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The main difference between an asteroid and a comet is that a comet shows a coma (tail) due to sublimation of its near-surface ices by solar radiation. A few objects were first classified as minor planets but later showed evidence of cometary activity.
A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing.This produces an extended, gravitationally unbound atmosphere or coma surrounding the nucleus, and sometimes a tail of gas and dust gas blown out from the coma.
Astronomical objects such as stars, planets, nebulae, asteroids and comets have been observed for thousands of years, although early cultures thought of these bodies as gods or deities. These early cultures found the movements of the bodies very important as they used these objects to help navigate over long distances, tell between the seasons ...
Astronomers posed over the past decade that dark comets, or objects that resemble asteroids but move like comets, may exist. Now, scientists have found a total of 14 of them.
The "speed" at which a planet goes around the Sun, in terms of revolutions per time, is given by the inverse of its period, and the speed difference between two planets is the difference between these. Since the time interval between two oppositions is the time it takes for 360° to be covered by that speed difference, the average interval is:
2I/Borisov comet, the second confirmed interstellar object, photographed in late-2019 beside a distant galaxy. An interstellar object is an astronomical object (such as an asteroid, a comet, or a rogue planet, but not a star or stellar remnant) in interstellar space that is not gravitationally bound to a star.
A small Solar System body can be an asteroid or a comet, thus an NEO is either a near-Earth asteroid (NEA) or a near-Earth comet (NEC). The organisations cataloging NEOs further limit their definition of NEO to objects with an orbital period under 200 years, a restriction that applies to comets in particular, [ 2 ] [ 26 ] but this approach is ...
The asteroid and comet belts orbit the Sun from the inner rocky planets into outer parts of the Solar System, interstellar space. [16] [17] [18] An astronomical unit, or AU, is the distance from Earth to the Sun, which is approximately 150 billion meters (93 million miles). [19] Small Solar System objects are classified by their orbits: [20] [21]