Earth’s New “Mini Moon” Confirmed by NASA JPL

First discovered by University of Hawaii’s Pan-STARRS 1 telescope on April 27, 2016, Earth’s new moon, or “mini moon” has been officially confirmed by NASA’s Jet Propulsion Laboratory (JPL).

Officially named “2016 HO3,” the newly discovered asteroid is dubbed a “mini moon” because it not only orbits the Sun–it orbits Earth, as well.

Although NASA JPL states the new mini moon is “too distant to be considered a true satellite of our planet,” nevertheless, 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.”

Earth's new
Earth’s new “mini moon” confirmed by NASA JPL. Credit:

Mini Moon 2016 HO3: “A Near-Earth Companion”

Considered “the best and most stable example to date of a near-Earth companion,” our new mini moon (or “minimoon”) is under NASA’s close scrutiny at the JPL Center for Near-Earth Object (NEO) Studies in Pasadena, California. Manager Paul Chodas reports, “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.”

Located on Haleakala, Hawaii, the Pan-STARRS 1 asteroid survey telescope is operated by the University of Hawaii’s Institute for Astronomy, funded by NASA’s Planetary Defense Coordination Office. Pan-STARRS 1 discovered the new mini moon on April 27, and NASA’s Center for Near-Earth Objects jumped on its trail immediately.

Asteroid 2016 HO3, as it is officially designated, has not undergone enough analysis yet to firmly establish its size, but it’s believed to be somewhere between 120 feet (40 meters) and 300 feet (100 meters) in size.

In case you’re wondering, our “real” moon is around 2,000 miles in diameter, and has been orbiting Earth for over 4 billion years. And you probably already know all this, but just in case you’d like a few official definitions:

  • An asteroid is a “relatively small, inactive, rocky body orbiting the Sun.”
  • A meteoroid is a “small particle from a comet or asteroid orbiting the Sun.”
  • A meteor, one of many in a meteor shower, is a shooting star, or “the light phenomenon which results when a meteoroid enters the Earth’s atmosphere and vaporizes.”

Leap-Frogging and Dancing with the Earth

With a tilted orbit around the Earth, Mini Moon 2016 HO3 joins us on our yearly cycle around the Sun. Just like our old big moon… only not.

Bobbing up and then down through Earth’s orbital plane once every year, this small asteroid spends around half of the year closer to the Sun, or in front of the Earth. The other half of the year is spent further from the Sun, or behind the Earth. NASA likens this pattern to “a game of leap frog with Earth that will last for hundreds of years.”

Think back to playing with a spirograph as Chodas explains the fascinating gravitational forces at play between the Earth and our new mini moon. Over the passage of years, 2016 HO3’s orbit twists slowly, swaying back and forth. “The asteroid’s loops around Earth drift a little ahead or behind from year to year,” says Chodas, “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.”

Chodas adds, “The same effect also prevents the asteroid from approaching much closer than about 38 times the distance of the moon. In effect, this small asteroid is caught in a little dance with Earth.”

The Mini Moon Phenomenon is Not New

According to a team of astronomers from the University of Hawaii at Manoa, the University of Helsinki, and the Paris Observatory, Earth “usually has more than one moon.” Mini moons are “much smaller cousins” of our beloved lunar satellite. In 2011, the team published The population of natural Earth satellites, in the journal Icarus.

Using the Jade supercomputer at the National Computer Center for Higher Education (Centre Informatique National de l’Enseignement Supérieur, or CINES) at Montpelier, France, the team calculated the probability of a mini moon being captured by Earth’s gravity.

The Jade supercomputer simulated 10 million asteroids passing by the Earth and tracked the trajectories of 18,000 objects subsequently captured in the Earth’s gravitational force. Jeremie Vaubaillon of the Paris Observatory claimed, “This was one of the largest and longest computations I’ve ever done.” He added, “If you were to try to do this on your home computer, it would take about six years.”

Conclusions drawn at the time anticipated crazy, complicated paths of a captured mini moon due to its anticipated small size and tug-of-war power struggles between gravitational forces of the Earth, Moon, and Sun. The scientists reported, “While the typical minimoon would orbit Earth for about nine months, some of them could orbit our planet for decades.”

Earth captures a mini moon.
Earth captures a mini moon. The path of a simulated minimoon that is temporarily captured by Earth. The object approaches Earth from the right along the yellow line and continues on its trajectory along the orange path and finally escapes capture along the red path to the upper right. The size of Earth and the Moon are not to scale but the size of the minimoon’s path is to scale in the Earth-Moon system.
Inset: Radar image of near-Earth asteroid 1999 JM8 made with NASA’s Goldstone Solar System Radar in California and the Arecibo Observatory in Puerto Rico by a team of astronomers led by Dr. Lance Benner of NASA’s Jet Propulsion Laboratory in Pasadena, California. Minimoons are captured from the much larger population of near-Earth asteroids that pass close to Earth. This two-mile-diameter asteroid is more than a thousand times larger than the biggest minimoons, but it shows the irregular shape and pockmarked surface expected on the much smaller minimoons. Credit: UH IFA

“Mini Moons are Scientifically Extremely Interesting”

In 2006, Mini Moon 2006 RH120 was discovered by the University of Arizona’s Catalina Sky Survey. Roughly the size of a passenger car, 2006 RH120 orbited the Earth for less than a year following its discovery and was last seen shooting for the Sun.

NASA’s Paul Chodas also recalls the brief visitation of Mini Moon 2003 YN107, which followed a similar orbital pattern as our present companion, 2016 HO3. “This new asteroid is much more locked onto us,” states Chodas.

Robert Jedicke of University of Hawaii at Manoa says, “Mini moons are scientifically extremely interesting.” He explains, “A mini moon could someday be brought back to Earth, giving us a low-cost way to examine a sample of material that has not changed much since the beginning of our solar system over 4.6 billion years ago.”

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