There’s more than just gravity at work in the solar system

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There’s more than just gravity at work in the solar system

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The sun releases a steady stream of charged particles called the solar wind. When it strikes unprotected surfaces like asteroids or the moon, it can change the chemistry and even create water molecules. Credit: NASA’s Goddard Space Flight Center/Mary Pat Hrybyk-Keith

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 neighborhood.

A new paper discusses how recoiling ice from comets can push them around and how the radiation pressure from the sun drives material outward. There are also relativistic effects 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.

The

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, authored by David Jewitt from the University of California and published in The Planetary Science Journal, 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 nongravitational 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 nongravitational 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 gases will carry momentum and exert a recoil force on the body. The process of sublimation depends largely on temperature and acts in the antisolar 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.

More information:
David Jewitt, Nongravitational Forces in Planetary Systems, The Planetary Science Journal (2025).

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There’s more than just gravity at work in the solar system (2025, January 27)
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#gravity #work #solar #system

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