Monday, September 24, 2007

The Yucatan Peninsula / The Chicx­u­lub Crat­er

Here are two articles on the same subject - a very interesting subject to me.
Just so you know, we're WAY overdue for another hit. I mean like in any day now. And all we have watching the near Earth objects are a handful of private people working their asses off watching 1-3% of the sky. We're JUST NOW at the end of the asteroid shower that wiped out the dinosaurs.

Distant space collision meant doom for dinosaurs

By Will Dunham

A collision 160 million years ago of two asteroids orbiting between Mars and Jupiter sent many big rock chunks hurtling toward Earth, including the one that zapped the dinosaurs, scientists said on Wednesday.
Their research offered an explanation for the cause of one of the most momentous events in the history of life on Earth -- a six-mile-wide (10-km-wide) meteorite striking Mexico's Yucatan peninsula 65 million years ago.
That catastrophe eliminated the dinosaurs, which had flourished for about 165 million years, and many other life forms, and paved the way for mammals to dominate the Earth and the eventual rise of humankind, many scientists believe.
The impact is thought to have triggered a worldwide environmental cataclysm, expelling vast quantities of rock and dust into the sky, unleashing giant tsunamis, sparking global wildfires and leaving Earth shrouded in darkness for years.
U.S. and Czech researchers used computer simulations to calculate that there was a 90 percent probability that the collision of two asteroids -- one about 105 miles wide and one about 40 miles wide -- was the event that precipitated the Earthly disaster.
The collision occurred in the asteroid belt, a collection of big and small rocks orbiting the sun about 100 million miles from Earth, the researchers report in this week's issue of the journal Nature.
The asteroid Baptistina and rubble associated with it are thought to be leftovers, the scientists said.
Some of the debris from the collision escaped the asteroid belt, tumbled toward the inner solar system and whacked Earth and our moon, along with probably Mars and Venus, said William Bottke of the Southwest Research Institute in Boulder, Colorado, one of the researchers.


The collision is believed to have doubled for a while the number of impacts occurring in this part of the solar system.
In fact, while the bombardment of this region of the solar system due to this shower of debris peaked about 100 million years ago, the scientists said the tail end of the shower continues to this day. Bottke said many existing near-Earth asteroids can be traced back to this collision.
"Imagine breaking up a big, big boulder on top of a hill and all the fragments rolling down the hill. And somewhere at the bottom is a village called Earth," Bottke said in a telephone interview.
The dinosaur-destroying meteorite, thought to have measured 6 miles across, plunged into Mexico's Yucatan Peninsula and blasted out the Chicxulub (pronounced CHIK-shu-loob) crater measuring about 110 miles wide. The researchers looked at evidence on the composition of this meteorite and found it consistent with the stony Baptistina.
The researchers estimated that there also was about a 70 percent probability that the prominent Tycho crater on the Moon, formed 108 million years ago and measuring about 55 miles
across, also was carved out by a remnant of the earlier asteroid collision.
Philippe Claeys of Vrije Universiteit Brussel in Belgium, who was not involved in the research, said by e-mail the findings were "clear evidence that the solar system is a violent environment and that collisions taking place in the asteroid belt can have major repercussions for the evolution of life on Earth."
Bottke emphasized that point. "Dinosaurs were around for a very long time. So the likelihood is they would still be around if that event had never taken place," Bottke said.
"Was humanity inevitable? Or is humanity just something that happened to arise because of this sequence of events that took place at just the right time. It's hard to say."

Asteroid “crime family” blamed in dinosaur wipeout

Sept. 5, 2007
Courtesy Southwest Research Institute
and World Science staff

As­tro­no­mers have long be­lieved that some sort of as­ter­oid or com­et im­pact killed the di­no­saurs about 65 mil­lion years ago. Now they say they have likely iden­ti­fied what the ob­ject was—or at least, which fam­i­ly it came from.

