1221 Amor
1221 Amor is a near-Earth asteroid that serves as the namesake for the Amor asteroid group, which includes objects that come within 0.3 astronomical units of Earth but do not cross its orbit. Discovered in March 1932 by Belgian astronomer Eugène Delporte, 1221 Amor is approximately 1 kilometer in diameter and has an orbital path that crosses Mars's orbit from the outside. Unlike many other asteroids, Amor asteroids vary significantly in composition, indicating diverse origins within the asteroid belt. The discovery of 1221 Amor was pivotal in advancing the understanding of near-Earth objects (NEOs) and their potential impacts on Earth, as past collisions have played a critical role in the planet's geological and biological history. Although Amor asteroids are not generally considered immediate threats due to their orbits, they have raised awareness about the need for monitoring and potential deflection strategies for NEOs. NASA's Near-Earth Object Program is actively involved in tracking these asteroids and developing methods, such as the Asteroid Redirect Mission, to study and potentially redirect them in the future. The ongoing research into Amor asteroids enhances our understanding of both our solar system's dynamics and the historical impacts on Earth.
1221 Amor
FIELDS OF STUDY: Astronomy; Observational Astronomy; Asteroid Impact Avoidance
ABSTRACT: 1221 Amor is the namesake asteroid of the Amor asteroid group. It was discovered in 1932 at an orbit about 16 million kilometers (about 9.9 million miles) from Earth. As the first asteroid seen orbiting close to Earth, it showed astronomers that asteroids exist in the solar system in places other than the asteroid belt. It also helped them realize that asteroids have the potential to collide with Earth and other planets.
Near-Earth Asteroids
1221 Amor is the namesake asteroid of the Amor asteroid group. Amor asteroids are small, irregularly shaped space objects that travel an elliptical path around the sun. They often cross the orbit of Mars. Amor asteroids are a type of near-Earth asteroid (NEA). This means that they come within 0.3 astronomical units (AU)—about 44.9 million kilometers, or 27.9 million miles—of Earth. An NEA’s perihelion, or closest point to the sun, is between 1 and 1.3 AU. When 1221 Amor was first discovered, it was orbiting at about 0.1 AU (16 million kilometers, or 9.9 million miles) from Earth. It was later determined that this is Amor’s closest point to Earth.
There are millions of asteroids in Earth’s solar system. Most of these can be found within the asteroid belt, a region of space between the orbits of Mars and Jupiter. However, some asteroids are ejected from the asteroid belt when they collide with other space objects or encounter the immense gravity around Jupiter. When these asteroids end up orbiting close to Earth and the sun, they are called NEAs. Amor asteroids are unique among NEAs because while they travel close to Earth, they do not cross its orbit. Most Amor asteroids cross the orbit of Mars. Some have orbital paths so eccentric (elongated) that their aphelions, or farther points from the sun, are beyond Jupiter.
NEAs are among the category of space objects known as near-Earth objects (NEOs). Other NEOs include meteoroids and comets that have been pulled by gravity into orbit near the four inner planets (Mercury, Venus, Earth, and Mars).
Defining Characteristics
Of all the asteroid groups, Amor asteroids vary the most in composition. Some are mainly rock, while others are composed of some combination of rock, mineral, and metal. This variation in composition suggests that Amor asteroids originated in a number of different places in the asteroid belt. Planetary scientists believe that Amor asteroids were forced into their current orbits by encounters with the gravity of either Jupiter or Mars. Many also believe that a number of Amor asteroids may be comets that have burned off their volatile substances and can no longer form a comet’s characteristic coma or tail.
In terms of appearance, Amor asteroids resemble other asteroids, with surfaces full of visible pits and craters. These are most likely the result of collisions with other objects in space. Amor asteroids also vary in size. The largest Amor asteroid is 1036 Ganymed, with an estimated diameter between 31 and 35 kilometers (19 and 22 miles).
