Nature loves spheres. It can’t get enough of them.

Soap bubbles are spherical because that shape most efficiently balances the outward pressure of the air within the bubble against the surface tension of the soap film.

When water splashes and for a brief instant a droplet of water is neither rising nor falling and is momentarily weightless, what shape does the droplet’s surface tension force the water to take?  A sphere.

Nature loves spheres. In the case of bubbles and droplets of liquid, surface tension creates a sphere to minimize surface area.

Stars are perfect examples of natural spheres.  The mass of a star is mind-bogglingly large and creates an equally mind-bogglingly large amount of gravity. What shape does Mother Nature give to so much mass to minimize its enormous volume?  A sphere.

Stars like our Sun are huge, dynamic, energy-producing concentrations of Hydrogen and Helium, compacted by their enormous gravity into spheres.

The reason planets appear spherical is because gravity compresses the planet into a shape that most evenly distributes the gravitational force among the planet’s mass.

Whether it is shaping water droplets, stars, soap bubbles or planets, nature seeks to minimize the surface area needed to contain a given volume, and the shape that keeps volume at the absolute minimum a sphere.

Any object in weightless space larger than a couple of hundred miles in diameter has enough mass for its gravity to overcome large-scale irregularities and force it into a spherical shape.  This gravitational compression also generates significant amounts of heat at the center of the planet. This heat melts, or at least softens, any solid materials within the planet, facilitating the planet’s collapse into a spherical shape.

Objects in space smaller than about 100 miles in diameter, such as most asteroids, comet nuclei and small moons, lack the mass to create a gravitational field strong enough to compress themselves into spheres.  These little worlds often take on what I call the “sick potato” look.

The 12.5 mile-long, 7.5 mile wide asteroid Gaspra, imaged in October 1991 from a distance of 1,600 miles by the Galileo spacecraft en route to Jupiter.

A really large asteroid, such as Ceres (diameter = 600 miles), has enough mass for its gravity to compress it into a sphere.

The 600 mile-wide asteroid Ceres as seen by the Hubble Space Telescope.

However, “perfect” spheres are hard to find in space.

Pretty much everything is space rotates, and rotating a non-rigid sphere causes it to “bulge” at its equator from the centrifugal forces acting on it.

This spinning distorts large planets into a slightly squashed shape known as an “oblate spheroid.” This means that a planet’s diameter measured through its poles is smaller than the diameter measured through its equator.

Whereas the difference between the polar diameter and the equatorial diameter of Earth is a barely noticeable 0.3%, the oblateness of Saturn, a large, gaseous and rapidly spinning planet,  is greater than 10%.  You can easily see Saturn’s polar flattening through a telescope.

Saturn's polar diameter is 33,700 miles, but its equatorial diameter is 37,360 miles.

There may not be such a thing as a “perfect” sphere in nature, but there is no doubt that spheres, nature’s favorite shape, are perfectly lovely.