The largest publication ever published on radar observations of near-Earth asteroids has been published, gathering years of data from the Arecibo Observatory in Puerto Rico.
Using Doppler delay radar observations collected by the observatory between December 2017 and December 2019, the study includes radar cross sections of 191 asteroids and Doppler frequency broadening. This data can be used as clues to the asteroids’ rotation periods and sizes, as well as polarization information for 110 of them, which can help understand surface and subsurface properties. Thirty-seven asteroids were presented in more detail with a more precise size estimate, a preliminary estimate of shape, information on how reflective they are on radar, and whether the radar observations match visual and near-infrared observations.
The work was recently published in Journal of Planetary Sciences.
As one of the only papers of its kind to include a large number of asteroid targets, the study serves as a “treasure trove of data” for planetary scientists, given that most existing literature focuses on just one object at a time, says Ann Virkey , the lead author of the study and a researcher in the Department of Physics at the University of Helsinki in Finland.
The researchers say the large amount of asteroid data in the study is important for many reasons.
For example, the characteristics of several potentially dangerous asteroids are included in the paper, which is notable because observations from Arecibo have contributed to past efforts to protect the planet, including the recent DART mission.
Although the Arecibo Planetary Radar Group focuses on supporting NASA’s Planetary Defense Program, the wealth of information in the survey also has economic benefits, providing asteroid mining companies with data on metal- and ice-rich near-Earth asteroids containing interesting resources.
The variety of asteroid data in general also tells other scientists about the formation and evolution of the solar system.
The radar is the best ground-based tool for characterizing near-Earth asteroids, says Flavian Venditti, head of Arecibo’s Planetary Radar Science Group and co-author of the study.
“The amount of valuable data collected is unique and these results could not have been achieved with any other existing facility,” says Venditti.
Although the telescope collapsed in 2020, scientists continue to analyze the accumulated data collected by it.
Through the study, scientists found two near-Earth asteroids with unusually high radar albedo, or radar reflectivity, suggesting they may be rich in metals. The possibility of two more is significant; few metal-rich NEAs have been discovered so far.
Another near-Earth high-radar albedo asteroid, rare equal-mass binary 2017 YE5, is assumed to have ice beneath its surface instead of metal richness due to its low bulk density. Classified in the survey as a D-type NEA, 2017 YE5 is potentially the first of its kind observed with radar.
More classifications were made with scientists listing five possible enstatite-rich or E-type asteroids that had not been identified as such before using polarization information from radar.
The data was accompanied by numerous images of asteroids with a resolution of 7.5 meters, an unusual feature in the existing literature. No other ground-based instrument, except radar, can take images with a resolution better than 10 meters of celestial objects farther than the Moon, and until the collapse of the telescope in 2020, the Arecibo radar was the most powerful and sensitive planetary radar in the world.
Although abundant in its data, the study leaves doors open for further research.
“This paper is like a teaser for a whole movie,” Virkey says.
Venditti says the research data shows how rich the information obtained with the radar is.
“In fact, there is still a lot of high-quality data to be analyzed in detail that could even help plan future spacecraft missions to small bodies,” says Venditti.
Funding for the research was provided through NASA’s Near-Earth Object Observation Program. The University of Central Florida operates the Arecibo Observatory for the US National Science Foundation under a cooperative agreement.
Study Title: Arecibo Planetary Radar Observations of Near-Earth Asteroids: December 2017 – December 2019.
Accreditations of researchers
Virkki received her PhD in Astronomy from the University of Helsinki in 2016. She currently works at the University of Helsinki in the Planetary Science Research Group. Virkey joined the Arecibo Observatory in April 2016 and the University of Central Florida in April 2018. She served as head of the Arecibo Planetary Radar Science Group from 2018 to 2021.
Venditti received her PhD in Space Engineering from the National Institute for Space Research in Brazil in 2013. She joined the Arecibo Observatory in 2017 and has served as head of its Planetary Radar Science Group since 2021.
Other Arecibo Planetary Radar members who contributed to the study include observatory scientists Sean Marshall and Maxime Devogel and data analysts Luisa Zambrano-Marin and Anna McGilvray.