[meteorite-list] Titanium Reveals Explosive Origins of the Solar System

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sun, 19 Apr 2009 19:28:51 -0700 (PDT)
Message-ID: <200904200228.TAA28191_at_zagami.jpl.nasa.gov>

http://www.newscientist.com/article/dn16969-titanium-reveals-explosive-origins-of-the-solar-system.html

Titanium reveals explosive origins of the solar system
by Rachel Courtland
New Scientist
16 April 2009

The solar system emerged from a well-blended soup of dust and gas
despite being cobbled together from the remains of multiple exploded
stars, new meteorite measurements suggest.

Meteorites form a fossil record of the conditions that existed when they
formed. By looking at the chemical makeup of some rocks, evidence has
mounted in recent years that sun and the rest of the solar system formed
from a cloud of debris blasted away from a number of supernovae.

But it is still unclear what that cloud - the solar nebula - looked like
or how many stars might have been involved in the Sun's birth. Now, a
team led by Martin Bizzarro of the Natural History Museum of Denmark has
found one clue.

Bizzarro and colleagues measured the levels of titanium in meteorites
from the moon and Mars as well as inclusions in some meteorites that are
thought to be the oldest rocks in the solar system.
      
Stable forms

Titanium is a good probe for conditions billions of years ago because it
does not evaporate easily. It also has a number of stable isotopes -
forms of the element that contain different numbers of neutrons - that
can be used to cross-check each other.

Although the concentration of titanium varied from rock to rock, the
team found that two isotopes of titanium - titanium-50 and titanium-46 -
were always found in the same ratio.

"It is quite astonishing," since these two different isotopes probably
formed in different stellar explosions, Bizzarro told New Scientist.
Titanium-46, which contains 22 protons and 24 neutrons, is created
inside the cores of massive collapsing stars.

Titanium-50, which contains 22 protons and 28 neutrons, is commonly
created when white dwarf stars explode as type Ia supernovae
after gorging on a companion star.
      
Well mixed

If these two types of titanium come from two sources but are always
found in the same ratio, the solar nebula must have been very well
mixed. The level of mixing seems to exceed what meteorite researchers
have seen in the isotopes of other elements, Bizzarro says.

"People thought that the isotope anomalies typically reflected that the
cloud from which the solar system formed was not very well homogenised,"
says Bizzarro. He suspects the differences that are seen between the
planets, asteroids, and other rocks came later, when the young sun was
more active, sending out vaporising solar flares.
      
Stray cloud

But there may be alternative explanations for the seemingly universal
ratio of titanium concentrations.

The mix could also be explained if a stray cloud of dust containing both
varieties of titanium hit the early solar system, says Jeff Hester of
Arizona State University in Tempe.

"Then you could have wild inhomogeneity in how the dust was distributed
in the solar disc, while preserving the association between the two
isotopes of titanium," he says.

Journal reference: Science <www.sciencemag.org> (vol 324, p 374)
Received on Sun 19 Apr 2009 10:28:51 PM PDT