Aquarius
03-09-2005, 08:59 PM
Sudden impact: Arizona meteor was a part of huge rock
1 hour, 17 minutes ago Science - AFP
PARIS (AFP) - Planetary scientists believe that a rock which smashed into Arizona around 49,000 years ago with the power of more than 150 Hiroshima bombs was just a fragment of a space goliath.
In a study published on Thursday, the pair believe they have resolved an enduring puzzle about Meteor Crater, located near Flagstaff in the Arizona desert and one of the most-studied impact sites in the world.
By some calculations, the rock -- an asteroid or a comet that crossed Earth's path -- should have hit the ground at 72,000 kilometers (45,000 miles) per hour, for it left a huge crater 1.2 kilometers (0.75 miles) across and 150 metres (500 feet) deep.
If so, the high-velocity collision should have released so much heat that the iron-rich impacting rock itself, or at least part of it, should have melted in a flash. But no substantial signs of melted mineral have ever been found there.
The reason, according to a new study: the rock was merely the largest chunk from a space bruiser that probably measured 42 metres (136 feet) across.
After entering Earth's atmosphere, the giant broke apart at an altitude of around 14 kms (45,000 feet) after it encountered a steadily denser atmosphere, whose pressure both cushioned the descent and caused the rock to fracture.
The fragments then descended in a pancake-shaped cluster, with atmospheric drag acting as a brake.
The piece that created Meteor Crater was probably around 20 metres (65 feet) across and hit the ground at 43,000 kph (25,000 mph), releasing the equivalent force of 2.5 megatonnes of TNT, or at least 150 times the "Little Boy" atomic bomb dropped on Hiroshima in 1945, the study suggests.
The remainder of the impact energy -- about 6.5 megatonnes of TNT -- was released into the atmosphere, triggering a powerful shockwave.
The research, authored by University of Arizona scientist Jay Melosh and Gareth Collins of Imperial College, London, appears on Thursday in the British weekly science journal Nature.
Big objects from space can deliver catastrophic damage because they impact at tens of thousands of kilometers (miles) per hour.
The last known collision between a large space object and Earth occurred in 1908, when a rock estimated to be 50 metres (165 feet) across exploded eight kms (five miles) over Tunguska, Siberia, destroying 2,000 square kms (770 square miles) of forest.
The long reign of the dinosaurs is believed to have ended when a big rock smashed into modern-day Mexico about 65 million years ago, kicking up a cloud of dust, soot and ash that cooled the heat from the Sun and changed Earth's climate.
1 hour, 17 minutes ago Science - AFP
PARIS (AFP) - Planetary scientists believe that a rock which smashed into Arizona around 49,000 years ago with the power of more than 150 Hiroshima bombs was just a fragment of a space goliath.
In a study published on Thursday, the pair believe they have resolved an enduring puzzle about Meteor Crater, located near Flagstaff in the Arizona desert and one of the most-studied impact sites in the world.
By some calculations, the rock -- an asteroid or a comet that crossed Earth's path -- should have hit the ground at 72,000 kilometers (45,000 miles) per hour, for it left a huge crater 1.2 kilometers (0.75 miles) across and 150 metres (500 feet) deep.
If so, the high-velocity collision should have released so much heat that the iron-rich impacting rock itself, or at least part of it, should have melted in a flash. But no substantial signs of melted mineral have ever been found there.
The reason, according to a new study: the rock was merely the largest chunk from a space bruiser that probably measured 42 metres (136 feet) across.
After entering Earth's atmosphere, the giant broke apart at an altitude of around 14 kms (45,000 feet) after it encountered a steadily denser atmosphere, whose pressure both cushioned the descent and caused the rock to fracture.
The fragments then descended in a pancake-shaped cluster, with atmospheric drag acting as a brake.
The piece that created Meteor Crater was probably around 20 metres (65 feet) across and hit the ground at 43,000 kph (25,000 mph), releasing the equivalent force of 2.5 megatonnes of TNT, or at least 150 times the "Little Boy" atomic bomb dropped on Hiroshima in 1945, the study suggests.
The remainder of the impact energy -- about 6.5 megatonnes of TNT -- was released into the atmosphere, triggering a powerful shockwave.
The research, authored by University of Arizona scientist Jay Melosh and Gareth Collins of Imperial College, London, appears on Thursday in the British weekly science journal Nature.
Big objects from space can deliver catastrophic damage because they impact at tens of thousands of kilometers (miles) per hour.
The last known collision between a large space object and Earth occurred in 1908, when a rock estimated to be 50 metres (165 feet) across exploded eight kms (five miles) over Tunguska, Siberia, destroying 2,000 square kms (770 square miles) of forest.
The long reign of the dinosaurs is believed to have ended when a big rock smashed into modern-day Mexico about 65 million years ago, kicking up a cloud of dust, soot and ash that cooled the heat from the Sun and changed Earth's climate.