NASA 2016 --Identifies Eight Potentially Hazardous Near-Earth Objects: "Major Impact Could Cause Evolutionary Change"
NASA's asteroid-hunting spacecraft released a treasure trove of survey data, revealing hundreds of Near-Earth objects (NEOs) of which 72 are newly detected and eight of the 72 NEOs classified as potentially hazardous asteroids (PHA) in 2016 based on their size and how close their orbits approached our planet. Impact rates depend on how many comets and asteroids exist in a particular planetary system. In general there is one major impact every million years -a mere blink of the eye in geological time. It also depends on how often those objects are perturbed from safe orbits that parallel the Earth's orbit to new, Earth-crossing orbits that might, sooner or later, result in a catastrophic K/T or Permian-type mass extinction.
"The NEOWISE analysis shows us we've made a good start at finding those objects that truly represent an impact hazard to Earth," said Lindley Johnson, program executive for the Near-Earth Object Observation Program at NASA Headquarters in Washington. "But we've many more to find, and it will take a concerted effort during the next couple of decades to find all of them that could do serious damage or be a mission destination in the future." The analysis also suggests that about twice as many PHAs as previously thought are likely to reside in "lower-inclination" orbits, which are more aligned with the plane of Earth's orbit. In addition, these lower-inclination objects appear to be somewhat brighter and smaller than theother near-Earth asteroids that spend more time far away from Earth. A possible explanation isthat many of the PHAs may have originated from a collision between two asteroids in the mainbelt lying between Mars and Jupiter. A larger body with a low-inclination orbit may have broken up in the main belt, causing some of the fragments to drift into orbits closer to Earth andeventually become PHAs.
Since December 2013, the Near-Earth Object Wide-field Survey Explorer (Neowise) mission has identified 439 NEOs — asteroids or comets that at some point orbited the Sun and became close to the Earth. With the release of this fresh batch of data, Neowise has completed another milestone in its mission to detect, track and classify the comets and asteroids that approach the planet.
An asteroid is considered an NEO when its distance from the Sun during its closest approach is less than 1.3 times the average Sun-Earth distance, experts said.
In September 2013, WISE was reactivated as Neowise to distinguish populations of potentially-dangerous NEOs.
Neowise principal investigator Amy Mainzer said the spacecraft discovers large and dark NEOs, helping scientists by complementing the network of ground-based telescopes that operate at visible-light wavelengths. "On average, these objects are many hundreds of meters across," said Mainzer.
NASA scientists said no NEOs are likely to hit the planet anytime soon. Still, space rocks can remain undetected, such as the Chelyabinsk meteor that streaked across Russian skies on Feb. 15, 2013. The meteor exploded, shattering glass windows and injuring more than 1,100 residents. Experts say this meteor was the result of a collision between two astronomical bodies.Fragments of the meteor revealed that the collision did not happen days or months before it hit Earth, but about 290 million years ago.
Meanwhile, NASA unveiled an asteroid detection program in early January 2016 which would help defend the planet in case any dangerous hidden asteroids are near Earth.
Because the telescope detected the infrared light, or heat, of asteroids, it was able to pick up both light and dark objects, resulting in a more representative look at the entire population. The infrared data allowed astronomers to make good measurements of the asteroids' diameters and, when combined with visible light observations, how much sunlight they reflect.
“The threat of the Earth being hit by an asteroid is increasingly being accepted as the single greatest natural disaster hazard faced by humanity,” according to Nick Bailey of the University of Southampton's School of Engineering Sciences team.
In 2009, Bailey and his colleagues used raw data from multiple impact simulations to rank each country based on the number of times and how severely they would be affected by each impact. The software, called NEOimpactor(from NASA's "NEO" or Near Earth Object program), was developed for measuring the impact of 'small' asteroids under one kilometer in diameter.
Results indicated that in terms of population lost, China, Indonesia, India, Japan and the United States face the greatest overall threat; while the United States, China, Sweden, Canada and Japan face the most severe economic effects due to the infrastructure destroyed.
The top ten countries most at risk are China, Indonesia, India, Japan, the United States, the Philippines, Italy, the United Kingdom, Brazil and Nigeria.
“The consequences for human populations and infrastructure as a result of an impact are enormous,” says Bailey. “Nearly one hundred years ago a remote region near the Tunguska River witnessed the largest asteroid impact event in living memory when a relatively small object (approximately 50 metres in diameter) exploded in mid-air. While it only flattened unpopulated forest, had it exploded over London it could have devastated everything within the M25. Our results highlight those countries that face the greatest risk from this most global of natural hazards and thus indicate which nations need to be involved in mitigating the threat.”
The team also examined how the consequences of an impact change with increasing impact energy. Initial results indicate that a 100 meter diameter asteroid will predominantly cause localized casualties and damage across a few countries when impacting on either land or ocean. However, the consequences of a 200 meter diameter asteroid hitting the ocean increase significantly, with the generated tsunamis reaching a global scale. At 500 meters in diameter, almost any ocean impact will generate significant casualties and economic cost across the world.
As Stephen Hawking says, the general consensus is that any comet or asteroid greater than 20 kilometers in diameter that strikes the Earth will result in the complete annihilation of complex life - animals and higher plants. (The asteroid Vesta, for example, one of the destinations of the Dawn Mission, is the size of Arizona).
The asteroid that hit Vredefort located in the Free State Province of South Africa is one of the largest to ever impact Earth, estimated at over 10 km (6 miles) wide, although it is believed by many that the original size of the impact structure could have been 250 km in diameter, or possibly larger(though the Wilkes Land crater in Antarctica, if confirmed to have been the result of an impact event, is even larger at 500 kilometers across). The town of Vredefort is situated in the crater (image).
Dating back 2,023 million years, it is the oldest astrobleme found on earth so far, with a radius of 190km, it is also the most deeply eroded. Vredefort bears witness to the world’s greatest known single energy release event, which caused devastating global change, including, according to many scientists, major evolutionary changes.
The Daily Galaxy via NASA: nasa.gov/wise, wise.astro.ucla.edu and jpl.nasa.gov/wise
