According to NASA, planet Earth is set for a terrifying close encounter with a “hazardous” monster asteroid the size of Buckingham Palace tomorrow. The size of this asteroid is still in question, but it won’t matter if it hits the Earth.

NASA originally assumed the asteroid, dubbed 2017 VR12, was about the size of Buckingham Palace, or 250 meters wide. Now they say it may be slightly smaller. But all this size-wrangling would be largely academic if it hit Earth because the object is definitely big enough to wipe out a city.

According to Metro, it said the rock was one potential destination for a future mission to land a probe on the surface of an asteroid. If the asteroid was as big as the first estimate of 470 meters, it could have a surface area of almost 55 acres. The newer estimate would give it a surface area of just over 15 acres. Buckingham Palace takes up about 19 acres, with its gardens occupying another 40 acres.

But most scientists say this one won’t actually hit Earth this time around. The space rock will zoom past us at about 14,092 miles per hour at about four times the distance between the Earth and Moon, or 897,161 miles.  Luckily, it’s not going to hit us, because if it did it would release more energy than all the nuclear weapons detonated in the entirety of human history. The impact would create a crater of more than two miles wide, killing millions if it hit near a populated area.

It will reach the closest point of its journey past Earth tomorrow and you can watch live footage of the asteroid zooming by on The Virtual Telescope Project website.