NASA and other scientists have begun training simulations to plan for asteroids colliding with Earth, according to Space.com. Scenarios have been developed that would grant us eight years’ warning to avert a disaster. As we look at the asteroid belt, it holds many mysteries, threats, and fascinating facets.
The hypothetical asteroid defense scenario is an exercise that was recently run at the International Academy of Astronautics’ Planetary Defense Conference (or IAAPDC), which was held in late April 2019 in College Park, Maryland. According to the article on Space.com, the scenario is “fully fleshed out so that scientists, engineers, policymakers, and emergency management experts can work through questions and concerns that might arise if scientists ever do identify such a threat.” In the meantime, we’ve learned a great many things about the asteroid belt and its two largest asteroids, Ceres and Vesta.
Earthbound Asteroid – Creating the Asteroid Belt
The creation of the Sun and our solar system began with the gravitational implosion of stardust and some very dense gas pockets. As the materials collapsed inward, most of them gained heat and speed and formed a protostar. Then things get interesting. “The rest of the matter around the protostar flattens into a disk due to its mutual gravity and the rotation of the system,” said Dr. David M. Meyer, Professor of Physics and Astronomy at Northwestern University. “This disk of gas and stardust will eventually coalesce into planets around the star. This total formation process, on average, we think takes about 100 million years.”
Water molecules were abundant in this early solar system. Within a certain radius around the star—a distance of 2.7 astronomical units, or 2.7 times the distance of the Earth to the Sun—it was too warm for the water to turn from gas to ice. This radius is called the “frost line.” Inside the frost line, dirt and rocks collided and gained mass, eventually becoming the first four planets of the solar system. Outside the frost line, ice particles joined the mix of colliding dirt and rocks, forming enormous planets like Jupiter and Saturn. Meanwhile, solar winds and the gravitational pull of the larger outer planets cleared out miscellaneous gases and enormous icy rock giants from the middle of the frost line, leaving what we now know as the asteroid belt—millions of rocks orbiting the solar system loosely between the first four planets and the larger, outer planets.
Largest Asteroids – Meeting Ceres and Vesta
Among the asteroids in the asteroid belt, the largest by far is Ceres. “Ceres is actually big enough to be classified a dwarf planet like Pluto,” Dr. Meyer said. “Ceres appears to be a rock/ice mix, and it actually probably formed just beyond the frost line.” In 2015, the space probe Dawn—launched by NASA in 2007—reached a point at which it could provide close-up pictures of Ceres, which have since been sent back to Earth to reveal a beautiful celestial body with notable features including huge craters.
However, Vesta, another of the largest asteroids in the belt, proved to have been positively pummeled by other asteroids. Though much smaller than Ceres, Vesta shows a considerably higher number of impact marks and craters across its surface. The Dawn probe was able to capture such a significant amount of imagery of Vesta that scientists have since mapped and named several of its features. “If we look at the south polar region of Vesta, we see a huge mountain,” Dr. Meyer said. “This mountain is at the center of a really big crater. This crater, named Rheasilvia, has a diameter of 500 kilometers and a crater count analysis indicates that it is about a billion years old.” Dr. Meyer explained that the mountain at Rheasilvia’s center stands 25 kilometers above the crater floor, making it the second-tallest mountain in the solar system next to Mars’s Olympus Mons.
Any asteroid threatening Earth is purely hypothetical at this point. However, NASA scientists agree it’s better to be prepared just in case. The treasure trove of knowledge we have about our asteroid belt and its biggest asteroids can help us understand and counter a threat, should one come our way.
Dr. David M. Meyer contributed to this article. Dr. Meyer is Professor of Physics and Astronomy at Northwestern University, where he is also Director of the Dearborn Observatory and Co-Director of the Center for Interdisciplinary Exploration and Research in Astrophysics. He earned his B.S. in Astrophysics from the University of Wisconsin, and his M.A. and Ph.D. in Astronomy from the University of California, Los Angeles.