Just-Discovered Giant Asteroid Barely Misses Earth: Takes Another Shot At Earth In December

An asteroid approaches Earth

An asteroid as large as a 10-story building buzzed the Earth, coming within about 120,000 miles (193,121 kilometers) of the planet, on January 9 and, according to preliminary projections, will again approach the Earth for another swing toward the Sun in December. At present, not much is known about the path of asteroid 2017 AG13, because the space rock was only discovered on January 7. With only two days of data to calculate a projected orbital path, the numbers are still a bit suspect, but with a (NEO) Near-Earth Object this size, astronomers will keep a close watch and adjust the orbital calculations to give us at least a few months warning if the asteroid might just impact the Earth on its next trip Sun-ward.

At present, no one is sounding an alarm, so there doesn’t seem to any need to panic. At least, not with asteroid 2017 AG13…

As redOrbit reported this week, asteroid 2017 AG13, a NEO measured by astronomers at the Minor Planet Center in Cambridge, Massachusetts, to be between 36 and 111 feet (11 to 34 meters) at its widest, was traveling at 10 miles (16 kilometers) per second — that is equivalent to 36,000 miles per hour — as it passed between the Earth and orbit of the Moon. Astronomers note that the reason the asteroid wasn’t found sooner was due to its velocity (relative to Earth, which, too, is also in motion as it flies around the Sun) and its rather low magnitude, making it very difficult to detect.

Scientists at the Slooh Observatory quickly put together a live event broadcast to monitor the passing asteroid. Eric Feldman, an astronomer with Slooh, noted as 2017 AG13 made its fly-by, “This is moving very quickly, very nearby to us. This one has a particularly elliptical orbit. It actually crosses the orbits of two planets, Venus and Earth.”

The elliptical orbit Feldman mentioned will take the asteroid to within 0.55 astronomical units (one unit is equal to the distance between the Sun and Earth) of the Sun at perihelion (an orbit’s closest point to the Sun) and out to 1.36 astronomical units at aphelion (an orbit’s farthest point from the Sun), according to calculations made by the University of Arizona-based Catalina Sky Survey, which originally detected 2017 AG13.

Slooh’s broadcast pointed out that the buzzing space rock was “roughly the same size as the asteroid that struck Chelyabinsk, Russia in 2013.” But given the dimensions, 2017 AG13 may have been slightly larger. Regardless, this means that if the asteroid had actually impacted Earth, the effects might have been comparable.

The Chelyabinsk bolide scorched through the upper atmosphere and detonated with a yield of roughly 500 kilotons of energy (the Hiroshima atomic bomb, by comparison, released about 15 kilotons of energy), shattering windows in cities for tens of miles and injuring about 1,500 people. According to Purdue University’s asteroid-impact simulator “Impact Earth!” (per Business Insider), if asteroid 2017 AG13 had hit the Earth (or swings back around to do so in December) — and allowing that it collided with the Earth’s atmosphere at a 45-degree angle, it, too, would explode in the atmosphere in an airburst.

An asteroid enters the Earth's atmosphere

Not mentioned in the coverage of the near-miss fly-by of 2017 AG13 is that each passage through its elliptical loop through the inner Solar System (perihelion for the asteroid takes it as far out almost as far as the orbit of Mars, but not actually near it because the asteroid orbits at an angle to the Solar ecliptic, which is the imaginary flat plane that extends out from the Sun’s equator, through the Earth, and into infinity) affects its next orbit. This orbital run not only had the asteroid coming so close to the Earth and Moon that it passed in such proximity to the pair as to be affected by the duo’s gravity fields. After passing by, it is also projected to pass within the orbit of Venus (although it is unclear if it will pass near enough to be affected by that planet’s gravity field). The entire time, 2017 AG13 will be subject to the Sun’s immense gravitational tug as well.

In short, only after some time is spent observing the movement of the newfound NEO will astronomers be able to provide an accurate orbital path — which means that experts cannot yet predict with certainty exactly where 2017 AG13 will be when — and if (assuming that the Catalina Sky Survey’s initial calculations are correct) — the space rock comes back around in its estimated 347 day orbit.

So there is a bit of uncertainty as to whether or not the 10-story asteroid might impact Earth in December or, given that its orbit is a little less than a year’s time, sometime in the near or far future. It is not a process that takes very long for calculation, though — as long as astronomers are able to track, or backtrack, the target asteroid.

An asteroid impacts the Earth

Space Daily reported that determining the trajectory of an NEO or PHA (Potentially Hazardous Asteroid) becomes more accurate as astronomers obtain more images of an asteroid are found — accomplished by looking through astronomical archives. This was done with the discovery of 2016 WJ1, which was first detected by the same Catalina Sky Survey. More images of the asteroid — which had originally been calculated, using preliminary orbital data, as having a 1 in 8,000 chance of colliding with Earth in 2065 — were found.

“The additional images allowed us to refine our knowledge of the trajectory sufficiently to begin searching astronomical archives, to see if anyone had previously imaged this asteroid without having recognized it as such,” said Marco Micheli, an observer at the NEO center.

The archives search turned successful as well and astronomers were able to make orbital calculations that showed that asteroid 2016 WJ1 was not an actual threat to impact Earth in the near or far future.

As for the future path of asteroid 2017 AG13, time — and the collection of tracking data — will tell whether or not it will possibly be on a collision course with Earth.

[Featured Image by Elenarts/NASA/Shutterstock]