Planetary Radar Captures Detailed View of Oblong Asteroid
On February 3, 2023, an asteroid more than three times as long as it is wide safely flew past Earth at a distance of about 1.8 million kilometers (1.1 million miles, or a little under five times the distance between the Moon and Earth). While there was no risk of the asteroid — called 2011 AG5 — impacting our planet, scientists at NASA’s Jet Propulsion Laboratory (JPL) in Southern California closely tracked the object, making invaluable observations to help determine its size, rotation, surface details, and most notably, shape.
This close approach provided the first opportunity to take a detailed look at the asteroid since it was discovered in 2011, revealing an object about 500 meters (1,600 feet) long and about 150 meters (500 feet) wide, dimensions comparable to the Empire State Building. The powerful 70-meter (230-foot) Goldstone Solar System Radar antenna dish at the Deep Space Network’s facility near Barstow, California, revealed the dimensions of this extremely elongated asteroid.
“Of the 1,040 near-Earth objects observed by planetary radar to date, this is one of the most elongated we’ve seen,” said Lance Benner, principal scientist at JPL who helped lead the observations.
The Goldstone radar observations took place between January 29 and February 4 and captured several other details: Along with a large, broad concavity in one of the asteroid’s two hemispheres, 2011 AG5 has subtle dark and lighter regions that may indicate small-scale surface features a few dozen meters across. And if the asteroid were viewed by the human eye, it would appear as dark as charcoal. The observations also confirmed 2011 AG5 has a slow rotation rate, taking nine hours to fully rotate.
Beyond contributing to a better understanding of what this object looks like up close, the Goldstone radar observations provide a key measurement of the asteroid’s orbit around the Sun. Radar provides precise distance measurements that can help scientists at NASA’s Center for Near Earth Object Studies (CNEOS) refine the asteroid’s orbital path. Asteroid 2011 AG5 orbits the Sun once every 621 days and won’t have a very close encounter with Earth until 2040, when it will safely pass our planet at a distance of about 1.1 million kilometers (670,000 miles, or nearly three times the distance between the Moon and Earth).
“Interestingly, shortly after its discovery, 2011 AG5 became a poster-child asteroid when our analysis showed it had a small chance of a future impact,” said Paul Chodas, the director of CNEOS at JPL. “Continued observations of this object ruled out any chance of impact, and these new ranging measurements by the planetary radar team will further refine exactly where it will be far into the future.”
CNEOS calculates every known near-Earth asteroid orbit to provide assessments of potential impact hazards. More information about planetary radar, CNEOS, and near-Earth objects can be found at https://www.jpl.nasa.gov/asteroid-watch.