If the solar system only had Jupiter, Mars, Earth, Mercury, and Neptune, Jupiter’s gravity would slowly turn the whole system into a long‑term gravitational drama rather than an instant demolition.

Big picture: what Jupiter’s gravity tends to do

Astrophysicists already model how Jupiter’s gravity influences the real inner solar system, and those models give good hints about this simplified version. They show that Jupiter can:

  • Nudge inner planets’ orbits, changing their eccentricity (how stretched they are) and inclination (tilt) over very long timescales.
  • Destabilize Mercury’s orbit in particular, leading to scenarios where Mercury can fall into the Sun, get ejected, or collide with another planet—even in our current, more complex system.
  • Redirect small bodies (asteroids, comets) either away from or toward Earth, playing both “shield” and “sniper” roles for impacts.

In a system with fewer planets, Jupiter becomes an even more dominant architect of everyone else’s orbits.

Likely long‑term effects on each planet

Assume the Sun is still there and the planets initially start roughly where they are now, just without Venus, Saturn, and Uranus.

Mercury

  • Jupiter already participates in long‑term resonances that can destabilize Mercury in realistic simulations.
  • With fewer other planets to “spread out” the gravitational influences, Mercury would still be the most vulnerable: its orbit could be pumped to higher eccentricity, making it more elongated.
  • Over hundreds of millions to billions of years, plausible outcomes include:
    • Mercury spiraling into the Sun.
    • Mercury being flung into a crossing orbit with Earth or Mars.
    • Mercury being ejected from the solar system entirely.

Earth

  • In most simulations of similar setups, Jupiter does not immediately destroy Earth; its gravitational pull at Earth’s distance is real but modest compared to the Sun’s.
  • Jupiter would:
    • Slowly alter Earth’s orbital eccentricity and tilt.
    • Cause long‑term climate cycles as Earth’s orbit gets slightly more or less elongated over millions of years.
  • Only in rare, “bad‑luck” configurations would Earth be pushed into a severely unstable path (like colliding with another planet or being ejected).

Mars

  • Mars, being farther from the Sun than Earth, feels Jupiter’s tug more strongly relative to the Sun’s.
  • Its orbit could:
    • Become more eccentric, giving it more extreme seasons.
    • Wander into stronger resonances with Jupiter that might eventually destabilize it, potentially ejecting it or making its orbit cross Earth’s.

Neptune

  • Neptune is far away, but Jupiter is massive; the pair would exchange angular momentum over time.
  • Neptune’s orbit might be:
    • Gradually reshaped (more eccentric or more inclined).
    • In some configurations, Neptune could be moved outward or inward, or in very extreme, rare cases eventually ejected as a rogue planet.

System‑wide behavior over time

Think in terms of millions to billions of years , not days or centuries:

  1. Early stage (first few hundred million years)
    • Orbits remain mostly recognizable.
    • Jupiter’s gravity quietly tweaks the orbital elements of Mercury, Mars, Earth, and Neptune.
  2. Middle stage (hundreds of millions to ~1–2 billion years)
    • Resonances (gravitational rhythm locks) between Jupiter and other planets can grow stronger.
    • Mercury is the leading candidate to go unstable first: its orbit might become very stretched, leading to close encounters or a plunge into the Sun.
  1. Late stage (multi‑billion‑year horizon)
    • After one planet is removed or scattered, the gravity “balance” shifts, changing how Jupiter perturbs the survivors.
    • New resonances can appear, possibly destabilizing Mars or even Neptune later on.
    • Earth can survive a long time in many scenarios, but in some unlucky initial alignments, it could eventually suffer a close gravitational encounter, changing its orbit drastically or ejecting it.

In essence, Jupiter acts like a slow‑motion chaos engine for the architecture of this stripped‑down system.

What it wouldn’t do (common misconceptions)

  • No instant sucking‑in of planets.
    Jupiter can’t “vacuum up” Earth or Mars just by being massive; the Sun’s gravity still overwhelmingly dominates at their distances, and planets in stable orbits don’t simply spiral into Jupiter.

  • No turning into a second star.
    Even in reality, Jupiter would need to be about 80 times more massive to ignite hydrogen fusion like a star, and this thought experiment doesn’t change its mass.

  • No guaranteed doom for Earth.
    While Jupiter can increase the risk of orbital chaos and collisions over immense timescales, many plausible configurations leave Earth intact for billions of years.

One way to picture it

Imagine a calm carousel (the Sun and planets) with one very heavy rider (Jupiter) and only a few lighter riders (Mercury, Earth, Mars, Neptune). The heavy rider doesn’t immediately fling anyone off. But over many, many rotations, their weight subtly shifts the platform’s balance, sometimes pushing lighter riders into riskier positions at the edge. Most of the time, everyone keeps going in circles—until, occasionally, one rider gets nudged just enough to fly off the ride.

Bottom note: Information gathered from public forums or data available on the internet and portrayed here.