What is the Total Number of Moons in the Solar System?

When observing the night sky, the moon is typically the brightest and largest object visible without a telescope, making it the only natural satellite most people can see with the naked eye. This limited visibility often leads to misconceptions about moons and their abundance in the cosmos.

Contrary to popular belief, there are hundreds, if not thousands, of natural satellites within our solar system. These range from small, irregularly shaped space rocks to large, rounded bodies that could be considered planets due to their size. This variety highlights the diversity and prevalence of moons.

The Complexity of Counting Moons

The number of moons in the solar system depends on the definition used. The International Astronomical Union (IAU) recognizes 288 planetary moons around the eight major planets. Additionally, NASA’s Jet Propulsion Laboratory identifies 473 “small-body satellites” orbiting asteroids and dwarf planets, bringing the total to 761 natural satellites as of June 2024.

“This figure is likely an underestimate,” according to Edward Ashton from the Academia Sinica Institute of Astronomy and Astrophysics. He notes that “many new moons have been discovered recently, and advancements in technology will likely lead to even more discoveries in the near future, indicating that we have only begun to uncover the full extent of the solar system’s moons.”

Defining what constitutes a moon can be complex. A basic definition is an object that orbits a larger, non-stellar body. However, this excludes human-made satellites, which, despite fitting the definition, are not natural and have finite lifespans. Moreover, some natural satellites, like quasi-moons and minimoons, do not follow true orbits around planets, adding further complexity to the definition of a moon.

The Intricacies of Defining and Categorizing Moons

Brett Gladman, an astronomer at the University of British Columbia, points out that size plays a crucial role in defining moons. For instance, the tiny rock fragments that constitute the rings of planets like Saturn and Uranus are not considered moons despite orbiting their host planets. Objects smaller than a few hundred feet, known as “ring moons” or “moonlets,” also have ambiguous definitions and are not classified as true moons.

The classification of moons involves further complexity. Planetary moons can be categorized into regular moons, which are typically larger with small, circular orbits close to the planet’s equator, and irregular moons, which are smaller with larger, elliptical orbits. “Among the regular moons, about 20 are considered major moons because they are large enough to have a rounded shape due to their gravity.”

Mercury and Venus, the two closest planets to the sun, lack true moons due to the sun’s gravitational influence. Venus does host one quasi-moon, Zoozve, which orbits the sun rather than Venus itself. Earth possesses one major moon, along with seven quasi-moons and occasional minimoons that last about a year. Mars, on the other hand, has two small moons, Phobos and Deimos, which orbit closely to the planet. Phobos is gradually moving towards Mars and is projected to collide with its surface at some point in the future.

Moons of the Giant Planets

Moving to the giant planets, the dynamics become increasingly fascinating. Jupiter, the first gas giant, boasts an impressive 95 moons, including four major ones: Callisto, Europa, Io, and Ganymede, the largest moon in our solar system. Saturn surpasses even Jupiter with at least 146 moons, featuring six major ones like Titan, Mimas, and Enceladus.

The ice giants Uranus and Neptune possess 28 and 16 moons, respectively, and together account for seven major moons. However, these counts have seen significant changes recently. Since early 2023, astronomers, including Ashton and Gladman, have discovered 62 new irregular moons around Saturn, 12 new moons around Jupiter, and additional moons around Uranus and Neptune.

Advances in Moon Detection Technology

Advances in technology, particularly in telescopes, have enabled astronomers to detect smaller moons, especially irregular ones abundant around giant planets, Ashton noted. This trend suggests that “the tally of moons in our solar system will likely rise sharply in the coming years. “Ashton himself has identified new planetary moons awaiting confirmation through follow-up observations before submission to the IAU.

The potential for discovering more moons extends beyond known planets. Hypothetical worlds like Planet Nine thought to exist on the solar system’s fringes, could harbor multiple moons if found. Additionally, rogue planets captured from interstellar space by the sun might also possess moons.

The Vast Potential for Moon Discoveries

Astronomers, including Edward Ashton, suggest that the solar system likely hosts as many small-body satellites as planetary moons, with most of these satellites still undiscovered. Estimates vary widely due to the unknown parent populations of host objects, making it challenging to pinpoint exact numbers. Currently, over 700 natural satellites are documented in the solar system, a figure expected to rise significantly as technology improves.

The potential for discovery remains vast, especially with advancements in telescope capabilities. There could be hundreds, if not thousands, of tiny planetary moons waiting to be found. Despite uncertainties, Ashton ventures an estimate of around 10,000 moons in total within the solar system, underscoring the ongoing challenge of fully mapping these celestial bodies.

Read the Original Article: Live Science

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