Getting to Know Your Asteroid Foes


Did you watch Phil Plait’s “Bad Universe” the other night? If so, then you know that an asteroid impact is a rather serious threat from space. Eventually, we’re going to get hit with an asteroid or comet and we need to be ready. One great way to prepare is to actually know the danger, and that is just what several astronomers plan to do with the Spitzer Space Telescope.

SLIDE SHOW: The top 10 near-Earth objects (NEOs) as selected by the Discovery News team.

Near-Earth Objects, or NEOs, are debris in our solar system that actually cross Earth’s orbit. Monitoring programs are in place across to globe to detect the faint bit of light reflecting off of NEOs that move through the field of view of ground-based optical telescopes.

WATCH VIDEOS: From meteors to asteroids, browse this Discovery News video playlist and discover what it takes for a piece of space rock to turn potentially hazardous for life on Earth.

However, the albedo, or reflectivity of a given asteroid, is difficult to determine from those observations alone, thus the sizes are not known for the vast majority of NEOs. Is a bright object bright because it is big, or just because it is really reflective? Almost 99% of all NEOs are not well-measured, and most of these are smaller than a kilometer in size, but still large enough to do some serious damage.

Enter Spitzer. This space-based infrared telescope ended its main mission when the coolant ran out, as scheduled, in 2009, after five and a half years of stunning observations. Without the coolant, the telescope can still use its two shortest wavelength detectors in an extended project called the “Warm Spitzer” mission.

WIDE ANGLE: Find out more about Bad Universe and how asteroids could really mess with your day.

A team of sixteen astronomers has ambitiously set out to use Spitzer to characterize the sizes of 700 NEOs over the next few years. Using both optical and infrared data, the albedo of the asteroids can be measured, thus giving astronomers an understanding of the size distribution of our potential foes.

The first 101 objects show a wide range of albedos, thus a wide range of compositions. As we learned in “Bad Universe,” the composition and structure of an asteroid headed for Earth will have a serious impact (pun intended) on our mitigation strategy. In other words, deflecting an interplanetary “rubble pile” will be different from dealing with a solid rocky or metallic object.

Don’t get me wrong, it’s not all doom and gloom. These objects are interesting from a scientific standpoint as well. The size distribution can tell astronomers something about how these rocks go to their present orbits through collisions and interactions and where in the solar system they originally came from. Some of these asteroids may be ex-comets that have shed all their ices, which has important implications for the history of the solar system and life on Earth.

The real-life implications of this study do tend to take center-stage. As Congress mandated that 90% of all NEOs larger than 140 meters be identified by 2020, this work will be crucial to understanding just how many are out there in the first place. Not to mention, how many astronomers can say that their research could potentially save the world?

Image: Eros, as imaged by the NEAR spacecraft in 1998. Observations of this well-studied object helped the researchers refine their albedo models. Credit: NASA/NEAR

This work has been accepted by The Astronomical Journal, and the preprint is available on

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