[meteorite-list] Meteorites Date Jupiter's Formation

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Tue, 13 Jun 2017 21:12:33 -0500
Message-ID: <105614.95714.bm_at_smtp113.sbc.mail.bf1.yahoo.com>

Dear List,

"Meteorites are made up from two
genetically distinct nebular reservoirs
that coexisted but remained separated
between 1 million and 3-4 million
years after the solar system formed."

https://phys.org/news/2017-06-evidence-jupiter-oldest-planet-solar.html

http://www.pnas.org/content/early/2017/06/06/1704461114

"By looking at tungsten and
molybdenum isotopes on iron
meteorites , the team, made
up of scientists from Lawrence
Livermore National Laboratory
and Institut f?r Planetologie at
the University of M?nsterin
Germany, found that meteorites
are made up from two genetically
distinct nebular reservoirs that
coexisted but remained separated
between 1 million and 3-4 million
years after the solar system formed.

"The most plausible mechanism
for this efficient separation is the
formation of Jupiter, opening a
gap in the disc (a plane of gas
and dust from stars) and
preventing the exchange of
material between the two
reservoirs," said Thomas Kruijer,
lead author of the paper appearing
in the June 12 online issue of,
Proceedings of the National
Academy of Sciences. Formerly
at the University of M?nster,
Kruijer, is now at LLNL.
"Jupiter is the oldest planet
of the solar system, and its
solid core formed well before
the solar nebula gas dissipated,
consistent with the core accretion
model for giant planet formation."

Jupiter is the most massive
planet of the solar system and
its presence had an immense
effect on the dynamics of the
solar accretion disk. Knowing
the age of Jupiter is key for
understanding how the solar s
ystem evolved toward its
present-day architecture.
Although models predict that
Jupiter formed relatively early,
until now, its formation has
never been dated.

"We do not have any samples
from Jupiter (in contrast to
other bodies like the Earth,
Mars, the moon and asteroids),"
Kruijer said. "In our study, we
use isotope signatures of
meteorites (which are derived
from asteroids) to infer Jupiter's
age."

The team showed through isotope
analyses of meteorites that
Jupiter's solid core formed
within only about 1 million
years after the start of the solar
system history, making it the
oldest planet. Through its rapid
formation, Jupiter acted as an
effective barrier against inward
transport of material across the
disk, potentially explaining why
our solar system lacks any super-
Earths (an extrasolar planet with
a mass higher than Earth's).

The team found that Jupiter's
core grew to about 20 Earth
masses within 1 million years,
followed by a more prolonged
growth to 50 Earth masses until
at least 3-4 million years after
the solar system formed.

The earlier theories proposed
that gas-giant planets such as
Jupiter and Saturn involved
the growth of large solid cores
of about 10 to 20 Earth masses,
followed by the accumulation of
gas onto these cores. So the
conclusion was the gas-giant
cores must have formed before
dissipation of the solar nebula?
the gaseous circumstellar disk
surrounding the young sun?
which likely occurred between
1 million years and 10 million
years after the solar system
formed.

In the work, the team confirmed
the earlier theories but we're able
to date Jupiter much more
precisely within 1 million years
using the isotopic signatures of
meteorites.

Although this rapid accretion
of the cores has been modeled,
it had not been possible to date
their formation.

"Our measurements show that
the growth of Jupiter can be
dated using the distinct genetic
heritage and formation times
of meteorites," Kruijer said.

Most meteorites derive from
small bodies located in the
main asteroid belt between
Mars and Jupiter. Originally
these bodies probably formed
at a much wider range of
heliocentric distances, as
suggested by the distinct
chemical and isotopic
compositions of meteorites
and by dynamical models
indicating that the gravitational
influence of the gas giants led
to scattering of small bodies
into the asteroid belt.

Read more at:
https://phys.org/news/2017-06-evidence-jupiter-oldest-planet-solar.html#jCp

Sterling K. Webb
Received on Tue 13 Jun 2017 10:12:33 PM PDT