Definition Of PHAs
Thousands of asteroids orbit our own solar system. The most dangerous ones are labelled Potentially Hazardous Asteroids, PHAs, which NASA watches closely.
All told, PHAs number over 1,400 as of 2013. Obviously, NASA telemetry has escalated proportionally since the very first asteroid was located in 1973.
The asteroids considered hazardous are fairly large (minimum 460 ft), and their orbits pass within 4.7 million miles of Earth. Even though their orbits haven’t intersected Earth’s yet, its highly likely several factors will change their orbit and force a collision.
At that time, just over 7,000 NEAs had been discovered, while today we know of over 12,000 NEAs, an increase of 70%. The percentage increase in the number of accessible asteroids in the catalog has been even greater: On January 18, 2015 – a little over four years since the NHATS assessments began – the 1332nd NHATS-compliant asteroid was identified, doubling the number of known accessible NEAs. The sizes of these asteroids range from as small as a few meters to as large as a few kilometers. While all these asteroids are more dynamically accessible than a round-trip mission to Mars, many of them (hundreds) require less energy to visit (round-trip) than does the lunar surface, and dozens of them require less energy to visit than does a low orbit around the Moon. NASA uses the automated NHATS system (http://neo.jpl.nasa.gov/nhats/) to monitor the NEA population for mission accessibility. This monitoring assists the identification of attractive destinations for future robotic and crewed missions.
NASA/JPL Near-Earth Object Program Office
Gravity usually forces orbits around Earth. Asteroids’ close proximity only exacerbates their gravimetric forces. An eventual collision is inevitable. If the asteroid is large enough (several miles), mass extinction will likely occur.
NASA performed the first Near-Earth Object Human Space Flight Accessible Targets Study, NHATS, in 2010. 666 of the known Near-Earth Asteroids, NEAs, were identified as “NHATS-compliant.” Therefore, likely to intersect earth’s orbit and collide.
Sheer Numbers Of PHAs
In 2010, over 7,000 NEAs had been discovered, and over 12,000 more in 2014. That’s an increase of 70% of known asteroids. NASA does not ‘extrapolate’, but a little reveals finding at least double the last known number every following year.
Most asteroids are totally dark, or invisible to a telescope until too late. Unless some have been seen, and orbits of close Earth-approaches have been calculated, there could be thousands of PHAs with earth’s name on it. With the sheer number of rogue asteroids likely existing, and the ever-attractive forces of gravity on close-passing objects, a cataclysmic encounter is inevitable. The only real question is when the impact will occur.
Locating An Asteroid
In Nature, March 1996, Drs. Taylor, Baggaley and Street, discussed results of year-long radar pulses on incoming meteors. When meteorites slam into the atmosphere, momentary ionization causes radar echos to give velocity, altitude and distance. The “AMOR” radar in New Zealand recently detected 350,000 faint echoes-1000 every day.
Every day, Earth is receiving almost 19,000 meteorites. Fewer than 10 are recovered every year. About 2800 meteorites are in museums, and chemically represent about 20 parent-bodies.
Every day, over 100 tons of meteoroids enter Earth’s atmosphere. William Cooke, head of NASA’s Meteoroid Environment Office, reveals most meteorites fall in the ocean, lakes, forests, and the Antarctic, never to be found.
A kilometer “sized” asteroid impacting Earth releases energy of a 20,000 megaton blast. It would leave a 13-km crater, and throw debris into the atmosphere causing “nuclear winter.”
Most Asteroids From Different Solar Systems
Objects typically originate in the giant Oort cloud existing outside our Solar System. Perturbations from nearby stars cause objects to fall into the Solar system. If anything passes close to Jupiter, its orbit is converted into a highly eccentric ellipse and the object becomes periodic. It will come back regularly.
A Near-Earth Asteroid, NEA, 2004MN4 [Apophis], discovered by NASA’s Spaceguard Survey, makes an unusually close pass in 2029. Estimated by NASA at ~1000 feet in diameter, Apophis will make a close-encounter by coming within 48,000 miles of Earth, passing just behind it, but well within geostationary satellite orbit. Even though a 2029 collision will not occur, this close encounter will significantly alter its orbit, and create a real possibility the asteroid will return to impact Earth in 2036. It would hit the Atlantic creating a massive tsunami, with an impact estimated at $400 billion.
The November asteroid 2009 VA barely missed Earth when it flew just 14,000 km above it. Its flight was inside the “Clarke Belt” of geosynchronous satellites (22,236 mi). Without warning, 2009VA was discovered just 15 hours before closest approach, by Catalina Sky Survey.
In 2002, asteroid 2002MN, the size of a soccer field, passed less than one-third of the distance to the moon. And 2002NT7 is a thousand-yard-wide asteroid heading for a collision with Earth-878 years from now. Asteroid 1950DA is currently scheduled to slam into Earth on March 16, 2880.
Asteroid 1997XF11 should pass only 30,000 miles from Earth in 2028. Any impact would create huge tsunami when hitting the Atlantic. All of the coastal cities would be wiped clean. Impact: 2 million atomic bombs.
Found Asteroids Exponentially Growing
Now NASA admits Earth is threatened by almost 6200 asteroids. A highly detailed study of PHAs using the Wide-field Infrared Survey Explorer, WISE, is constantly identifying more asteroids closing-in on earth’s orbit. The Yarkovsky Effect, ‘YARP’ Effect, and Poynting-Robertson Effect, all affect asteroid orbits.
Previous calculations can be off just enough to force an asteroid through the necessary “keyhole” catastrophically colliding with Earth. Science estimates 100,000-1,000,000 undiscovered asteroids on Earth-crossing orbits.
Most troubling is that most midsize asteroids (300-3000 feet) remain undiscovered.
With known PHAs almost doubling every year, the end of the world as we know it, will come in the next 500, 50, 5, or less years, as God says it will. That is, if another cataclysmic disaster does not beat it to the punch by then.