The space around our planet feels a lot more crowded these days. Over the past few decades, astronomers have discovered more than 35,000 asteroids whose orbits come close to Earth’s orbit around the Sun. And the total keeps going up – they find a couple of hundred more every month.

Asteroids are chunks of rock and ice. Most are tiny, but the largest are hundreds of miles in diameter. Most of them inhabit the asteroid belt – a wide zone between the orbits of Mars and Jupiter – more than 1.3 million of them so far.

But near-Earth asteroids come much closer to the Sun – and Earth. Their orbits bring them within 120 million miles of the Sun, which is not far outside Earth’s orbit. And quite a few of them actually cross our orbit.

Some of these asteroids could someday hit Earth. They’re known as potentially hazardous asteroids. Astronomers have cataloged more than 2700 of them. None is on a known collision course. But a few will come close. In 2029, for example, the asteroid Apophis will pass less than 20,000 miles from our planet.

Several search projects are scanning the heavens for other near-Earth asteroids. They’re trying to find everything that’s big enough to present a major threat. Early detection might allow us to deflect an asteroid on a collision course – keeping us safe in our crowded region of the solar system.

More about near-Earth asteroids tomorrow.

Script by Damond Benningfield