New Arecibo Radar Images Show Comet Responsible for Camelopardalids is an Icy, Cratered Mini World

by Nancy Atkinson on May 30, 2014

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Radar images of Comet 209P/LINEAR taken from May 23 through May 27, 2014. The Earth is at the bottom of these images: the “side view” is a result of the radar imaging method. Several features are visible on the comet, perhaps ridges or cliffs. This is only the fifth comet nucleus imaged by Arecibo in the last 16 years, and the most detailed. Resolution in the vertical direction is 7.5 meters (25 feet) per pixel.  Image credit: Arecibo Observatory/NASA/Ellen Howell.

Radar images of Comet 209P/LINEAR taken from May 23 through May 27, 2014. The Earth is at the bottom of these images: the “side view” is a result of the radar imaging method. Several features are visible on the comet, perhaps ridges or cliffs. This is only the fifth comet nucleus imaged by Arecibo in the last 16 years, and the most detailed. Resolution in the vertical direction is 7.5 meters (25 feet) per pixel. Image credit: Arecibo Observatory/NASA/Ellen Howell.

When Comet 209P/LINEAR — the comet that brought us the Camelopardalids meteor shower last weekend – was first discovered in February of 2004, astronomers initially thought it was an asteroid. However, subsequent images of the objects showed it had a tail, and so it was reclassified as a comet. Now, new images taken by the Arecibo Observatory planetary radar system reveal Comet 209P/LINEAR has complex surface features that will require more analysis to fully interpret. This mini world seems to be filled with ridges and cliffs along with its icy surface.

“This is the highest resolution radar image we have obtained of a comet nucleus,” said Dr. Ellen Howell from the Universities Space Research Association, who led the observations of the comet at Arecibo, located in Puerto Rico.

The Arecibo Observatory is taking advantage of the approaching close pass of Earth by Comet 209P/LINEAR, taking these new radar images which confirm this comet to be about 2.4 by 3 km kilometers (1.5 x 1.8 miles) in size and elongated in shape. Earlier optical observations suggested this size range, but now these radar observations are the first direct measurement of the nucleus dimensions.

Radar images of Comet 209P/LINEAR taken from May 23 through May 27, 2014. The Earth is at the bottom of these images: the “side view” is a result of the radar imaging method. Several features are visible on the comet, perhaps ridges or cliffs. This is only the fifth comet nucleus imaged by Arecibo in the last 16 years, and the most detailed. Resolution in the vertical direction is 7.5 meters (25 feet) per pixel.  Image credit: Arecibo Observatory/NASA/Ellen Howell

Radar images of Comet 209P/LINEAR taken from May 23 through May 27, 2014. The Earth is at the bottom of these images: the “side view” is a result of the radar imaging method. Several features are visible on the comet, perhaps ridges or cliffs. This is only the fifth comet nucleus imaged by Arecibo in the last 16 years, and the most detailed. Resolution in the vertical direction is 7.5 meters (25 feet) per pixel. Image credit: Arecibo Observatory/NASA/Ellen Howell

Comets very rarely come this close to Earth, but don’t worry: Comet 209P/LINEAR is not coming close enough to cause any problems or concerns.

“Comet 209P/LINEAR has no chance of hitting Earth,” said data analyst Alessondra Springmann from Arecibo. “It comes no closer than 8.3 million kilometers (5.2 million miles) to Earth, safely passing our planet.”

But this relatively close pass makes this an extraordinary opportunity to get images of the surface. As Dr. Howell noted, these observations of are some of the most detailed. Just six comet nuclei have been imaged by spacecraft, and a wide variety of surface features and structures have been observed on these icy objects.

“We are being cautious,” Howell told Universe Today. “Radar images are not regular “spatial” images, and one can easily be misled by treating them as a regular picture. But proper analysis will take weeks or months, not minutes. What these radar images show is certainly not ordinary, but we don’t really have anything to compare to. The image looks different than asteroids we have imaged, but I don’t know what is due to surface feature differences and what might be scattering differences by the surface material.”

Comets have a central nucleus made of ice, dust, and rocks, and a coma of dust and gas. Two tails, one made of ions and one of dust, form in the direction pointing away from the sun.

