Notable Historical Close Approaches
A rundown of the closest, largest, and most-studied near-Earth object approaches on record, from Chelyabinsk to modern radar-confirmed flybys.
Tunguska (1908)
On June 30, 1908, an object roughly 50–60 meters across exploded in the atmosphere over the Podkamennaya Tunguska River in Siberia. The airburst flattened an estimated 80 million trees across roughly 2,150 square kilometers, with an energy release estimated at 10–15 megatons of TNT. No crater was ever found, consistent with an airburst rather than a ground impact. It remains the largest impact event in recorded history and a reference point for what an undetected mid-size object can do.
Chelyabinsk (2013)
On February 15, 2013, a roughly 20-meter asteroid entered the atmosphere over Chelyabinsk, Russia, undetected in advance because it approached from the direction of the Sun, where ground telescopes can't see it coming. It exploded about 30 km up with an energy release around 500 kilotons — more than 20 times the Hiroshima bomb — and the resulting shockwave shattered windows and injured roughly 1,500 people, mostly from flying glass. It is the largest known object to have hit Earth's atmosphere since Tunguska, and it happened on the same day, coincidentally, that a much larger and well-tracked asteroid (2012 DA14) made an unrelated close approach.
Asteroid 99942 Apophis
Discovered in 2004, the roughly 340-meter asteroid Apophis briefly generated headlines when early orbit calculations suggested a non-negligible chance of an Earth impact in 2029. Additional observations, including precision radar measurements, ruled out any impact risk for at least the next century. Apophis will still pass closer than many geostationary satellites on April 13, 2029 — about 32,000 km from Earth's surface — making it one of the closest approaches by an object this large ever predicted in advance, and a rare opportunity to observe a sizeable asteroid with the naked eye.
2020 QG — the closest known non-impacting approach
On August 16, 2020, a small asteroid (a few meters across) named 2020 QG passed just 2,950 km above Earth's surface — closer than many satellites — and was not detected by the Zwicky Transient Facility survey until hours after it had already passed. Because of its small size, it posed no threat and likely would have burned up harmlessly if it had entered the atmosphere. It illustrates a real limitation of current surveys: very small objects on approach from unfavorable angles can still slip through undetected until after the fact.
2029 and beyond: what to watch for
Beyond Apophis in 2029, NASA's CNEOS Close Approach tables (and the live feed on this site) list every catalogued NEO passing within a given distance of Earth on any given day. The vast majority are small, routine, and unremarkable — but each recorded approach adds another data point that refines the object's known orbit for the future.