You can worry when the Torino score gets to 5.
Asteroid 2005 YU55, caught by radar during a close pass in 2011.
The newly discovered asteroid 2013 TV135 is one of those rare space objects assigned a number on the Torino scale. Discovered last month by astronomers working at the Crimean Astrophysical Observatory in Ukraine, the rock came within about 6.7 million kilometers of Earth on this pass.
The asteroid is about 400 meters in diameter, and based on what we know today, has a 1-in-63,000 chance of colliding with Earth in 2032. That’s enough to give it a value of “1” on the Torino scale, which ranks threats to Earth from asteroids. The only other object currently assigned a number other than zero is 2007 VK184, about 130 meters in diameter, which has a 1-in-1820 chance of impacting Earth in 2048, giving it a Torino score of 1. Both objects are likely to be downgraded to zero as astronomers learn more about their orbits.
The highest Torino rating in recent years went to the asteroid 99942 Apophis, which was briefly assigned a 4 when early observations indicated a 2.7 percent probability that it would collide with Earth in 2029. ...