Asteroid headed towards Earth -Impacting the Earth

 

A huge asteroid is coming to earth.so we must understand about  An asteroid. Asteroid headed towards Earth may arrive on Valentine's Day 2046 - Nasa. Image caption, Asteroid 2023 DW has a better chance of hitting a date of 14 February than our planet, NASA says. A newly detected asteroid has a very small chance of impacting the Earth in 2046, Nasa tweeted.

An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. 

Of the roughly one million known asteroids the greatest number are located between the orbits of Mars and Jupiter, approximately 2 to 4 AU from the Sun, in the main asteroid belt. Asteroids are generally classified to be of three types: C-type, M-type, and S-type. These were named after and are generally identified with carbonaceous, metallic, and silicaceous compositions, respectively. The size of asteroids varies greatly; the largest, Ceres, is almost 1,000 km (600 mi) across and qualifies as a dwarf planet. The total mass of all the asteroids combined is only 3% that of Earth's Moon. The majority of main belt asteroids follow slightly elliptical, stable orbits, revolving in the same direction as the Earth and taking from three to six years to complete a full circuit of the Sun.

Asteroids have been historically observed from Earth; the Galileo spacecraft provided the first close observation of an asteroid. Several dedicated missions to asteroids were subsequently launched by NASA and JAXA, with plans for other missions in progress. NASA's NEAR Shoemaker studied Eros, and Dawn observed Vesta and Ceres. JAXA's missions Hayabusa and Hayabusa2 studied and returned samples of Itokawa and Ryugu, respectively. OSIRIS-REx studied Bennu, collecting a sample in 2020 to be delivered back to Earth in 2023. NASA's Lucy, launched in 2021, will study ten different asteroids, two from the main belt and eight Jupiter trojans. Psyche, scheduled for launch in 2023, will study a metallic asteroid of the same name.

Near-Earth asteroids can threaten all life on the planet; an asteroid impact event resulted in the Cretaceous–Paleogene extinction. Different asteroid deflection strategies have been proposed; the Double Asteroid Redirection Test spacecraft, or DART, was launched in 2021 and intentionally impacted Dimorphos in September 2022, successfully altering its orbit by crashing into it.

The first discovered asteroid, Ceres, was originally considered a new planet. It was followed by the discovery of other similar bodies, which with the equipment of the time appeared to be points of light like stars, showing little or no planetary disc, though readily distinguishable from stars due to their apparent motions. This prompted the astronomer Sir William Herschel to propose the term asteroid, coined in Greek as ἀστεροειδής, or asteroeidēs, meaning 'star-like, star-shaped', and derived from the Ancient Greek ἀστήρ astēr 'star, planet'. In the early second half of the 19th century, the terms asteroid and planet (not always qualified as "minor") were still used interchangeably.

Traditionally, small bodies orbiting the Sun were classified as comets, asteroids, or meteoroids, with anything smaller than one meter across being called a meteoroid. The term asteroid never had a formal definition,[28] with the broader term small Solar System bodies being preferred by the International Astronomical Union (IAU). As no IAU definition exists, asteroid can be defined as "an irregularly shaped rocky body orbiting the Sun that does not qualify as a planet or a dwarf planet under the IAU definitions of those terms".

When found, asteroids were seen as a class of objects distinct from comets, and there was no unified term for the two until small Solar System body was coined in 2006. The main difference between an asteroid and a comet is that a comet shows a coma due to sublimation of near-surface ices by solar radiation. A few objects have ended up being dual-listed because they were first classified as minor planets but later showed evidence of cometary activity. Conversely, some (perhaps all) comets are eventually depleted of their surface volatile ices and become asteroid-like. A further distinction is that comets typically have more eccentric orbits than most asteroids; "asteroids" with notably eccentric orbits are probably dormant or extinct comets.

For almost two centuries, from the discovery of Ceres in 1801 until the discovery of the first centaur, 2060 Chiron in 1977, all known asteroids spent most of their time at or within the orbit of Jupiter, though a few such as 944 Hidalgo ventured far beyond Jupiter for part of their orbit. When astronomers started finding more small bodies that permanently resided further out than Jupiter, now called centaurs, they numbered them among the traditional asteroids. There was debate over whether these objects should be considered asteroids or given a new classification. Then, when the first trans-Neptunian object (other than Pluto), 15760 Albion, was discovered in 1992, and especially when large numbers of similar objects started turning up, new terms were invented to sidestep the issue: Kuiper-belt object, trans-Neptunian object, scattered-disc object, and so on. They inhabit the cold outer reaches of the Solar System where ices remain solid and comet-like bodies are not expected to exhibit much cometary activity; if centaurs or trans-Neptunian objects were to venture close to the Sun, their volatile ices would sublimate, and traditional approaches would classify them as comets and not asteroids.

The innermost of these are the Kuiper-belt objects, called "objects" partly to avoid the need to classify them as asteroids or comets. They are thought to be predominantly comet-like in composition, though some may be more akin to asteroids. Furthermore, most do not have the highly eccentric orbits associated with comets, and the ones so far discovered are larger than traditional comet nuclei. (The much more distant Oort cloud is hypothesized to be the main reservoir of dormant comets.) Other recent observations, such as the analysis of the cometary dust collected by the Stardust probe, are increasingly blurring the distinction between comets and asteroids, suggesting "a continuum between asteroids and comets" rather than a sharp dividing line.

The minor planets beyond Jupiter's orbit are sometimes also called "asteroids", especially in popular presentations. However, it is becoming increasingly common for the term asteroid to be restricted to minor planets of the inner Solar System. Therefore, this article will restrict itself for the most part to the classical asteroids: objects of the asteroid belt, Jupiter trojans, and near-Earth objects.

When the IAU introduced the class small Solar System bodies in 2006 to include most objects previously classified as minor planets and comets, they created the class of dwarf planets for the largest minor planets – those that have enough mass to have become ellipsoidal under their own gravity. According to the IAU, "the term 'minor planet' may still be used, but generally, the term 'Small Solar System Body' will be preferred." Currently only the largest object in the asteroid belt, Ceres, at about 975 km (606 mi) across, has been placed in the dwarf planet category.