Massive Asteroid Passing Earth Is ‘Time Machine’ From Early Solar System

NASA has discovered an asteroid as large as 2,000-feet that is barreling towards Earth, but is not expected to make an impact. NASA’s Center for Near-Earth Object Studies has identified the asteroid as 481394 (2006 SF6). It’s likely to be closest to our planet on Nov. 20 just after 7 p.m. EST.

Walter Freeman is an assistant teaching professor in the physics department at Syracuse University’s College of Arts and Sciences. He says asteroids like the one passing Earth soon remind us of how the planets were born and shaped, and remind us that the solar system is still evolving.

Professor Freeman answers three questions about the asteroid event later on this month.

What are asteroids made of?

“These asteroids are mostly debris left over from the early solar system. They are time machines, of a sort. In the first hundred million years of its life, most of the material in the early Solar System accumulated into the growing planets, as smaller pieces of material collided with them. But not all of them found their way into the planets; some are still around, like this one. These asteroids remind us how the planets were born and shaped — and remind us that, four and a half billion years later, the solar system is still slowly changing.

How do scientists calculate which ones pose a danger of potential impact on Earth, and which do not?

“In thinking about the danger that these things might pose to us, the first issue is that space is big and mostly empty, and compared to the scale of the solar system, Earth does not present a very big target. For every 500,000 objects that pass as close as this asteroid to us, only one of them will actually hit Earth. This asteroid is large enough to cause significant damage if it hits Earth, however. NASA tracks ‘potentially hazardous objects’ like this one that are large enough to cause significant damage and that have orbits that take them close to us, and uses computers to calculate their motions to determine how close they might actually come to Earth in the future. Smaller asteroids do occasionally strike Earth and cause damage, but the risk that these visitors from space pose to us is tiny compared to the risk from the natural processes of our planet like earthquakes and hurricanes, and even tinier compared to the risk that human activity poses to our own safety through things like air pollution and climate change.”

What else is there to know about how asteroids like this one are formed and where they came from in our solar system?

“The solar system formed from a cloud of gas and dust that collapsed under its own gravity. Most of the matter fell into the center and was compressed more and more tightly by its own weight, until the immense pressure ignited nuclear fusion at its core — this is the Sun. A small fraction of the matter was left, and collected into small pieces over time. At first this happened because of static electricity; as they got bigger, gravity took over.

“Most of these pieces accumulated into ever larger chunks — the largest becoming the familiar major planets. But not all of them did. Some of the primordial ones are still out there, and astronomers refer to them as ‘minor planets.’ Some of them have also survived collisions and are broken-off bits of larger objects. Most of these are in the ‘asteroid belt’ between Mars and Jupiter, but there are others whose orbits bring them near Earth.

“We understand the motions of objects in the solar system very well. Newton’s laws of motion, combined with a computer, allow us to calculate how these objects will move in the future with very high precision. NASA JPL has a very nice animation of their orbits at this link.”

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