In contrast, 1221 Amor is on the smaller side, at about 1 kilometer (0.6 mile) in diameter. Its semimajor axis, or the most distant point of its orbital radius, lies between Mars and the asteroid belt. It crosses the orbit of Mars from the outside. Amor has been observed orbiting close to Earth numerous times since its discovery. It reaches its closest point to Earth (about 0.1 AU) every eight years.
Amor is a faint object with an absolute magnitude of 17.7. Absolute magnitude measures how bright an object appears from a distance of 10 parsecs (about 309 trillion kilometers, or 192 trillion miles). The smaller the number, the brighter the object is. The brightest objects in the universe have a negative absolute magnitude.
Discovery of 1221 Amor
Belgian astronomer Eugène Delporte (1882–1955) discovered sixty-six asteroids during his lifetime. He achieved this by taking countless photographs of the night sky and studying them closely. Delporte found 1221 Amor in March 1932 while working at the Royal Observatory of Belgium. Amor was the first asteroid to be found so close to Earth. It was originally designated 1932 EA1 but was later renamed. Since then, astronomers have identified more than 4,700 Amor asteroids in the solar system. In fact, they make up about 38 percent of all known NEAs.
The gravitational fields of nearby planets may capture some Amor asteroids and change their orbital paths. Some planetary scientists hypothesize that Mars’s two moons, Phobos and Deimos, are actually Amor asteroids that were pulled in by Mars’s gravity.
Significance of Discovery
The discovery of 1221 Amor was significant for planetary scientists because it made them realize that some asteroids travel close to Earth. This helped scientists to uncover truths about life on Earth, but it also raised new concerns about a possible collision between Earth and an asteroid that might get too close. Most planetary scientists agree that planet-asteroid collisions were probably fundamental to the formation of Earth as it exists today. Such collisions caused asteroids to deposit substances on Earth that are necessary for life to occur, including water and organic material.
More recent collisions have had more catastrophic effects. An immense crater near Chicxulub, Mexico, is believed to be evidence of a collision between Earth and a large asteroid about sixty-five million years ago. This event would have released energy equivalent to a massive nuclear explosion and may have been a major factor in the Cretaceous-Tertiary mass extinction, which resulted dinosaurs and other large life-forms dying out.
Amor asteroids such as 1221 Amor are generally not considered an immediate threat because they do not cross Earth’s orbit in space. However, some Amor asteroids have been known to become caught in the gravity around Mars and evolve into Apollo asteroids. Apollo asteroids are asteroids that cross the orbits of both Earth and Mars.
NASA and the Threat of NEAs
The National Aeronautic and Space Administration (NASA) created the Near-Earth Object Program to search for unknown NEOs and keep careful track of known NEOs. The goals of the program are to learn more about these objects and to develop sophisticated technologies that will someday allow scientists to divert NEOs away from Earth. Teams of international experts use state-of-the art technologies, such as massive radars that bounce radio waves off asteroids, to conduct their work.
The Asteroid Redirect Mission (ARM) is NASA’s first attempt to physically capture an NEA so scientists can study it directly. The ARM team is developing technologies that will allow scientists to redirect NEAs into the orbit around Earth’s moon. Once the NEA is moved into the moon’s orbit, astronauts plan to land on it and explore it firsthand. An initial test toward developing the project occurred in 2021 when NASA launched the Double Asteroid Redirection Test (DART) , an attempt to redirect an asteroid by crashing a spacecraft into the space rock. DART is targeting 65803 Didymos, a 2,500-foot (760-meter) wide Near Earth Asteroid.
PRINCIPAL TERMS
- Amor asteroid group: a group of near-Earth asteroids that come within 0.3 astronomical units (AU) of Earth but do not cross its orbit, although most do cross Mars’s orbit.
- aphelion: the point in a space object’s orbital path that is farthest from the sun.
- asteroid: a small, irregularly shaped celestial body that orbits the sun and is composed of rock, metal, and silicate.
- near-Earth asteroid: an asteroid that travels within 0.3 astronomical units (AU) of Earth’s orbit and within 1.3 AU of the sun.
- perihelion: the point in a space object’s orbital path that is closest to the sun.
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