Wellesley's Small Telescope Contributes To Big News About Asteroids

"The science results reported in Nature reveal a phenomenon that was never before even predicted, namely that some clusters of asteroids have spin directions that are correlated," Slivan said. "All prior theories suggest that they should be random."

The findings have potentially far-reaching impact.

"The main scientific goal is to find clues to help us understand how our solar system, and Earth in particular, originally formed and subsequently evolved into what we see today," Slivan said. "A second aspect of interest is to study specifically how asteroids break apart in collisions, which would be a useful thing to know when deciding how to deal with the future possibility of an Earth-crossing asteroid someday colliding with our planet."

Slivan says Wellesley's small telescope contributed to the findings.

"Data I obtained using Wellesley's Whitin Observatory 24-inch telescope last November, only about two weeks after I began teaching here, are included in the data from which the results were derived," he said. "The fact that small telescopes in the Northeast (Wellesley's 24-inch, MIT's 24-inch and Colgate's 16-inch) can produce results meriting publication in Nature defies the 'common knowledge' that only big observatories at mountaintop sites can do world-class research."

Another factor in his study belies another fallacy: that first-year college students do not contribute to important research. At Wellesley, they most certainly did.

"Erin Marie Collins, then a first-year student, availed herself of the opportunities for early involvement in real research, encouraged and supported by the Astronomy Department faculty, and directly assisted me in obtaining the Wellesley data by observing with the 24-inch telescope," Slivan said. "Our lightcurve from that night appears in the Nature article. The details of the observing program will appear in a longer second manuscript currently in review at the planetary science journal Icarus."

Collins, of Smyrna, Ga., is excited about her contribution. "At the time, I had no idea that that what I was observing would be such a big deal," she said. "It's thrilling to know that I contributed to such a significant project." Now a sophomore majoring in psychology and minoring in astronomy, Collins continues to work at the Wellesley observatory using the 24-inch telescope this fall along with other students.

Here's a summary of Slivan's findings, in his own words:

"My research is a long-term observational study of the largest members of the Koronis family of asteroids. Asteroids are small, rocky bodies in the solar system that orbit the sun and are thought to be bits of material that never formed into a planet. They offer us clues about the conditions under which the solar system, including Earth, originally formed.

"Even though asteroids seem to be primitive material, we expect that they've not remained completely unchanged since the solar system originally formed. Collisions between asteroids have probably played a major role in creating the asteroids that we see today from larger objects that existed in the past. When a large asteroid is shattered and dispersed by a collision, the resulting fragments can form an 'asteroid family' whose members all have nearly identical orbits. To some extent we can think of the family as the outcome of a huge natural collision experiment, much more energetic than anything that humans have ever experienced. By studying the sizes, shapes and orientations of the pieces (that is, the family members) we can better understand what happened in the collision. The hope is that, eventually, this knowledge could be applied to the asteroids as a whole to help figure out how the present asteroid population is related to the original population.

"One of the most populous of these groupings is the Koronis family, whose members orbit among the main belt asteroids between Mars and Jupiter. Determining the shapes and orientations of Koronis family members from Earth presents a challenge because they're far enough away that even the largest members (diameters of about 40 km) are too small to appear as anything but a small dot of light, just like a faint star. The trick is to take advantage of the fact that asteroids in this size range tend to be irregularly shaped, exhibiting a change in brightness as they rotate and alternately present end-on and side-on views. A plot of these brightness changes over time is called a lightcurve. By observing lightcurves of an object over many years as the viewing geometry changes, it's possible to get enough data to work backwards and deduce information about the object's shape, the orientation of its spin axis and which way it's spinning on that axis.

"Prior to 1992 only a handful of Koronis family lightcurves had been recorded, far fewer than needed to do shape and spin solutions. Since that time I've been observing more lightcurves, and by the summer of 2001 I'd accumulated enough new data that I could run shape and spin solutions for nine of the largest members of the Koronis family.

"The results proved to be quite a surprise. Theoretical models of family formation and laboratory-scale collision experiments both predict that the tremendous amount of energy released in a large asteroid collision yields fragments that randomly spin off into space, but my observations show that, at least for the Koronis family, the spin axes are markedly clustered into only two preferred directions. Even more surprising is that there's an obvious correlation between the two spin orientations and two preferred rotation rates. As of now, current understanding of how families form and evolve has no consistent way to explain how these objects could possibly be aligned in the way they are. In the Nature paper, I very briefly speculate that perhaps secondary collisions after the family-forming collision formed the two observed 'spin clusters,' or perhaps some previously unsuspected dynamical effect can organize randomly oriented spins into the observed groupings."

For more on the Wellesley Astronomy Department and Whitin Observatory, go to http://www.wellesley.edu/Astronomy/.

The full text of Slivan's article can be found on the Nature web site at http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v419/n6902/full/nature00993_fs.html.

For a summary published by space.com, go to http://www.space.com/scienceastronomy/asteroid_siblings_020904.html.

Founded in 1875, Wellesley College has been a leader in liberal arts and the education of women for more than 125 years. The College's 500-acre campus near Boston is home to 2,300 undergraduate students.