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In an unusual observation, astronomers have used the very long basic chart of the National Science Foundation (VLBA) to study the effects of radio waves coming from a distant galaxy when an asteroid from our solar system was passing by. the Galaxy. The observation allowed them to measure the size of the asteroid, to obtain new information on 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 from the galaxy were slightly bent around the edge of the asteroid, in a process called diffraction. As these waves interacted, they produced a circular shape of stronger and weaker waves, similar to the patterns of dark and light circles produced in terrestrial laboratory experiments with light waves.
"By analyzing the characteristics of the radio waves diffracted during this event, we were able to learn a lot about the asteroid, including its size and precise position, and to gain valuable insights into its shape," said Jorma Harju, of the University of Helsinki in Finland.
The asteroid, named Palma, lies in the main belt of asteroids between Mars and Jupiter. Discovered in 1893 by the French astronomer Auguste Charlois, Palma completes an orbit around the Sun every 5.59 years. On May 15, 2017, he disguised the radio waves of a galaxy called 0141 + 268, the shadow of the radio tracing a path roughly from south-west to northeast, crossing the Brewster VLBA station , in the state of Washington. The shadow crossed the surface of the Earth at 32 miles per second.
In addition to the VLBA Brewster antenna, astronomers have 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 occultation, affected the characteristics of the signals received at Brewster when they were combined with those of each of the other antennas.
A thorough analysis of these effects has allowed astronomers to draw conclusions about the nature of the asteroid. In close agreement with previous observations, they measured the diameter of the asteroid at 192 kilometers. They also learned that Palma, like most other asteroids, differs significantly from a perfect circle, with an edge probably hollowed out. According to astronomers, the determination of the shape can be improved by combining the radio data with the previous optical observations of the asteroid.
Astronomers, both amateur and professional, generally observe the occultations of asteroid stars and record the variation in brightness or intensity of starlight as the asteroid passes in front of them. she. The VLBA observation is unique because it has also allowed astronomers to measure the amount of displacement of wave peaks by diffraction, an effect called phase shift.
"This allowed us to limit Palma's shape with a single, short measure," said Leonid Petrov, an affiliate of the geodesy and geophysics laboratory at NASA Goddard Space Flight Center.
"The observation of an asteroid obscuration with the help of VLBA has proved to be an extremely powerful method for asteroid sizing." Moreover, these radio data will reveal immediately special shapes or binary companions, "said Kimmo Lehtinen of the Finnish Geospatial Research Institute in Masala, Finland.
A major result of the observation was to improve the accuracy with which the orbit of the asteroid can be calculated.
"Although Palma's position has been measured more than 1,600 times in the last 120 years, this VLBA metric has reduced orbital uncertainty calculated by a factor of 10," he said. Mikael Granvik, from the Lulea University of Technology in Sweden and the University of Helsinki, Finland.
"This is a rather unusual use for the VLBA, and this demonstrates that VLBA's excellent technical capabilities, as well as its great flexibility as a research tool, can contribute unexpectedly to many areas of the world. astronomy, "said Jonathan Romney. Long Baseline Observatory, which operates the VLBA.
Harju, Lehtinen, Petrov and Romney, with Mikael Granvik from the Lulea University of Technology in Sweden, Karri Muinonen from the University of Helsinki, Uwe Bach from the Max Planck Institute for Radio Astronomy in Bonn, Germany, and Markku Poutanen of the Finnish Geospatial Research Institute, presented its findings in the Astronomical Journal.
The Long Baseline Observatory is a facility of the National Science Foundation, operated under a cooperative agreement by Associated Universities, Inc.
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