An asteroid the size of a mountain, known as 2011 UL21, will come unusually close to Earth today, hurtling past our planet at a speed of 58,000 mph. This near-Earth asteroid orbits around the sun once every three years, occasionally approaching within 1.3 astronomical units of the sun. Measuring between 1.1 and 2.4 miles wide, this asteroid is larger than 99% of known near-Earth asteroids.

Although 2011 UL21 is significantly smaller than the asteroid that led to the extinction of the dinosaurs, it still holds the potential to cause continental-scale damage and alter the climate significantly. Despite its “planet killer” designation, this particular asteroid will pass by at a safe distance of approximately 4.1 million miles from Earth, which is the closest it has been in over a century.

While there is no immediate threat to Earth from this passing asteroid, it is considered one of the ten largest space rocks to approach within 4.7 million miles of our planet since 1900. The asteroid’s close approach can be witnessed through a live stream provided by the Virtual Telescope Project from Italy, starting at 4 p.m. ET on June 27.

For those interested in observing the asteroid in the night sky, it will be at its brightest on June 28 and June 29, visible from the Northern Hemisphere. This unique opportunity to view 2011 UL21 will not recur until 2089, when it is expected to come within 1.7 million miles of Earth.

While the current asteroid poses no threat, scientists warn of potential close calls with smaller asteroids in the future. For instance, the asteroid Apophis, capable of devastating an entire city, is predicted to pass closer to Earth than some satellites in 2029. Despite the absence of any imminent “planet killer” asteroids, vigilance is necessary for smaller threats in the years to come.