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Everything about Jupiter is enormous. Its circumference is no different, whether you measure it at the equator or through the poles. The equatorial circumference of Jupiter is 449,197 km. Compared to Earth’s equatorial circumference of 40,075 km, Jupiter is 11 times larger. Since Jupiter spins quickly on its axis, it is flattened quite a bit. That flattening makes the planet’s circumference at the poles 9,275 km smaller that it is at the equator.
Some scientists believe that the circumference of Jupiter may have protected the inner Solar System from much heavier bombardment by meteors, but little research has been done to test the idea. Some of the best work on the theory is set forth in a series of papers by J. Horner and B. W. Jones. These papers explore the effects of Jupiter’s gravitational pull on three different types of objects: main belt asteroids, short period comets, and in their newest publication, and the Oort cloud comets. In the case of the main belt asteroids, they determined, ”that the notion that any ‘Jupiter’ would provide more shielding than no ‘Jupiter’ at all is incorrect.” The researchers noted that Jupiter might provide protection from some asteroids, it is also the main gravitational force perturbing their orbits; bringing them into the inner solar system to begin with. The tests showed that a less massive planet would provide better protection for Earth by not perturbing the orbits of asteroids so much.
Next, the short period comets were tested. This set of tests showed that Jupiter might be effective at clearing these objects from the Solar System, but did so by pushing them into the orbital path of Earth. Based on this study, the scientist concluded that Jupiter’s gravitational push and pull was more dangerous than it was helpful. Lastly, a set of simulations were run involving Oort cloud objects. These objects are considered the largest potential threat since they have a greater distance to travel into the inner Solar System; therefore, picking up exponentially more momentum. In this case the circumference of Jupiter did provide better protection. Horner and Jones believe that this is because Oort cloud objects are so far from the Sun and are scarcely bound to the Solar System. Any amount of extra momentum gained from Jupiter’s gravity would be sufficient to eject them from the Solar System all together. Overall, the authors of the papers agree that the results are somewhat inconclusive.
Whether the circumference of Jupiter helped protect our planet from meteorites so that life could evolve, we may never know for certain. What we do know is that the largest planet in our Solar System does not divulge its secrets easily.
We’ve written many articles about Jupiter for Universe Today. Here’s an article about how Jupiter might have protected Earth from asteroid impacts. And here’s an article about how Jupiter captured a comet as a temporary Moon.
We’ve also recorded an episode of Astronomy Cast all about Jupiter. Listen here, Episode 56: Jupiter.