The Russian meteor that slammed into Earth’s atmosphere on Friday (injuring over 1,000 people) hit just hours before larger Asteroid 2012 D14 made its closest approach to Earth. Asteroid experts initially have said there was no connection between the two events1 and that it was just a “cosmic coincidence“2 that both events occurred on the same day.
About the terminology used in this article:
What is the difference between an asteroid, meteoroid, meteor, and meteorite?
Asteroid = A small rocky object that orbits the Sun. Asteroids are composed of rock and metal, but they also can contain organic compounds. Although there still is no formal agreement on a definition, asteroids are usually thought of as small solar system objects larger than 10 meters which are not comets. (Asteroids are inactive bodies, while comets have ice on them that can vaporize in sunlight and form a tail of gas and dust.) The International Astronomical Union prefers the broader term “minor planet.”
Meteoroid = A small rock or particle of debris in our solar system, usually defined as ranging in size from dust to around 10 meters in diameter. (Anything larger than 10 meters is usually referred to as asteroid.)
Meteor = A meteoroid (or small asteroid) that burns up as it passes through the Earth’s atmosphere.
Meteorite = A meteoroid (or piece of meteoroid or asteroid) that survives falling through the Earth’s atmosphere and impacts the Earth’s surface
Near Earth Object (NEO) = Any solar system object (asteroid, meteoroid, comet, human spacecraft and satellites, space junk) whose orbit brings it into close proximity with Earth. In simple terms, these are all of the objects that potentially can collide with Earth.
Odds of Such a Coincidence
The small asteroid that entered Earth’s atmosphere and blew apart over the Chelyabinsk region of Russia was approximately 15 meters (or about 50 feet) wide and 7,000 metric tons in weight. It is estimated that a Near Earth Object (NEO) in that size range impacts Earth an average of once every 100 years. The last object that size to hit the Earth was the NEO that exploded over Tunguska5 in 1908 and flattened millions of trees over 820 square miles of remote Siberian forest. The 105 years between the Tunguska event and Friday’s meteor over Russia fits well with the estimate that these events occur about once every 100 years.
Asteroid 2012 D14 however, is about three times the size of Friday’s Russian meteor. 2012 D14 has a diameter of approximately 45 meters (or about 150 feet) across, with an estimated mass of about 130,000 metric tons. The odds of an NEO of that size encountering Earth are much slimmer, approximately once every 700 years.
Frequency: Stony Asteroid Impacts that Generate an Airburst
Impactor diameter Kinetic energy at atmospheric entry Airburst energy Airburst altitude Average frequency 4 m (13 ft) 3 kt 0.75 kt 42.5 km (139,000 ft) 1.3 years 7 m (23 ft) 16 kt 5 kt 36.3 km (119,000 ft) 4.6 years 10 m (33 ft) 47 kt 19 kt 31.9 km (105,000 ft) 10.4 years 15 m (49 ft) 159 kt 82 kt 26.4 km (87,000 ft) 27 years 20 m (66 ft) 376 kt 230 kt 22.4 km (73,000 ft) 60 years 30 m (98 ft) 1.3 Mt 930 kt 16.5 km (54,000 ft) 185 years 50 m (160 ft) 5.9 Mt 5.2 Mt 8.7 km (29,000 ft) 764 years 70 m (230 ft) 16 Mt 15.2 Mt 3.6 km (12,000 ft) 1900 years 85 m (279 ft) 29 Mt 28 Mt 0.58 km (1,900 ft) 3300 years
(The above table uses a density of 2600 kg/m3, velocity of 17 km/s, and an angle of 45 degrees)
(Source: Robert Marcus, H. Jay Melosh, and Gareth Collins (2010). “Earth Impact Effects Program”. Imperial College London / Purdue University.)
Applying some basic math, the odds of a 15-meter asteroid impacting Earth on the same day as a 45-meter asteroid’s near miss are approximately 1 in 26,500. For comparison purposes, that’s about the same odds a New Yorker had in 2011 of dying in a car accident, while this double asteroid whammy is 6,000 more likely than the odds you will win the next $50 million Powerball lottery (1 in 175,000,000).
