A Short History of Missions to Asteroids

As NASA's Osiris-Rex begins its mission to asteroid Bennu, take a look back at our previous asteroid missions.

NASA's Osiris-Rex spacecraft, which is due to launch at 7:05 p.m. EDT Thursday from Cape Canaveral Air Force Station in Florida, will be latest in a series of increasingly ambitious missions to visit asteroids. Here's a look at our previous robot explorers:

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Meet Gaspra, our very first encounter with one of the hundreds of thousands of rocky bodies swirling around the sun, mostly in the main asteroid belt between Mars and Jupiter, but thousands more in orbits that come closer to Earth. Gaspra, a 12.5-mile long rock in the main belt, was visited by NASA's Jupiter-bound Galileo spacecraft in 1991.

NASA's Near Earth Asteroid Rendezvous, or NEAR, spacecraft was the first to orbit an asteroid – and the first to land on one. The goal of the mission was to answer fundamental questions about the nature and origin of the many asteroids and comets in orbits that come close to Earth. The probe was launched in 1996 and put itself into orbit around Eros four years later. As it neared the end of its mission, NASA decided to attempt something not previously planned: land the probe on the asteroid, which was successfully accomplished on Feb. 12, 2001. NEAR continued sending back science data for another two weeks.

NASA took advantage of the Cassini spacecraft's trek to Saturn and the Stardust probe's journey to a comet to capture images and gather science information about asteroids. During its passage through the main belt, Cassini flew by the asteroid Masursky. Stardust passed about 3,300 miles from asteroid Annefrank, located in the inner part of the main belt, as a practice run for its encounter with Comet Wild 2 (pronounced "vilt 2".)

Japan's Hayabusa spacecraft arrived at the near-Earth asteroid Itokawa in 2005. It stayed for two years during which time it made several attempts to collect samples during touch-and-go maneuvers. During one try, the spacecraft lost communications with Earth and crash-landed on the asteroid. Despite this, JAXA managed to return the damaged Hayabusa probe to Earth on June 13, 2010. Though its sampling mechanism had failed, thousands of tiny particles were found in one of the sample containers, most likely as a result of the spacecraft's crash. Many particles turned out to be grains from the asteroid, but they were mixed with contaminant particles from the spacecraft. Instead of returning several grams of pristine asteroid material, Hayabusa ended up collecting less a milligram. Nevertheless, these first direct samples of an asteroid proved to have great scientific value, says NASA.

An innovative NASA spacecraft called Dawn, launched in 2007, is in the process of a detailed investigation of the dwarf planet Ceres, the largest object in the main asteroid belt. Before arriving at Ceres though, Dawn spent 14 months circling the second largest object in the belt, the asteroid Vesta. It collected evidence confirming that three classes of meteorites -- howardites, eucrites and diogenites, or HED meteorites – are related to Vesta.

The Japanese space agency launched a follow-on Hayabusa mission in December 2014, this time aiming for asteroid Ryugu. The probe is scheduled to arrive in July 2018 and spend about 18 months studying the asteroid before returning to Earth in December 2020 with samples. Hayabusa 2 also includes a European lander called MASCOT and an experiment to send a small impactor into the asteroid's surface to study the resulting crater and how the excavated debris resettles.

NASA's Origins Spectral Interpretation Resource Identification Security - Regolith Explorer spacecraft, nicknamed Osiris-Rex, is heading to the small, near-Earth asteroid Bennu. Once arriving in 2018, Osiris-Rex is designed to map the surface of the asteroid and inventory its minerals and chemicals. Scientists will pick a site for Osiris-Rex to collect at least 2 ounces, and hopefully more like 4 pounds, of gravel and soil from its surface. The samples are due to be flown back to Earth in September 2023. About 75 percent of the cache is to be archived for future scientists to study.