Web Desk) - Asteroids are constantly passing Earth - and every once in a while some make a direct hit.

Fortunately, the latter are all too small to pose any serious threat and burn up in the atmosphere.

Of course, the last major asteroid to hit Earth was 66million years ago which wiped out most dinosaurs.

The chances of another such event happening are small but Nasa and other space agencies are taking no chances.

Experts are constantly monitoring space for potential threats.

And there are efforts to plan ahead in case a big one does come directly toward us, with ideas such as hitting them to deflect their path.

Here are some of the most dangerous asteroids Nasa are keeping an eye on.

The important thing to note is that, despite the chances detailed below, they are all still rated as zero risk at present.

BENNU

Bennu is the most concerning asteroid to our knowledge at present because it poses the highest risk of hitting Earth.

The good news is, if the worst does happen it's not due for more than 150 years, so no living person today will be around.

As it stands, there is a 1 in 2,700 chance of Bennu striking Earth on September 24, 2182.

At 74million tonnes and 0.30 miles wide, Bennu wouldn't destroy the entire world.

But if it struct a densely populated region, the asteroid could cause millions of causalities, with energy equivalent to dropping 1.4billion tonnes of explosives, according to Live Science.

Nasa has taken a sample from Bennu, which came back to scientists in September 2023.

29075 (1950 DA)

Asteroid 29075 (1950 DA) may be the second riskiest but it would be one of the deadliest.

At 0.81 miles wide and with a mass of 78million tonnes, it has the power to wipe out humankind.

The reported energy equivalent is like 75billion tonnes of TNT.
There's a 1 in 34,500 chance that 29075 (1950 DA) could hit on March 16, 2880.

2023 TL4

2023 TL4 is 0.2 miles wide and has the mass of 47 million tonnes, meaning it would be like dropping 7.5billion tonnes of TNT on Earth.

Currently, there's a 1 in 181,000 chance it'll strike us.

But fear not, as it won't happen until October 10, 2119.

2007 FT3

The most pressing concern about the possibility of 2007 FT3 striking Earth is that it's within our lifetime.

Fortunately, Nasa has ruled out earlier reports that it could hit on October 5 this year.

But there is another chance again on March 3, 2030.

That said, the chances are pretty reassuring at 1 in 11.5million.

Measuring 0.21miles wide and with a mass of 54million tonnes, 2007 FT3 would be like detonating 2.6billion tonnes of TNT, enough for regional damage.

1979 XB

1979 XB is a lost asteroid last observed back in 1979, so our understanding of it is a little limited.

It's thought to be about 0.41miles wide and with a mass of 390million tonnes.

Scientists believe it has about a 1 in 1.8 million chance of hitting Earth on December 14, 2113.

If it did hit, this would be like 30billion tonnes of TNT.