from CNN Scientists study orbit of newly found asteroid. This asteroid currently matches the previous risk champ Asteroid 1950 DA for impact probability but in a mere 25 years rather than 800. It's near term threat gives it the highest Torino scale ranking ever.

We also have three asteroids ranking a 1 or higher on the Torino scale currently listed on JPL's NEO Sentry page which is as high as I've seen. 1997 XR2 is a practically permanent list member because it has not been tracked since 1997 after only 44 days of tracking. 2004 VD17's more specific Palermo scale ranking has been stable for several weeks after a similar period of observation with about 4 times as many individual observations and will probably take long term observation to eliminate from the list. By comparison 2004 MN4 has been tracked for 187 days but with only 55 observations compared to 144 for 1997 XR2 despite being almost as big as 2004 VD17. It has an impact risk above the background level on the Palermo scale. Most deleted threats of significance were below -1 on the palermo scale at peak concern although many reached 1 on the Torino scale.

1950 DA with a potential 2880 impact does remain the only known global scale impactor with significant impact probability. The two biggest threats currently on the next 100 year Sentry list will have roughly 1/8 the impact energy due to being half as big. I didn't check the differences in relative velocity and I doubt we know much about density differences

Regards,
Mark