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The Universe Tonight

Nov 3, 2012 6:00pm
University of Hawai'i 2.2



Saturday, November 3rd, 2012 at 6:00PM

Mark Willman


Young Asteroids Get the Blues

In April 2012 a half dozen billionaires formed a company, Planetary Resources, to mine asteroids for platinum group metals and ice.  Although there are shops on Earth that sell meteorites, this is the first commercial enterprise involving the asteroids and represents a significant expansion in the territory used by humans to exploit resources.  However, to obtain the minerals and ice in asteroids we need to be able to identify them by remote observation.

There are still some difficulties in making that identification.  The study of asteroids, islands of rock that orbit in a belt between Mars and Jupiter, only dates from 1800.  In the early 20th century astronomers identified the inner main belt asteroids as the likely source for meteorites falling on Earth.  It was expected that the same type of rock in both asteroids and meteorites would lead to similar colors.  However in the 1970s a discrepancy appeared when the asteroids turned out to be redder than the meteorites.  One suggestion for explaining this color mismatch was space weathering, the idea that some space process might gradually redden the asteroids from the original unweathered bluer color displayed by meteorites on Earth.

This idea fell out of favor for decades but finally carried the day in 2000 due to lab experiments and the colors of moon craters.  During the past decade telescopic observations revealed that groups of asteroids of different age show different stages of reddening compared to meteorites.

To estimate the age we use groups of asteroids that have similar orbits. These groups are called asteroid families because they are created when a parent asteroid is smashed into fragments during a collision.  The more different the orbits in a family are, the longer it has been since the collision and this yields an age estimate.

Combining the color and age of asteroid families allows us to determine the rate at which space weathering occurs.  The final goal of this modeling is to separate the color effect of weathering from the original color of the rock and thereby accurately identify rock types from spectra. Then remote observation could survey the thousands of asteroids in near Earth orbits for those that might be lucrative, while doing this same search by spacecraft would be prohibitively expensive.On the first Saturday of each month, the Visitor Information Station (VIS) hosts The Universe Tonight, a special presentation on the current research and discoveries occurring on Mauna Kea. The presentation begins at 6:00 PM and is followed by the regular evening stargazing program at the VIS.




Mark Willman got his Ph.D. from the Institute of Astronomy at UH Manoa in 2010, one of the two Hawaii resident grads over the last decade, both from Pahoa.  He first looked through a telescope in high school in Taiwan where he grew up and in grad school he studied space weathering of asteroids, the process causing asteroids to slowly change color, with Dr. Robert Jedicke.  His research determined that space weathering occurs on a time scale of about a half billion years although this is still under debate. A longtime Puna resident, he has been a commercial orchid grower and tour operator, but returning to science in astronomy was natural as Hawaii is a leader in the field.  Mark is now support astronomer assisting observers with cameras at the UH88 telescope.



The Universe Tonight typically features an astronomer from one of the observatories on Mauna Kea giving a presentation on recent observations and discoveries from their telescope. Observatories are on a rotating schedule. If you would like to know about upcoming presentations, please call the VIS at (808) 961-2180 during operational hours.

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