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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 Ty­cho crat­er on the Moon is clear­ly vis­i­ble at the top of this im­age. Rays ap­pear­ing to spread out­ward mark the re­mains of fly­ing de­bris from the vi­o­lent im­pact. (Cour­te­sy NA­SA)


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.

The find­ings are to ap­pear in the Sept. 6 is­sue of the re­search jour­nal Na­ture.


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Astronomers have long believed that some sort of asteroid or comet 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 tail end of the bombardment. The U.S.-Czech research team combined observations with various computer simulations to reach the conclusion. They estimated that the parent body of the dinosaur-killer was some 170 kilometers (106 miles) wide. Some 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 one-third its diameter, creating thousands of large chunks. One of these 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 on 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 fashion, with some 2 percent of those going on to strike Earth. The result: a pronounced increase in the number of large asteroids striking Earth, 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 composition of the 180-kilometer wide Chicxulub crater, long believed 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. The findings are to appear in the Sept. 6 issue of the research journal Nature.