Debunking a myth about the high density of asteroids in the main asteroid belt between Mars and Jupiter

Between Mars and Jupiter lies an asteroid belt comprising a large number of rocky planet infinitesimal early in the failed gestation process to becoming a planet. Being small in size and roughly spherical in shape, their orbit around the sun are constrained by the gravitational tug of the gas giant Jupiter as well as that of Mars. While many of the asteroids (i.e., planet infinitesimal) are small in size, there exists several large dwarf planet lookalike in the asteroid belt such as the two asteroids, Ceres and Vesta, visited, imaged and mapped by the Dawn spacecraft.


With many asteroids of myriad size in the asteroid belt, one may ask how do spacecraft navigate the asteroid belt without collision risk from asteroids in the belt. Fundamentally, it must be recognized that there is always a finite risk of a spacecraft colliding with an asteroid in the asteroid belt as the spacecraft transitions from the inner Solar System to the outer Solar System. Though usually small and factored into during the launch and navigation phase of the space mission, collision risk is a parameter constantly in the minds of mission scientists as well as engineers who monitor and operate the spacecraft on a daily basis. Typically, collision risk with foreign objects such as space debris, comets or asteroids could be significantly reduced by scheduling mission launch to coincide with a trajectory that avoids most of the dangerous objects capable of damaging a spacecraft.


During navigation, mission controllers are constantly on the look out for large high speed objects able to impact and critically damage a spacecraft. Using thrusters with liquid fuel, mission engineers calculate a precise burn time for specific sets of thrusters able to direct a spacecraft away from a collision course with foreign objects. But, in navigating through the asteroid belt, are there such a high density of asteroids and space debris in the belt such as to make the asteroid belt unnavigable? The answer is no. Specifically, the popular notion that there is a high density of asteroids and objects in the asteroid belt able to do significant amount of damage to a spacecraft is exaggerated. However, the impact risk is not small and must be carefully factored into mission planning, particularly in equipping the spacecraft with thrusters able to maneuver it away from dangerous objects.


Hence, while the popular idea in many astronomical journals as well as web videos depict the asteroid belt between Mars and Jupiter to be highly dense in myriad objects of different shapes and sizes, the reality differs significantly from the illustrated “truth”. In particular, significant number of different objects do exist in the asteroid belt and pose substantial collision risk with spacecrafts attempting to navigate through it for journeying into the outer Solar System. But, the density of objects in the asteroid belt able to pose a collision risk to spacecraft is not great enough to prevent navigating through the belt. Nevertheless, considering the large collision risk between the spacecraft and objects in the belt, where a high speed object of 10 cm is able to destroy the spacecraft, mission engineers and controllers are on a daily minute by minute watch for any foreign objects speeding towards the spacecraft. Once in note of the collision threat, thrusters are fired for moving the spacecraft to a trajectory of smaller collision risk. Why is the collision risk smaller and not zero after the thrusters are fired for avoiding impact? Because, while it is possible to estimate the trajectory of a high speed foreign object, its collision risk with the spacecraft can never be reliably reduced to zero.


Category: space exploration,

Tags: asteroid belt, collision risk, asteroids, mission planning, trajectory changes,








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