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1994 CC was discovered by Spacewatch's Jim Scotti at Kitt Peak National Observatory on 3 February 1994. [2] In June 2009 it was shown to be a triple system, i.e. the largest body is orbited by two satellites; only about one percent (1%) of near-Earth asteroids observed by a radar are found to be triple systems such as this one. [9]
Asteroids have historically been observed from Earth. The first close-up observation of an asteroid was made by the Galileo spacecraft. Several dedicated missions to asteroids were subsequently launched by NASA and JAXA, with plans for other missions in progress. NASA's NEAR Shoemaker studied Eros, and Dawn observed Vesta and Ceres.
Radar imaging of (136617) 1994 CC from Goldstone during a 2009 flyby. Because of their distance from Earth and their small dimension, minor planets such as asteroids represent a challenge for astronomical instruments to resolve.
A newly discovered asteroid named 2024 YR4 now has a 2.2% chance of affecting Earth in 2032 after recent observations.
Outside the top four, the ranking of all the asteroids is uncertain, as there is a great deal of overlap among the estimates. The largest asteroids with an accurately measured mass, because they have been studied by the probe Dawn, are 1 Ceres with a mass of (939.3 ± 0.5) × 10 18 kg, and 4 Vesta at (259.076 ± 0.001) × 10 18 kg.
The only other unambiguously identified triple asteroids in the near-Earth population are (136617) 1994 CC, which was discovered to be a triple system in 2009, and 3122 Florence, which was found to be a triple system in September 2017. [13]
This is a list of asteroids that have impacted Earth after discovery and orbit calculation that predicted the impact in advance. As of December 2024, all of the asteroids with predicted impacts were under 5 m (16 ft) in size that were discovered just hours before impact, and burned up in the atmosphere as meteors.
Below is the list of predicted close approaches of near-Earth asteroids larger than magnitude 27, that were predicted to occur in 2021. [ note 1 ] This relates to the effectiveness of asteroid cataloging systems at predicting close approaches in 2021.