Imagine a bathtub swirling as a small whirlpool forms—a miniature version of how, 4.6 billion years ago, a collapsing cosmic gas cloud gave birth to our solar system. This nebula’s gravity formed the Sun, while leftover dust and gas flattened into protoplanetary disks.
These disks encircled the Sun for billions of miles. Within them, dust and gas collided to form pebbles, which grew into boulders. Over time, boulders gathered more material, becoming protoplanets—large enough to become planets. This gradual process, called accretion, formed everything in our solar system, from planets to comets.
Despite significant technological advances, planetary scientists still debate the order of birth of the planets in our solar system. Determining which are the youngest and oldest remains challenging and is pivotal to understanding planetary formation.
Estimating the age of each planet is difficult, but evidence suggests Jupiter is the oldest. Understanding planetary ages is crucial, as it shapes our perspective on how the solar system formed.
Jupiter likely formed first, within 3 million years, which accounts for its massive size—318 Earths by mass and room for over 1,300 Earths by volume. Saturn formed next, followed by Neptune and Uranus. By then, Jupiter and Saturn had already cleared much of the outer system’s gas.
Four rocky planets and dwarf planets formed in the inner solar system from debris. These formed over about 100 million years through collisions between rocky bodies.
Fundamentally, the argument is that the four rocky planets closest to the Sun are the youngest, while Jupiter and Saturn are the oldest, according to current scientific approaches. This age distribution resulted from how gas was dispersed during formation, affecting planetary development.
This 90 million-year gap seems large, but it is less than 1% of the universe’s age—picture Jupiter as Earth’s older sibling, about 3 years older in this cosmic analogy.
Some space scientists agree that a planet’s surface age reflects its overall age. Preserved surfaces can be ancient, while active ones suggest a younger age. Typically, scientists estimate the age of solid astronomical bodies by counting surface craters, which show how long the surface has stayed unchanged. When surfaces are renewed, estimating the actual age means mostly measuring recent surface changes rather than the planet’s formation. In this light, Earth can be considered one of the youngest planets, as its surface is constantly changing, with Venus and Mars next.
Some researchers argue that Earth or Uranus is the youngest planet, based on major collisions. Primordial Earth collided with a Mars-sized body, reshaping Earth and forming the Moon. This impact shaped Earth’s climate and potential for life. Uranus also experienced a significant collision, tilting it and altering its magnetic field.
After forming, planets migrated inward or outward before settling in their orbits. For example, Neptune moved outward, pushing Uranus and many icy bodies into the Kuiper Belt, home to Pluto, Eris, and millions of comets.
Jupiter moved inward, its gravity drawing some planets near the Sun, destroying them, and ejecting others from the system. The remaining debris formed the Asteroid Belt as Jupiter finalized the positions of the inner planets, including Earth’s.
Ultimately, determining which planets are youngest and oldest reveals how planetary origins shaped Earth’s fate. Jupiter’s formation played a crucial role, placing Earth in the ideal spot for life. The lasting mysteries of the solar system’s creation invite us to keep questioning.
