Could Earth Be Hit, Like Jupiter Just Was?

The recent bruising Jupiter received from a cosmic impact is a violent reminder that our solar system is a shooting gallery that sometimes blasts Earth.
Still, what are the odds of a cosmic impact threatening our planet?
So far 784 near-Earth objects (NEOs) more than a half-mile wide (1 km) have been found.
"If an object of about the same size that just hit Jupiter also hit Earth — it was probably a typical cometary object of a kilometer or so in size (0.6 miles) — it would have been fairly catastrophic," explained astronomer Donald Yeomans, manager of NASA's Near-Earth Object program office at the Jet Propulsion Laboratory in Pasadena, Calif.
Scientists have ruled out the chances of an Earth impact for all of these 784 large NEOs. Still, lesser objects also pose a risk, and researchers estimate more than 100 large NEOS remain to be found.
Small risk
Billions of years ago, impacts were far more common. Our moon retains a record of the pummeling it and Earth took: the moon's craters remain, while on Earth, most scars of ancient impacts have been folded back into the planet or weathered away.
Today's solar system is far less crowded, and in fact Jupiter, having more mass and gravity, scoops up a lot of the dangerous objects, as does the sun.
Currently just one NEO of all the objects scientists are tracking poses any significant chance of hitting the Earth — 2007 VK184. If this roughly 425-foot-wide (130 meters) asteroid hit our planet, it would strike with an energy of roughly 150 million tons of TNT, or more than 10,000 times that of the atom bomb dropped on Hiroshima.
Roughly 100 telescopic observations made so far suggest that 2007 VK184 has a 1-in-2,940 chance of hitting Earth 40 to 50 years from now. However, if the past is any guide, further observations to refine computations of its orbit very likely will downgrade its probability of hitting Earth to virtually nothing, Yeomans said.
Of remaining concern are the NEOs that we do not see. Researchers suspect about 156 large NEOs 1 kilometer in diameter or larger remain to be found, and when it comes to dangerous NEOs in general, "when we get down to 140 meters (460 feet) or larger diameter objects, we think we've discovered about 15 percent of them, and with 50 meters (164 feet) or larger diameter, we've discovered less than 5 percent of them," Yeomans explained.
On average, an NEO roughly a half-mile wide or larger hits the Earth roughly every 500,000 years, "so we're not expecting one anytime soon," Yeomans explained.
"For 500 meters (1,640 feet), we're talking a mean interval of about 100,000 years," he added. "When you get down to 50 meters, the mean interval is about 700 years, and for 30 meters (98 feet), about 140 years or so, but by then you're getting down to a size where you won't expect any ground damage, as they burn up in the atmosphere at about 25 meters (82 feet) in diameter and smaller, probably for an impressive fireball event."
When it comes to truly monstrous NEOs some 10 kilometers (6.2 miles) or larger, of the size thought to have helped kill off the dinosaurs, "that's a 100 million year event, and in fact, I don't think there is anything like that we see right now," Yeomans said. "The largest near-Earth object that can actually cross the Earth's path, Sisyphus, has a diameter of 8 kilometers (5 miles), and the largest that is termed a potential hazard is Toutatis, which has a diameter of approximately 5.4 km (3.35 miles)."
Keeping watch
There are currently four teams worldwide actively looking for both large and small NEOs, Yeomans said. "We're concentrating on the large ones for now, but hopefully with the next generation of search, we'll be more efficient in finding the smaller objects, to find 90 percent of the total population of potential hazards larger than 140 meters," he added.
Keeping an eye on NEOs might not just be healthy for humanity, but also help lead us out into space.
"They're easy objectives to get to, and asteroids have significant metal resources that can be mined, while comets have significant water resources for space habitats or travel," Yeomans said. "If you want to build a habitat in space, you're not going to build it all on the ground and launch it up, since that's too expensive — you want to go up and look for resources instead."
Furthermore, asteroids and comets are among the objects that have changed the least since the birth of the solar system roughly 4.6 billion years ago, and might reveal vital clues behind the mysterious process.
"They may well have delivered the water and carbon-based molecules to Earth that allowed life to form, so they're extremely important for study in that direction," Yeomans added.
source:http://news.yahoo.com/s/space/20090728/sc_space/couldearthbehitlikejupiterjustwas

