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® All images are property of the Arecibo Observatory, Universities Space Research Association.
Please credit all images with: "Courtesy of the NAIC-Arecibo Observatory, a facility of the NSF. The Arecibo Planetary Radar program is supported by NASA's Near Earth Object Observations program."
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Near-Earth Asteroid 2015 TB145 passes by without a fright!


Scientists from the Planetary Radar Group at the Arecibo Observatory, facility of the National Science Foundation (NSF), observed near-Earth asteroid 2015 TB145 on the eve of Halloween, October 30, 2015. The NASA-funded planetary radar system measured 2015 TB145 to be about 600 meters (1,968.5 feet) in diameter, which is much larger than expected, with a rotation of approximately 5 hours and velocity of 35 km per second.

This asteroid, discovered on October 10, will make its closest approach to Earth on the morning of Halloween, October 31, 2015, when it is 1.3 times farther away from Earth than the Moon. Observers with small telescopes may catch a glimpse of Asteroid 2015 TB145 near the constellation Ursa Major.

Observations of this asteroid were also conducted jointly with other radio telescopes across the United States, including NASA Jet Propulsion Laboratory’s Goldstone Solar System Radar and National Radio Astronomy Observatory’s Green Bank Telescope and Very Long Baseline Array. Data from these observations will be used to determine the asteroid’s shape, rotation, and surface properties as well as allow for refinement of the asteroid’s orbit, which can be used to better assess its impact hazard. The Arecibo Observatory will also observe this asteroid on Halloween Day.

Asteroid 2015 TB145 was recently discovered by the Pan-STARRS I survey in Hawaii and classified as a potentially hazardous asteroid due to its size and relative proximity to Earth. “One of the directives of the Arecibo Observatory is to measure with high precision the distance to asteroids and their speed, which can be used to study the asteroid’s orbit and predict its motion for hundreds of years,” said Dr. Edgard Rivera-Valentin, a Universities Space Research Association (USRA) Planetary Scientist at the Arecibo Observatory. Tracking of 2015 TB145 has shown that it is not a threat and will not have a similarly close approach to Earth during this century.

“Our measurements also allow for high-resolution images surpassed only by dedicated space missions sent to asteroids. The difference is our work is much more cost efficient and can survey many times more asteroids,” added Dr. Patrick Taylor, USRA Group Lead for the Planetary Radar Group.

Radar images obtained at the Arecibo Observatory appear to rotate clockwise, which is noticeable by the movement of bright features. “The bright and dark features are indication of surface irregularities. For example, the central dark feature may be a large circular depression, possibly an impact crater”, commented Dr. James Richardson, USRA Scientist in the Planetary Radar Group.

The Arecibo Observatory has observed over 80 asteroids so far this year and will continue to monitor the skies to improve our understanding of the impact hazard objects such as Asteroid 2015 TB145 pose to Earth.


Arecibo Observatory provides the first detailed images of a rare asteroid


Scientists from the Arecibo Observatory observed Asteroid (436724) 2011 UW158 on Tuesday July 14th, providing the first detailed images of this asteroid on from 6.9 million kilometers away (4.3 million miles or roughly 9 times the distance to the Moon), revealing that this object is not the average asteroid.

Many asteroids observed to date seem to be numerous smaller rocks held together loosely by gravity.Asteroid 2011 UW158, though, was found to have an odd shape much like an unshelled walnut with a diameter of 300 by 600 meters (1000 by 2000 feet),the size of two Arecibo telescopes, and it rotates very rapidly, once every 37 minutes, which agrees with previous optical observations.

While many watched as the New Horizons spacecraft made a historic flyby of the dwarf planet Pluto, Arecibo Observatory was watching this much smaller- and closer- object fly by Earth.“Its size, shape, and rotation suggest there is something more than gravity holding this object together or else the asteroid would break up due to its fast spin”, explained Dr. Patrick Taylor, a scientist in the Planetary Radar department and lead of the observations.

One possibility is that the asteroid is one solid body rather than many smaller rocks held together by gravity. Only two other asteroids this large and rotating this fast have been observed before. “We expect that something this big should have been shattered into smaller pieces by collisions with other asteroids over the age of the Solar System. It is interesting that something this large and apparently solid is still around,” described Dr. Taylor. He added that this asteroid will not make a similar fly by until 2108 and is not considered a potential threat to Earth.

“Such observations provide clues to how asteroids formed and changed over time”, added Dr. Edgard Rivera-Valentin,a member of the Planetary Radar department and part of the observation team.The group of observers also included project specialist Linda Ford and Benjamin Sharkey, a student in the educational research program Research Experience for Undergraduates, program funded by the National Science Foundation.

Located in Puerto Rico, the Arecibo Observatory is home to the largest and most sensitive single dish radio telescope in the world. The Arecibo Observatory is operated by SRI International in partnership with Ana G. Méndez University System-Universidad Metropolitanaand Universities Space Research Administration (USRA) under a cooperative agreement with the NSF. The Arecibo Planetary Radar program is supported by NASA's Near Earth Object Observation program.

