Asteroid 1981 ET3, also known as Florence, will skim past Earth on September 1 at a distance of seven million kilometres.
That is about 18 times the distance between the Earth and the moon and the closest this asteroid has been since 1890.
The next time such a space rock will fly this close is in 2050, according to Nasa.
At a staggering 4.8 kilometres wide – the largest that has ever been discovered since Nasa began tracking asteroids.
To put that into context, scientists have calculated that any space rock that is wider than 0.9 kilometres could wipe out life on Earth.
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Paul Chodas, manager of Nasa’s Center for Near-Earth Object Studies (CNEOS) at the agency’s Jet Propulsion Laboratory, said: “While many known asteroids have passed by closer to Earth than Florence will on September 1, all of those were estimated to be smaller.
“Florence is the largest asteroid to pass by our planet this close since the NASA program to detect and track near-Earth asteroids began.”
Due to its massive size, boffins at the space agency believe that it is an ideal candidate to test out new asteroid observation technologies.
Using new Earth-based radars, Nasa says that it can capture surface details on the giant asteroid that would be as small as 10 metres.
Nasa said in a statement: “When these small, natural remnants of the formation of the solar system pass relatively close to Earth, deep space radar is a powerful technique for studying their sizes, shapes, rotation, surface features and roughness, and for more precise determination of their orbital path.”