On April 1, an asteroid large enough to do some serious damage will make its closest recorded approach to the Earth. In the spirit of April Fools, 2007 FF1 is just kidding, however, passing 19 times as far from us as the Moon.

Closer passes by asteroids are common, but the reason this one is noteworthy is not just the date of its closest approach. 2007 FF1 is at least 82 meters (270 feet) in diameter, and possibly as much as 260 meters (660 feet) across. It's potentially up to two-thirds the diameter of 99942 Apophis, generally considered the asteroid top of our worry list. We may have more exact estimates after it has passed by, but either way, this is a space rock large enough we need to keep an eye on it.

The rock is small compared to the dino-killer, and certainly not large enough to end civilization, Nevertheless, 2007 FF1 could annihilate a city and plenty of territory around it if it hit on land, or create tsunamis on a scale humanity has never seen in the more likely event of an ocean splashdown. 

With an orbital period of 1.9 years, 2007 FF1 is a regular visitor to the vicinity of Earth's orbit, but often we're on the other side of the Sun when it approaches. At a distance of 7.4 million kilometers, this year's passage is less than half the distance of its 2020 pass. It will come very slightly further from Earth in 2037. After that it won't get within 17 million kilometers until March 2144, and not much closer then.

Even your grandchildren are unlikely to have to worry about this rock, whether or not they're living in satellite cities in space by then.

Although its current orbit does not allow it to impact Earth, gravity from planets and pressure from sunlight will slowly change 2007 FF1's path. Like other Apollo class asteroids, 2007 FF1 will keep hanging around the inner Solar System until it either runs into a planet or a close approach radically changes its orbit.

Looking far enough into the future, the odds are on an eventual collision with Earth, the Moon, or Mars, and we're the biggest target in that set.

Amateur astronomers will struggle to spot it, even at its closest, but professional observatories are tracking its passage far into the northern sky to calculate its size and orbit more precisely.

If we are to treat 2007 FF1 as a sentient being, however, it would appear it doesn't know the well-established rule that April Fools day jokes rebound on the maker after midday. Aside from the population of Hawaii, the world will be well past noon when the closest approach occurs at 9:35 GMT.