### If an Asteroid was to strike the Earth, would it affect the Earth's rotation?

• If an Asteroid was to strike the Earth, would it affect noticeably the Earth's rotation, and if so, how large would this Asteroid have to be?

It'd be the least of our worries.

haha XD @gerrit still an interesting thought though because if it's possible, then it is also possible to have a different rotation than that existed during the dinosaur era- before an asteroid wiped them out.

There certainly *is* a different rotation now that 65 million years ago, as the Earth rotation is slowing down. I don't know the answer to your question, though.

Right, well I meant in terms of an outer space projectile directly affecting its rotation. +1 for the cool fact though

Everything has some effect, but it's pretty tiny. Even the Chicxulub impact, about 5 miles across, the largest in over 100 million years had a tiny amount of energy compared to the Earth's rotation. I can try to run the math later, but you'd need a really big impact to have a significant effect. A 100 mile in diameter space rock would obliterate the Earth's surface and boil the oceans but it's mass would be just a bit over a millionth that of the Earth. Even at a perfect impact angle at a few tens of thousand MPH, it would only add or remove a tiny bit of rotational velocity.

That was very interesting @userLTK , thanks! I guess if you think about a hand ball being thrown at a basketball which is spinning rather rapidly (like the earth), it would definitely have an impact and alter the rotation, but slightly. I guess there is a threshold to which the size of the impactor will be big enough to alter the rotation vs completely destroy the impactee

• James K Correct answer

7 years ago

To have a noticeable effect the impactor needs to be BIG.

Most questions about "what would happen if ... hits" can be answered by the "Earth impact effects program" (http://impact.ese.ic.ac.uk/)

Here are calculations for a 100km stony asteroid...

A brute like this would have a good chance of wiping out most complex life on the planet. There has been nothing like this in the last 4 billion years (or so)... It could cause the length of the day to change by "up to 2.42 seconds"

As gerrit said, it would be the last of our worries.

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