Date on Senior Honors Thesis


Document Type

Senior Honors Thesis

Degree Name



Physics and Astronomy

Degree Program

College of Arts and Sciences

Author's Keywords

boulders; near-earth asteroid; pole direction; shape; 1992 UY4; radar


In August 2005, the near-Earth Asteroid 1992 UY4 made a close flyby, coming within 0.04 au of our planet. Between the dates of 1-10 August 2005, it was observed via delay-Doppler radar imaging by the Arecibo Observatory (2380 MHz, 13 cm) and the DSS-14 antenna at the Goldstone Deep Space Communications Complex (8560 MHz, 3.5 cm). The images achieve a resolution as fine as 7.5 m/pixel and reveal a lumpy and modestly asymmetric object. The images also revealed the presence of numerous large boulders/blocks on the surface of 1992 UY4. By using the modeling software SHAPE, which is standard in the field of asteroid radar imaging, and by using a visual examination of the models vs. radar images and the chi-square statistic as a relative (but not absolute) probability metric, I found two potential pole directions: one at lambda = 285 ±10 deg., beta = -80 ±10 deg.,and one at lambda = 110 ± 10 deg., beta = 75 ± 10 deg., the mirror direction. They represent a north-south ambiguity: 1992 UY4 may rotate either prograde or retrograde. I find that the models for the first pole direction better match the observations and I conclude that 1992 UY4 is most likely a retrograde rotator.

I identified 18 boulder candidates on 1992 UY4’s surface based on independent visual inspection of the images by Dr. Michael Busch, myself, and standard astronomical image statistics. Their distribution is concentrated in those longitudes that were seen in multiple observations from Arecibo. There are few boulders on the edges of Arecibo’s field of view, but this is likely observing bias. With the available data and without more complex modeling and statistical techniques, I cannot determine if boulders are uniformly distributed across the surface of 1992 UY4 or not. Further observations would be needed to map the rest of the asteroid. Unfortunately, there are no upcoming opportunities for future ground-based radar observations, since 1992 UY4 will not pass as near to Earth as it did in 2005 for the next several hundred years. However, thanks to my study of 1992 UY4, in addition to details about the asteroid itself, I have enabled the improvement of its trajectory.

Lay Summary

1992 UY4 is a near-Earth asteroid (NEA). I am interested in studying this asteroid because NEAs can give you insight into the origins of life and the formation of our Solar System. NEAs are also potential threats to Earth, so it is important to characterize as many of these small bodies as possible. Few asteroids of 1992 UY4's size make a close enough flyby of Earth to make detailed radar observations. This NEA has been studied by other groups of people but there are still unknown characteristics. Thus, I set out to make a detailed analysis of this NEA and to answer these questions:

1) What is the spin axis of 1992 UY4?

2) How well can we characterize the boulder population?

By conducting this research, we can gain knowledge on the evolution and structure of asteroids (specifically NEAs) and perhaps get an idea of where we came from. The spin axis can be used to refine trajectory predictions of the NEA, which can have vital consequences. Agencies, such as NASA, plan their missions based on this data and these missions continue to increase our knowledge of our Solar System. In addition, if we have accurate trajectory predictions, one could possibly prepare a proper contingency against a potential impactor. Only a handful of asteroids have been properly characterized and I hope that my work with 1992 UY4 will contribute to the overall field of NEA research.