Jupiter not only shields the earth from space debris, it also ensures that the asteroid belt does not fling asteroids into the sun or form an accretion disc and develop into a new planet. This is accomplished due to Jupiter’s mass and extraordinary gravitational effects. Space debris that could pose a danger to our planet may come in three forms. Man-made debris such as left over rocket stages, and a group of asteroids known as Hildas and Trojans.
Every planet has a gravitational pull on space debris. Any celestial body with substantial mass has an area in space between itself and another massive body known as a Lagrangian point, L-point, where the gravitational pull of both bodies settles to an average and anything stuck in this area, known as a Trojan hereon, is locked into orbit. Trojans share an orbit with planets but follow an oscillating movement along the orbit, called libration. 6 of the 8 planets in our system, including earth, have Trojans in their L-points. Earth and Venus have one each while Mars has seven. Jupiter has more than 6000 documented Trojans.
This represents data collected between 2005–2017 on the movement of both Trojans (Green) and Hildas (purple). The effects of Jupiter’s gravitational pull is evident.
Jupiter’s Trojans are classified into The Greek camp and The Trojan camp, in the leading and trailing edge of Jupiter’s orbit respectively. Jupiter’s gravitational pull is 2.5 times that of earth, and it essentially shepherds asteroids along its orbit. Hildas observe an elliptical orbit which slows their movement near aphelion. This causes them to congregate near Jupiter's L-point and create the appearance of a triangular orbit.
Jupiter is doing us a solid, no doubt, but its not our last line of defense. Not by a long shot. In case anything escapes Jupiter’s gravitational pull and heads straight for earth, our moon will be waiting.
In 1969, object J002E3, third stage of the Apollo 12 Saturn V rocket, was improperly injected into a heliocentric orbit and instead went into an unstable high earth orbit that switches between heliocentric and geocentric orbits in a 40 year cycle. It was spotted in 2003. In its approach to Earth, it was noted just how essential a part the moon plays in protecting us from debris as well.
5-year Update, April 2023:
Thanks to all the upvotes, questions, contributions and suggestions to this topic. I’m glad its peaking interest. I have updated some more info regarding the Asteroids, specifically the Hildian asteroids explaining their orbit.
