We think of space as this vast, empty void when, in fact, it is filled with all sorts of things. Dark matter. Small solar system bodies like comets and asteroids. The solar wind. Cosmic dust. Other stuff. There's all kinds of debris in an almost endless variety of trajectories out there.
The Earth, as with the other planets, is nested in a fairly stable orbit around our Sun. But, that doesn't mean our orbit is free from all the possible collisions with debris of various sizes. In fact, the Earth is hit by about 40,000 tons of various types of space debris every year. This is not counting all the space junk launched by humans in the past that periodically falls back to Earth.
So, our planet's collision with tiny particles of star dust is a routine, every day occurrence. But, if you widen your perspective beyond the stretch of your life span you will see that every few million years something far larger than interstellar dust strikes.
A large asteroid came within 202,000 miles of the Earth today at about 6:28pm EST. That's closer than Earth's distance from the Moon and the closest any object of this size has come near Earth since 1976. This asteroid was about the size of a city block. Another will pass fairly close in the year 2028. But it will not hit us.
The asteroid is dubbed 2005 YU55. We discovered it about six years before it passed out way today.
This is just another day of gravity at play in the universe. A near-Earth object came close to hitting the Earth back in 1883. One actually exploded above Siberia in 1908. There have been other impact events as recently as 1979, 2002, and 2008. All minor incidents, of course. We know the Earth has been hit several times by major interstellar objects in the past. Our technology is sophisticated enough to see them a few years or decades in advance. But, all we can do is watch and wait.
Large chunks of space debris hit the Earth every few million years. It is an inevitability that such objects will hit the Earth before our Sun begins to become a Red Giant in about one billion years. Obviously, anything that happens over millions of years can happen many times when the timeframe is in the billions.
With this in mind, many people are thinking in terms of deflecting through a variety of means potential near-Earth impact objects. There is a planetary defense special interest devoted to this.
But, the science for all this in inexact at best. In 2003, there was a brief flurry of news about a giant asteroid that could hit Earth in 2014. Only it turns out this object will now pass us safely.
It begs the question, though, if we could be so wrong about a near-miss can we also be wrong about future objects that we currently consider no threat at all to us. One such piece of space debris is 99942 Apophis. As of today there appears to be only a small chance it could hit the Earth. Let's hope they're spot on with that prediction.
We are groping in the darkness of space and we are, in fact, near-blind. We have cataloged hundreds of potential near-Earth objects, but we still have no idea what might come our way in the debris of space a century from now. Maybe another global impact. Probably not. But...one day...