How to see the 'planet killer' asteroid plunge past Earth - the largest space rock to come this close in 125 years

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A giant 'planet killer' asteroid is set to plunge past Earth on Thursday, marking the largest to come this close in 125 years.

The Mount Everest-sized space rock, 2011 UL21, has an estimated diameter of more than 7,500 feet across and could cause significant climate changes should it impact our planet.

The 'potentially hazardous' asteroid will soar 58,000 miles per hour within four million miles of Earth.

The flyby is set for around 4pm ET, but skygazers in the Northern Hemisphere will have the best views on June 28 and 29 when 2011 UL21 will be its brightest.

A giant 'planet killer' asteroid is set to plunge past Earth on Thursday, marking the largest to come this close in 125 years

'This asteroid is larger than 99 percent of all known near-Earth objects,' the European Space Agency shared in an announcement.

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'However, it won’t come anywhere near as close to Earth.

'At its closest point on 27 June, it will still be more than 17 times as far away as the Moon.'

But the asteroid is set to return to Earth in 2089 when it will come within 1.7 million miles of our planet.

2011 UL21 was documented by the Catalina Sky Survey project, a series of telescopes located in Arizona, on October 17, 2011.

'2011 UL21 is quite large and falls into the category of Apollo asteroids,' SETI Institute shared.

'Named after the Greek god Apollo, who was known for his epic journeys, these asteroids come in a variety of sizes from a few meters to several kilometers across, like 2011 UL21. 

'More importantly, Apollo asteroids get up close and personal by crossing Earth's orbit, although their orbits around the Sun are larger than Earth's.'

2011 UL21 is scheduled to come within four million miles of Earth on June 27, its closest approach in 110 years - the asteroid orbits the sun approximately every 1,130 days

Astronomers have been closely watching 2011 UL21 for months, monitoring its path to ensure the people of Earth are safe. 

'The term 'Potentially Hazardous Asteroid' (PHA) is a precise formal definition, referring to minor planets larger than approximately 460 feet that can come within 4.6 million miles from the Earth,' said Gianluca Masi, astrophysicist and scientific director of the Virtual Telescope Project that is hosting a live-stream for the event.

'In other words, only the largest asteroids capable of approaching close enough to our planet are flagged as PHAs, which does not mean they are going to hit the Earth, but they nonetheless warrant a better monitoring.'

2011 UL21 is also categorized as a 'planet killer,' which is defined as an asteroid capable of damage on a continental scale and producing enough debris upon impact that would trigger significant climate changes, LiveScience reports.

Scientists at the Massachusetts Institute of Technology revealed in 2023 that an asteroid in that category will not impact Earth for at least the next 1,000 years.