asteroid and Earth
September 6, 2017

Mountain-sized asteroid narrowly misses Earth

A nearly three-mile-wide asteroid originally discovered in 1981 has just made a record-breaking fly-by of Earth, passing within just 4.4 million miles (7.0 million kilometers) of our home planet on September 1, various online media outlets reported over the Labor Day weekend.

According to Seeker and Space.com, the approximately 2.7-mile-wide (4.4 kilometer) space rock known as Asteroid 3122 Florence is one of the 10 or so largest objects of its kind, and at 8:06 am EDT on Friday, it passed within just 18 times the distance separating the Earth and the moon.

“Nothing this big has passed this close to Earth since we've been tracking. This is a once-in-40-year-event kind of thing,” Paul Chodas, manager of the Center for Near-Earth Object Studies at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, told Space.com.

Discovered by astronomer Schelte "Bobby" Bus at Australia's Siding Spring Observatory in 1981 and named in honor of Florence Nightingale, Florence was the largest asteroid to fly by the Earth in more than a century, according to New Scientist. Fortunately, Chodas said, there was no risk of the object hitting the planet’s surface, and it poses no threat for at least the next few centuries.

Florence found to be a fast-spinning triple-asteroid system

Asteroid 3122 Florence travels around the sun in an elliptical orbit, taking 2.35 years to complete one trip around our galaxy’s central star, according to Seeker and Space.com. During that voyage it comes to within one astronomical unit (AU), or the distance separating Earth and the sun.

Furthermore, Chodas told Space.com that Florence spins very rapidly, taking less than 2.5 hours to complete a single rotation. “If it were spinning any faster, it would fly apart,” he noted. “What often happens is, asteroids that are spinning this quickly rearrange into the shape of a top, where they have kind of a bulge at the equator.”

The asteroid is also highly reflective, according to New Scientist, meaning that ground telescopes should been able to get a good look at it during its fly-by. Astronomers based in both Puerto Rico and California used radar imaging to study the object, and those observations may enable them to more precisely determine its size and shape, the website noted.

Observations conducted at JPL also revealed something else interesting about Florence: there are two moons in orbit around it, making it just the third “triple system” discovered out of the around 16,400 near-Earth objects detected thus far. Those moons, New Scientist reported, are 100 to 300  meters (328 to 984 feet) in size.

Florence isn’t expected to get this close to the Earth again until at least 2500 – which is definitely a good thing, because if the asteroid were to hit the planet’s surface, it would create a 35 mile (55 kilometer) wide, 0.62 mile (1 kilometer) deep crater that would be catastrophic for biological life and the ecosystem, according to published reports.

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Image credit: NASA