Jupiter may have robbed Mars of mass, new report indicates

Study reveals an unexpected twist in the early lives of Jupiter and Saturn as well.

By Southwest Research Institute, San Antonio, Texas — Published: June 6, 2011

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

Photo by 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 the journal Nature this week 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 (AU, the distance from the Sun to the Earth) 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.

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SAM PLATTS from CALIFORNIA said:

Why would it be necessary for Jupiter to wander into Mars' neighborhood to steal formation material? Wouldn't its gravity be strong enough to sweep much of Mars' orbit without itself being moved closer to Mars?

Submitted: 6/18/2011 12:41:17 AM (CST)

MICHAEL STAPEL said:

This is fascinating! It is exciting when a new perception opens up our view of the universe. It makes me wonder, with the advances of science in these times, how will humans understand the formation of the solar system 50 years from now?!

Submitted: 6/16/2011 6:16:12 AM (CST)

STUART HERRING from ALABAMA said:

Aidan Mancinu, Earth is thought to have been struck by a protoplanet of approximately the size of Mars, not by Mars itself. (The debris from the collision coalesced into the Moon.)

Submitted: 6/11/2011 1:20:05 PM (CST)

JOSEPH T MCCAWLEY from MASSACHUSETTS said:

Couldn't Jupiter make up its mind where it wanted to be? How come its massive presence at 1.5 AU did not stunt the growth of Earth as well? What made it migrate inward and not keep going?

This hypothesis needs more work.

Submitted: 6/11/2011 12:06:01 PM (CST)

DONALD HAYES from CALIFORNIA said:

Interesting. Jupiter being a Jovian planet, made up of hydrogen, helium and helium compounds, retrograding into a Terrestrial, rocky
arena, where it is warmer and closer to our Sun and robbing Mars of some it's mass. Even with Jupiter's huge mass and tidal force, the sun's heat should cause Jupiter to lose some of its mass over time and accretion could have occurred.

Submitted: 6/10/2011 6:13:26 PM (CST)

GARY GARB from PENNSYLVANIA said:

This sounds ironically like a Velikovsky theory. Of course, he claimed that the phenomena of planetary orbital migrations and collisions occurred in historical times, not during the original era of planetary formation. But this is a very imaginative scenario that begs more explanation and description.

Submitted: 6/10/2011 4:10:13 PM (CST)

DAVID LUTHER from CALIFORNIA said:

Seems quite logical. Was under the assumption that this was already the "standard thought" as this is exactly what I told my daughter when we made her model of the Solar System earlier this year.

Submitted: 6/10/2011 11:10:10 AM (CST)

RICHARD MCCONNELL said:

This raises more questions than it answers: didn't Saturn form at the same time as Jupiter? What would cause Jupiter to migrate first into the inner solar system and then out again?
Very puzzling.
Richard McConnell

Submitted: 6/10/2011 3:11:12 AM (CST)

MARTIN LEE COLLIN from NEBRASKA said:

Sounds reasonable. But why, if Jupiter had circulated for such a long time in the 1.5 AU orbit, hadn't it likewise starved Earth of growth material, as it had Mars?

Submitted: 6/10/2011 1:44:44 AM (CST)

AIDAN MANCINU SR said:

nah i don't believe... wasn't it when the planets were getting made mars hit earth and most of mars got taken off and that's how it became small?

Submitted: 6/7/2011 2:39:52 AM (CST)