Which object(s) formed last in our solar system?
the Sun
the solar nebula
the inner planets
the planetesimals
The inner planets, including Earth, formed after the Sun, the solar nebula, and the planetesimals in our solar system.
The Sun formed first in our solar system. It formed from a large cloud of gas and dust called the solar nebula. As the nebula collapsed under its own gravity, the core formed and eventually ignited, giving birth to the Sun.
After the Sun's formation, the remaining material in the solar nebula began to accrete into small, solid bodies called planetesimals. These planetesimals collided and merged over time to form larger objects, including the inner planets.
Therefore, the planetesimals formed last in our solar system. The inner planets, such as Mercury, Venus, Earth, and Mars, were created through the accumulation and merging of these planetesimals.
The object that formed last in our solar system is the Sun. To understand why this is the case, let's go through the formation process of our solar system step by step.
The formation of our solar system began about 4.6 billion years ago from a giant molecular cloud of gas and dust called the solar nebula. This cloud started to collapse under its own gravity, leading to the formation of a rotating disk of material known as the protoplanetary disk.
Within the protoplanetary disk, particles began to collide and stick together due to a process called accretion. These small clumps of dust and gas gradually grew larger, forming planetesimals. Planetesimals are the building blocks of planets, and they range in sizes from roughly a kilometer to several kilometers in diameter.
Over time, through continued collisions and gravitational interactions, planetesimals merged to form larger bodies called protoplanets. Protoplanets are the precursors to full-grown planets. The protoplanets continued to grow and eventually became the inner planets of our solar system, including Mercury, Venus, Earth, and Mars.
However, the formation of the Sun was a separate process. As material continued to fall into the center of the protoplanetary disk, enormous amounts of gas and dust accumulated. At a critical point, the pressure and temperature in the core of this gas cloud became high enough for nuclear fusion to occur. This process ignited the Sun, marking the birth of our star.
In summary, the Sun formed last in our solar system. The solar nebula collapsed and formed the protoplanetary disk which gave rise to planetesimals. These planetesimals collided and merged to form protoplanets, which eventually became the inner planets. While this was happening, the Sun was forming separately in the center of the protoplanetary disk.