Caption: Animation of Arecibo radar images of 2011 UW158 showing three full rotations of the asteroid. Each pixel is equal to 7.5 m (25 feet) of distance. The shape is about twice as long as it is wide and looks like a walnut with parallel ridges along the length of the body.


Arecibo Watches Asteroid (285331) 1999 FN53 Safely Pass by Earth

Scientists from the Arecibo Observatory captured images of the Asteroid 1999 FN53, which was visible since this past Tuesday until today Friday, May 15th, 2015. Its diameter is of 800-900 meters, with a rotation period of 3.5 hours. Its distance is approximately 27 times more distant than our Moon. In comparison, the Asteroid 2004 BL86, which was observed in January, was only 3.5 times more distant than our Moon.

This asteroid is not categorized like a potentially hazardous asteroid, so it does not present any type of danger. Dr. Edgard Rivera- Valentin member of the Planetary Department, explained "in fact, Asteroid 1999 FN53 does not pass very near to any planet." The team in charge of this observation was Dr. Michael Nolan, Dr. Ellen Howell, Dr. Patrick Taylor, Dr. Edgard Rivera-Valentin, Dr. James Richardson and Mrs. Linda Ford.

Caption: Series of images of Asteroid 1999 FN53 captured by the Arecibo Observatory. Each image indicates 10 minutes of rotation, where the brightest point rotates to the left.

Arecibo Watches Asteroid (357439) 2004 BL86 Make Close Approach to Earth

Scientists from the Arecibo Observatory captured images of Asteroid 2004 BL86 as it passed close to Earth, about 3.5 times further away than our Moon (1.35 million km. or 840,000 miles). The asteroid's visibility from Arecibo started at 11:20 p.m. Monday, January 26.

By transmitting and receiving radio waves, it was determined that Asteroid 2004 BL86 measures about 330 meters wide, slightly larger than the reflector of the Arecibo Observatory which measures 305 meters (1,000 feet). Scientists also confirmed that the asteroid is accompanied by a moon about 60 meters in diameter, orbiting the asteroid like our Moon orbits the Earth. The presence of the moon was suggested by astronomers Joe Pollock from Appalachian State University and Petr Pravec from the Academy of Sciences of the Czech Republic, based on observations with optical telescopes and then first confirmed by the Goldstone Solar System Radar in California, who observed this asteroid on January 25, before it was visible to Arecibo.

The moon moves subtly from image to image because its orbit takes much longer to complete than the observation time at Arecibo. "In fact, the first images from Arecibo did not show the moon, suggesting the moon was actually hidden in the radar "shadow" of the larger body before peeking out into view of our radar beam," explained Dr. Patrick Taylor, team leader in Arecibo. The team included Dr. Ellen Howell, Dr. Edgard Rivera-Valentin, Dr. James Richardson and Ms. Agata Rozek.

In addition to the motion of the moon, the larger body rotates noticeably in a clockwise direction, shown by the motion of a bright feature on its surface. "It's almost like a hand on a clock moving from about 8 to 9o'clock, consistent with a rotation period of 2.6 hours suggested by Pollock and Pravec," detailed Taylor.

In addition to Arecibo transmitting and receiving its own signal, Arecibo transmitted to the asteroid while telescopes in the Very Long Baseline Array, spread across the southwest United States, received the echo. This will help better determine how the larger body rotates.


The Arecibo Solar System Studies "Year in Review" for 2014 was presented to the Arecibo Observatory Users Committee on May 29, 2015 by Dr. Edgard Rivera-Valentin.

Arecibo Discovers Equal-Mass Binary Near-Earth Asteroid 1994 CJ1

Asteroid 1994 CJ1 is only the second equal-mass binary system found in the near-Earth region. The first such system known, (68230) Hermes, was also discovered by Arecibo back in 2003.

At left is a radar image of the 1994 CJ1 binary system with resolution of 75 meters per pixel. Rather than having one large and one small component, the 1994 CJ1 system is made up of two very similar-size objects, each less than 150 m in diameter (500 feet or half the size of the Arecibo telescope). In addition to being a rare equal-mass binary, 1994 CJ1 may also be the smallest known binary asteroid. Often the components in a binary asteroid system are at least a few hundred meters in diameter.

