Antarctic craters reveal mulitple BIG strikes

[silylene old]

This is interesting !<br /><br /><b>Antarctic craters reveal strike</b><br /><br /> http://news.bbc.co.uk/1/hi/sci/tech/3580230.stm<br /> <br />The asteroid may have raised sea levels by up to 60cm <br />Scientists have mapped enormous impact craters hidden under the Antarctic ice sheet using satellite technology. <br />The craters may have either come from an asteroid between 5 and 11km across that broke up in the atmosphere, a swarm of comets or comet fragments. <br /><br />The space impacts created multiple craters over an area of 2,092km (1300 miles) by 3,862km (2,400 miles). <br /><br />The scientists told a conference this week that the impacts occurred roughly 780,000 years ago during an ice age. <br /><br />When the impacts hit, they would have melted through the ice and through the crust below. <br /><br />Professor Frans van der Hoeven, from Delft University in the Netherlands, told the International Geographical Union Congress in Glasgow that the biggest single strike seared a hole in the ice sheet roughly 322km (200 miles) by 322km. <br /><br />Impact melt <br /><br />This would have melted about 1% of the ice sheet, raising water levels worldwide by 60cm (2ft). <br /><br />The research suggests that an asteroid the size of the one blamed for killing off the dinosaurs 65 million years ago could have struck Earth relatively recently. <br /><br />Early humans would have been living in Africa and other parts of the Old World at the time of the strikes. <br /><br />But the impacts would have occurred during an ice age, so even tidal waves would have been weakened by the stabilising effect of icebergs on the ocean. <br /><br />The craters were resolved using satellite data to map gravity anomalies under the ice sheet. <br /> <br /> <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[rogers_buck]

How do you get a severe whammy dead center south pole? It seems that the impactor wasn't orbiting in the ecliptic? Anyone worked this out?

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>How do you get a severe whammy dead center south pole? It seems that the impactor wasn't orbiting in the ecliptic? Anyone worked this out?<p><hr /></p></p></blockquote><br /><br />That's a good point, but then, the Earth is tilted relative to the ecliptic, so that makes it easier. Puls, I don't the impactor doesn't have to be coming absolutely precisely dead-on, so I think that makes it plausible. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>The earth orbits very close to the ecliptic, anyway. The point is that asteroid and meteors can be often in fairly any orbit and do not obey the ecliptic tendencies of the orbits of the major planets.<p><hr /></p></p></blockquote><br /><br />This is very true. Most asteroids are fairly close to the ecliptic (perhaps 20 degrees inclination or less) for the same reason that the planets are, but as stevehw33 points out, there are many that aren't. I don't know of any examples offhand, but to give an example of how an object can be shifted into such an orbit, consider the Ulysses probe. It used nothing more than a flyby of Jupiter at the right angle to shift itself into a polar heliocentric orbit. If Ulysses could do it deliberately, an asteroid or comet could do it by chance. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[jitte]

Asteroid 2002 NT7 is in an orbit which is highly inclined with respect to the Earths orbit about the Sun. <br /><br /><br />------------------------

 

[narses]

I think we are all missing the point here !<br />As far as I know, there is no sign of this event in the fossil record, especially no sign of any sort of extinction event.<br />In view of the fact that this impact appears to be of a very similar size to our famous friend in the Yucatan which is blamed as the cause of the end Cretaceous extinction event, the most interesting question is surely, why didn't it cause any signs in the fossil record ?<br />I find suggestions that impacting on an ice sheet somehow ameliorated the effect unconvincing - any sizeable impact will surely blast through any reasonable thickness of ice down to the bedrock, as indeed the simple existance of the craters shows. And icebergs dampened the tsumami's ? Maybe, but as far as I am aware tsumani's have never been seriously proposed as a major cause of mass extiction events which usually involve global climate change, toxic fallout from the impact etc etc.<br />So why did the chixculub impact kill a substantial proportion of the species then existing, and this antarctic impact none at all ?

 

[silylene old]

I agree Narses!<br /><br />The impacts were large enough to leave significant craters below km's of ice. The holes must've melted many cubic km's of ice cap. That means that HUGE amounts of water vapor were injected into the atmosphere. The giant clouds should've had some effect on weather, at least in the southern hemisphere. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>