Today, June 30, is Asteroid Day, a UN designated day to build public awareness of the risks of asteroid impacts.
June 30 is the day of the largest asteroid impact in recorded history - the Siberia Tunguska event in 1908.
Asteroid Day was co-founded by astrophysicist and famed musician Brian May, Apollo 9 astronaut Rusty Schweickart, filmmaker Grig Richters, and B612 Foundation President Danica Remy.
As of today and according to statistics maintained by CNEOS, 32,268 Near-Earth Asteroids (NEAs) have been discovered, ranging in size from 1 meter up to 32 km. The number of near-Earth asteroids over 1 km in diameter is estimated to be about 853, of which over 90% have been discovered. 2,343 of the NEAs are classified as potentially hazardous asteroids (PHAs). https://cneos.jpl.nasa.gov/stats/totals.html https://en.wikipedia.org/wiki/Potentially_hazardous_object #AsteroidDay
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Today's Near Earth Object (NEO), on Asteroid Day, is asteroid 2023 MZ5, 16 - 23 m wide, which approached within a safe distance of 2.629 times the lunar distance (LD) from earth at 10:00 UTC today.
See https://cneos.jpl.nasa.gov/ca/ for a list of NEOs approaching earth in the near future.
Various telescopes and observatories around the world, some now defunct, are used to find and track asteroids.
The following chart shows the number of Near-Earth Asteroid (NEA) discoveries per year, by survey.
According to abundant geological evidence, an asteroid roughly 10 km in size hit Earth about 65 million years ago. This impact made a huge explosion and a crater about 180 km across. Debris from the explosion was thrown into the atmosphere, severely altering the climate, and leading to the extinction of roughly 3/4 of species that existed at that time, including the dinosaurs.
Luis Alvarez first published the theory linking the dinosaur extinction event to an asteroid strike.
By comparison, 433 Eros, the 2nd-largest near-Earth object, has a rather ominous appearance.
Size: 34.4 × 11.2 × 11.2 km
Mean diam: 16.84 km
Mass: 6.7E15 kg
Eros crosses the orbit of Mars, but not of earth. Calculations suggest that Eros may evolve into an Earth-crosser within as short an interval as 2 million years, and has a roughly 50% chance of doing so over 100-1000 million years.
The largest NEO is 1036 Ganymed at 35 km diameter.
Who can forget the NASA DART mission, where the spacecraft rammed into asteroid Didymos's moonlet Dimorphos on Sep 26, 2022, to demonstrate the kinetic impactor technique for changing the trajectory of an asteroid.
The impact shortened Dimorphos's orbital period of 11 hour and 55-minute by 33 minutes.