Look to the Skies -- It's International Asteroid Day
Active Asteroids: Dozens of worldlets in asteroid-like orbits spout comet-like tails, challenging our understanding of small bodies in the solar system.
The Blast that Shook the World: Ten years ago, as the sun rose over Chelyabinsk, Russia, the sky exploded. Since the Chelyabinsk impact, two spacecraft have not only approached small asteroids but also collected samples from them; one, Hayabusa2, already dropped off its samples back at Earth, and the other, OSIRIS-REx, will do so later this year. To that end, in November 2021 NASA launched the Double Asteroid Redirection Test (DART) mission, which slammed a half-ton impactor into the 170meter-wide asteroid Dimorphos - a moon of the larger asteroid Didymos. Chelyabinsk was a wake-up alarm for Earth —a loud one.
How Did We Get the Asteroid Belt? - The asteroid belt divides the solar system in two, with rocky planets near the Sun and giants relegated to the outskirts. Because Mars sits so close to the asteroid belt, the same process that swept away the planet's initial reservoir of building material would also have removed part of the asteroid belt. He points out that the model not only covers many features of the asteroid belt and solves the small Mars problem, it also answers several other questions about the solar system, such as why it lacks the super-Earths abundant around other stars