
The depth of Tolstoj is estimated to be 2.0 ± 0.7 km from the stereo derived digital elevation models based on Mariner 10 images of the planet. This is significantly less than the depth of lunar basins of the similar size indicating that Tolstoj probably has relaxed from its post impact shape.
The Tolstoj basin is used to define a time-stratigraphic system, the Tosltojan system, with the age of around 4.0–3.9 billion years. The older system (< 4.0 billion years) is called pre-Tosltojan, while the younger is called Calorian (3.9–3.5 billion years).
Despite Tolstoj's great age and its embayment by the ancient inter-crater plains, it retains an extensive and remarkably well preserved, radially lineated ejecta blanket around two-thirds of its circumference. Part of the ejecta was disrupted by the impact of the crater Liszt. The ejecta tends to be blocky and only weakly lineated between the inner and outer rings. Radial lineations with a slight swirly pattern are best seen on the southwest side of Tolstoj. The unusual rectilinear map pattern of the ejecta suggests: (1) control of the ejecta pattern by prebasin structures, (2) preferential burial along structural trends of an originally symmetrical ejecta blanket by the intercrater plains material, or (3) formation of Tolstoj by an oblique impact from the northwest that produced an ejecta blanket with bilateral symmetry and little or no deposition uprange. Analysis of stereophotography of Tolstoj ejecta northeast of the crater suggests that this deposit has been upwarped to a higher elevation relative to the surrounding plains.
Caloris Planitia is a plain within a large impact basin on Mercury, informally named Caloris, about 1,550 km (960 mi) in diameter. It is one of the largest impact basins in the Solar System. "Calor" is Latin for "heat" and the basin is so-named because the Sun is almost directly overhead every second time Mercury passes perihelion. The crater, discovered in 1974, is surrounded by the Caloris Montes, a ring of mountains approximately 2 km (1.2 mi) tall.
The geology of Mercury is the scientific study of the surface, crust, and interior of the planet Mercury. It emphasizes the composition, structure, history, and physical processes that shape the planet. It is analogous to the field of terrestrial geology. In planetary science, the term geology is used in its broadest sense to mean the study of the solid parts of planets and moons. The term incorporates aspects of geophysics, geochemistry, mineralogy, geodesy, and cartography.
An ejecta blanket is a generally symmetrical apron of ejecta that surrounds an impact crater; it is layered thickly at the crater's rim and thin to discontinuous at the blanket's outer edge. The impact cratering is one of the basic surface formation mechanisms of the solar system bodies and the formation and emplacement of ejecta blankets are the fundamental characteristics associated with impact cratering event. The ejecta materials are considered as the transported materials beyond the transient cavity formed during impact cratering regardless of the state of the target materials.
Odin Planitia is a large basin on Mercury. It was named after the Norse god Odin in 1976 by the IAU. It was first observed in detail by Mariner 10. The plain is approximately 473 kilometers in diameter.
Tir Planitia is a large plain on the planet Mercury. The name Tir (تیر) is the Persian word for "Mercury",, and the name was approved in 1976. It was first observed in detail by Mariner 10. It lies between the large crater Mozart and the ancient Tolstoj basin.
The Borealis quadrangle is a quadrangle on Mercury surrounding the north pole down to 65° latitude. It was mapped in its entirety by the MESSENGER spacecraft, which orbited the planet from 2008 to 2015, excluding areas of permanent shadow near the north pole. Only approximately 25% of the quadrangle was imaged by the Mariner 10 spacecraft during its flybys in 1974 and 1975. The quadrangle is now called H-1.
Goethe Basin is an impact basin at 81.4° N, 54.3° W on Mercury approximately 317 kilometers in diameter. It is named after German poet Johann Wolfgang von Goethe.
The Victoria quadrangle is a region on Mercury from 0 to 90° longitude and 20 to 70 ° latitude. It is designated the "H-2" quadrangle, and is also known as Aurora after a large albedo feature.
The Tolstoj quadrangle in the equatorial region of Mercury runs from 144 to 216° longitude and -25 to 25° latitude. It was provisionally called "Tir", but renamed after Leo Tolstoy by the International Astronomical Union in 1976. Also called Phaethontias.
