S-band Spotlight

Arecibo radar tracks close flyby of asteroid 2019 OK

On July 24, 2019, the near-Earth asteroid 2019 OK passed by the Earth at 1/5 of the distance to the moon. The object is between 50 - 130 meters in size, but was detected just 24 hours before its close flyby. Arecibo radar was used to greatly refine the asteroid's predicted orbit so that it can be tracked for the next century.

The figure on the left shows the detection of the asteroid from Arecibo radar. The 30 Hz offset of the reflected radio signal is used to refine the velocity and predicted trajectory of 2019 OK. The width of the observed signal is used to determine its rotation period. On the right, a schematic from JPL Horizons shows the proximity of 2019 OK to Earth during its close flyby.

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About Us


The Planetary Radar Science group is a department of the Arecibo Observatory, which is an NSF facility operated under cooperative agreement by the University of Central Florida (UCF), Yang Enterprises, Inc. (YEI), and Universidad Ana G. Mendez (UAGM). The Arecibo Observatory Planetary Radar program is fully funded by NASA's Near-Earth Object Observations program.

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Recently Observed Objects


For media inquiries, please contact our communications lead, Ricardo Correa

All observations in 2020 - most recent first

Comet 289P/Blanpain
2020 AB
2019 YM3
2019 YF4

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.

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
250577 (2005 AC) Feb 05 Astrometry 18.2 Period unknown
137924 (2000 BD19) Feb 08-10 Imaging 17.2 10.6-h period, Yarkovsky?
163379 (2002 PZ39) Feb 09-19 High-res Imaging 18.9 Y Y PHA, long period?
35107 (1991 VH) Feb 11-12 Astrometry 16.7 Y BINARY, PHA, 2.6-h period
2017 BM123 Feb 21-26 Imaging 23.7 NHATS, 2.2-h period
2015 BK509 Feb 27-29 Astrometry 22.4 Period unknown
4581 Asclepius Mar 18-31 Imaging 20.7 Y PHA, NHATS, Binary?

The following may be detectable if scheduled for radar observations. 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 it is potentially hazardous or NHATS-compliant, 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
2013 BA74 Jan 29-Feb 02 Astrometry 25.5 Low Period unknown
2003 OC3 Mar 11-26 Imaging 18.6 Medium PHA, period unknown
2019 UO9 Apr 26-27 Astrometry 19.9 1 arcmin Medium PHA, period unknown

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