VLBA Measures Asteroid’s Characteristics

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.

“By analyzing the patterns of the diffracted radio waves during this event, we were able to learn much about the asteroid, including its size and precise position, and to get some valuable clues about its shape,” said Jorma Harju, of the University of Helsinki in Finland.

The asteroid, named Palma, is in the main asteroid belt between Mars and Jupiter. Discovered in 1893 by French astronomer Auguste Charlois, Palma completes an orbit around the Sun every 5.59 years. On May 15, 2017, it obscured the radio waves from a galaxy called 0141+268 with the radio shadow tracing a path running roughly southwest to northeast, crossing the VLBA station at Brewster, Washington. The shadow sped across the Earth’s surface at 32 miles per second.

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.

Extensive analysis of these effects allowed the astronomers to draw conclusions about the nature of the asteroid. In close agreement with earlier observations, they measured the diameter of the asteroid as 192 kilometers. They also learned that Palma, like most other asteroids, differs significantly from a perfect circle, with one edge probably hollowed out. The shape determination, the astronomers said, can be further improved by combining the radio data with previous optical observations of the asteroid.

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.

“This allowed us to constrain the shape of Palma with a single, short measurement,” said Leonid Petrov, affiliated with the Geodesy and Geophysics Lab, NASA Goddard Space Flight Center.

“Observing an asteroid occultation using the VLBA turned out to be an extremely powerful method for asteroid sizing. In addition, such radio data would immediately reveal peculiar shapes or binary companions. That means that these techniques will undoubtedly be used for future asteroid studies,” said Kimmo Lehtinen, of the Finnish Geospatial Research Institute, in Masala, Finland.

One major result from the observation was to improve the precision with which the asteroid’s orbit can be calculated.

“Although Palma’s position has been measured more than 1,600 times over the past 120 years, this one VLBA measurement reduced the uncertainty in the calculated orbit by a factor of 10,” said Mikael Granvik, of Lulea University of Technology in Sweden and the University of Helsinki, Finland.

“This is a rather unusual use for the VLBA, and it demonstrates that the VLBA’s excellent technical capabilities, along with its great flexibility as a research tool, can contribute in even some unexpected ways to many fields of astronomy,” said Jonathan Romney of the Long Baseline Observatory, which operates the VLBA.

Harju, Lehtinen, Petrov, and Romney, along with Mikael Granvik of the Lulea University of Technology in Sweden, Karri Muinonen of the University of Helsinki, Uwe Bach of the Max Planck Institute for Radioastronomy in Bonn, Germany, and Markku Poutanen of the Finnish Geospatial Research Institute, reported their findings in the Astronomical Journal.

The Long Baseline Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

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NRAO Director Tony Beasley Appointed to New Five-Year Term

 

Dr. Tony Beasley, Director of the National Science Foundation’s National Radio Astronomy Observatory (NRAO), has been appointed to a new five-year term. The Board of Trustees for AUI— which operates NRAO under a cooperative agreement— and the NRAO Director Review Committee conducted a thorough review of Beasley’s leadership and performance earlier this year, and have appointed the Director to the new term through May 2027.

 

“Tony is an outstanding leader and stalwart champion for NRAO, the field of radio astronomy, the beauty of science, and the critical role of big facilities in the R&D ecosystem,” said Adam Cohen, President and CEO of AUI, which operates NRAO under a cooperative agreement. “He continues to support very innovative education and outreach programs to help build the workforce of the future, as well as programs and activities to enhance diversity, equity, and inclusion in our workplaces.” 

 

Over the course of more than two decades, Beasley’s leadership has shaped the present and future of NRAO’s leading-edge radio astronomy facilities, including the Atacama Large Millimeter/submillimeter Array (ALMA), Very Long Baseline Array (VLBA), and Very Large Array (VLA). More recently, he has collaborated on efforts to encourage cooperation between commercial spectrum users and research facilities and has created partnerships to explore the use of Green Bank Observatory’s radar systems in planetary science and defense applications. 

 

Beasley recently has generated significant support for the future of NRAO’s facilities, reaching major milestones in 2021. The observatory’s proposed next generation Very Large Array (ngVLA) received high priority for new ground-based observatories in the U.S. National Academy of Sciences’ Astronomy and Astrophysics Decadal Survey (Astro2020). Late last year, NRAO’s Central Development Laboratory (CDL) received approval and funding through the ambitious ALMA2030 Development Plan to upgrade its Band 6 receivers, which are ALMA’s most productive receivers. 

 

An ardent supporter of diversity, equity, and inclusion in astronomy and astrophysics, Beasley has elevated the efforts of NRAO’s Office of Diversity and Inclusion, Broader Impacts, and community development initiatives, including the National Astronomy Consortium (NAC), RADIAL, National and International Non-traditional Exchange (NINE), Research Experiences for Undergraduate students (REU), and most recently, grants for women in engineering fellowships and the development of a next generation Learning Center (ngLC). 

 

“Being a part of NRAO for more than 20 years has given me the opportunity to observe, contribute to, and lead growth and change in astronomy that positively impacts our facilities and allows us to collaborate with other like-minded institutions,” said Beasley. “I am proud of the work our teams have accomplished in research, engineering, outreach, and equity, and look forward to serving the NRAO community for another five years.”

 

Beasley, who holds a Doctorate in Astrophysics from the University of Sydney, was first appointed as NRAO Director in February 2012, after previously serving the observatory and the radio astronomy community in multiple capacities. He joined NRAO as a Postdoctoral Fellow in 1991 and served as Deputy Assistant Director in 1997 and Assistant Director from 1998 to 2000. He briefly left NRAO that year to become Project Manager for the Combined Array for Research in Millimeter-wave Astronomy (CARMA). In 2004, he returned to NRAO as Assistant Director, as well as Project Manager for the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. From 2008 to 2012, Beasley served as the Chief Operating Officer and Project Manager of NSF’s National Ecological Observatory Network (NEON). In addition to his role as NRAO Director, Beasley presently serves as the AUI Vice President for Radio Astronomy Operations. 

 

In January 2022, Beasley was honored as a Lifetime Fellow of the American Association for the Advancement of Science (AAAS) in recognition of his significant contributions to the field of radio astronomy. 

 

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