Arecibo and Goldstone Team Up to Observe Asteroid 2014 HQ124

USRA Press Release

Arecibo and Green Bank Team Up to Observe Asteroid (304330) 2006 SX217

The Arecibo 305-meter telescope, with a little help from our friends at the 100-meter National Radio Astronomy Observatory (NRAO) Green Bank Telescope in West Virginia, got some pretty radar images of asteroid 2006 SX217 on April 23, 2014. When our receiver at Arecibo had a problem, a quick call to Green Bank allowed us to successfully keep doing our observations. To do this experiment, Arecibo transmitted a radar signal to the asteroid, the signal bounced off the asteroid, and was received by the Green Bank Telescope. That means we were simultaneously using the largest fixed-dish telescope in the world AND the largest steerable-dish telescope in the world! This asteroid is about 1.2 kilometers across, four times bigger than the Arecibo dish, and was passing Earth at a distance of 4.8 million kilometers (3 million miles or 12.5 times further than the Moon). The images have 15-meter resolution in the vertical direction; the horizontal direction is actually a measure of how fast the asteroid is rotating. The asteroid is roughly spherical, but you can also see bright features that may be ridges or boulders on the surface and the smudge at the top left of the first and second images may be part of a large crater on the surface! Radar images of this asteroid from the 70-m Goldstone Solar System Radar facility show more features, including the suspected crater on the surface!

Arecibo Captures Images of the Nucleus of Comet 209P/LINEAR

USRA Press Release


Arecibo Captures Exquisite Images of Binary Near-Earth Asteroid (285263) 1998 QE2

USRA Press Release

More images and further information on this object can be found here.


Arecibo Finds Newly Discovered Asteroid 2012 LZ1 is Larger Than Expected

USRA Press Release

Using the planetary radar system at Arecibo Observatory, astronomers have determined that asteroid 2012 LZ1 is twice as large as originally estimated based on its brightness and large enough to have serious global consequences if it were to hit the Earth. However, a new orbit solution also derived from the radar measurements shows that this object does not have any chance of hitting the Earth for many centuries to come.

Asteroid 2012 LZ1 was discovered on June 10, 2012, at Siding Spring Observatory in Australia, and scientists at Arecibo observed the asteroid just one week later on June 19, 2012, to measure its orbit more precisely and to determine its size, rotation rate, and shape.

The asteroid, pictured at left with resolution 7.5 meters (25 feet) per pixel, is about 1 kilometer (0.6 miles) in its largest dimension. The new size determination suggests that 2012 LZ1 must be quite dark, reflecting only 2-4% of the light that hits it. "The sensitivity of our radar has permitted us to measure this asteroid's properties and determine that it will not impact the Earth at least in the next 750 years," said Dr. Mike Nolan, Director of Planetary Radar Sciences at Arecibo Observatory. Dr. Ellen Howell added: "This object turned out to be quite a bit bigger than we expected, which shows how important radar observations can be, because we're still learning a lot about the population of asteroids."


Arecibo and Green Bank Watch Close Fly by of Asteroid (308635) 2005 YU55

USRA Press Release

The asteroid 2005 YU55, pictured at left with resolution 7.5 meters (25 feet) per pixel, is about 360 meters (1200 feet) in diameter, just a little bit larger than the Arecibo 305-meter (1000-feet) dish. The radar-bright feature at the lower left might be a large boulder up to 30 meters (100 feet) in diameter poking up above the surrounding terrain and preferentially reflecting the radar echo back to the telescope. At the time this image was obtained, the asteroid was roughly 5 million kilometers (3.1 million miles) from Earth. More images and further information on this object can be found here.


Arecibo Discovers the Second Triple Near-Earth Asteroid: (136617) 1994 CC

Image of 1994 CC.


Arecibo Discovers the First Triple Near-Earth Asteroid: (153591) 2001 SN263

The Arecibo Planetary Radar discovered that near-Earth Asteroid 2001 SN263 is a triple asteroid system.


Arecibo Helps Make the First Direct Detection of the Asteroidal YORP Effect


Arecibo Discovers the First Binary Near-Earth Asteroid: (185851) 2000 DP107

2000 DP107 was the first asteroid identified by radar as a binary system. The primary is roughly spherical with a diameter of 800 meters (half a mile) and the smaller secondary, which orbits it in 1.8 days, is about 300 meters (1000 feet) in diameter. The primary has a low density of 1.7 g/cc and is assumed to be a "rubble pile" of rocks and voids. It is spinning at a rate near the breakup point for strengthless bodies, and therefore any slight disturbance could pull it apart. We now know that binaries are very common among near-Earth asteroids, about 1 in every 6 has its own satellite!

Binary asteroid 2000 DP107

A composite of images of 2000 DP107 obtained at Arecibo Observatory in September-October 2000. The frame is 5.8 km vertically, with distance from the observer increasing downward, and 12.2 Hz horizontally, with Doppler frequency or line-of-sight velocity increasing to the right. Rotation and revolution appear counterclockwise. The illuminated front of a roughly spherical primary is visible, as well as the satellite at different phases of the orbital cycle. In this image the satellite appears much smaller than the primary because its spins more slowly. The actual size ratio is about 8 to 3. Also, the orbit appears elliptical in this image, but it is actually circular in space.


Division of Planetary Sciences resolution on the Arecibo planetary radar

The Division of Planetary Sciences of the American Astronomical Society unanimously passed a resolution on the status of Arecibo radar.

"One-page" description of the Arecibo planetary radar

We have prepared a one-page informational flyer that may be useful as a handout to interested parties.

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