Amor Asteroids
Amor asteroids are a specific category of near-Earth asteroids (NEAs) that follow elliptical orbits around the sun, typically crossing the path of Mars but not that of Earth. They are part of a broader group of near-Earth objects (NEOs), which also includes comets, and are considered remnants from the solar system's formation approximately 4.6 billion years ago. Composed mostly of rock, these asteroids can vary significantly in size and are identifiable by their distinctive orbital characteristics. An estimated 1,500 Amor asteroids have been cataloged, making up about 32 percent of all known NEAs.
Scientists study Amor asteroids due to their potential to provide insights into the early solar system and to assess any risks they may pose to Earth. While smaller meteors frequently enter Earth's atmosphere, larger NEA collisions have occurred in the past, such as the one that formed the Chicxulub crater, linked to the mass extinction of dinosaurs. Recent advancements in space exploration, including robotic missions by NASA, aim to deepen our understanding of these celestial bodies and enhance monitoring systems to track potential threats.
Amor Asteroids
FIELDS OF STUDY: Astronomy; Observational Astronomy; Cosmology
ABSTRACT: Amor asteroids are a type of near-Earth asteroid (NEA) that often cross the orbit of Mars as they travel an elliptical path around the sun. Their orbits are sometimes large enough to extend beyond Jupiter. Although Amor asteroids travel close to Earth, they do not cross its orbit.
Near-Earth Asteroids
Amor asteroids are small, irregularly shaped space objects that follow an elliptical orbit around the sun. Their orbital paths often cross that of Mars. Amor asteroids are a type of near-Earth asteroid (NEA), which are asteroids that come within 0.3 AU (about 44.8 million kilometers, or 28 million miles) of Earth. Amor asteroids are unique among NEAs because although they travel close to Earth, they do not cross its orbit.
The solar system contains millions of asteroids. Most of these are found within the asteroid belt, a doughnut-shaped ring located between the orbits of Mars and Jupiter, about 2 to 4 AU (300 to 600 million kilometers) from the sun. However, not all asteroids stay within the asteroid belt. For example, if two asteroids collide, one or both of them can be pushed out of the belt and into the larger solar system. Similarly, an encounter with the immense gravity around Jupiter, the largest planet, can also fling an asteroid out into space. When such asteroids end up orbiting close to Earth and the sun, they are referred to as NEAs.
NEAs belong to the category of space objects known as near-Earth objects (NEOs). NEOs include both comets and asteroids that have been pulled near the solar system’s four inner planets—Mercury, Venus, Earth, and Mars—by the force of gravity.
Amor Asteroid Characteristics
Asteroids are composed mainly of rock but may also include clay, minerals, and metals. Their outer surfaces are full of visible pits and craters, which scientists believe are the result of collisions with other objects in space. Asteroids vary greatly in size. The largest known asteroid, Ceres, measures about 940 kilometers (nearly 600 miles) in diameter. Most asteroids are much smaller; in fact, many are only the size of small rocks.
NEAs can be distinguished from one another by characteristics such as their average distance from the sun and the size and shape of their orbital paths. Amor asteroids can be identified through their distinct orbital paths, which often cross the orbital path of Mars but do not cross that of Earth. Some Amor asteroids have such wide orbits that they travel beyond Jupiter.
Astronomers have identified about fifteen hundred Amor asteroids in the solar system. These objects make up about 32 percent of all known NEAs. Additionally, the gravitational forces that surround Earth and Mars may capture some Amor asteroids. When this occurs, scientists believe these asteroids change paths and evolve into Apollo asteroids, which are asteroids that cross the orbits of both Earth and Mars.
NEA Impacts on Earth
Scientists are interested in Amor asteroids and other NEAs because they are thought to be leftover debris from the formation of the solar system about 4.6 billion years ago. They can provide valuable information about what happened at this time. Additionally, about 20 percent of NEAs come close enough to Earth to raise concerns about potential collisions. Although smaller space objects such as meteors collide with Earth frequently, these objects are usually small enough to burn up in Earth’s atmosphere before reaching the planet’s surface.
However, major collisions between Earth and NEAs have occurred. For example, a huge crater near Chicxulub, Mexico, is believed to be evidence of a past collision between Earth and a large NEA. Many experts believe this collision, which probably had the force of a nuclear explosion, played a major role in the Cretaceous-Tertiary mass extinction sixty-five million years ago, during which dinosaurs and other large life-forms on the planet died out.
Other NEAs have collided with Earth more recently. For example, in February 2013, a relatively small NEA exploded over Russia, releasing the energy of a large atomic bomb.
Asteroid Missions
In the twenty-first century, the National Aeronautics and Space Administration (NASA) and its international counterparts have focused on robotic missions. These missions involve sending unmanned spacecraft into the solar system to learn more about space objects. The NEAR Shoemaker mission, for example, landed on Amor asteroid 433 Eros in February 2001. This spacecraft sent valuable data back to Earth, furthering scientific knowledge of asteroids and other space objects.
NASA also created the Near Earth Object Search Program (NEOP) to detect and track NEOs and to develop new technologies for both robotic and manned space research. In 2021, NASA launched its Double Asteroid Redirection Test (DART) during which is redirected the course of an asteroid. NASA considered this to be its first test of its planetary defense.
PRINCIPAL TERMS
- near-Earth asteroid: a small, irregularly shaped celestial body with an orbital path that brings it within 0.3 astronomical units (AU) of Earth’s orbit and within 1.3 AU of the sun.
Bibliography
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