## September 10, 2016

### Small asteroid passes ten time closer than the moon

A small asteroid designated 2016 RB1 safely flew past Earth today at 10:20 a.m. PDT (1:20 p.m. EDT / 17:20 UTC) at a distance of about 25,000 miles (40,000 kilometers, or just less than 1/10th the distance of Earth to the moon). Because the asteroid’s orbit carried it below (or over) Earth’s south pole, it did not pass within the orbits of communication or weather satellites. 2016 RB1 is estimated to be between 25 to 50 feet (7 and 16 meters) in diameter. It is the closest the space rock will come to Earth for at least the next half century.

Asteroid 2016 RB1 was discovered on Sept. 5, 2016, by astronomers using the 60-inch Cassegrain reflector telescope of the Catalina Sky Survey, located at the summit of Mount Lemmon in the Catalina Mountains north of Tucson, Arizona -- a project of NASA'S NEO Observations Program in collaboration with the University of Arizona.

If this was a porous rock asteroid with 16 meters diameter traveling at 17 kilometers per second then it would have been an airburst [Imperial college of london impact calculator] This calculator is based on a 30 page paper Earth Impact Effects Program: A Web-based computer program for calculating the regional environmental consequences of a meteoroid impact on Earth

Distance from Impact: 500.00 meters ( = 1640.00 feet )
Projectile diameter: 16.00 meters ( = 52.50 feet )
Projectile Density: 1500 kg/m3
Impact Velocity: 17.00 km per second ( = 10.60 miles per second )
Impact Angle: 45 degrees
Target Density: 2000 kg/m3
Target Type: Crystalline Rock
The projectile begins to breakup at an altitude of 72500 meters = 238000 ft
The projectile bursts into a cloud of fragments at an altitude of 30900 meters = 101000 ft
The residual velocity of the projectile fragments after the burst is 11.9 km/s = 7.42 miles/s
The energy of the airburst is 2.35 x 10^14 Joules = 56 kilotons
No crater is formed, although large fragments may strike the surface.

If it was made of iron (8 times denser than water) and 16 meters in diameter then

The projectile begins to breakup at an altitude of 14000 meters = 46000 ft
The projectile bursts into a cloud of fragments at an altitude of 5120 meters = 16800 ft
The residual velocity of the projectile fragments after the burst is 6.76 km/s = 4.2 miles/s
The energy of the airburst is 2.09 x 10^15 Joules =500 kilotons.
Large fragments strike the surface and may create a crater strewn field. A more careful treatment of atmospheric entry is required to accurately estimate the size-frequency distribution of meteoroid fragments and predict the number and size of craters formed.

This animated gif of asteroid 2016 RB1’s close approach to Earth was imaged by astronomer Gianluca Masi on the evening of Sept. 6, 2016, using the Virtual Telescope located in Ceccano, Central Italy.
Credits: VT/Masi

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