A sequence of radar images of the near-Earth asteroid (3200) Phaethon was obtained in December 2017 by astronomers using the NASA-funded planetary radar system at NSF’s Arecibo Observatory in Puerto Rico, when the asteroid was about 1.1 million miles (1.8 million km) from our planet.
These colorized radar images show the near-Earth asteroid Phaethon. At time of closest approach on December 16, 2017, Phaethon was about 1.1 million miles (1.8 million km) away. The encounter is the closest the asteroid will come to Earth until 2093. Image credit: Arecibo Observatory / NASA / NSF.
Phaethon was discovered on October 11, 1983, by NASA’s Infrared Astronomical Satellite (IRAS).
This asteroid is the parent body of the Geminid meteor shower of mid-December.
It is categorized as a so-called Apollo asteroid, as its orbital semi-major axis is greater than that of the Earth’s at 118 million miles (190 million km, or 1.27 AU).
The new observations of Phaethon were conducted at the Arecibo Observatory from December 15 through 19, 2017.
The radar images reveal Phaethon, which made its closest approach on December 16 at 6 p.m. EST (3 p.m. PST, 11 p.m. UTC) at a distance of about 1.1 million miles (1.8 million km, or about 4.6 times the distance from Earth to the Moon), is spheroidal in shape.
The object has a large concavity, or depression, at least several hundred feet in extent near its equator, and a conspicuous dark, circular feature near one of the poles.
“These new observations of Phaethon show it may be similar in shape to asteroid Bennu, the target of NASA’s OSIRIS-REx spacecraft, but more than 1,000 Bennus could fit inside of Phaethon,” said Dr. Patrick Taylor, a scientist at the Universities Space Research Association and group leader for the planetary radar at Arecibo.
“The dark feature could be a crater or some other topographic depression that did not reflect the radar beam back to Earth.”
The radar images also indicate Phaethon has a diameter of about 3.6 miles (6 km) — roughly 0.6 miles (1 km) larger than previous estimates.
“Arecibo is an important global asset, crucial for planetary defense work because of its unique capabilities,” said Dr. Joan Schmelz, deputy director of Arecibo Observatory and a scientist at the Universities Space Research Association.
“We have been working diligently to get it back up and running since Hurricane Maria devastated Puerto Rico.”
