[meteorite-list] Solar System: Lethal Billiards

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 6 Sep 2007 15:43:16 -0700 (PDT)
Message-ID: <200709062243.PAA17571_at_zagami.jpl.nasa.gov>

http://www.nature.com/nature/journal/v449/n7158/full/449030a.html;jsessionid=C86A202A339FC94B54A1662F47B156BD

Nature 449, 30-31 (6 September 2007) | doi:10.1038/449030a; Published
online 5 September 2007

Solar System: Lethal billiards
Philippe Claeys1 & Steven Goderis1

Abstract

A huge collision in the asteroid belt 160 million years ago sent
fragments bagatelling around the inner Solar System. One piece might
have caused the mass extinction that wiped out the dinosaurs 65 million
years ago.

What are the chances of the sky falling on our heads? If it's an
asteroid hitting Earth that we're talking about, we can't be too sure.
Not only do estimates of the current terrestrial meteorite impact rate
differ by a factor of five to ten, depending on the approximations used,
but, but we don't know for certain whether that rate has remained
constant or has varied throughout geological time.

A current theory proposes that the impact rate has increased during the
past 100 million years or so. On page 48
</nature/journal/v449/n7158/full/nature06070.html> of this issue, Bottke
et al.[2] present an intriguing explanation for why this might be,
invoking errant fragments from a powerful ancient collision in the
asteroid belt between Mars and Jupiter.

Clusters of impact craters and layers of material ejected in meteorite
impacts, as well as higher levels of extraterrestrial material in some
sedimentary rocks, seem to indicate that, during several glacial
periods, the Earth-Moon system has suffered abnormally high rates of
bombardment. The late Miocene epoch around 8 million years ago, for
example, was marked by an increased flux of interplanetary dust
particles between 1 microm and 1 mm across, which might have been
produced by a collision within the asteroid belt [3]. An asteroid or
comet shower has similarly been put forward to explain the higher
dust-particle flux in the late Eocene around 35 million years ago, an
event that seems to be coupled with an unusually high concentration of
impact craters [4,5]. These include the two largest craters in
recent geological history, Popigai in Siberia (100 km in diameter) and
Chesapeake Bay off the Maryland coast (around 85 km in diameter).

And we can go even farther back in recording periods of heavy
bombardment. The abundant micrometeorites in the 480-million-year-old
Ordovician limestones of southern Sweden most probably reached Earth
after a significant disruption had occurred in the asteroid belt [6].
Several impact craters also seem to cluster around this age, although
here the geological record is rather poor. Farther back still,
recognized ejecta layers are concentrated in two time windows between
2.65 billion and 2.5 billion years ago and 3.47 billion and 3.24 billion
years ago [7]. Finally, the most dramatic series of events is
undoubtedly the Late Heavy Bombardment of 3.8 billion years ago, the
occurrence of which is inferred from the lunar cratering record8 [8].
Although its traces have been erased by geological activity on Earth,
extrapolation of the lunar data indicates [9]. the formation of up to
22,000 terrestrial craters with a diameter of more than 20 km. This
catastrophic bombardment probably resulted from colliding asteroids
disturbed by changes in the orbits of the giant gas planets [10].

Bottke et al.[2] have discovered the remnants of another huge
collision hidden in the inner region of the main asteroid belt. These
comprise the Baptistina asteroid family (BAF), a class of variously
sized objects of similar composition and orbital geometry, typified by
the 40-km-diameter asteroid known as (298) Baptistina. The authors use a
computer simulation to track the orbits of these fragments back to the
moment of their formation, and find that the collision must have taken
place about 160 million years ago. The best fit to the data is given by
an object of 60-km diameter colliding almost vertically with a
170-km-diameter body. This collision, at a velocity of 3 km s-1,
generated more than 1,000 large bodies greater than 1 km in diameter.

