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Wednesday, 18 March 2015

Search for Near Earth Objects (e.g., asteroids)

In the 1998 movie Armageddon (www.imdb.com/title/tt0120591/combined) Bruce Willis saves our planet by taking a space craft, landing on a massive meteor, drilling a hole, plugging a nuclear bomb into it, and detonating it. Though such a movie may seem farfetched, NASA is actually working on such future robotic and crewed missions. A substantial number of scientists claim that the dinosaurs became extinct from exactly such a collision (see #8 below).

National Geographic made a list of 10 very serious asteroid hits on planet Earth:
1. Vredefort Crater, Free State, South Africa. Estimated 2 billion years ago. Specs: estimated radius of 190 kilometres, making it the world's largest known impact structure. UNESCO World Heritage.
2. Sudbury Basin, Ontario, Canada. Est. 1.8 billion years ago. Specs: est. diameter of 130 km.
3. Acraman Crater, South Australia. Est. 580 million years ago. Specs: estimated diameter of 90 km.
4. Woodleigh Crater, Western Australia. Est. 364 million years ago. Specs: not exposed at the surface. Reports on its diameter vary from 40 to 120 km.
5. Manicouagan Crater, Quebec, Canada. Est. 215 million years ago. Specs: one of the largest and best-preserved craters on Earth, with an estimated diameter of 100 kilometres.
6. Morokweng Crater, South Africa. Est. 145 million years ago. Specs: Located near the Kalahari Desert in South Africa, this crater contained the fossilised remains of the meteorite that created it.
7. Kara Crater, Russia. Est. 70.3 million years ago. Specs: now greatly eroded. Some have claimed that the impact structure actually consists of two adjacent craters.
8. Chicxulub Crater, Yucat√°n, Mexico. Est. 65 million years ago. Specs: many scientists believe that the meteorite that left this crater caused or contributed to the extinction of the dinosaurs. Estimates of its actual diameter range from 170 km to 300 km, which if proved right could mean it's the biggest.
9. Popigai Crater, Siberia, Russia. Est. 35.7 million years ago. Specs: Russian scientists claim this crater contains trillions of carats of diamonds, making it one of the world's largest diamond deposits.
10. Chesapeake Bay Crater, Virginia, USA. Est. 35 million years ago. Specs: discovered in the early 1980s, located some 200 km from Washington, D.C. Estimates suggest this crater is 85 km wide.

The human response time for a hit is either decades or none at all. Decades for known Near Earth Objects (NEOs) and none for unknown objects (e.g., 2013 Russia). So far some 12,000 NEOs have been discovered out of a total population thought to number in the millions. The Earth’s atmosphere protects us from most NEOs smaller than a modest office building (40 m diameter). Estimated frequency: small 5-10 per year. From this size up to about 1 km diameter, an impacting NEO can do tremendous damage on a local scale (e.g., 2013 Russia). Estimated frequency: once every 5 years. Above a diameter of some 2 km, an impact will produce severe environmental damage on a global scale. Estimated frequency: 1-2 per million years. As of the end of 2011, astronomers had discovered more than 90% of the larger Near Earth Asteroids (diameter greater than 1 km). None of the known asteroids is a threat, but we have no way of predicting the next impact from an unknown object. 

The count of known NEAs can be obtained daily from the NASA Program Office website at http://neo.jpl.nasa.gov/. On 2 April 2014 NASA announced that recent observations have removed NEO 2007 VK184 (diameter 130 meter) from its asteroid impact hazard list, which was known to pose the most significant risk of Earth impact over the next 100 years.

So, in short it's either CARPE DIEM or MEMENTO MORI. I prefer Carpe Diem.