why do comets create gravity

Q: why do comets create gravity

Comets create gravity simply because they have mass. According to Newton's law of universal gravitation, every object with mass exerts a gravitational pull on every other object with mass. Even small comets generate gravity, though their gravitational influence is incredibly weak compared to planets or stars.

The Deep Dive

Gravity is not a special property reserved for large celestial bodies—it is a fundamental force that emerges from mass itself. Isaac Newton first described this universal attraction in 1687, demonstrating that the same force pulling an apple to Earth also governs planetary orbits. Every grain of ice and rock within a comet contributes to its total mass, and that mass curves the fabric of spacetime around it. Albert Einstein refined this understanding in 1915 with his general theory of relativity, revealing that gravity is not a mysterious pulling force but rather the consequence of massive objects warping the geometry of space and time. A typical comet nucleus ranges from hundreds of meters to tens of kilometers across, containing a mixture of frozen water, carbon dioxide, methane, and silicate dust. Though modest compared to planets, this mass still generates a measurable gravitational field. The comet 67P/Churyumov-Gerasimenko, studied by the Rosetta mission, has a mass of roughly 10 billion metric tons—enough to weakly hold its surface material together and shape its distinctive bilobed form. Without this gravitational self-attraction, comets would simply disintegrate as they tumble through space.

Why It Matters

Understanding comet gravity is essential for space exploration. When the European Space Agency's Rosetta mission deployed the Philae lander onto comet 67P in 2014, engineers had to precisely calculate the comet's weak gravitational pull—about 1/100,000th of Earth's—to ensure the lander would stay anchored rather than bounce back into space. This knowledge also helps scientists predict how comets fragment near the Sun, explain why some comets develop twin-lobed shapes through gentle collisions, and model how cometary debris forms meteor showers when Earth passes through their trails. Gravitational interactions with planets can also redirect comets into the inner solar system or eject them permanently.

Common Misconceptions

A widespread myth is that small objects like comets do not produce any gravity because they are too tiny. In reality, even a single atom exerts gravitational force—comets simply have too little mass for humans to notice their pull in daily life. Another misconception confuses a comet's glowing tail with its gravitational field. The spectacular ion and dust tails visible from Earth are created by solar radiation and solar wind pushing material away from the comet's surface, not by the comet's own gravity. In fact, a comet's gravity is often too weak to retain the material being blasted off by the Sun, which is why tails always point away from our star regardless of the comet's direction of travel.

Fun Facts

If you could stand on comet 67P/Churyumov-Gerasimenko, you could jump into orbit because its escape velocity is only about 1 meter per second—slower than a casual walk.
The gravitational influence of Jupiter is so powerful compared to most comets that it can capture or eject entire comets from the solar system, a phenomenon responsible for the famous Shoemaker-Levy 9 collision in 1994.