A relatively large newly discovered asteroid designated 2018 AH flew past Earth at 0.77 LD / 0.00199 AU (~297 699 km / 184 982 miles) on January 2, 2018. This is the 1st known asteroid to flyby Earth within 1 LD this year, 54th since January 1, 2017 and the largest within 1 LD since 2011.
2018 AH was first observed at ATLAS-MLO, Mauna Loa on January 4, 2018, two days after its close approach to Earth. The closest approach to Earth took place at 04:25 UTC on January 2 at a speed (relative to the Earth) of 13.76 km/s.
It belongs to the Apollo group of asteroids, the most common one, and it has an estimated diameter of 84 - 190 m (275 - 693 feet), making it the largest known near-Earth object to flyby Earth within 1 lunar distance since 2011.
It is also the 9th largest known near-Earth object (asteroids + comets) to flyby Earth within 1 lunar distance ever. Over the past 18 years, only 2 asteroids larger than 2018 AH flew past us this close and 8 since 1918.
As of January 5, 2018, there are 17 566 known near-Earth objects around our planet, 17 460 of them are asteroids. Of the total number of known NEOs, 7 999 have an estimated diameter roughly 140 m (460 feet) or larger, including 2018 AH.
For comparison, asteroid 2018 AH is about 5 - 10 times larger than Chelyabinsk meteorite (estimated size 20 m / 65 feet). The Chelyabinsk object exploded some 29.7 km (18.5 miles) above the Russian city of Chelyabinsk at 09:20 YEKT (03:20 UTC) on February 15, 2013, damaging over 3 000 buildings and injuring over 1 500 people (mostly by broken window glass). Its light was brighter than the Sun and visible up to 100 km (62 miles) away, take a look:
Check your speakers. Loud asteroid explosion on video.
The next Earth flyby of this asteroid will take place on November 13, 2109 at a nominal distance of 0.17 AU.
Curious about what this object would do if it hit Earth?
Although not all needed parameters are known, our best estimate is that this object would produce a spectacular atmospheric entry, survive it in a broken condition and hit the ground with a force large enough to leave an approximately 400 m (1 340 feet) deep and 2.9 km (1.8 miles) wide crater.
If you would happen to be located 10 km (6.2 miles) away from the impact, you'd feel major shaking comparable to M6.2 earthquake 2 seconds after the impact. Air blast would arrive at your location approximately 30 seconds later with peak overpressure of 236 000 Pa (2.36 bars), max wind velocity of 320 meters per second and sound intensity of 107 dB. Damage caused by air blast would include collapsed multistory wall-bearing buildings, almost completely collapsed wood frame buildings, collapsed highway truss bridges, shattered glass windows and up to 90% of trees blown down. The fine dusting of ejecta with occasional larger fragments would arrive at your location approximately 45 seconds after the impact.
The calculation was based on a projectile diameter of 180 m, impact angle of 45 degrees, impact velocity of 17 km/s, projectile density of 3 000 kg/m3 and target density of 2 500 kg/m3 (sedimentary rock). You can repeat the calculation using this Purdue University tool.
Featured image: Featured image: The green line indicates the object's apparent motion relative to the Earth, and the bright green marks are the object's location at approximately one-hour intervals. The Moon's orbit is grey. The blue arrow points in the direction of Earth's motion and the yellow arrow points toward the Sun. Credit: Minor Planet Center.