Arecibo Observatory Sees Comet 209P/LINEAR
The Arecibo Observatory planetary radar system observed periodic comet 209P/LINEAR from May 23 through May 27, 2014, finding it to be about 2.4 by 3 km kilometers (1.5 x 1.8 miles) in size and elongated in shape. This is consistent with the size range suggested by optical observations, but is the first direct measurement of the nucleus dimensions. Discovered by the Lincoln Near-Earth Asteroid Research project in 2004, 209P/LINEAR was responsible for the recent Camelopardalids meteor shower of May 2014.
Comets rarely come this close to Earth, making it an extraordinary opportunity to get images of the surface. Observations were led by the Universities Space Research Association's astronomer Dr. Ellen Howell, who 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. The planetary radar group at Arecibo Observatory is led by deputy director, Dr. Michael Nolan.
Images: 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. Radar imaging produces a projection of the object that will be analyzed in the weeks ahead to determine the true appearance of the comet nucleus. The Earth is at the bottom of these images. Credit: Arecibo Observatory/NASA/Ellen Howell, Patrick Taylor
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. Comet 209P's orbit brings it by Earth once every five years. However, this comet will be out of reach for radar imaging again for at least 50 years - close approaches of comets are extremely rare events. In fact, this is the closest known comet to pass by Earth since 1983 (Comet IRAS-Araki-Alcock) and although the comet 209P/LINEAR is periodic, and orbits the sun every 5 years or so, there will not be another radar observing opportunity for the foreseeable future.
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 away from the sun. Six comet nuclei have been imaged by spacecraft, which reveals a wide variety of surface features and structures on these icy objects.
Howell led a team which included USRA researchers Dr. Patrick Taylor, Alessondra Springmann, Linda Rodriguez Ford and Luisa Zambrano Marin. "Comet 209P/LINEAR has no chance of hitting Earth," said data analyst Alessondra Springmann. "It comes no closer than 8.3 million kilometers (5.2 million miles) to Earth, safely passing our planet."
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.
Arecibo radar has observed other comets including 103P/Hartley 2 in 2010 , 8P/Tuttle in 2007 and 2008 , and 73P/Schwassmann-Wachmann 3 in 2006 . These images of 209P/LINEAR are the highest resolution comet radar images we have obtained to date.
Located in Puerto Rico, the Arecibo Observatory is home to the world's largest and most sensitive single-dish radio telescope at 305 meters (1000 feet) across. This facility dedicates hundreds of hours a year of its telescope time to improving our knowledge of near-Earth asteroids and comets.
About Arecibo Observatory
The Arecibo Observatory is operated by SRI International in alliance with Ana G. Méndez-Universidad Metropolitana and the Universities Space Research Association, under a cooperative agreement with the National Science Foundation (AST-1100968). The Arecibo Planetary Radar program is supported by NASA's Near Earth Object Observation program. The Arecibo Observatory is sponsored by the National Science Foundation. Any opinions, findings and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Universities Space Research Association (USRA) is an independent, nonprofit research corporation where the combined efforts of in-house talent and university-based expertise merge to advance space science and technology. USRA works across disciplines including biomedicine, astrophysics, and engineering and integrates those competencies into applications ranging from fundamental research to facility management and operations. USRA engages the creativity and authoritative expertise of the research community to develop and deliver sophisticated, forward-looking solutions to Federal agencies and other customers - on schedule and within budget.