The Shakespeare quadrangle is a region of Mercury running from 90 to 180° longitude and 20 to 70° latitude. It is also called Caduceata.
The Caloris group is a set of geologic units on Mercury. McCauley and others have proposed the name “Caloris Group” to include the mappable units created by the impact that formed the Caloris Basin and have formally named four formations within the group, which were first recognized and named informally by Trask and Guest.
The Kuiper quadrangle, located in a heavily cratered region of Mercury, includes the young, 55-km-diameter crater Kuiper, which has the highest albedo recorded on the planet, and the small crater Hun Kal, which is the principal reference point for Mercurian longitude. Impact craters and basins, their numerous secondary craters, and heavily to lightly cratered plains are the characteristic landforms of the region. At least six multiringed basins ranging from 150 km to 440 km in diameter are present. Inasmuch as multiringed basins occur widely on that part of Mercury photographed by Mariner 10, as well as on the Moon and Mars, they offer a potentially valuable basis for comparison between these planetary bodies.
The Bach quadrangle encompasses the south polar part of Mercury poleward of latitude 65° S. It is named after the prominent crater Bach within the quadrangle, which is in turn named after Baroque composer Johann Sebastian Bach. The quadrangle is now called H-15.
The Beethoven quadrangle is located in the equatorial region of Mercury, in the center of the area imaged by Mariner 10. Most pictures of the quadrangle were obtained at high sun angles as the Mariner 10 spacecraft receded from the planet. Geologic map units are described and classified on the basis of morphology, texture, and albedo, and they are assigned relative ages based on stratigraphic relations and on visual comparisons of the density of superposed craters. Crater ages are established by relative freshness of appearance, as indicated by topographic sharpness of their rim crests and degree of preservation of interior and exterior features such as crater floors, walls, and ejecta aprons. Generally, topography appears highly subdued because of the sun angle, and boundaries between map units are not clearly defined.
Beethoven is a crater at latitude 20°S, longitude 124°W on Mercury. It is 630 km in diameter and was named after Ludwig van Beethoven. It is the eleventh largest named impact crater in the Solar System and the third largest on Mercury.
The Discovery quadrangle lies within the heavily cratered part of Mercury in a region roughly antipodal to the 1550-km-wide Caloris Basin. Like the rest of the heavily cratered part of the planet, the quadrangle contains a spectrum of craters and basins ranging in size from those at the limit of resolution of the best photographs to those as much as 350 km across, and ranging in degree of freshness from pristine to severely degraded. Interspersed with the craters and basins both in space and time are plains deposits that are probably of several different origins. Because of its small size and very early segregation into core and crust, Mercury has seemingly been a dead planet for a long time—possibly longer than the Moon. Its geologic history, therefore, records with considerable clarity some of the earliest and most violent events that took place in the inner Solar System.
The Michelangelo quadrangle is in the southern hemisphere of the planet Mercury, where the imaged part is heavily cratered terrain that has been strongly influenced by the presence of multiring basins. At least four such basins, now nearly obliterated, have largely controlled the distribution of plains materials and structural trends in the map area. Many craters, interpreted to be of impact origin, display a spectrum of modification styles and degradation states. The interaction between basins, craters, and plains in this quadrangle provides important clues to geologic processes that have formed the morphology of the mercurian surface.
Eminescu is a peak ring crater on Mercury 125 kilometers (78 mi) in diameter. Since there are very few later craters superposed on it, Eminescu appears to be a young crater formed around one billion years ago. It has a transitional morphology between larger more complex impact basins like Raditladi and smaller simpler central peak craters.
Raditladi is a large impact crater on Mercury with a diameter of 263 km. Inside its peak ring there is a system of concentric extensional troughs (graben), which are rare surface features on Mercury. The floor of Raditladi is partially covered by relatively light smooth plains, which are thought to be a product of the effusive volcanism. The troughs may also have resulted from volcanic processes under the floor of Raditladi. The basin is relatively young, probably younger than one billion years, with only a few small impact craters on its floor and with well-preserved basin walls and peak-ring structure. It is one of 110 peak ring basins on Mercury.