Duck! It’s an Asteroid! February 12, 2014Posted by Lofty Ambitions in Science, Space Exploration.
Tags: JPL, Physics
If you’re celebrating today, you’re probably celebrating Lincoln’s birthday, a welcome mid-winter holiday for us as children growing up in Illinois. Or maybe you’re celebrating the natal day of Charles Darwin, the renowned naturalist and geologist who was born on the same day as Abraham Lincoln in 1809. By mapping out his theory of natural selection, Darwin changed the way we think about ourselves, our history, and the natural world of which we are part.
Lofty Ambitions is also celebrating an asteroid landing. On this date in 2001, a robotic space probe named NEAR Shoemaker landed on 433 Eros, the second largest near-Earth asteroid. NEAR, in fact, stands for Near Earth Asteroid Rendezvous. It wasn’t exactly Armageddon—no Razzie Awards for this accomplishment. A spacecraft had never before orbited and landed on an asteroid.
How near an asteroid to Earth is 433 Eros? Less than a year after NEAR Shoemaker landed there, the asteroid passed within 17 million miles of Earth, which was still more than seventy times farther from Earth than the Moon. In fact, NEAR Shoemaker launched on February 17, 1997 (a year before Armageddon was released), and finally began orbiting 433 Eros almost three years later, on February 14, 2000. The probe spent a year orbiting and relaying back data about the asteroid’s physical characteristics and motion before landing on February 12, 2001.
How big an asteroid is 433 Eros? 433 Eros has an elongated shape, estimated to be more than 20 x 8 x 8 miles in size. 1036 Ganymed is larger, with a diameter of roughly 20 miles. Asteroids are small in relation to the size of Earth, but 433 Eros travels at 15 miles per second, so a collision with Earth would be devastating. Consider how small and light the piece of foam was when it hit Space Shuttle Columbia during launch—velocity matters in the damage a collision causes.
How many of these NEAs are there? According to NASA, as of this month, “10,693 Near-Earth objects have been discovered. Some 868 of these NEOs are asteroids with a diameter of approximately 1 kilometer or larger. Also, 1,454 of these NEOs have been classified as Potentially Hazardous Asteroids.”
We’ve written about risk and scale before, and thinking about asteroids today brings up these same issues again. Almost a year ago, on February 15, 2013, a meteor exploded over Chelyabinsk, Russia, and reminded us that objects from space aren’t just statistics. In fact, Space.com reported that studies of that meteor and where it originated led some scientists to conclude that the risk of impact by an object from space is ten times higher than we’d previously thought.
NASA’s Jet Propulsion Laboratory keeps track of NEOs and shares a chart of potential risks. Even so, NASA’s website on NEO risk points out, “Whenever a newly discovered NEA is posted on the Sentry Impact Risk Page, by far the most likely outcome is that the object will eventually be removed as new observations become available, the object’s orbit is improved, and its future motion is more tightly constrained.” The more we know about each object and its motion, the more accurately we can determine whether it’s likely to come close enough to Earth to pose a problem.
Using our Earth-bound sense of distance, those two large, near asteroids are not that close. But if we think about these objects in relation to the vast universe, proximity means something different. It’s mid-boggling to try to imagine millions and billions of miles of space and to think of 17 million miles as nearby.
We’ve been reading novelist and physicist Alan Lightman’s recent essay collection, The Accidental Universe: The World You Thought You Knew. There, he talks of scale in “The Gargantuan Universe”:
Of all these aspects of things, none seems more immediate and vital than size. Large versus small. Consciously and unconsciously, we routinely measure our physical size against dimensions of other people, animals, trees, oceans, mountains. As brainy as we think ourselves, our bodily size, our bigness, our simple volume and bulk are the first carrying cards we present to the world. I would hazard a guess that somewhere in our fathoming of the cosmos, we must keep a mental inventory of plan size and scale, going from atoms to micobes to us humans to oceans to planets to stars. And some of the most impressive additions to that inventory have occurred at the high end. Simply put, the cosmos has gotten larger and larger. At each new level of scale, we have to contend with a different conception of the world that we live in.