It's called a 'planet killer' - a massive asteroid orbiting near earth, lit up by the brilliance of the sun has just been discovered.

On Monday, astronomers wrote in the Astronomical Journal that they spotted an asteroid that's more than a mile wide -- that had been lurking undetected within the glare of the sun.

As one scientist put it -- if an asteroid that big hit earth, "It would be a mass extinction event like hasn't been seen on earth in millions of years."

But they say it wouldn't happen for centuries -- and even then, scientists don't know the asteroid's orbit with enough precision to say how dangerous it could become in the future.

Still -- the team expects to find more planet killer asteroids over the next couple of years.

Already -- more than 27,000 near-earth asteroids exist in all shapes and sizes.

No asteroids are currently on a direct impact course with earth, but detecting the threat of near-earth objects that could cause massive damage is a primary focus of NASA and other space organizations around the world.