An international team of scientists led by Dr. Kevin Walsh of Southwest Research Institute is using complex modeling techniques to better understand the formation of our solar system. The “Grand Tack Scenario” demonstrates that the gas giant Jupiter may have briefly migrated into the inner solar system and influenced the formation of Mars (right), stripping away materials that resulted in its relatively small size in comparison to Venus (left) and the Earth. Image: NASA |
Planetary scientists have long wondered
why Mars is only about half the size and one-tenth the mass of Earth. As
next-door neighbors in the inner solar system, probably formed about the same
time, why isn’t Mars more like Earth and Venus in size and mass? A paper
published in Nature provides the
first cohesive explanation and, by doing so, reveals an unexpected twist in the
early lives of Jupiter and Saturn as well.
Dr. Kevin Walsh, a research scientist
at Southwest Research Institute (SwRI), led an international team performing
simulations of the early solar system, demonstrating how an infant Jupiter may
have migrated to within 1.5 astronomical units of the Sun, stripping a lot of
material from the region and essentially starving Mars of formation materials.
“If Jupiter had moved inwards from
its birthplace down to 1.5 AU from the Sun, and then turned around when Saturn
formed as other models suggest, eventually migrating outwards towards its
current location, it would have truncated the distribution of solids in the
inner solar system at about 1 AU and explained the small mass of Mars,”
says Walsh. “The problem was whether the inward and outward migration of
Jupiter through the 2 to 4 AU region could be compatible with the existence of
the asteroid belt today, in this same region. So, we started to do a huge
number of simulations.
“The result was fantastic,”
says Walsh. “Our simulations not only showed that the migration of Jupiter
was consistent with the existence of the asteroid belt, but also explained
properties of the belt never understood before.”
The asteroid belt is populated with two
very different types of rubble, very dry bodies as well as water-rich orbs
similar to comets. Walsh and collaborators showed that the passage of Jupiter
depleted and then re-populated the asteroid belt region with inner-belt bodies
originating between 1 and 3 AU as well as outer-belt bodies originating between
and beyond the giant planets, producing the significant compositional
differences existing today across the belt.
The collaborators call their simulation the “Grand Tack Scenario,”
from the abrupt change in the motion of Jupiter at 1.5 AU, like that of a
sailboat tacking around a buoy. The migration of the gas giants is also
supported by observations of many extra-solar planets found in widely varying
ranges from their parent stars, implying migrations of planets elsewhere in
universe.
