The largest meteor to strike Earth can be defined in several ways: the largest piece of space rock recovered, the biggest geological impact event, or the largest object currently tracked in space. While “meteor” technically refers only to the bright streak of light as an object enters the atmosphere, records for size are held by the objects that survive this passage or the enormous impact structures they leave behind. Understanding these distinctions helps appreciate the scale of cosmic collisions throughout our planet’s history, ranging from the recovery of a single massive boulder to the formation of geological features that span hundreds of kilometers.
Defining the Space Rock Family
Scientists classify space rocks based on their location relative to Earth. A meteoroid is a fragment of an asteroid or comet traveling through space, ranging in size from a grain of sand up to a few meters in diameter. These objects are essentially space debris before they encounter a planetary atmosphere.
When a meteoroid enters Earth’s atmosphere, friction causes it to heat up and glow, producing the visible streak of light known as a meteor, or “shooting star.” Most meteoroids disintegrate completely during this phase. If a meteoroid is large enough to survive atmospheric entry, the remaining rock that lands on the Earth’s surface is called a meteorite. The confusion around the term “meteor” arises because the largest impact events are named after the object that caused them, even though the ground impactor was technically a meteorite or a much larger asteroid/comet.
The Largest Recovered Meteorite
The largest single piece of space rock ever recovered is the Hoba Meteorite, located in Namibia, near the town of Grootfontein. This massive, single iron-nickel mass was discovered in 1920 by a farmer plowing his field. Its size prevented it from ever being moved from its original impact site.
The Hoba meteorite has an estimated mass of about 60 tons and is composed primarily of iron (82%) and nickel (16%). Scientists classify the Hoba as an ataxite, a rare type of iron meteorite characterized by its high nickel content. Its dimensions are roughly 2.7 meters by 2.7 meters, with a thickness of about 0.9 meters. The lack of a substantial impact crater suggests the object entered the atmosphere at a shallow angle and slowed significantly before impact, allowing it to remain mostly intact.
Earth’s Biggest Impact Structures
When considering the largest impact event, the scale moves far beyond any single recovered meteorite, shifting focus to the enormous geological structures left behind. The largest verified impact structure on Earth is the Vredefort Dome, located in South Africa. Formed approximately 2.023 billion years ago, the original crater is estimated to have been between 170 and 300 kilometers in diameter.
The massive scale of the Vredefort impact suggests the original bolide, likely an asteroid, was enormous, with estimates placing its size between 20 and 25 kilometers across. Though heavily eroded over billions of years, the Vredefort Dome represents the central uplift of the ancient impact site. This collision is considered the greatest single energy release event in the planet’s history.
Another of the world’s largest impact structures is the Sudbury Basin in Ontario, Canada, formed about 1.85 billion years ago. The original crater was estimated to be at least 200 kilometers in diameter, but subsequent geological processes deformed it into its current elliptical shape. The impact fractured the crust, leading to a massive influx of melted rock that created rich deposits of nickel and copper, forming the basis of the region’s mining industry. For context, the famous Chicxulub crater in Mexico, which caused the extinction of the dinosaurs 66 million years ago, had an original diameter of around 180 to 200 kilometers.
Monitoring Future Threats (NEOs)
The largest potential future impactors are classified as Near-Earth Objects (NEOs). These are asteroids and comets orbiting the Sun that come within 30 million miles of Earth’s orbit. The U.S. Congress set a goal for NASA to find and track 90% of NEOs larger than 140 meters in diameter. An object of this size is large enough to cause significant regional devastation if it were to strike land.
NASA’s Planetary Defense Coordination Office (PDCO), established in 2016, is responsible for managing the detection, tracking, and characterization of these objects. The office uses a system called Sentry to monitor potential long-term impact risks over the next 100 years by continuously calculating the orbits of known NEOs. This ongoing effort involves a global network of ground-based telescopes and specialized space missions, like the planned NEO Surveyor, to improve the catalog of potentially hazardous objects (PHOs).
The largest known PHOs are much smaller than the impactors that created the Vredefort structure, but they still represent a significant threat. Tracking their orbits allows scientists to predict close approaches and rule out potential collision risks decades in advance. The goal is to provide enough warning time to potentially implement mitigation strategies, such as deflection technologies, should an object be found to be on a collision course with Earth.