Bottke and colleagues [2] propose that the collisional break-up of an
asteroid 160 million years ago was the ultimate cause of the mass
extinction on Earth at the Cretaceous-Tertiary boundary some 95 million
years later. This occurred when one particularly large fragment, the
Chicxulub impactor, hit Earth. The inset shows an inferred remnant of
this meteorite, retrieved from clays in the northern Pacific dating to
the same time as that event [11].

The authors' dynamic modelling indicates that the Baptistina disruption
took place in a region of the asteroid belt where the gravitational
influence of Mars and Jupiter would have caused a number of large
objects to be perturbed into Earth-crossing orbits. The collision of
just a small fraction of these fragments with Earth would account for
the increased cratering rate during the Cretaceous period (from around
145 million to 65 million years ago) and the early Cenozoic era that
followed. The fragments would in fact have formed an asteroid shower in
the inner Solar System lasting some 100 million years.

According to spectroscopic measurements, the composition of (298)
Baptistina is similar to that of primitive 'carbonaceous chondrite'
meteorites, a rather infrequent type of meteorite that contains
unusually large amounts of water and organic compounds. This is
front-page news, as a 10-km-sized carbonaceous chondrite is most
probably the projectile that formed the Chicxulub crater on the Yucat?n
peninsula in Mexico [11, 12] (Fig. 1 , inset). This
impact almost certainly triggered what is known as the K/T mass
extinction, including the demise of the dinosaurs, at the boundary
between the Cretaceous and Tertiary periods 65 million years ago.

By comparing the impact rate of BAF near-Earth objects with the
background occurrence of objects with a similar composition, Bottke and
colleagues [2] estimate that there is a 90% chance that the Chicxulub
projectile came from the BAF. Other craters formed during the same
period on the inner bodies of the Solar System could share the same
origin: one candidate is Tycho on the Moon, which was formed 109 million
years ago at what would have been the climax of the BAF asteroid shower.

This hypothesis is nothing if not provocative. It implies that a
significant number of terrestrial craters that formed during the past
160 million years resulted from carbonaceous chondrite projectiles. The
concentrations of platinum-group elements and the chromium-isotopic
signatures measured in rocks melted in meteorite impacts provide precise
information on the projectile type, and can be used to distinguish
carbonaceous chondrites from other types of meteorite. Of the eight
craters on Earth that are larger than 1 km in diameter (implying a
projectile 50 m or more across) and less than 200 million years old for
which the projectile composition has been unequivocally identified,
Chicxulub stands out as an anomaly - it is the only one formed by a
carbonaceous chondrite [13]. So did the other, smaller BAF objects
miss Earth, or is this apparent anomaly due to the fact that projectile
type is well characterized for relatively few craters?

That question must remain unanswered for now. Nevertheless, unless a
rogue comet came from the outer edge of the Solar System (a rather
unlikely event), the BAF remains a likely source for the Chicxulub
projectile. It is a poignant thought that the Baptistina collision some
160 million years ago sealed the fate of the late-Cretaceous dinosaurs
well before most of them had even evolved.

The most important point raised by Bottke and colleagues' discovery
[2] of the Baptistina asteroid family is how severe the repercussions
of cataclysmic collisions in the asteroid belt can be for the Earth-Moon
system. The terrestrial impact record needs to be scrutinized more
closely to identify and understand these periods of more intense
bombardment, and to link them to the huge and dangerous game of
billiards continuously being played out between the orbits of Mars and
Jupiter.

