While there has not been much talk about this event in the US media, the Earth is about to get a “special visitor” from the vast expanses of our Solar System.  Asteroid 2012 TC4 is making a close approach at 05:42 UTC (12:42 Central Daylight Time in the US) on October 12, 2017.  There has been lots of interest in this heavenly body since it is only expected to be 1/10 of the distance from the center of the Earth to the center of the Moon.  Estimates from the “Center for Near Earth Objects of NASA’s Jet Propulsion Laboratory for the question of “How close is it going to be?” are ranging from 6,800 km to 35,000 km above the surface of the Earth.  Considering satellites function at a height of roughly 36,000 km above the surface of the Earth, this little space rock is coming in awfully close!


Currently, the asteroid is reported to be 16 metres long, although estimates for its size range between 10-30 metres.  It is relatively slow moving at roughly 9.6 km/sec. 


In comparison, the meteor which was sighted in the daylight hours over Chelyabinsk, Russia on February 13, 2013 was 20 metres long.  It crash-landed on the surface of a frozen lake, making a 6 metre diameter hole in the ice.  Since the Chelyabinsk meteor was a companion “space rock” to another asteroid and the sun wasn’t reflecting from its surface, nobody detected that this second meteor was going to be in the atmosphere until the actual streaks of light and explosions at 97,000 km above the Earth’s surface were actually observed.  Even so, it created quite a damaging shock wave, creating an “infrapulse” that was measured around the globe, but locally causing some 100,000 homes to be affected (mostly from broken windows) and 1491 people had sought hospital care for injuries from flying debris (mostly glass).


So, since this Chelyabinsk meteor is somewhat similar in size compared to asteroid 2012 TC4, people are wondering if the Earth is going to experience the same problems with damage which Russia experienced in 2013.  While some speculators are saying, “Duck and cover!!”, most astronomers are saying that we will not be experiencing the same atmospheric entry, mid-atmosphere explosion, and shock wave. 


Which brings one to ask, how close can a meteor come to the surface of the Earth without actually impacting the planet?  The Center for Near Earth Objects doesn’t believe that any space rocks greater than 5/100 (or 1/20 for the least common denominator folks out there) of the distance from the center of the Earth to the center of the Moon will enter the atmosphere—these are the asteroids reported as “Hazardous Objects” (all others are reported as “Potentially Hazardous”, and there is another category for farther-out objects unlikely to affect the Earth anytime in the future).  However, astronomers think that meteors of an average size of 20 metres long which are below 70-100 km are the ones likeliest to hit the Earth’s surface.  So, we have quite a margin of “wiggle room” with this asteroid!  Most meteors which enter the atmosphere above this point are burned in the friction created with air molecules as the object descends towards the Earth.  But that doesn’t mean that Asteroid 2012 TC4 will never impact the Earth.


Coming as close as it may to the Earth, the Earth’s gravity is likely to affect the asteroid’s trajectory and bend its path to a new one even closer to the Earth.  So, that means when 2012 TC4 asteroid comes around to visit again (likely in another 4 years since it has been 4 years since it was last seen), scientists will need to reassess if this body is “potentially hazardous” vs. “hazardous”.


The only concern which experts have now is akin to the Chelyabinsk meteor saga – that is, will 2012 TC4 have an accompanying asteroid that is close on its heels which nobody can see yet?  The potential for one such asteroid to enter the atmosphere would be unknown at that time where it is initially detected.  Unfortunately, with the Chelyabinsk meteor, that time was during the undetected space rock’s descent into the atmosphere as it burned and exploded. 


Until our “special visiting” Asteroid 2012 TC4 approaches Earth at its closest trajectory, experts are watching this extraordinary body with great interest to see if it yields any other clues about what conditions will be like at the time of its visitation.  

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