Killer Rocks

One of the aspects of my career as a professional astronomer that has always bothered me is that, well, I’ve chosen a kind of ….  selfish profession.  Oh sure, astronomers try to rationalize their line of work by making claims that technological advancements that further the study of the stars also end up in our homes and enhance our lives, or that such research provides much-needed perspective to the world at-large and underscores the fact  that we are but a fragile island of humanity living on this small rock, promoting the cause of peace and good-will and satisfying humankind’s innate thirst for knowledge and exploration.  All the above sounds good, and indeed I’ve likely been guilty of making similar arguments, but honestly?  Astronomy, along with a few other pure research science fields, really is about the joy of discovery and desire to know more about the Universe. If one has a strong need to “save the world” or promote world peace,  then astronomy is probably not the profession for you.  Or so I thought, until a few weeks ago. 

About 3 weeks ago, I was contacted by some fellow scientists at my institution, inviting me to join a team whose explicit focus is to design a low-cost space-based mission that would identify Near Earth Objects (NEOs) that could cause harm to Earth if they impacted.  These NEOs are asteroids and comets whose orbits take them close to that of Earth. There’s a lot of ’em out there, as can be seen in this really cool animation (the small yellow dots are the potential killers):

The yellow dots are the asteroids we have to worry about:  they cross the Earth's orbit (the blue dots are asteroids that a benign, with orbits that don't allow a possible collision with Earth).   Credits: http://iskywatch.com/2013/01/asteroids-and-you/asteroidmovie_neomb/

The big dot in the center is the Sun, and the other big white dots are the planets (Earth is the 3rd white dot from the Sun). The yellow dots (the guys inside the blue ring) are the asteroids we have to worry about: they cross the Earth’s orbit. (The blue dots are asteroids that are benign, with orbits that don’t allow a possible collision with Earth). Credits: http://iskywatch.com/2013/01/asteroids-and-you/asteroidmovie_neomb/

 

There are several observatories already in existence that are looking for asteroids large enough to cause wide-spread or even global destruction.  But there is still a niche to fill in searching for the smaller, elusive asteroids — those objects that are too large to completely burn up in the Earth’s atmosphere but too small to be easily detected by existing telescopes. An example is the Chelyabinsk meter in Russia last year that was believed to have started out as a 20-meter object before impact.

The key to detecting these small-but-deadly rocks is where my expertise comes in:  infrared observations! Infrared “light” is the light that is redder than the reddest light that your eye can see.  When it comes to detecting asteroids — especially the dark-colored ones — infrared observations are superior to observations taken at visible “wavelengths” (the kind of light that your eyes can see, the colors of the rainbow).  This superiority can be summed up by a single picture:

The surface of asteroids can be dark and sooty, or white and shiny.  The dark asteroids don't reflect much light, and so those asteroids show up very dimly at visible wavelengths.  That same, dark asteroid shows up about as brightly as a white/shiny asteroid of similar size in the infrared.  Why?  Because infrared light is generated by the temperature of the asteroid's surface, not by reflected light from the Sun, the infrared brightness is not as dependent on how dark or shiny the surface is.  Image credit: NASA/JPL-Caltech

The surfaces of asteroids range from dark and sooty to  white and shiny. The dark asteroids don’t reflect much light, and so those asteroids show up very dimly at visible wavelengths.  In contrast, a dark asteroid and a shiny asteroid of same size will have similar infrared brightnesses.  Why? Infrared light is generated by the temperature of the asteroid’s surface, not by reflected light from the Sun.  Therefore,  the infrared brightness of an asteroid is much more dependent on how big the asteroid is than  on how dark or shiny the surface is. Image credit: NASA/JPL-Caltech (http://www.nasa.gov/mission_pages/WISE/multimedia/gallery/neowise/pia14732.html)

Notice how the visible brightness  is completely dependent on how “shiny” the asteroid surface is, but the infrared brightness seems to be independent of the surface color.  The “take away” message is: infrared observations are able to spot the dark, sneaky asteroids that might go undetected by visible-light observations.

So far, I’ve had a lot of fun learning about asteroids and working with a diverse group of scientists and engineers on this project.  And who knows, maybe this work will actually save a life someday!

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