Other comets seen by Arecibo radar include 103P/Hartley 2 and 8P/Tuttle, and 73P/Schwassmann-Wachmann 3.

Radar images of Comet 209P/LINEAR taken from May 23 through May 27, 2014. The Earth is at the bottom of these images: the “side view” is a result of the radar imaging method. Several features are visible on the comet, perhaps ridges or cliffs. This is only the fifth comet nucleus imaged by Arecibo in the last 16 years, and the most detailed. Resolution in the vertical direction is 7.5 meters (25 feet) per pixel.  Image credit: Arecibo Observatory/NASA/Ellen Howell

Radar images of Comet 209P/LINEAR taken from May 23 through May 27, 2014. The Earth is at the bottom of these images: the “side view” is a result of the radar imaging method. Several features are visible on the comet, perhaps ridges or cliffs. This is only the fifth comet nucleus imaged by Arecibo in the last 16 years, and the most detailed. Resolution in the vertical direction is 7.5 meters (25 feet) per pixel. Image credit: Arecibo Observatory/NASA/Ellen Howell

Unlike long period comets Hale-Bopp and the late Comet ISON that swing around the Sun once every few thousand years or few million years, Comet 209P/LINEAR visits our neighborhood frequently, coming ‘round every 5.09 years. However, it will not be close enough to Earth again for radar imaging any time in the next 100 years.

With a rotation period of approximately 11 hours as determined by Carl Hergenrother at the University of Arizona using the 1.8 meter VATT telescope, this comet is one of the many Jupiter family comets, which orbit the Sun twice for every time Jupiter orbits once.

It was discovered by the Lincoln Laboratory Near-Earth Asteroid Research (LINEAR) automated sky survey.

The Arecibo Observatory, located in Puerto Rico, is home to the world’s largest and most sensitive single-dish radio telescope at 305 meters (1000feet) across. This facility dedicates hundreds of hours a year of its telescope time to improving our knowledge of near-Earth asteroids and comets.

Dr. Howell specializes in studying comets and asteroids using radar, as well as passive radio and infrared spectroscopy techniques to determine the surface and coma properties of small solar system bodies. She was assisted in these observations of Comet 209P/LINEAR by Michael Nolan, Patrick Taylor, Alessondra Springmann, Linda Ford, and Luisa Zambrano.

Arecibo Observatory, and the complementary Goldstone Solar System Radar in California run by NASA’s Jet Propulsion Laboratory, are both observing comet 209P/LINEAR during its pass by Earth in May. These radar facilities are unique among telescopes on Earth for their ability to resolve features on comets and asteroids, while most optical telescopes on the ground would see these cosmic neighbors simply as unresolved points of light.

For more images and information on Comet 209P/LINEAR, see the Arecibo Observatory’s planetary radar page.

The Arecibo Observatory is operated by SRI International under a cooperative agreement with the National Science Foundation, and in alliance with the Sistema Universitario Ana G. Méndez-Universidad Metropolitana and the Universities Space Research Association. The Arecibo Planetary Radar program is supported by NASA’s Near Earth Object Observation program.

About 

Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with Astronomy Cast. Nancy is also a NASA/JPL Solar System Ambassador.

qraal May 30, 2014 at 5:45 PM

Wow! That’s truly impressive RADAR work! Arecibo is a wonder!

Tony Mach May 31, 2014 at 2:40 AM

Cool!

But please, don’t call a radar image a “side view”. Radar “images” are special. As per the quote in the text: “Radar images are not regular “spatial” images, and one can easily be misled by treating them as a regular picture.”

On the y-axis of the “image” you have distance (with top being farther away from Earth), so for that it is somewhat similar to a normal “image”.

But AFAIK on the x-axis you have Doppler, on the one side stuff is moving faster (e.g. “away from Earth”), on the other what is moving slower, and in the middle is stuff that moves at the speed of the object (asteroid/comet).

With the radar image, people can create a digital 3D model of the object (and a very approximate model at that!), and the 3D model in turn can be used to create an image (again, very approximate).

Jeffrey Boerst May 31, 2014 at 5:47 AM

Kudos to Sondi and her team of cats down there!!

BCstargazer May 31, 2014 at 5:01 PM

Too bad we haven’t found a way to image the radar absorbing Monolith yet….

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