References

   1. French, B. M. Traces of Catastrophe: A Handbook of
      Shock-Metamorphic Effects in Terrestrial Meteorite Impact
      Structures (Lunar Planet. Inst., Houston, TX, 1998).
   2. Bottke, W. F., Vokrouhlick?, D. & Nesvorn?, D. Nature 449, 48-53
      (2007). | Article
      <http://www.nature.com/doifinder/10.1038/nature06070> |
   3. Farley, K. A., Vokrouhlick?, D., Bottke, W. F. & Nesvorn?, D.
      Nature 439, 295-297 (2006). | Article
      <http://www.nature.com/doifinder/10.1038/nature04391> | PubMed
      <http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?holding=npg&cmd=Retrieve&db=PubMed&list_uids=16421563&dopt=Abstract> | ISI
      <http://links.isiglobalnet2.com/gateway/Gateway.cgi?&GWVersion=2&SrcAuth=Nature&SrcApp=Nature&DestLinkType=FullRecord&KeyUT=000234682100035&DestApp=WOS_CPL> | ChemPort
      <http://chemport.cas.org/cgi-bin/sdcgi?APP=ftslink&action=reflink&origin=npg&version=1.0&coi=1:CAS:528:DC%2BD28XkvF2lsw%3D%3D&pissn=0028-0836&pyear=2007&md5=07f184e1b9f5857b0037c27d16757322> |
   4. Farley, K. A., Montanari, A., Shoemaker, E. M. & Shoemaker, C. S.
      Science 280, 1250-1253 (1998). | Article
      <http://dx.doi.org/10.1126/science.280.5367.1250> | PubMed
      <http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?holding=npg&cmd=Retrieve&db=PubMed&list_uids=9596575&dopt=Abstract> | ISI
      <http://links.isiglobalnet2.com/gateway/Gateway.cgi?&GWVersion=2&SrcAuth=Nature&SrcApp=Nature&DestLinkType=FullRecord&KeyUT=000073852500044&DestApp=WOS_CPL> | ChemPort
      <http://chemport.cas.org/cgi-bin/sdcgi?APP=ftslink&action=reflink&origin=npg&version=1.0&coi=1:CAS:528:DyaK1cXjt1Gqtro%3D&pissn=0028-0836&pyear=2007&md5=803d8fcfc2fad7c590f69e62fbaa2dab> |
   5. Tagle, R. & Claeys, P. Science 305, 492 (2004). | Article
      <http://dx.doi.org/10.1126/science.1098481> | PubMed
      <http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?holding=npg&cmd=Retrieve&db=PubMed&list_uids=15273387&dopt=Abstract> | ISI
      <http://links.isiglobalnet2.com/gateway/Gateway.cgi?&GWVersion=2&SrcAuth=Nature&SrcApp=Nature&DestLinkType=FullRecord&KeyUT=000222828900031&DestApp=WOS_CPL> | ChemPort
      <http://chemport.cas.org/cgi-bin/sdcgi?APP=ftslink&action=reflink&origin=npg&version=1.0&coi=1:CAS:528:DC%2BD2cXmtVWqtLY%3D&pissn=0028-0836&pyear=2007&md5=6c9212b34618a8b96bff24e5200bd6e3> |
   6. Heck, P. R., Schmitz, B., Baur, H., Halliday, A. N. & Wieler, R.
      Nature 430, 323-325 (2004). | Article
      <http://www.nature.com/doifinder/10.1038/nature02736> | PubMed
      <http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?holding=npg&cmd=Retrieve&db=PubMed&list_uids=15254530&dopt=Abstract> | ISI
      <http://links.isiglobalnet2.com/gateway/Gateway.cgi?&GWVersion=2&SrcAuth=Nature&SrcApp=Nature&DestLinkType=FullRecord&KeyUT=000222631200033&DestApp=WOS_CPL> | ChemPort
      <http://chemport.cas.org/cgi-bin/sdcgi?APP=ftslink&action=reflink&origin=npg&version=1.0&coi=1:CAS:528:DC%2BD2cXls1eqsL8%3D&pissn=0028-0836&pyear=2007&md5=35bf718a8d61a01632c3878f9d0fbf4d> |
