Planetary Radar

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Planetary Radar studies the celestial bodies in our solar system: planets, moons, asteroids and comets. Directed by the 1000 foot reflector, a powerful beam of radio energy is transmitted in the direction of the target object. A very small portion of this energy is reflected by the target, back in the direction of earth. This weak radio echo is collected, focused and detected by the Arecibo Telescope. The signal is processed, then analyzed to yield information about the surface roughness, composition, size, shape, rotation and path of the target object. The Arecibo Radio Telescope has been used to measure the rotation rate of Mercury and to generate surface maps of large areas on Mercury, Venus and the Moon, locating mountain ranges, craters and rift valleys. The first detection of radar echo from a comet was made at Arecibo.

Science Group

The Planetary Radar Science group is a department of the Arecibo Observatory, which is a facility of the National Science Foundation operated under cooperative agreement by the University of Central Florida (UCF), Yang Enterprises, Inc. (YEI), and Universidad Ana G. Mendez (UAGM).

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The Arecibo Observatory Planetary Radar program is fully funded by NASA's Near Earth Object Observations Program and proudly supports NASA's efforts to track and characterize near-Earth objects for planetary defense. For information about asteroid and comet orbits, including close approaches to Earth, please see the websites of the NASA Center for Near-Earth Object Studies and the NASA Planetary Defense Coordination Office.

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In the 2030’s, two spacecrafts - NASA’s Europa Clipper and the European Space Agency’s Jupiter Icy Moons Explorer (JUICE) missions - will enter orbit around Jupiter to study the planet’s largest moons. Until then, observations of the Galilean satellites - named for their discoverer - are restricted to observations from Earth. Read More


The Arecibo Observatory in Puerto Rico is following an asteroid approaching Earth this week and while it poses no threat, it appears to know our planet is facing a pandemic. “The small-scale topographic features such as hills and ridges on one end of asteroid 1998 OR2 are fascinating scientifically,” says Anne Virkki, head of Planetary Radar at the observatory. “But since we are all thinking about COVID-19 these features make it look like 1998 OR2 remembered to wear a mask.” The National Science Foundation facility, which is managed by the University of Central Florida, has a team of experts who monitors near-Earth asteroids. This asteroid is in a special class of near-Earth asteroids called Potentially Hazardous Objects (PHOs).

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S-Band Spotlight

Arecibo Radar Observations Remove Asteroid 2020 NK1 from CNEOS Sentry List

Arecibo, Puerto Rico – August 7, 2020

Arecibo Observatory radar observations have removed the near-Earth asteroid 2020 NK1, originally estimated at more than 500 meters (1600 feet) across, from the CNEOS Sentry List. Before the Arecibo observations, 2020 NK1 was calculated to be one of the biggest threats out of all known asteroids on NASA’s list of potential impactors, with about one chance in 70,000 of impacting the Earth between 2086 and 2101.

Arecibo’s Planetary Radar Group made it a priority to observe 2020 NK1 when it came within 5 million miles of the Earth and therefore in range for the AO radar system. However, the approaching Tropical Storm Isaias, due to slam into the island at the same time, threatened the observation plans since any storm damage to the telescope or sustained winds would prevent the observations from taking place.

Radar range-Doppler image of 2020 NK1 reveals an elongated asteroid approximately 1 km (0.6 mi) along the long axis. The image resolution in the vertical dimension is 30 m/pixel. Image credit: Arecibo Observatory/NASA/NSF.

“Fortunately, the storm passed quickly without damage to the telescope or the radar system, and the Observatory staff made all the possible efforts to reactivate the telescope from hurricane lockdown in time for the observations scheduled for July 31”, described Dr. Sean Marshall, an observatory scientist who led the radar observations of the Potentially Hazardous Object (PHO) at Arecibo.

“Fortunately, the storm passed quickly without damage to the telescope or the radar system, and the Observatory staff made all the possible efforts to reactivate the telescope from hurricane lockdown in time for the observations scheduled for July 31” - Dr. Sean Marshall, Observatory Scientist at Arecibo Observatory

The team of scientists and telescope operators were able to observe the asteroid on July 31st for two and half hours, collecting precise measurements of the asteroid’s velocity and distance from Earth, and high-resolution images of the asteroid itself. “These measurements greatly improve our knowledge of 2020 NK1’s orbit and allow for predictions of its future whereabouts for decades to come,” says Dr. Patrick Taylor, a scientist at the Lunar and Planetary Institute, part of Universities Space Research Association, who participated in the observation remotely.

The radar images obtained reveal an elongated shape with a diameter along its longest axis of approximately 1 km. The observations showed the asteroid is not expected to get close enough to Earth to pose a danger in the future, with its closest approach coming in 2043 when it will pass about 2.25 million miles from Earth – or more than 9 times farther away than the Moon, the team concluded.

“This event was a great example of the important role that the Arecibo planetary radar system plays in planetary science and planetary defense, with very quick response times and high-precision radar measurements and imaging capabilities, in spite of storms, the COVID-19 pandemic, and earthquakes with which Puerto Rico has dealt with this year”, says Dr. Anne Virkki, the head of the Planetary Radar group at the Arecibo Observatory.

2020 NK1 is one of many PHOs that NASA tracks. Asteroids are considered PHOs if they are bigger than 500 feet in diameter and come within 5 million miles of the Earth’s orbit. No known PHOs pose an immediate danger to the Earth, but observations like those conducted at the Arecibo Observatory are used to determine their future trajectories and risk.

Other team members participating in the radar observation of 2020 NK1 were Dr. Flaviane Venditti and Telescope Operators Israel Cabrera and Juan Marrero at Arecibo. Virkki and Dr. Dylan Hickson, also from Arecibo, participated in the data analysis.

UCF manages the NSF facility under a cooperative agreement with Universidad Ana G. Méndez and Yang Enterprises Inc. The Arecibo Planetary Radar Project is fully supported by NASA’s Near Earth Object Observations Program in NASA’s Planetary Defense Coordination Office through a grant awarded to UCF. Arecibo has played a role in analyzing NEOs for decades, observing up to 130 objects per year.

Click here for the UCF press release about these observations!

The Arecibo Planetary Radar program is a project of the Near-Earth Object Observations Program in NASA’s Planetary Defense Coordination Office.


Publications making use of Arecibo Observatory Data

NOTE: Any opinions, findings, or recommendations expressed here do not necessarily reflect the views of the Arecibo Observatory, the National Science Foundation (NSF), University of Central Florida (UCF), Yang Enterprises (YEI), and Universidad Metropolitana (UMET), or the National Aeronautics and Space Administration (NASA). This website section is maintained by Dr. Sean Marshall