Question

Pluto and Eris. How does the nebular theory explain the origin of objects like Pluto and Eris? How was their formation similar to that of jovian and terrestrial planets, and how was it different?

Short answer

The nebular theory explains their formation through accretion. Like planets, they formed in the solar nebula but remained small and icy, beyond the main planetary region.

Step-by-step solution

Understanding the Nebular Theory

The nebular theory suggests that the solar system formed from a large cloud of gas and dust, known as the solar nebula. This process gave rise to the Sun and all planetary objects, including planets, comets, and distant dwarf planets like Pluto and Eris.

Formation Similarities

Much like the jovian and terrestrial planets, Pluto and Eris formed from the accretion of particles in the solar nebula. Initially, small solid particles began to collide and stick together to grow into larger bodies, a process that also initiated planet formation.

Location and Composition

Pluto and Eris formed further out in the solar system where the temperature was lower. This environment, consisting of more ices and less rocky material, is akin to that of the jovian planets, which have large amounts of ice and volatile compounds.

Differences in Size and Location

Although Pluto and Eris have some similarities with jovian planets in terms of icy compositions, their location in the Kuiper Belt means they did not become as large as the jovian planets, which accreted a vast amount of gas in addition to ices. They are, therefore, smaller and are classified as dwarf planets.

Key concepts

Dwarf Planets

Dwarf planets, like Pluto and Eris, are celestial bodies in our solar system that share many traits with traditional planets but also have distinctive characteristics. A dwarf planet is an object that orbits the Sun and is not a satellite. It must be massive enough for its gravity to shape it into a near-spherical form. However, unlike planets, dwarf planets have not cleared their orbital paths of other debris.

Pluto and Eris both fall into the category of dwarf planets. Though they both orbit the Sun, their paths cross other objects in the Kuiper Belt, which differentiates them from being recognized as full-fledged planets.
The composition of dwarf planets often includes ice and rock, reflective of their formation in colder parts of the nebula where water and other volatiles solidified. As part of their dynamic nature, dwarf planets might show activity such as geological reshaping due to internal processes or external impacts.

Kuiper Belt

The Kuiper Belt is a crucial part of our solar system where many icy bodies, including dwarf planets, can be found. Located just beyond Neptune's orbit, it is a ring-shaped region populated with a variety of small bodies and remnants from solar system formation.

This region is named after the astronomer Gerard Kuiper, who helped expand our understanding of the accumulation of icy objects that orbit the Sun. The Kuiper Belt holds a reservoir of comets like the well-known short-period comets. Short-period comets are linked to this area due to their journey from the Kuiper Belt into the inner solar system.
The formation of objects in the Kuiper Belt, including Pluto and Eris, occurred in a part of the nebula farther away from the Sun, allowing them to accumulate ice-rich material. This ice-rich composition distinguishes them from the rockier inner planets.

Solar System Formation

The formation of our solar system is a fascinating story of cosmic dust and gases coalescing into the celestial bodies we observe today. The prevailing theory explaining this process is the nebular theory, which suggests that everything started from a large cloud of gas and dust known as the solar nebula.

As this nebula collapsed due to gravity, it began to spin and flatten into a disc with the Sun forming at its center. Within this disc, particles collided and stuck together, gradually building into planetesimals, and eventually, planets and other bodies.
The solar system's architecture, including the placement and composition of planets, was shaped by temperature gradients in the disk. Inner regions, warmer and filled with metallic and silicate material, led to rocky terrestrial planets. Further out, cooler areas rich in icy compounds led to the formation of gas giants and icy bodies like those found in the Kuiper Belt.
The diversity in temperature and material across the nascent solar nebula allowed for the wide array of objects, from rocky planets like Earth to icy dwarf planets like Pluto.