NASA scientists have announced that the Earth now has a second “mini-moon” orbiting it. Earth’s new mini-satellite, named asteroid 2016 HO3, has probably been orbiting Earth for about a century, and will likely remain in orbit for a few more centuries, according to NASA.
The discovery means that the Moon can longer be described as Earth’s only natural satellite. However, NASA scientists say that Earth’s new “mini-moon” cannot be considered a true natural satellite, but more appropriately, a quasi-satellite or near-Earth companion.
“It is too distant to be considered a true satellite of our planet, but it is the best and most stable example to date of a near-Earth companion, or ‘quasi-satellite,'” NASA said in a statement.
Although it could be described as being in orbit around Earth, technically, it is in orbit around the Sun. However, its orbital path around the Sun also traces an orbital path around Earth.
Note: The video below is an animation illustrating the orbital path of asteroid 2016 HO3 around Earth.
Asteroid 2016 HO3’s orbit keeps it closer to the Sun than Earth about half of the time. But despite its distance, it never strays too far for Earth.
“Since 2016 HO3 loops around our planet, but never ventures very far away as we both go around the sun, we refer to it as a quasi-satellite of Earth.”
The asteroid’s gravitational “dance” with Earth may last only a few centuries before it moves out of its current orbital trajectory. Scientists say that Earth’s capture of a mini-moon illustrates the dynamic nature of the gravitational interaction between Earth and near-Earth objects (NEOs).
Earth’s new moon was first detected on April 27 by the Planetary Defense Coordination Office’s Pan-STARRS 1 asteroid survey telescope at Haleakala, Hawaii.
The Planetary Defense Coordination Office (PDCO) manages NASA’s program for detecting and tracking near-Earth objects (NEOs). It is responsible for overseeing all NASA-funded projects to document asteroids and comets that pass near Earth’s orbital path around the Sun.
The office also coordinates efforts between agencies and governments to respond to impact threats.
Although the size of asteroid 2016 HO3 has not been established firmly, it is believed to be a small space object not larger than 120 feet (36.5 meters) across and smaller than 300 meters (91 meters) wide.
The small size of the asteroid explains why it took astronomers so long to detect it.
Asteroid 2016 HO3 maintains an irregular orbit around Earth that varies between 38 to 100 times the distance of the Moon from Earth. The orbital path of the mini-moon was observed to weave or bob relative to the Earth’s orbital plane.
The “bobbing” motion of the asteroid across the Earth’s orbital plane has been compared to a tiny float on choppy water.
“In effect, this small asteroid is caught in a little dance with Earth.”
NASA has assured that the asteroid is not a threat to Earth and the Moon and that it is unlikely to come into a collision course with Earth or the Moon when it finally leaves Earth’s orbit.
“The asteroid’s loops around Earth drift a little ahead or behind from year to year, but when they drift too far forward or backward, Earth’s gravity is just strong enough to reverse the drift and hold onto the asteroid so that it never wanders farther away than about 100 times the distance of the moon,” said NASA’s Paul Chodas, who manages the Jet Propulsion Laboratory’s Center for Near-Earth Object Studies in Pasadena, California.
“The same effect also prevents the asteroid from approaching much closer than about 38 times the distance of the moon,” he continued. “In effect, this small asteroid is caught in a little dance with Earth.”
“Our calculations indicate 2016 HO3 has been a stable quasi-satellite of Earth for almost a century, and it will continue to follow this pattern as Earth’s companion for centuries to come,” he concluded.
[Image via NASA/JPL-Caltech]