Does Earth have a second moon? Not quite. But astronomers discovered that asteroid 2016 HO3 does orbit the sun while it circles our planet—establishing its status as a quasi-satellite. Scientists are deeply interested in 2016 HO3, and NASA even envisions an exploration mission to the asteroid.
What are quasi-satellites?
On April 27, 2016, the asteroid now known as 2016 HO3 was first located by astronomers located at Haleakala, Hawaii. Many suspected it was merely space junk until Vishnu Reddy, assistant professor at the University of Arizona’s Lunar and Planetary Laboratory, and his team completed their observations and presented them at the recent 49th annual Division for Planetary Sciences meeting in Utah. According to their findings, 2016 HO3 is indeed an ordinary asteroid and quasi-satellite.
Astronomers at NASA’s Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in Pasadena, California wrote, “[2016 HO3] 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.’”
Earth currently hosts five quasi-satellites, but 2016 HO3 maintains the most stable orbit. Yet, in part, it’s this unstable orbit that defines 2016 HO3 status as a quasi-satellite, as opposed to an actual satellite—or moon. A quasi-satellite’s lack of orbital stability may cause its path to substantially change over time.
Paul Chodas, manager of the Center for NEO Studies explained, “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.”
While many quasi-satellites no longer qualify as such after a few years, 2016 HO3 is expected to remain fairly stable for hundreds of years.
Chodas said, “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.”
Our quasi-satellites come from a population of NEOs that the Earth nudged in a particular way, causing them to tag along with us; in the case of 2016 HO3 this created a unique co-orbital configuration.
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