On February 12, 2001, NASA’s NEAR Shoemaker spacecraft achieved the first-ever landing on an asteroid, marking a pivotal milestone in space exploration.
In 1772, astronomer Johann Bode and mathematician Johann Titus formulated a mathematical sequence that described the orbital distances of the known planets. Their work hinted at a missing planet between Mars and Jupiter at roughly 2.8 astronomical units (AU) from the Sun. Astronomers sought this gap and, in 1801, Italian astronomer Giuseppe Piazzi discovered a faint body at that distance, which he named Ceres. Though dimmer than Mars or Jupiter, Ceres was recognized as a small celestial object, and the term “asteroid” (meaning star‑like) was subsequently applied to similar bodies.
In 2006, Ceres was reclassified as a dwarf planet due to its substantial mass. NASA’s Dawn spacecraft visited Ceres in 2015–2018, becoming the first mission to land on a dwarf planet and providing unprecedented insights into its composition.
Asteroids are rocky, airless remnants from the early Solar System. The majority reside in the Main Asteroid Belt between Mars and Jupiter, spanning distances of 2.1 to 3.2 AU (approximately 1.95–3.0 × 108 miles). Over one million asteroids have been cataloged by NASA, ranging from meter‑scale boulders to the kilometer‑sized Vesta, which has a radius of 530 km. Their irregular shapes and rotation periods—typically 3 to 30 hours—are inferred from photometric variations.
Scientists classify asteroids primarily by composition:
Asteroids originate from two distinct sources:
Jupiter’s immense gravity has continuously reshaped the asteroid belt, occasionally ejecting objects into the inner Solar System. Some of these, known as Near‑Earth Objects (NEOs), cross Earth’s orbit and are monitored by NASA to mitigate potential impact threats. The Double Asteroid Redirection Test (DART) successfully demonstrated the ability to alter an asteroid’s trajectory in 2022.
Launched in February 1996, NEAR (Near Earth Asteroid Rendezvous) was the first spacecraft to orbit a small Solar System body. It performed a close flyby of asteroid Mathilde in June 1997, then entered orbit around asteroid 433 Eros in February 2000. Eros—discovered in 1898—measures 33.8 km in length and 12.9 km across, rotating every five hours. NEAR’s year‑long mission mapped Eros’s surface, measured its gravity, and conducted extensive spectroscopic studies.
On February 12, 2001, NEAR landed on Eros, making history as the first spacecraft to touch an asteroid’s surface. The lander operated for two weeks before extreme cold (-279 °F, -173 °C) severed communication, concluding the mission. NEAR’s data remain invaluable for understanding asteroid geology and composition.
Asteroids are rocky, airless bodies formed from leftover planetesimals. Comets are icy, dusty objects that originate from the outer Solar System and display visible comas and tails when near the Sun.
Asteroid Apophis will pass within 19,000 miles (30,578 km) of Earth on April 13, 2029. Current observations confirm it will not impact Earth.
Apophis measures roughly 1,100 feet (340 meters) in diameter.
NASA estimates that a meteor‑sized asteroid, roughly the size of a car, enters Earth’s atmosphere annually. Most burn up in the atmosphere as fireballs before reaching the surface.
NEAR Shoemaker – NASA (accessed September 20, 2023).
