There’s More Than Just Gravity at Work in the Solar System

Ever since Isaac Newton famously talked about gravity, its dominance as a force in our Solar System has been well known. It’s responsible for the orbits of the planets and their satellites but there are other forces that have shaped our planetary neighbourhood. A new paper has been released where an astronomer discusses how recoiling ice from comets can push them around and how the radiation pressure from the Sun drives material outwards. There are also relativistic effects too that can cause particles to spiral inward toward the Sun. 

Gravity is the force that governs the structure and motion of the solar system, keeping celestial bodies together in a cosmic dance. The Sun, with its immense mass, generates the strongest gravitational pull, anchoring planets, asteroids, comets, and other objects in orbit around it. Each planet’s orbit results from the balance between its velocity and the Sun’s gravitational force, creating elliptical paths described by Kepler’s laws of motion. Similarly, moons remain in orbit around their host planets due to the gravitational forces exerted by their parent planet. Gravity not only maintains the stability of these orbits but also influences phenomena like tides on Earth, caused by the Moon’s gravitational pull.

In the paper authored by David Jewitt from the University of California he explores other forces that shape our Solar System. Gravity certainly describes the motion of planetary mass bodies but there are other forces that impart forces upon smaller bodies that are susceptible to their effects. These forces include, but are not limited to recoil (as per Newton’s third law of motion that every action has an equal and opposite reaction,) torque from mass loss, radiation pressure and more. 

The aim of the paper is to offer a simple yet informative overview of the various non-gravitational forces at play in the Solar System. There are references to relevant applications from existing papers and publications, presenting them in a way that is accessible to non-specialists. An important point to note is that the paper assumes that all orbits are circular, whereas real bodies are not perfectly spherical and orbits are not perfectly circular. The author asserts that these approximations ensure that rough estimates of the magnitudes of forces can still be achieved. 

Among the non-gravitational forces considered in the paper, the largest by far is the recoil produced by the sublimation of ice on comets and asteroids. The heat from the Sun causes the ice to immediately turn into a gas rather than melt to a liquid, this is the sublimation process. Like a bullet leaving a gun however, and in accordance with Newton’s laws, when the ice sublimates, the escaping volatile gasses will carry momentum and exert a recoil force on the body. The process of sublimation depends largely on temperature and acts in the anti-solar direction. 

Related to the appearance of comets is another force, radiation pressure, that shapes their distinctive tails. It’s the force exerted by light when photons transfer momentum to an object such as cometary dust and gas pushing them away. The pressure depends on the intensity of the radiation and the object’s reflectivity, with more reflective objects experiencing greater force. Though small, radiation pressure can shape comet tails and gradually alter the orbits of small bodies in the solar system.

Source : Non-gravitational Forces in Planetary Systems

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