I still kept wondering, however, if there was another more likely explanation than random chance for these two asteroids showing up on the same day. One of the hallmarks of science is that it seeks to explain observations and phenomena as simply as possible.
Shoemaker-Levy 9 and Multiple Collisions with Jupiter
There is precedence for large objects such as comets and asteroids breaking apart, resulting in multiple impacts with a planet. In July 1992, Comet Shoemaker-Levy 9 (formally known as Comet D/1993 F2) broke apart after a close encounter with Jupiter — Jupiter’s tidal forces tore the comet into fragments ranging up to 2 km (1.2 mi) in diameter. Then two years later, at least 21 fragments of Shoemaker-Levy 9 collided with Jupiter and were observed burning up in its atmosphere over a six day period.6
Could Asteroid 2012 D14 have broken into two (or more) pieces in the past, with one of those fragments hitting Earth this past Friday while another larger fragment zipped past on a near miss? The main piece of evidence against this is that the object which exploded over Russia Friday apparently approached Earth from a different direction than 2012 D14 did. If they had been fragments of the same original asteroid, both would have approached Earth on roughly the same trajectory.
There’s a Bad Moon on the Rise
But even after seeing that Asteroid 2012 D14 and the Russian Meteor had approached Earth from different directions, my mind7 kept wondering if there could still be a connection. And then the light bulb went on in my head! What if (I thought to myself) the Russian meteor had been on roughly the same trajectory as Asteroid 2012 D14 and had actually passed Earth several days before 2012 D14 arrived? And what if that meteor had missed Earth at roughly the distance of the Moon’s orbit? Because it was such a dark asteroid, we didn’t see the Russian asteroid on Friday until it became a fireball in Earth’s atmosphere, so it’s completely plausible that we would have missed an earlier pass by that same asteroid. So imagine the Russian meteor missing Earth, but then getting so close to the Moon that the Moon’s gravity slingshot it back right at the Earth. By the time we’d first see it in the skies over Chelyabinsk, it would be traveling in almost the opposite direction of it’s original trajectory (and look like it had come from somewhere different than Asteroid 2012 D14 did).
I quickly began checking the trajectory information available for the Russian meteor and comparing that to the Moon’s position over the last several days.8 Alas, my hypothesis imploded when faced with actual data and orbital mechanics. The Moon was nowhere near where it needed to be for my “lunar slingshot” idea to have occurred.
And in the end...
Ultimately my really crazy (yet cool) hypothesis about Asteroid 2012 D14 and the Russian meteor being fragments of the same object wasn’t supported by the facts. So unless someone else comes up with a better idea, I’ve accepted that the fact both asteroids showed up on the same day really was a coincidence.
- “It’s simply a coincidence,” Paul Chodas, an asteroid researcher at NASA’s Jet Propulsion Laboratory (JPL), told NBC News. Don Yeomans, manager of the Near-Earth Object Program Office at JPL, told CNN, “They are completely unrelated objects — it’s a strange coincidence they are happening at the same time.” [↩]
- “This is literally a cosmic coincidence, although a spectacular one,” Prof Alan Fitzsimmons, of the Astrophysics Research Centre at Queen’s University Belfast told the BBC just hours after the fireball streaked across Russia’s skies.
Ironically, nearly every quote I found from qualified experts about the proximity of these two events contained the word “coincidence,” which itself seems at first an interesting coincidence. I highly doubt, however, there is some vast conspiracy to control media coverage of the Russian meteor — in this case, coincidence really is the best word to describe two highly unlikely events that those experts believe to be unrelated. [↩]
- Groan! [↩]
- As I stated before, I am not someone who suspects conspiracies behind major events, especially since there almost always are simpler, most-straightforward explanations. [↩]
- Another coincidence — that both of the last two objects of this size exploded over Russia. But unless you believe there is a conspiracy of aliens throwing large space rocks at unfortunate Russian citizens, it really is a just coincidence. [↩]
- July 16–22, 1994 [↩]
- Admittedly, my thinking has been impacted by decades of reading science fiction, as well as all of the science fact weirdness that astronomers keep discovering. [↩]
- All the time, in my mind I was preparing for the inevitable interviews as the “amateur astronomer who made this major discovery.” [↩]