It's not large bodies we need to be concerned about
Scientists with the Institute of Astronomy of the Russian Academy of Sciences have recalculated the path of a large asteroid, Apophis; the refined data indicates a significantly low likelihood of a hazardous encounter with Earth, the institute's leading research fellow Viktor Shor said on Wednesday.
The Apophis asteroid is approximately the size of two-and-a-half football fields; its orbit is slightly offset to that of Earth's. Discovered in 2004, astronomers have determined that the asteroid will make a very close flyby in 2029 and might even hit Earth.
The initial calculation for the asteroid Apophis orbit was made using only two sets of observations.
Russian scientists recalculated its path taking into account a subtle effect changing the orbit of the asteroid - the thrust from sunlight absorbed and re-radiated as heat by the asteroid (the so-called Yarkovsky effect).
"Scientists give various orbital determinations for Apophis. But earlier calculations for the orbit did not include the Yarkovsky effect. This effect could strongly deflect the path of the asteroid," Shor said speaking at the International Aerospace Congress in Moscow.
The refined orbital determination indicates the significantly low likelihood of a hazardous encounter with Earth in 2029, Shor continued.
The exact path Apophis follows on its flyby in 2029 will determine whether it smashes into Earth seven years later, the scientist said.
The science of predicting asteroid orbits is based on a physical model of the solar system which includes the gravitational influence of the sun, moon, other planets and the three largest asteroids.
Comment: It's not large bodies we need to be concerned about. In her book,
The Apocalypse: Comets, Asteroids and Cyclical Catastrophes, Laura Knight-Jadczyk writes:
What I have prepared for today is The List, by no means exhaustive, of all the incidents I have been able to uncover of meteorite, asteroid, or cometary impacts that have caused death and destruction, property damage, or were near misses. Major parts of The List are extracted from the work of John S. Lewis, Professor of Planetary Sciences at the Lunar and Planetary Laboratory, Codirector of the NASA/University of Arizona Space Engineering Research Center, and Commissioner of the Arizona State Space Commission, in specific, his books entitled Rain of Iron and Ice and Comet and Asteroid Impact Hazards on a Populated Earth. In this latter volume, he writes:
The most intensively studied impact phenomenon, impact cratering, is of limited importance, due to the rarity and large mean time between events for crater-forming impacts. Almost all events causing property damage and lethality are due to bodies less than 100 meters in diameter, almost all of which, except for the very largest and strongest, are fated to explode in the atmosphere. ... [W]e are forced to conclude that the complex behavior of smaller bodies is closely relevant to the threat actually experienced by contemporary civilization.
Based on the data he collected, Lewis noted that:
[O]n the century time scale, firestorm ignition and direct blast damage by rare, strong, deeply penetrating bodies are the most common threats to human life, with average fatality rates of about 250 people per year. ... On a 1000-year scale, the most severe single event, which is usually a 10 to 100 megaton Tunguska-type airburst, accounts for most of the total fatalities. On longer time scales, regional impact-triggered tsunamis become the most dangerous events. ...The exact impactor threshold size for global effects remains poorly determined. [...]
Perhaps most interesting is the implication that the large majority of lethal events (not of the number of fatalities) are caused by bodies that are so small, so faint, and so numerous that the cost of the effort required to find, track, predict, and intercept them exceeds the cost of the damage incurred by ignoring them. [Lewis, 1999]
Comment: It's not large bodies we need to be concerned about. In her book, The Apocalypse: Comets, Asteroids and Cyclical Catastrophes, Laura Knight-Jadczyk writes: