ON Feb. 15, an asteroid designated 2012 DA14 will pass safely within about
17,200 miles of Earth’s surface — closer than the communication satellites that
will be broadcasting the news of its arrival. The asteroid is about 150 feet in
diameter and has a mass estimated at about 143,000 tons.
Should an object of that size hit Earth, it would cause a blast with the energy
equivalent of about 2.4 million tons — or 2.4 megatons — of TNT explosives, more
than 180 times the power of the atomic blast that leveled Hiroshima.
It’s almost as if nature is firing a shot across our bow to direct our attention
to the vast number of nearby rocky asteroids and a few icy comets that make up
what we call the near-Earth object population. We should take the warning
seriously.
While no known asteroids or comets represent a worrisome impact threat now,
NASA’s Jet Propulsion Laboratory shows more than two dozen asteroids have better
than a one in a million chance of smacking into Earth within the next 100 years.
That may sound reassuring, but we estimate that less than 10 percent of all
near-Earth objects have been discovered. And while we are keeping a vigilant eye
out for these objects in the Northern Hemisphere, we are considerably less
watchful in the Southern Hemisphere.
It has been only within the last 15 years that astronomers, mostly supported by
NASA, have begun discovering the vast number of near-Earth objects. Our findings
have led us to the realization that Earth runs its course around the sun in a
cosmic shooting gallery — with us as the target. Basketball-size rocky objects
enter Earth’s atmosphere daily and Volkswagen-size objects every few months, but
they burn up before they hit the ground.
Objects larger than about 100 feet in diameter, the size of a large house,
strike Earth with an average interval of a few hundred years. The last one of
about this size to hit was on June 30, 1908, in a sparsely populated region of
Siberia called Tunguska. The Tunguska blast released about four megatons of
energy and leveled millions of trees across 825 square miles.
A much larger asteroid or comet, six miles in diameter, collided with Earth some
65 million years ago, killing most of the large vertebrates, including the
dinosaurs. Fortunately, Earth collisions with objects so big happen only at
average intervals of 100 million years.
What can be done if a rogue asteroid is judged to be on a trajectory that
threatens Earth? Our best option would be to send a spacecraft to collide with
the asteroid and modify its trajectory to ensure that the Earth is missed by a
wide margin. We have the technology to do this — and, in fact, did it in 2005,
when we intentionally slammed a spacecraft into the comet Tempel-1. As the
science fiction author Larry Niven once said, the dinosaurs became extinct
because they didn’t have a space program.
In April 2010, President Obama called upon NASA to send a human mission to an
asteroid by 2025 as a steppingstone for the much more difficult human
exploration of Mars. The technologies and life support systems needed for the
Mars expedition could be tested first at a nearby asteroid with the round trip
taking only a few months instead of a few years.
QUITE apart from their menacing reputations or as steppingstones to Mars,
near-Earth objects are important in their own right. They are the leftover bits
and pieces from the formation of the solar system 4.6 billion years ago, so they
provide insights into the original chemical mix and environment of our nascent
solar system.
They may also have played a key role in how life arose on Earth. Asteroids and
comets most likely brought to the earth much of the water and carbon-based
materials that allowed life to form more than 3.5 billion years ago. Subsequent
impacts then punctuated evolution, allowing only the most adaptable species to
evolve further. Remember the dinosaurs? We mammals may owe our very existence
and our position atop the food chain to near-Earth objects.
There are compelling reasons to use these objects as sources of raw materials
for the future construction of space habitats and supply depots. They are rich
in minerals, metals and platinum-group elements, and their clays and ices could
provide water resources. (Within the last year, two United States companies,
Planetary Resources and Deep Space Industries, announced plans to mine asteroids
for their resources.) The water could be broken down into hydrogen and oxygen,
the most efficient form of rocket fuel. Near-Earth objects may serve as the
watering holes and fueling stations for interplanetary exploration.
We’ll also need to continue to aggressively discover and track them, if we are
to be assured of having a future as a species.
Three NASA-supported observatories with modest telescopes in the southwestern
United States and in Hawaii are making more than 95 percent of near-Earth object
discoveries. Because of budget limitations, an observatory at Siding Spring,
Australia, the only one looking for these objects in the Southern Hemisphere,
has reduced its operations to only occasional observations, leaving a blind spot
for unknown objects approaching from the southern skies.
Ground-based observatories will always be important as we follow these
intriguing objects. But a space-based, wide field-of-view telescope operating in
the more sensitive infrared light wavebands is the best way to find the majority
of hazardous asteroids within the next decade.
NASA and its domestic and international partners need to be allowed to redouble
the search for near-Earth objects with more powerful search telescopes, both
ground-based and space-based, so we are not caught off guard. We need to find
them before they find us.
LOS ANGELES
(AP) — An asteroid as big as an aircraft carrier zipped by Earth on Tuesday in
the closest encounter by such a massive space rock in more than three decades.
Scientists ruled out any chance of a collision but turned their telescopes
skyward to learn more about the object known as 2005 YU55.
Its closest approach to Earth was pegged at a distance of 202,000 miles at 6:28
p.m. EST. That's just inside the moon's orbit; the average distance between
Earth and the moon is 239,000 miles.
The last time a large cosmic interloper came that close to Earth was in 1976,
and experts say it won't happen again until 2028.
Scientists at NASA's Deep Space Network in the California desert have tracked
the quarter-mile-wide asteroid since last week as it approached from the
direction of the sun at 29,000 mph.
Astronomers and amateur skygazers around the world kept watch, too.
The Clay Center Observatory in Brookline, Mass., planned an all-night viewing
party so children and parents could peer through research-grade telescopes and
listen to lectures. The asteroid can't be detected with the naked eye.
For those without a telescope, the observatory streamed video of the flyby live
on Ustream, attracting several thousand viewers. The asteroid appeared as a
white dot against a backdrop of stars.
"It's a fantastic opportunity to educate the public that there are things out in
space that we need to be aware of," including this latest flyby, said
observatory director Ron Dantowitz.
Dantowitz added: "It will miss the Earth. We try to mention that in every
breath."
If an asteroid that size would hit the planet, Purdue University professor Jay
Melosh calculated the consequences. The impact would carve a crater four miles
across and 1,700 feet deep. And if it slammed into the ocean, it would trigger
70-foot-high tsunami waves.
Since its discovery six years ago, scientists have been monitoring the
spherical, coal-colored asteroid as it slowly spins through space and were
confident it posed no danger.
Asteroids are leftovers from the formation of the solar system some 4.5 billion
years ago. Scientists believe their growth was stunted by Jupiter's
gravitational pull and never had the chance to become full-fledged planets.
Pieces of asteroids periodically break off and make fiery plunges through the
atmosphere as meteorites.
Don Yeomans, who heads NASA's Near Earth Object Program, said 2005 YU55 is the
type of asteroid that humans may want to visit because it contains carbon-based
materials and possibly frozen water.
With the space shuttle program retired, the Obama administration wants
astronauts to land on an asteroid as a stepping stone to Mars.
The last
time NASA visited the Tempel 1 comet, it was with fireworks, on July 4, 2005. On
that day, the Deep Impact spacecraft slammed an 820-pound projectile into Tempel
1, excavating a plume of ice and dust.
On Monday night — Valentine’s Day — NASA will return to Tempel 1 but will not
bombard it. This time, a different spacecraft, Stardust, will zip past at more
than 24,000 miles per hour, taking 72 high-resolution pictures of the comet’s
surface.
Stardust will make its closest approach, within 125 miles, at 11:37 p.m. Eastern
time.
Tim Larson, the mission’s project manager, said NASA was not deliberately
scheduling its missions to coincide with holidays. “That’s just how the orbital
mechanics worked out on these,” he said, “although it makes for great P.R.”
Tempel 1 will be the first comet to be seen at close range twice, and scientists
will make a then-and-now comparison — one that they expect will reveal a change
in topography and tell them more about the inner workings of comets.
“Here’s a chance where we can see what has changed, how much has changed,” said
Joseph Veverka, a professor of astronomy at Cornell and the mission’s principal
investigator, “so we’ll start unraveling the history of a comet’s surface."
For example, photographs taken by Deep Impact in 2005 showed areas that looked
old and others that seemed much younger. But the snapshots did not tell the ages
of any of them. “We have no idea whether we’re talking about things that have
been there for a hundred years, a thousand years, a million years,” Dr. Veverka
said.
In the five and a half years since Deep Impact’s visit, Tempel 1 — whose orbit
brings it as close to the Sun as Mars and as far away as Jupiter — has completed
a full orbit.
Stardust was launched in 1999 and arrived five years later at its primary
destination, a comet named Wild 2, where it collected particles of dust.
Stardust then looped back to Earth and released a canister containing the comet
dust, which parachuted back to the ground.
The spacecraft, still operating well, continued onward, and NASA decided to use
it for a return visit to Tempel 1. (Deep Impact, meanwhile, also extended its
scientific journey, visiting another comet last November.)
One more puzzle that scientists may be able to solve with the second look at
Tempel 1 involves depressions that look like the type of craters caused by
impacts. The depressions, though, could have been caused by explosions that were
a result of underground ice that converted to gas.
The scientists will now be able to compare the depressions with something they
know is definitely a crater — the scar left by Deep Impact. “Simple question,”
Dr. Veverka said, “direct answer.”
What a labourer thought was gunfire
was a rare meteorite
THE Natural History Museum at South Kensington has received a very rare and
interesting gift in the shape of a meteorite, which fell just before 1pm on
March 9 between Saffron Walden and Ashdon, in Essex.
The man who saw the meteorite fall was a labourer, who states that he heard a
“sissing” noise and supposed that an aeroplane was overhead. Looking up a second
or two after he saw what he thought was a projectile fall about ten to fifteen
yards from him, causing the earth to spout up like water.
He was much alarmed, because he considered that something had been discharged
from a gun. Three days later, in company with another man, he took the meteorite
up from where it had fallen. He says that there was a small hole where it had
entered the ground, and this hole increased in width as he dug deeper. The stone
was found at a depth of two feet.
The specimen weighs about 3lb, and is what is known as a white chondrite
meteoric stone. It is about 5in long by 4in wide and has a thickness of about
3in in its thickest part.
The surface of the stone shows with remarkable distinctness, the lines of flow
of fused materials radiated from the centre of the surface and proves that it
was partially fused owing to the high velocity at which it entered the earth’s
atmosphere.
The rarity of the occurrence of a meteor seen to be falling is evident by the
fact that only about fifteen falls have been recorded in the British Islands.
