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VLBA collaboration reveals new details of Palma asteroid

In an unusual observation, astronomers used the National Science Foundation's Very Long Baseline Array (VLBA) to study the effects on radio waves coming from a distant radio galaxy when an asteroid in our solar system passed in front of the galaxy. The observation allowed them to measure the size of the asteroid, gain new information about its shape and greatly improve the accuracy with which its orbital path can be calculated. When the asteroid passed in front of the galaxy, radio waves coming from the galaxy were slightly bent around the asteroid's edge in a process called diffraction. As these waves interacted with each other, they produced a circular pattern of stronger and weaker waves similar to the patterns of bright and dark circles produced in terrestrial laboratory experiments with light waves. In addition to the VLBA's Brewster antenna, the astronomers also used VLBA antennas in California, Texas, Arizona and New Mexico. The passage of the asteroid in front of the radio galaxy, an event called an occultation, affected the characteristics of the signals received at Brewster when combined with those from each of the other antennas. Astronomers, both amateur and professional, commonly observe asteroid occultations of stars and record the change in brightness, or intensity, of the star's light as the asteroid passes in front of it. The VLBA observation is unique because it also allowed the astronomers to measure the amount by which the peaks of the waves were displaced by the diffraction, an effect called a phase shift.

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