[meteorite-list] Meteorites Date Jupiter's Formation

[Sterling K. Webb]

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 für Planetologie at 
the University of Münsterin 
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 Münster, 
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