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Extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. [3] Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System.
These are asteroids in a near-Earth orbit without the tail or coma of a comet. As of December 2024, 37,255 near-Earth asteroids (NEAs) are known, 2,465 of which are both sufficiently large and may come sufficiently close to Earth to be classified as potentially hazardous. [1] NEAs survive in their orbits for just a few million years. [27]
Asteroids and comets visited by spacecraft as of 2019 (except Ceres and Vesta), to scale. NASA's Psyche, launched in October 2023, is intended to study the large metallic asteroid of the same name, and is on track to arrive there in 2029. ESA's Hera, launched in October 2024, is intended study the results of the DART impact. It is expected to ...
Outside the top four, the ranking of all the asteroids is uncertain, as there is a great deal of overlap among the estimates. The largest asteroids with an accurately measured mass, because they have been studied by the probe Dawn, are 1 Ceres with a mass of (939.3 ± 0.5) × 10 18 kg, and 4 Vesta at (259.076 ± 0.001) × 10 18 kg.
Periodic comets (also known as short-period comets) are comets with orbital periods of less than 200 years or that have been observed during more than a single perihelion passage [1] (e.g. 153P/Ikeya–Zhang). "Periodic comet" is also sometimes used to mean any comet with a periodic orbit, even if greater than 200 years.
Periodic comets usually have elongated elliptical orbits, and usually return to the vicinity of the Sun after a number of decades. The official names of non-periodic comets begin with a "C"; the names of periodic comets begin with "P" or a number followed by "P". Comets that have been lost or disappeared have names with a "D". Comets whose ...
Thus a probable candidate for the impactor is a carbonaceous asteroid, but a comet is also possible because comets are assumed to consist of material similar to carbonaceous chondrites. Probably the most convincing evidence for a worldwide catastrophe was the discovery of the crater which has since been named Chicxulub Crater.
These features were caused by the collision of meteors (consisting of large fragments of asteroids) or comets (consisting of ice, dust particles and rocky fragments) with the Earth. For eroded or buried craters, the stated diameter typically refers to the best available estimate of the original rim diameter, and may not correspond to present ...