An asteroid is a minor planet—an object that is neither a true planet nor a comet—that orbits within the inner Solar System. They are rocky, metallic, or icy bodies with no atmosphere. The size and shape of asteroids vary significantly, ranging from small rubble piles under a kilometer across to Ceres, a dwarf planet almost 1000 km in diameter.
Vesta is one of the largest objects in the asteroid belt, with a mean diameter of 525 kilometres (326 mi). It was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 29 March 1807 and is named after Vesta, the virgin goddess of home and hearth from Roman mythology.
Pallas is the second asteroid to have been discovered, after Ceres. Like Ceres, it is believed to have a mineral composition similar to carbonaceous chondrite meteorites, though significantly less hydrated than Ceres. It is the third-largest asteroid in the Solar System by both volume and mass, and is a likely remnant protoplanet. It is 79% the mass of Vesta and 22% the mass of Ceres, constituting an estimated 7% of the mass of the asteroid belt. Its estimated volume is equivalent to a sphere 507 to 515 kilometers in diameter, 90–95% the volume of Vesta.
A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate, rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, Venus, Earth and Mars. Among astronomers who use the geophysical definition of a planet, two or three planetary-mass satellites – Earth's Moon, Io, and sometimes Europa – may also be considered terrestrial planets. The large rocky asteroids Pallas and Vesta are sometimes included as well, albeit rarely. The terms "terrestrial planet" and "telluric planet" are derived from Latin words for Earth, as these planets are, in terms of structure, Earth-like. Terrestrial planets are generally studied by geologists, astronomers, and geophysicists.
Dawn is a retired space probe that was launched by NASA in September 2007 with the mission of studying two of the three known protoplanets of the asteroid belt: Vesta and Ceres. In the fulfillment of that mission—the ninth in NASA's Discovery Program—Dawn entered orbit around Vesta on July 16, 2011, and completed a 14-month survey mission before leaving for Ceres in late 2012. It entered orbit around Ceres on March 6, 2015. In 2017, NASA announced that the planned nine-year mission would be extended until the probe's hydrazine fuel supply was depleted. On November 1, 2018, NASA announced that Dawn had depleted its hydrazine, and the mission was ended. The derelict probe remains in a stable orbit around Ceres.
A cryovolcano is a type of volcano that erupts gasses and volatile material such as liquid water, ammonia, and hydrocarbons, collectively referred to as cryolava, from a reservoir of subsurface cryomagma. These eruptions can take many forms, such as fissure and curtain eruptions, effusive cryolava flows, and large-scale resurfacing, and can vary greatly in output volumes. Immediately after an eruption, cryolava quickly freezes, constructing geological features and altering the surface.
The geology of Pluto consists of the characteristics of the surface, crust, and interior of Pluto. Because of Pluto's distance from Earth, in-depth study from Earth is difficult. Many details about Pluto remained unknown until 14 July 2015, when New Horizons flew through the Pluto system and began transmitting data back to Earth. When it did, Pluto was found to have remarkable geologic diversity, with New Horizons team member Jeff Moore saying that it "is every bit as complex as that of Mars". The final New Horizons Pluto data transmission was received on 25 October 2016. In June 2020, astronomers reported evidence that Pluto may have had a subsurface ocean, and consequently may have been habitable, when it was first formed.
In astronomy or planetary science, the frost line, also known as the snow line or ice line, is the minimum distance from the central protostar of a solar nebula where the temperature is low enough for volatile compounds such as water, ammonia, methane, carbon dioxide and carbon monoxide to condense into solid grains, which will allow their accretion into planetesimals. Beyond the line, otherwise gaseous compounds can be quite easily condensed to allow formation of gas and ice giants; while within it, only heavier compounds can be accreted to form the typically much smaller rocky planets.
Ceres is a dwarf planet in the middle main asteroid belt between the orbits of Mars and Jupiter. It was the first known asteroid, discovered on 1 January 1801 by Giuseppe Piazzi at Palermo Astronomical Observatory in Sicily, and announced as a new planet. Ceres was later classified as an asteroid and then a dwarf planet, the only one always inside Neptune's orbit.
A dwarf planet is a small planetary-mass object that is in direct orbit around the Sun, massive enough to be gravitationally rounded, but insufficient to achieve orbital dominance like the eight classical planets of the Solar System. The prototypical dwarf planet is Pluto, which for decades was regarded as a planet before the "dwarf" concept was adopted in 2006.
Extraterrestrial liquid water is water in its liquid state that naturally occurs outside Earth. It is a subject of wide interest because it is recognized as one of the key prerequisites for life as we know it and is thus surmised to be essential for extraterrestrial life.
The geology of solar terrestrial planets mainly deals with the geological aspects of the four terrestrial planets of the Solar System – Mercury, Venus, Earth, and Mars – and one terrestrial dwarf planet: Ceres. Earth is the only terrestrial planet known to have an active hydrosphere.
Sotra Patera is a prominent depression on Titan, the largest moon of Saturn. It was formerly known as Sotra Facula; the current name was approved on 19 December 2012. It is a possible cryovolcanic caldera 30 km (19 mi) across and 1.7 km (1.1 mi) deep, and is immediately to the east of the largest putative cryovolcanic mountain on Titan, the 1.45 km (0.90 mi) high Doom Mons. Sotra Patera is the deepest known pit on Titan.
A planetary surface is where the solid or liquid material of certain types of astronomical objects contacts the atmosphere or outer space. Planetary surfaces are found on solid objects of planetary mass, including terrestrial planets, dwarf planets, natural satellites, planetesimals and many other small Solar System bodies (SSSBs). The study of planetary surfaces is a field of planetary geology known as surface geology, but also a focus on a number of fields including planetary cartography, topography, geomorphology, atmospheric sciences, and astronomy. Land is the term given to non-liquid planetary surfaces. The term landing is used to describe the collision of an object with a planetary surface and is usually at a velocity in which the object can remain intact and remain attached.
Several bright surface features were discovered on the dwarf planet Ceres by the Dawn spacecraft in 2015.
Ahuna Mons is the largest mountain on the dwarf planet and asteroid Ceres. It protrudes above the cratered terrain, is not an impact feature, and is the only mountain of its kind on Ceres. Bright streaks run top to bottom on its slopes which are thought to be salt, similar to the better known Cererian bright spots, and likely resulted from cryovolcanic activity from Ceres's interior. It is named after the traditional post-harvest festival Ahuna of the Sümi Naga people of India. In July 2018, NASA released a comparison of physical features, including Ahuna Mons, found on Ceres with similar ones present on Earth.
Kerwan is the largest confirmed crater and one of the largest geological features on Ceres. It was discovered on February 19, 2015 from Dawn images as it approached Ceres. The crater is distinctly shallow for its size, and lacks a central peak. A central peak might have been destroyed by a 15-kilometer-wide crater at the center of Kerwan. The crater is likely to be young relative to the rest of Ceres's surface, as Kerwan has largely obliterated the cratering in the southern part of Vendimia Planitia.
Lynnae C. Quick is an American planetary geophysicist and Ocean Worlds Planetary Scientist at NASA Goddard Space Flight Center. Her research centers on theoretical modeling of cryovolcanic processes on the icy moons and dwarf planets in the Solar System as well as modeling volcanic activity on Venus and the Moon. Quick is a member of the Dawn, Europa Clipper, and Dragonfly Mission science teams. She is also a member of the NASA Solar System Exploration Research Virtual Institute (SSERVI) Toolbox for Research and Exploration (TREX) team, and serves as co-chair of the Earth and Planetary Systems Sciences section of the National Society of Black Physicists.
