Near-Earth asteroid 2003 SD220, traveling at 14,000 miles per hour, hurtled past our planet on Saturday (Dec 22) at a distance of 1.8 million miles – that’s the equivalent of about seven and a half times the distance between Earth and Moon.
NASA says it was the closest the asteroid has got to us in four centuries, something that will not happen again until 2070 when it is expected to slip by “slightly closer.”
A day before the flyby, NASA released images of the approaching space rock it obtained between Dec 15 and Dec 17 by combining data from its 230-foot antenna at the Goldstone Deep Space Communications Complex in California, the 330-foot-long Green Bank Telescope at the National Science Foundation (NSF) in West Virginia, and the 1,000-foot antenna at the Arecibo Observatory in Puerto Rico.
The nearly one-mile-long asteroid bears a striking resemblance to the “exposed portion of a hippopotamus wading in a river” – at least that’s how it looks like to NASA, and even to yours truly, for that matter.
CNET’s Amanda Kooser thinks it can even pass off as a “space slug, or that creepy Ceti eel ear-bug thing from Star Trek II: The Wrath of Khan.”
Using a technique known as “bistatic radar configuration,” in which one telescope serves as a transmitter and another as the receiver of the transmitted signals, the space agency managed to produce three radar images of the painfully slow-rotating space hippo, if you will.
In this case, the Green Bank telescope served as the sole receiver of the power microwave signals, while the transmission work alternated between the Goldstone and the Arecibo Observatory antennas.
“Using one telescope to transmit and another to receive can yield considerably more detail than would one telescope, and it is an invaluable technique to obtain radar images of closely approaching, slowly rotating asteroids like this one,” said NASA in its Dec 21 news release.
NASA already knew from earlier radar images by Arecibo and from earlier “light curve” measurements of sunlight reflecting off the asteroid’s surface that asteroid 2003 SD220 rotates far too slowly at 12 days per rotation and that it has a random “non-principal axis” rotation like a “poorly thrown football.”
The latest images further consolidated the space agency’s earlier conclusions.
“The radar images achieve an unprecedented level of detail and are comparable to those obtained from a spacecraft flyby,” said Lance Benner, a scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, who led the Goldstone end of things.
Benner said that the most prominent feature of the 2003 SD220 is a 330-foot-high ridge “that appears to wrap partway around the asteroid near one end.”
“Numerous small bright spots are visible in the data and may be reflections from boulders,” he continued.
“The images also show a cluster of dark, circular features near the right edge that may be craters,” Benner added.
According to NASA, the new images, which are at least twenty times more refined than the ones captured during the hippo rock’s last close approach three years ago, will provide good science, such as data on the asteroid’s interior density distribution – “information that is available on very few near-Earth asteroids.”
“This year, with our knowledge about 2003 SD220’s slow rotation, we were able to plan out a great sequence of radar images using the largest single-dish radio telescopes in the nation,” said Patrick Taylor, a researcher at the Universities Space Research Association (USRA) at the Lunar and Planetary Institute (LPI) in Houston, Texas, who led the Green Bank bistatic radar observations.
Edgard Rivera-Valentín, also a scientist at USRA, LPI, said: “The new details we’ve uncovered, all the way down to 2003 SD220’s geology, will let us reconstruct its shape and rotation state, as was done with Bennu, target of the OSIRIS-REx mission.
“Detailed shape reconstruction lets us better understand how these small bodies formed and evolved over time.”
Classified as a ‘potentially hazardous object’ (PHO), asteroid 2003 SD220 was discovered in 2003 by astronomers at LONEOS (Lowell Observatory Near-Earth-Object Search) in Flagstaff, Arizona, as part of an early NASA-sponsored near-Earth Object (NEO) survey project, now discontinued.
The good thing is that the new findings further confirm the fact that Earth is under no impact threat from this the mile-long space hippo.
The radar image on the left is from Dec 15 when 2003 SD220 was some 2.8 million (4.5 million kilometers) away from Earth.
The one in the middle was produced with data coordinated on Dec 16, when the asteroid had closed the distance between itself and Earth to 2.5 million miles (4 million kilometers).
The Dec 17 image on the right was created when the rock was fast closing in from 2.2 million miles (3.6 million kilometers) away.
“The spatial resolution on the images is as fine as 12 feet (3.7 meters) per pixel,” NASA said.
Another 95-foot-wide “small body” asteroid called 2018 XE4 is fast approaching Earth and is expected to fly by our planet at a distance of 1.2 million miles at 8:37 p.m. GMT (3:37 pm Eastern Time) on Boxing Day (December 26).
For any Solar System body to qualify as a near-Earth object, its closest approach to the Sun has to be less than 1.3 astronomical units (AU), the equivalent of nearly 121 million miles.
With some 20,000 near-Earth asteroids and comets orbiting the Sun, NASA and other space agencies have been constantly tracking NEOs since the 1990s in a collective initiative called ‘Spaceguard.’
The biggest threat to Earth, however, is from a 500-meter-wide asteroid called Bennu, which has a 1-in-2,700 chance of smashing into Earth sometime between 2175 and 2196, say scientists.
For now, however, NASA’s ORISIS-REx has closed in on Bennu and is preparing to enter orbit to collect samples from the space rock’s surface and bring them back to Earth for research purposes.