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Asteroid 2011 ES4 will pass much closer than the moon on September 1

Schematics of orbits in light colors on black.

The orbit of asteroid 2011 ES4 (in white) is slightly similar to Earth’s (in blue) but inclined in relation to our planet’s orbit. The space rock completes an orbit around the sun every 416 days. It nearly intercepts our orbit on September 1, 2020, as seen in this illustration, via NASA/ JPL.

A healthy-sized chunk of space rock will pass closer than the moon on September 1, 2020. Although there is uncertainty in its orbit, scientists say it will not hit our planet. Asteroid 2011 ES4 is expected to pass at about 0.3 or 30% the Earth-moon distance. But it may pass farther, or as close as 0.19 lunar distances, since its orbit is still not completely defined. Our knowledge of this asteroid’s orbit might improve sometime today – or early tomorrow – if it is “recovered” via astronomers’ telescopes prior to closest approach.

The asteroid should pass closest around 16:12 UTC on September 1 (12:12 p.m. EDT; translate UTC to your time).

The asteroid has an estimated diameter of 72 to 161 feet (22 to 49 meters). That’s in the range of the Chelyabinsk meteor – around 17 meters (55 feet) in diameter – which swept through Earth’s atmosphere above Russia in February 2013, generating an enormous shock wave that broke windows in six Russian cities and caused some 1,500 people to seek medical treatment, mostly from flying glass.

Long, thick pink smoke trail from meteor, in a twilight sky.

Chelyabinsk meteor smoke trail, February 15, 2013. Image via Alex Alishevskikh., who caught it about a minute after the blast.

But back to asteroid 2011 ES4. The uncertainty about its orbit is due to the fact that observatories were able to track the space rock during only four days after it was detected on March 2, 2011, from the Mount Lemmon Survey in Arizona. After that, the asteroid became too faint to be observed.

Astronomers use an uncertainty scale from 0-9, in which 0 means the orbit is well known, and 9 means great uncertainty. Asteroid 2011 ES4 has an uncertainty of 7.  The uncertainty not only means it may pass farther or closer than expected, but also may cause it to occur a few hours earlier or later than expected.

Asteroid 2011 ES4 is classified as a Near-Earth Object (NEO). But it’s good to know that this Apollo-class asteroid is not classified as a Potentially Hazardous Asteroid. What’s the difference? A Potentially Hazardous Asteroid is defined as an object that passes relatively close to Earth, and also is large enough (more than 150 meters in diameter) to cause significant regional damage, were it to strike Earth.

Thus you may see that asteroid 2011 ES4 has the potential to come rather close. And it’s a healthy size, bigger, for example, than the tiny (truck-sized) asteroid that swept just 2,000 miles (3,000 km) from Earth on August 16, 2020. Yet – as asteroids go – asteroid 2011 ES4 is still relatively small, not large enough to cause significant damage upon impact (and it is not expected to get close enough to enter our atmosphere, much less impact).

So – to all of you worriers – you may all breathe easily now.

Chart of orbits of inner planets, with green shading - mostly around the orbits of Earth and Venus - showing orbits of Apollo asteroids.

Location of the Apollo asteroids compared to the orbits of the terrestrial planets of our solar system. Image via Wikimedia Commons.

If an asteroid as big as 2011 ES4 were to hit our planet, it wouldn’t be big enough to cause a major impact, much less an extinction-level event. However, a space rock with an average size of 98 ft (30 meters) in diameter, like this one, could cause a huge shock wave if it enters our atmosphere.

Fortunately, even with the margin of errors in calculations, asteroid 2011 ES4 should safely pass by Earth on September 1, 2020.

If asteroid 2011 ES4 is detected in the next few hours or days, it may at first be confused with a “new” asteroid, and get a temporary or provisional designation before models show it definitely has the same trajectory, indicating it’s in fact asteroid 2011 ES4 being “recovered” in our skies. After new observations are made, astronomers may be able to better define the space rock’s orbit.

We may see many news about close passes of asteroids, but most of those are about small space rocks. We don’t have to worry, because if a small asteroid hits our atmosphere, most of the space rock will disintegrate, and since Earth is around 70% covered by oceans, most events will occur over water, probably even unnoticed.

What about any big asteroid approaching Earth? Although there are many small asteroids whose orbit crosses the orbit of Earth, fortunately, there is no known big space rock with a dangerous orbit which poses a threat to our planet.

As part of nature, there will be, however, lots of other significant approaches in the future, including asteroid Apophis on April 13, 2029. That will be an exciting opportunity for scientists. And even for casual observers, the close approach of Apophis will be an amazing event, as the space rock may even be slightly visible to the unaided eye from some areas.

Bottom line: Asteroid 2011 ES4 is expected to pass at about 0.3 or 30% the Earth-moon distance on September 1, 2020. But it might pass farther, or as close as 0.19 lunar distances. The asteroid should pass closest around 16:12 UTC on September 1 (12:12 p.m. EDT; translate UTC to your time).

Eddie Irizarry