At Asteroid Day, we are very sorry to hear of the collapse of the Arecibo Observatory’s iconic 305-metre radio telescope. This is a sad loss for radio astronomers and asteroid scientists around the world. When used as a planetary radar, Arecibo has been at the forefront of characterising asteroids and helping with planetary defense by refining our knowledge of asteroid orbits.
Initially built 57 years ago, and administered by the US National Science Foundation’s (NSF), the Arecibo telescopes was already facing decommissioning, but the collapse of the telescope’s 900-tonne instrument platform onto the reflector dish below appears to have sealed its fate.
This is a big loss for NASA’s near-Earth object observations programme, which started funding the planetary radar programme in November 2011. Lindley Johnson, director of NASA’s Planetary Defense Coordination Office, is reported to have said, “This is a hard thing to have to take.” at a 30 November meeting of the agency’s Planetary Science Advisory Committee.
Although the Goldstone solar system radar can continue observing asteroids, Arecibo was unparalleled in its power and sensitivity.
Arecibo research scientist, Anne Vrikki, who leads the Planetary Radar Science Group at the observatory, has kindly sent us a list of Arecibo’s achievements in the realms of asteroids and planetary defense for the last two decades. It is an impressive list:
2000: Arecibo radar observations reveal the dog bone shape of main belt asteroid 216 Kleopatra (S. J. Ostro et al., Science, 2000).
2002: Arecibo radar observations reveal binary asteroids in the near-Earth asteroid population, yield mass/density measurements for both components, reveal spin-up and mass shedding as the likely formation mechanism (J. L. Margot et al., Science, 2002).
2003: Arecibo radar observations provide the first detection of the Yarkovsky effect, a non-gravitational force that affects asteroid trajectories (S. R. Chesley et al., Science, 2003; J. D. Giorgini et al., Science, 2002).
2005-2006 and 2012-2013: Arecibo radar observations help to predict that the 300-meter (1000-feet) in diameter asteroid 99942 Apophis will not impact the Earth in April 2029, but will pass safely by at less than 0.1 lunar distance (J. D. Giorgini et al. Icarus, 2008; M. Brozovic et al., Icarus, 2018).
2006: Arecibo radar observations provide detailed characterization of binary asteroid 1999 KW4 (S. J. Ostro et al., Science, 2006).
2007: Arecibo radar images and optical lightcurves reveal the YORP effect, a thermal torque which changes how asteroids rotate, on near-Earth asteroids 54509 2000 PH5 (P. A. Taylor et al., Science, 2007).
2008: Arecibo radar discovers the first triple near-Earth asteroid system: 2001 SN263 orbited by two moons (M. C. Nolan et al., Central Bureau Electronic Telegrams, 2008).
2013: Arecibo radar data is used for deriving the shape model of 101955 Bennu, the target of the OSIRIS-REx spacecraft, which successfully collected a sample from the asteroid’s surface in October 2020 (M. C. Nolan et al., Icarus, 2013).
2015: Arecibo detects its smallest near-Earth asteroid ever, 2015 TC25, at five lunar distances from earth; it is believed to be only two meters in diameter (V. Reddy et al. Astronomical Journal, 2016).
2017: Arecibo observes the parent body of the Geminid meteor shower, asteroid 3200 Phaethon, which is the target of the DESTINY+ spacecraft mission (P. A. Taylor et al. Planetary and Space Science, 2019).
2020: Arecibo radar data is used for deriving the shape model of asteroid 65803 Didymos, the target of the Double Asteroid Redirection Test (DART) mission, which is planned to conduct the first kinetic impactor test in space in October 2022 (S. P. Naidu et al., Icarus, 2020).
You can also find some recent press releases from Arecibo radar team here.
Anne Virkki contributed to Asteroid Day LIVE 2020. You can watch her contribution in the panel Asteroid Safari: Finding the Elusive Space Rocks Panel.