Image Shows Asteroid That Could Be 4000ft Wide Heading Towards Earth

A hulking asteroid is due to make a relatively close pass by Earth next month, and an astronomer has spotted it on its approach.

The asteroid, called 138971 (2001 CB21), is estimated to be up to 1.3 kilometers or 4,265 feet in diameter. Put another way, it is potentially four times as wide as the Eiffel Tower is tall.

2001 CB21 is due to pass by Earth on March 4 at about 3:00 a.m. ET, at which point it will be travelling at over 26,800 miles per hour.

But there's no need for concern—while the asteroid is classed as "potentially hazardous" by NASA's Center for Near Earth Object Studies (CNEOS) it is not in any danger of hitting us in the foreseeable future.

Although its pass by Earth next month is dubbed a "close approach" by CNEOS it will actually be more than three million miles away at its closest point, which is more than 10 times as far from us as the moon is.

On January 30, Gianluca Masi, an astronomer at the Virtual Telescope Project in Italy, captured an image of the 2001 CB21 via an Earth-based telescope when it was more than 21.5 million miles away from Earth.

The asteroid can be seen as a small white dot highlighted by an arrow in the center of the image, seen below. The image is the result of a single 420-second exposure, taken with a PlaneWave 17" robotic telescope unit.

A photo of the asteroid 2001 CB21, photographed by Gianluca Masi at the Virtual Telescope Project in Italy on January 30. Gianluca Masi/Virtual Telescope Project

2001 CB21 makes an orbit around the sun around once every 384 days, which is similar to Earth's own orbital period. Its large size makes it bigger than around 97 percent of known asteroids, according to

CNEOS' classification of the asteroid as "potentially hazardous" does not mean that the asteroid is ever expected to hit us. Instead, this classification is given based on the asteroid's potential to make what CNEOS calls "threatening close approaches" to Earth.

Essentially, if an asteroid is smaller than about 500 feet in diameter and if it can't get any closer to us than around 4.6 million miles, then it will not meet the potentially hazardous asteroid (PHA) classification.

PHAs are not especially rare: last month, the asteroid 1994 PC1—which also meets this classification—flew past Earth at a distance of around 1.2 million miles. Again, the asteroid was not expected to collide with our planet.

Space rock collisions with Earth are a genuine threat, though, and NASA is working on projects such as the Double Asteroid Redirection Test to expand humanity's capability of dealing with an impending asteroid strike.

A stock photo shows an illustration of an asteroid in space. Asteroids pass by Earth all the time—some closer and bigger than others. DigtialStorm/Getty