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How could Jupiter’s early migration explain the small size of Mars?

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photo of Jupiter taken by Voyager 1 — Jupiter Photograph of Jupiter taken by Voyager 1 on February 1, 1979, at a range of 32.7 million km (20.3 million miles). Prominent are the planet's pastel-shaded cloud bands and Great Red Spot (lower centre).

The "grand tack hypothesis" provides a compelling explanation for the relatively small size of Mars. According to this model, Jupiter initially formed at approximately 3.5 astronomical units from the Sun before migrating inward to about 1.5 AU—the current orbital location of Mars.1

As Jupiter moved through the inner solar system, its immense gravitational influence likely depleted the reservoir of material available for planet formation in the region where Mars was developing. By clearing out much of the gas and solid material in that area, Jupiter effectively "starved" the growing Mars, limiting the amount of matter it could accrete and resulting in its current small size compared to Earth. Eventually, Saturn migrated inward and entered an orbital resonance with Jupiter, causing both planets to migrate outward to their present-day positions.12