Asteroid Apophis is Coming

On June 19th, 2004, a group of astronomers using telescopes at the Kitt Peak Observatory in Arizona discovered an asteroid that passed by the Earth later that year, on December 21, 2004 at a distance of 14.41 million kilometers. Asteroids pass by the Earth all the time but as observations continued, something stood out with one that became known as Apophis.

Calculations of future orbits based on these observations suggested that this asteroid might actually hit the Earth in subsequent flybys. With a diameter of 350 meters, initial observations suggested that if indeed this object did hit us, the inhabitants of Earth would be in for a very bad day. Initial estimates predicted Apophis was going to make two extremely close passes of Earth. The first was going to be on April 13th 2029 and was going to get uncomfortably close to us. If it managed to miss us, then depending on the exact trajectory past us, astronomers worried the next flyby in late March of 2036 certainly could hit us.

How much damage a Near Earth Object impact would inflict on the Earth depends on whether it explodes in the atmosphere or if it strikes the Earth’s surface directly. Asteroids the size of Apophis don’t explode in the atmosphere - which are called airbursts - they are too large.

At 370 meters, this rocky asteroid would impact the Earth directly releasing the equivalent energy 2800 million tons of TNT, or roughly two thousand nuclear bombs.

So it was with great interest that astronomers from around the world followed this discovery of a potentially fatal asteroid. Based on early observations, Apophis would next arrive at Earth on Friday, April 13, 2029. Friday the 13th was about to deserve its reputation.

Apophis orbits the Sun once every 323.6 days and after it’s initial discovery, astronomers continued to refine their observations using radar astrometry and other imagery until they were able to determine more precisely the path of the asteroid.

This new, more precise orbital solution for Apophis obtained in January 2005 after Apophis came around the Sun, showed that it would not, in fact hit the Earth. Sighs of relief from Astronomers everywhere could be heard round the globe.

Still, until 2006, a possibility remained that during the 2029 encounter with Earth, Apophis could pass through a gravitational keyhole, a region of only 800 meters that if traversed, would setup a future impact exactly seven years later on April 13, 2036. It wasn’t until August of 2006 using better and more complete observations that the probability Apophis would pass through that keyhole became small enough that the possibility of that collision was also ruled out.

Now, in 2020 after over a decade of observations since its discovery astronomers are now sure this Near Earth Object will not collide with Earth in April of 2029 nor later in 2036.

But it will get close to us - very close. An object the size of Apophis only gets this close to Earth about once every thousand years and this encounter will be the largest we’ve had since the Tunguska event in 1905.

Now, instead of being alarmed, astronomers are getting excited. This once in a thousand years flyby will provide an excellent opportunity for people who study NEO’s and worry about planetary protection to examine up close this amazing event. The world will be drawn in as well.

When Apophis reaches us in 2029, it will be bright enough at magnitude 3.1 that over two billion people will be able to see it with the naked eye when it flies overhead. Apophis will pass ten times closer than the Moon, within 5.8 Earth radii - that is so close that it will travel underneath the altitude of geosynchronous satellites.

As it passes us, the path over the Earth will cross western Europe, Africa, the Atlantic Ocean, the United States, and fly away while over the Pacific Ocean.

This encounter, while no longer life-threatening, does provide a valuable scientific opportunity. Astronomers want to use the 2029 flyby to learn more about large Potentially Hazardous Asteroids (PHA’s) like Apophis and they are making plans right now to study it up close and personal.

Scientists can also use the flyby to shore up our planetary defenses.

Right now, efforts are underway to launch a rendezvous mission to Apophis.

What we know so far is that Apophis has a mean radar diameter of 340 meters, has a spin state consisting of 27.38 hours in precession and a rotation period of 263 hours and has spectral characteristics that place it in the LL chondrite class of asteroids. The LL means it has low iron, low metal content and these asteroids account for only 8 or 9 percent of all meteorite falls but are a common class of Potentially Hazardous Asteroid population.

So astronomers want to know more. Specifically, what happens to the asteroid during the encounter with Earth? By understanding how this body encounters the Earth, we can improve our situational understanding of how to deal with PHA’s.

To this end, astronomers are planning a variety of missions to fly in space and observation programs on the ground to study Apophis.

MIT’s Project Apophis wants to send a NASA Discovery Class probe to the asteroid in March 2026.

A group of German astronomers want to send a 12-cubesat mission to the asteroid based on ESA’s Miniaturized Asteroid Remote Geophysical Observer to also observe the asteroid and understand how it interacts with the Earth during the close encounter.

The close encounter with the Potentially Hazardous Asteroid known as Apophis, while no longer considered a danger to humanity and the Earth, provides a perfect scientific opportunity to learn about what may happen to these bodies as they closely interact with a rocky planet. Apophis is not going to hit the Earth, and it may take out a few geosynchronous satellites with it as it passes by, but it will also leave us with priceless knowledge of how we may prepare for and possibly survive death from the skies.