Solar eclipse pits superstition against science

MUMBAI (AFP) – Indian astrologers are predicting violence and turmoil across the world as a result of this week's total solar eclipse, which the superstitious and religious view as a sign of potential doom.
But astronomers, scientists and secularists are trying to play down claims of evil portent in connection with Wednesday's natural spectacle, when the moon will come between the Earth and the sun, completely obscuring the sun.
In Hindu mythology, the two demons Rahu and Ketu are said to "swallow" the sun during eclipses, snuffing out its life-giving light and causing food to become inedible and water undrinkable.
Pregnant women are advised to stay indoors to prevent their babies developing birth defects, while prayers, fasting and ritual bathing, particularly in holy rivers, are encouraged.
Shivani Sachdev Gour, a gynaecologist at the Fortis Hospital in New Delhi, said a number of expectant mothers scheduled for caesarian deliveries on July 22 had asked to change the date.
"This is a belief deeply rooted in Indian society. Couples are willing to do anything to ensure that the baby is not born on that day," Gour said.
Astrologers have predicted a rise in communal and regional violence in the days following the eclipse, particularly in India, China and other Southeast Asian nations where it can be seen on Wednesday morning.
Mumbai astrologer Raj Kumar Sharma predicted "some sort of attack by (Kashmiri separatists) Jaish-e-Mohammad or Al-Qaeda on Indian soil" and a devastating natural disaster in Southeast Asia.
An Indian political leader could be killed, he said, and tension between the West and Iran is likely to increase, escalating into possible US military action after September 9, when fiery Saturn moves from Leo into Virgo.
"The last 200 years, whenever Saturn has gone into Virgo there has been either a world war or a mini world war," he told AFP.
It is not just in India that some are uneasy about what will transpire because of the eclipse.
In ancient China they were often associated with disasters, the death of an emperor or other dark events, and similar superstitions persist.
"The probability for unrest or war to take place in years when a solar eclipse happens is 95 percent," announced an article that attracted a lot of hits on the popular Chinese web portal Baidu.com.
Sanal Edamaruku, president of the Indian Rationalist Association, dismissed such doomsday predictions.
"Primarily, what we see with all these soothsayers and astrologers is that they're looking for opportunities to enhance their business with predictions of danger and calamity," he told AFP.
"They have been very powerful in India but over the last decade they have been in systematic decline."
Astronomers and scientists are also working to educate the public about the eclipse.
Travel firm Cox and Kings has chartered a Boeing 737-700 aircraft to give people the chance to see the eclipse from 41,000 feet (12,500 metres).
Experts will be on board to explain it to passengers, some of whom have paid 79,000 rupees (1,600 dollars) for a "sun-side" seat on the three-hour flight from New Delhi.
The eclipse's shadow is expected to pass over the aircraft at 15 times the speed of sound (Mach 15), said Ajay Talwar, president of the SPACE Group of companies that promotes science and astronomy.
"It's coming in the middle of the monsoon season. On the ground, there's a 40 percent chance of seeing it in India. On the aircraft you have almost a 90 percent chance of seeing the eclipse," he added.
Siva Prasad Tata, who runs the Astro Jyoti website, straddles the two worlds.
"There's no need to get too alarmed about the eclipse, they are a natural phenomenon," the astrologer told AFP.
But he added: "During the period of the eclipse, the opposite attracting forces are very, very powerful. From a spiritual point of view, this is a wonderful time to do any type of worship.
"It will bring about good results, much more than on an ordinary day."

Source:http://news.yahoo.com/s/afp/20090720/sc_afp/scienceastronomyeclipseasiatourismsuperstition