The di­no­saurs fell vic­tim to one of many broken-up chunks of a once-bigger as­ter­oid, a group known as Bap­tis­tina family as­ter­oids, re­search­ers say. In fact, they add, frag­ments of that same rock have been pelt­ing Earth for eons, and we’re only about now at the bom­bard­ment’s end.
The U.S.-Czech re­search team com­bined ob­serva­t­ions with com­put­er sim­ula­t­ions to reach the con­clu­sions. They es­ti­mat­ed that the par­ent body of the di­no­saur-killer was some 170 kilo­me­ters (106 miles) wide.

Around 100 mil­lion years be­fore the di­no­saurs’ cat­a­stroph­ic end, this co­los­sus was float­ing through space deep in­side the So­lar Sys­tem’s main as­ter­oid belt be­tween Mars and Ju­pi­ter, the sci­en­tists said. That’s when it slammed in­to an­oth­er as­ter­oid about a third as wide, cre­at­ing thou­sands of large chunks.

One of those even­tu­ally found its way here and wiped out the great rep­tiles, the sci­en­tists con­tin­ued. With 90 per­cent cer­tain­ty it left the gi­ant pock­mark now called Chicx­u­lub crat­er on Mex­i­co’s Yu­ca­tan Pen­in­su­la, they said.

But that frag­ment was­n’t the only one to dis­rupt Earth or its neigh­bor­hood, the sci­en­tists added: a huge Moon crat­er called Ty­cho al­so has 70 per­cent like­li­hood of be­ing caused a Bap­tis­tina fa­mily mem­ber.

When the par­ent body broke up, its off­spring con­tin­ued mov­ing in si­m­i­lar or­bits to its own, the re­search­ers ex­plained. But these or­bits grad­u­ally changed due to forc­es pro­duced when they ab­sorbed sun­light and re-emitted the en­er­gy as heat. The family spread out, and some mem­bers drifted in­to a near­by “dy­nam­i­cal su­per­high­way,” a zone from which they could es­cape the main as­ter­oid belt and slip in­to or­bits that cross Earth’s path.

The com­puta­t­ions sug­gest that about 20 per­cent of sur­viv­ing mul­ti­-kilometer- sized frag­ments in the Bap­tis­tina family were lost in this way, with some 2 per­cent of those go­ing on to strike Earth. The re­sult: a pro­nounced in­crease in the num­ber of large as­ter­oids hit­ting our pla­net, the re­search team said.

Both Earth and Moon show ev­i­dence of a two-fold in­crease in the forma­t­ion rate of large crat­ers over the last 100 to 150 mil­lion years, they con­tin­ued. “The Bap­tis­tina bom­bard­ment pro­duced a pro­longed surge in the im­pact [rate] that peak­ed roughly 100 mil­lion years ago,” said Da­vid Nes­vorny of the South­west Re­search In­sti­tute in San An­to­nio, Tex­as, one of the re­search­ers.

“We are in the tail end of this show­er now. Our sim­ula­t­ions sug­gest that about 20 per­cent of the pre­s­ent-day, near-Earth as­ter­oid popula­t­ion can be traced back to the Bap­tis­tina fam­i­ly,” said the in­sti­tute’s Wil­liam Bot­tke, an­oth­er col­la­bo­ra­tor.

Fur­ther ev­i­dence im­pli­cat­ing the Bap­tis­ti­nas comes from the 180-kilometer wide Chicx­u­lub crat­er, long thought to be as­so­ci­at­ed with the di­no­saurs’ mis­for­tune, re­search­ers added. Sam­ples from the crat­er re­veal a chem­i­cal com­po­si­tion con­sist­ent with that of the Bap­tis­tina as­ter­oids, which are of a type known as car­bo­na­ceous chon­drites. These are of great in­ter­est to sci­en­tists be­cause of their prim­i­tive make­up: they’re be­lieved to con­sist of pris­tine ma­te­ri­al si­m­i­lar to that of the cloud from which the So­lar Sys­tem formed.

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