An asteroid as big as the oldest and largest known pyramid and one of the Seven Wonders of the Ancient World will pass Earth this weekend.
2021 SM3 will zip past the planet on October 15. The asteroid, which was only discovered this year, has an estimated diameter of up to 160 meters, one and one-fifth the size of the Great Pyramid of Giza in Cairo, Egypt.
At its closest, the asteroid will come within about 3 million miles of Earth. That’s much closer than either of Earth’s closest planetary neighbors, Venus at around 77 million miles, and Mars, which is about 244 million miles from our planet.
2021 SM3 is classified by NASA’s Jet Propulsion Laboratory (JPL) as a near-Earth object or NEO. This is an asteroid or comet that comes within a distance of around 120 million miles of Earth.
The agency’s Center for Near-Earth Object Studies (CNEOS) defines NEOs as comets and asteroids that have been nudged by the gravitational attraction of nearby planets into orbits that bring them into the Earth’s neighborhood.
CNEOS uses observations of asteroid orbits to calculate their trajectory through the solar system, charting their progress from 1900 forward until 2200. This allows them to calculate which NEO asteroids are also Potentially Hazardous Asteroids (PHAs).
A PHA is an asteroid with a diameter greater than about 140 meters and comes with about 4.5 million miles of our planet. While 2021 SM3 qualifies on these criteria, it fails to make the PHA list kept by CNEOS known as the Sentry Table as it has been ruled out from impacting Earth for at least 100 years.
The asteroid 2021 SM3 is considered part of the Apollo asteroid group. These are asteroids with an orbit that is wider than that of Earth that cross the path of our planet as it loops around the sun.
2021 SM3 won’t be the only asteroid passing Earth in the lead-up to Halloween.
An asteroid with a diameter of up to 230 meters, more than the length of the Golden Gate Bridge, will pass Earth on October 20. 1996 VB3 is another Apollo asteroid and will come within around 2 million miles of our planet on the evening of the Blood Moon.
The asteroid 1996 VB3 will be followed by 2017 SJ20 on October 25, an asteroid with an estimated diameter of up to 200 meters, that will pass within around just over 4 million miles of our planet.
One of the closest approaches an asteroid will make in the month of October will occur on Sunday, when 2021 TT1 passes within 300,000 miles of Earth. The object is just 34 meters in diameter.
A stock illustration of an asteroid making its way past Earth. An asteroid larger than the Great Pyramid of Giza will pass our planet on October 15. dottedhippo/Getty