NASA's Arecibo Observatory Planetary Radar in the United States Puerto Rico Island made significant observations on the size and features of the 3200 Phaethon asteroid which made its close visit to Earth on December 16, 2017,
The radar observatory found that the asteroid has around 3.6 miles (6 kilometers) diameter which makes it the second largest "Potentially Hazardous" near-Earth asteroid. The asteroid had passed by Earth at a distance of 6.4 million miles (10.3 million kilometers), which is around 27 times the distance between Earth and Moon.
The radar images taken by the observatory revealed that the asteroid is roughly ball shaped with a large depression of at least several hundred meters near its equator. It also had a dark, circular feature near the poles.
Patrick Taylor, a Universities Space Research Association (USRA), Columbia, scientist and group leader for Planetary Radar at Arecibo Observatory said, "These new observations of Phaethon show it may be similar in shape to asteroid Bennu, the target of NASA's OSIRIS-Rex spacecraft, but over 1,000 times larger. The dark feature could be a crater or some other topographic depression that did not reflect the radar beam back to Earth."
The Arecibo Observatory, which has been regarded as the most powerful astronomical radar system on Earth, has significant importance in tracking and characterizing potentially hazardous asteroids (PHA) which passes near Earth's orbit. NASA's Planetary Defense Coordination Office finds, tracks, and characterizes any potentially hazardous asteroids and comets to issues warning about any impact threats.
The radar system studies the sizes, shapes, rotation, surface features and roughness of asteroids and determines its orbital path during a flyby near Earth.
Joan Schmelz of USRA and deputy director of Arecibo Observatory said, "Arecibo is an important global asset, crucial for planetary defense work because of its unique capabilities. We have been working diligently to get it back up and running since Hurricane Maria devastated Puerto Rico."
The radar observatory suffered minor structural damage due to Hurricane Maria. Power supply to the observatory had stopped due to damages caused in the powerlines. It had been later re-established in early December. Generators had been made available exclusively for the radar.
Asteroid 3200 Phaethon which is responsible for the Geminid meteor shower during December had been discovered by NASA's Infrared Astronomical Satellite (IRAS) on October 11, 1985.
The scientists claim that the asteroid would travel at a closer distance in 2093. There won't be any closer encounter till that date. The 3200 Phaethon asteroid had made a closer voyage near the Earth at around half the present distance in 1974.
Astronomers around the globe studied the visit of the first interstellar asteroid "Oumuamua" which traveled through the solar system during October. The studies on the interstellar asteroid had given insights of the presence of interstellar objects which could be hazardous for Earth.
Planetary Defence Coordination Office aims to develop technology to avoid any potential impact by any near-Earth asteroids.