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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.

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.

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.

Recently Observed Objects


Past Observations

Upcoming Radar Targets

The following tables list: (1) targets with submitted observing proposals, including those from our annual high and medium priority proposals and (2) possible radar targets, often newly discovered asteroids, that may be detectable, but have not yet been scheduled for observation. Further details on these objects are available including SNR estimates, specific observing tracks, and pointing, Doppler, and range uncertainties.

These tables are not comprehensive lists of all asteroids visible from Arecibo. For more complete lists of possible targets of opportunity and long-term future radar targets, updated daily, see: all asteroids visible today (SNR > 2/day), this month (SNR > 2/day), and in the next five years (SNR > 100/day). Note that these tables inevitably include objects that are currently "lost," often suggested by "1d" in the Type column, which stands for "one apparition with a days-long arc," so observer beware!

Requests for Optical/Infrared Observations

Astrometry: optical astrometry is specifically requested for objects with three-sigma plane-of-sky pointing uncertainties (from the JPL Horizons database) of tens of arcseconds or more. The plane-of-sky uncertainties refer to the first date of the radar observing window listed. Often these are lower limits as the pointing uncertainty often grows with time, especially for newly discovered objects; however, in some cases the pointing uncertainty is much lower prior to the object entering the Arecibo field of view. Optical observers are asked to submit astrometry to the Minor Planet Center as soon as possible after observations.

Lightcurves: optical lightcurves and period estimates are specifically requested for objects that will produce high-resolution images (i.e., possible shape models), for targets of IRTF thermal-infrared observations, for candidate binary asteroids, and for potential human-exploration targets. Lightcurve observers are asked to relay period estimates to the radar team to help with the planning of radar observations. During the analysis and modeling process, the radar team may request to use available lightcurve data.

Spectra: spectra refers broadly to optical or infrared spectra and colors, which are most important for completeness of the strongest radar targets, for candidate binary asteroids, and for potential human-exploration targets. Observers are asked to relay probable spectral-class information to the radar team to compare with characteristics suggested by radar.

Object Dates Expected
H mag Request
Maintenance Ongoing Cable break

The following may be detectable if scheduled for radar observations. Further details on these objects are available including SNR estimates, specific observing tracks, and pointing, Doppler, and range uncertainties. Requests for optical astrometry are indicated where the pointing uncertainties are a significant fraction of, or larger than, our 2 arcmin pencil beam. Priority level (high, medium, low) is noted: high = likely to propose urgent radar observations, medium = may observe as a target of opportunity during other scheduled observations, low = unlikely to pursue. Priority level is subjective and is based on how detectable the object is, whether the object is potentially hazardous, NHATS-compliant, or on the SENTRY list of possible impactors, and how likely it is to be scheduled. Objects may move from this table to the table above as they are scheduled on the telescope.

Object Dates Expected
H mag Request
Priority Level Notes
No Targets Planned While Telescope Is Being Evaluated

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