I’ll start off by saying that we are constantly detecting new asteroids which could harm Earth. Our detection methods aren’t perfect, and we don’t have very many systems in place to detect these rocks. So, the possibility for smaller rocks hitting us is more likely, but since we can’t see them, we don’t know how likely.
The most likely asteroid to hit Earth seems to be the year (29075), 1950 DA according to the Palermo scale.
Now this asteroid, or any asteroid for that matter, isn’t as likely to hit Earth as you might think. The chance of impact of any asteroid we can detect is well below 1%. The asteroid I have given has a 1/20,000 percent chance of hitting us, not only that but it would hit in the year 2880, so don’t sell your stocks just yet. Every time this thing swings by, the probability of it hitting us drops. In 2013 it had a 1/4000 percent chance of hitting us, like I said earlier, it is now 5 time less likely to hit us.
“So then why was Russia hit in 2013, huh?” Well that asteroid was pretty small. The sizes we can detect are much larger.
Asteroids were discovered in 1950 by Carl A. Wirtanen at Lick Observatory, 1950 DA is a 1 km wide asteroid. By comparison, the asteroid that killed the dinosaurs was about 15 km in diameter. This asteroid made its closest approach on March 5, 2001 at 0.0520726 AU. It seems to be a very dense, made of nickel and iron. If this asteroid hit it would dramatically alter the climate on Earth, devastating humanity.
The next, and most popular, asteroid to hit us would be 99942 Apophis. This asteroid gets talked about a lot, but it too is perpetually being demoted in terms of hazard.
The biggest concern is that when the asteroids swings by, our or some other body’s gravity with move them enough to line them up for impact the next time they swing around. Hopefully by 2880 humans will have developed ways to counter the threat of asteroids.