   7. Simonson, B. M. & Glass, B. P. Annu. Rev. Earth Planet. Sci. 32,
      329-361 (2004). | Article
      <http://dx.doi.org/10.1146/annurev.earth.32.101802.120458> | ISI
      <http://links.isiglobalnet2.com/gateway/Gateway.cgi?&GWVersion=2&SrcAuth=Nature&SrcApp=Nature&DestLinkType=FullRecord&KeyUT=000221752500013&DestApp=WOS_CPL> | ChemPort
      <http://chemport.cas.org/cgi-bin/sdcgi?APP=ftslink&action=reflink&origin=npg&version=1.0&coi=1:CAS:528:DC%2BD2cXkvVyisrs%3D&pissn=0028-0836&pyear=2007&md5=133b50fe2debf4370b1489f29530fe2c> |
   8. Ryder, G., Koeberl, C. & Mojzsis, S. J. in Origin of the Earth and
      Moon (eds Canup, R. M. & Righter, K.) 475-492 (Univ. Arizona
      Press, Tucson, 2000).
   9. Kring, D. A. & Cohen, B. A. J. Geophys. Res. 107,
      10.1029/2001JE001529 (2002).
  10. Gomes, R., Levison, H. F., Tsiganis, K. & Morbidelli, A. Nature
      435, 466?469 (2005). | Article
      <http://www.nature.com/doifinder/10.1038/nature03676> | PubMed
      <http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?holding=npg&cmd=Retrieve&db=PubMed&list_uids=15917802&dopt=Abstract> | ISI
      <http://links.isiglobalnet2.com/gateway/Gateway.cgi?&GWVersion=2&SrcAuth=Nature&SrcApp=Nature&DestLinkType=FullRecord&KeyUT=000229337800048&DestApp=WOS_CPL> | ChemPort
      <http://chemport.cas.org/cgi-bin/sdcgi?APP=ftslink&action=reflink&origin=npg&version=1.0&coi=1:CAS:528:DC%2BD2MXksVeisL8%3D&pissn=0028-0836&pyear=2007&md5=9e2d50138e685bbf1caaa64264418261> |
  11. Kyte, F. T. Nature 396, 237?239 (1998). | Article
      <http://www.nature.com/doifinder/10.1038/24322> | ISI
      <http://links.isiglobalnet2.com/gateway/Gateway.cgi?&GWVersion=2&SrcAuth=Nature&SrcApp=Nature&DestLinkType=FullRecord&KeyUT=000077110400038&DestApp=WOS_CPL> | ChemPort
      <http://chemport.cas.org/cgi-bin/sdcgi?APP=ftslink&action=reflink&origin=npg&version=1.0&coi=1:CAS:528:DyaK1cXns12mtL4%3D&pissn=0028-0836&pyear=2007&md5=aad0223ed5427b5388e73cde80849d4f> |
  12. Shukolyukov, A. & Lugmair, G. W. Science 282, 927?929
      (1998). | Article
      <http://dx.doi.org/10.1126/science.282.5390.927> | PubMed
      <http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?holding=npg&cmd=Retrieve&db=PubMed&list_uids=9794759&dopt=Abstract> | ISI
      <http://links.isiglobalnet2.com/gateway/Gateway.cgi?&GWVersion=2&SrcAuth=Nature&SrcApp=Nature&DestLinkType=FullRecord&KeyUT=000076727300044&DestApp=WOS_CPL> | ChemPort
      <http://chemport.cas.org/cgi-bin/sdcgi?APP=ftslink&action=reflink&origin=npg&version=1.0&coi=1:CAS:528:DyaK1cXntFOjt70%3D&pissn=0028-0836&pyear=2007&md5=48705ef1c6ef5ba3ad9eb829fa7f7aaa> |
  13. Tagle, R., Goderis, S. & Claeys, P. Lunar and Planetary Science
      Conference 2007, League City, TX, abstr. 2216.


   1. Philippe Claeys and Steven Goderis are in the Department of
      Geology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels,
      Belgium.
      Email: phclaeys at vub.ac.be <mailto:phclaeys at vub.ac.be>
Received on Thu 06 Sep 2007 06:43:16 PM PDT