APOD: 2021 February 13 - Stereo Eros

Good morning, Rallypoint. Today's Astronomy Picture of the Day (APOD) is titled "Stereo Eros." The story behind asteroid 433 Eros is interesting, even without the stereo glasses. It was discovered on Aug. 13, 1898 by Gustav Witt, director of the Urania observatory in Berlin, and independently on the same day by Auguste H.P. Charlois at Nice, France. Less than two weeks later, Adolf J. Berberich computed that the object's orbit brought it well inside the orbit of Mars, making it the first-known near-Earth asteroid.

Before ground-based radar was available to observe extraterrestrial bodies, astronomers used Eros to help them calculate the mass of the Earth-moon system and the value of the astronomical unit (the AU, equivalent to the distance from the sun to Earth's orbit). Launched in February 1996, the NEAR (Near Earth Asteroid Rendezvous) spacecraft first flew by Eros on Dec. 23, 1998 at a distance of about 2,400 miles (about 3,800 kilometers). After several trajectory adjustments, NEAR finally moved into orbit around Eros on Valentine's Day (befitting an asteroid named for the Greek god of love), Feb. 14, 2000. After nearly a year in orbit, during which time the spacecraft was renamed "NEAR Shoemaker" in honor of astrogeology pioneer Eugene Shoemaker (remember the Shoemaker-Levy comet that broke up and crashed into Jupiter in the 1990s?), the mission carried out humanity's first asteroid landing on Feb. 12, 2001. Eros was 196 million miles (315 million kilometers) from Earth at the time.

The spacecraft wasn't expected to survive the landing but its instruments remained operational, leading to the first use of a gamma-ray spectrometer that had ever been done on the surface of a body other than Earth. The spacecraft issued its final transmission from the surface of Eros on Mar. 1, 2001.