Posted by: Kash Farooq | September 25, 2011

Is Asteroid Apophis going to kill us all in 2029 or 2036? Almost definitely not.

Update (January 2013):

After tracking asteroid 99942 Apophis with NASA’s giant Goldstone radar dish, astronomers are now certain that the threatening asteroid has essentially no chance of striking Earth in 2036.

Full article: Sky and Telescope.

This is Asteroid Apophis:

Asteroid Apophis

Asteroid Apophis (the moving dot in the middle). Credit: Osservatorio Astronomico Sormano

Its full designation is 99942 Apophis. It is about 270 metres in width and has a mass of 2.7×1010 kg.

Annoyingly, its orbit around the Sun crosses Earth’s orbit:

Apophis and Earth orbits

Apophis and Earth orbits – the line in red is the orbit of Apophis.

It rose to prominence after initial observations in 2004; it was calculated to have a 2.7% chance of hitting Earth in 2029. Improved observations and data eliminated the possibility of impact in 2029, but there remained a possibility that Apophis would pass through a gravitational keyhole, which would then set up a future rendezvous date on April 13, 2036.

A gravitational keyhole (also known as a resonance keyhole) is a small region near a planet that could alter the course of a passing asteroid, and setup a collision with the planet on the asteroid’s next orbital pass.

Additional data reduced the collision probability further. The probability of an impact on 13th April 2036 impact is now considered to be 1 in 250,000.

You can interactively view NASA’s data on near-Earth objects at the Jet Propulsion Labs Small-Body Browser. Simply search for the object you want to look at – in this case Apophis – and then click the “Orbit Diagram” link. Then select a date (I entered 1 Jan 2029), zoom in a bit and hit the >> button. You then see the orbits of the planets and the asteroid played out. You can centre on a planet or the Sun. You can also pause at any time and click “Save Image”. Here is what I got for 8th March 2029:

2029-03-08 - Asteroid Apophis approaches...

2029-03-08 – Asteroid Apophis approaches…

And here is what I got a few weeks later – 13th April 2029.

2029-04-13 - Asteroid Apophis is a little too close for comfort!

2029-04-13 – Asteroid Apophis is a little too close for comfort!

Blimey! That’s a bit close. And if having an orbit that crosses Earth’s isn’t annoying enough, 13th April 2029 is a Friday. Which just adds to the WORLD IS GOING TO END hysteria.

Now let’s look at the current predictions:

Date Impact Probability Palermo Scale Torino Scale
2036-04-13 0.0000043 -3.08 0
2056-04-13 0.0000001 -4.97 0
2068-04-13 0.0000025 -3.70 0
2068-04-13 0.00000011 -5.04 0
2076-04-13 0.00000022 -4.79 0
2103-04-13 0.00000013 -5.17 0

[The above table is adapted from JPL’s 99942 Apophis Earth Impact Risk Summary. I’m unsure why they have two entries for 2068. Perhaps an old calculation that wasn’t deleted when updated data was obtained?]

As you can see, the impact probability is pretty low.

The Palermo Technical Impact Hazard Scale enables near-Earth object scientists to categorize potential impacts. Values of less than -2 indicate no likely consequences. All the values in the above table are less than -2.

The Torino Impact Hazard Scale ranges from 0 (No Hazard) to 10 (Certain). Again, the value for each date in the table above is zero.

The description for Torino value 10 is a little scary:

A collision is certain, capable of causing global climatic catastrophe that may threaten the future of civilization as we know it, whether impacting land or ocean. Such events occur on average once per 100,000 years, or less often.

And on that cheery note, I’ll end this post with what a Torino 10 event might look like:

Massive Impact

What a Torino 10 massive impact might look like…

All images from Wikimedia Commons and Trajectory images for 2029 created by me using the Jet Propulsion Labs Small-Body Browser.



  2. Interesting article and great imagery representation! I covered the topic of Apophis too in an article of mine. take a look


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