Our
solar system emerged in surprisingly good order from the violence of planetary
creation, according to a new simulation.
Researchers
found that planetary formation in the first few million years often resembles a
violent wrestling match among hungry siblings, with planets fighting to feed on
gas and dust while pulling at each other with gravitational arms.
"There's
massive bodies competing with each other and flinging each other around,"
said Edward Thommes, a physicist at the University of Guelph in Ontario, Canada, and lead author on the new research published in the Aug. 7 issue of the journal
Science.
The
simulation traces the creation of a planetary system from almost beginning to
end, for the first time, and suggests that our solar system started with just
the right mass to become a relatively orderly place in the universe.
"You
have to have the conditions just right," Thommes told SPACE.com.
"They have to be in a fairly narrow range."
Thommes
and his former colleagues at Northwestern University ran the simulation through
over 100 scenarios to see how gas
giants formed from the gas disks that surrounded young stars. Newborn
planets typically seemed to get pushed toward the central star by the gas disk
remnant surrounding them.
"The
same disk from which they're born is also trying to kill them," Thommes said.
Too
much starting mass in the disk results in a swarm of gas giants crowding into
the central star. However, too little mass produces nothing bigger than Neptune-like
ice giants.
The
tussle among gas giants can typically lead to loopy elliptical orbits.
Sometimes a gas giant even acts as a slingshot to throw a sibling into deep
space.
By
comparison, our solar system's gas giants – Saturn
and Jupiter – have nearly circular orbits that suggest less violent
interaction. The two planets also appear to have stayed close to where they
grew up, instead of migrating into the sun.
"They
never really got into each other's face, so to speak," Thommes said.
"They kept their personal space."
The
simulated planetary systems mostly line up with observations of more than 300
exoplanets discovered so far. But Thommes cautioned that the observed exoplanets
represent those that are relatively easiest to find, or "a filtered
sample" of what astronomers can see.
The
researchers chose to sacrifice some detail in their simulation in order to
model planetary systems from start to finish. They hope to extend their hybrid
model approach so that they can eventually model planets spiraling all the way
into the central star. Currently, the simulation cannot track such planets
beyond a certain point.
An
outside essay accompanying the Science paper and written by John
Papaloizou, an astrophysicist at the University of Cambridge in the UK, calls
the new simulation "compelling" and says that it achieves
"reasonable success" in modeling what astronomers have observed.
Papaloizou
pointed out that some simulated planetary orbits do not match up with the usual
equatorial plane of star systems, something that astronomers have not seen in
exoplanetary systems so far. However, he also adds that current knowledge of
exoplanetary systems remains limited.
For
his part, Thommes remained confident that our solar system was uniquely quiet, especially
considering the birthing process.
"What
our solar system seems to represent in all of this is a peaceful and quiet form
of this process," Thommes said.
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