Just last week, Planet Earth had a close call.
The asteroid was seen coming, and predicted to fly by (at breathtaking speed) on a path that was only 17000 miles away from Earth's surface. If the path of the asteroid had been slightly different, things might have gotten very bad very rapidly. Another, smaller one, left a streak of light across the sky and caused much damage in a city in Russia. (Russia as a nation has bad luck for such things...the last such hit was a century ago.)
Weirdly, I had just begun reading a book on that subject.
I'd call it science-fiction, but it isn't the usual kind of science fiction. No futuristic technology or travel to the stars.
Instead, it's a book about a heavenly object falling to Earth; causing lots of destruction and chaos. The book is titled Lucifer's Hammer, written by a pair of authors who usually write science-fiction together.
Feels kind of weird, reading a book written in the 70s. NASA astronauts talk about the Space Shuttle as a coming attraction. There are no cell phones. The Internet isn't discussed, either as a research project or a potential society-changing technology. The American Space Program has to cooperate with the Soviet Space Program...
The description of what one piece of God's creation—a comet—can do to Earth is frightening. It brings to mind several things; among them the world-ending catastrophes of the book of Revelation.
Or possibly the questions by geologists and historians as to whether a comet or asteroid struck Earth before the extremely cold years of 535-536.
The 1970s-era U.S.A of the novel could not mount any attempt to keep Earth safe from such an impact. In the novel, they barely got a team of American and Russian astronauts into Earth orbit to see a comet fly-by. These astronauts saw the prediction of impact go from 1-in-a-million to 1-in-ten-thousand to 1-in-a-thousand to oh-crap-it's-going-to-hit.
There are many frightening things that might happen to Earth's climate, but few of them would be as catastrophic as a really big asteroid-strike.
As several commentators have pointed out, near-misses by asteroids are also one way of asking about how various space programs are doing.