Place the following events in the order that corresponds to the formation of a planetary system. a. Gravity collapses a cloud of interstellar gas. b. A rotating disk forms. c. Small bodies collide to form larger bodies. d. A stellar wind "turns on" and sweeps away gas and dust. e. Primary atmospheres form. f. Primary atmospheres are lost. g. Secondary atmospheres form. h. Dust grains stick together by static electricity.

The formation of a planetary system begins with the collapse of a cloud of interstellar gas. Interstellar gas, mostly composed of hydrogen and helium, exists in vast clouds known as molecular clouds. Under the influence of gravity, a region within a cloud can become unstable and start to collapse. This gravitational collapse is the very first step in the birth of a new planetary system.
As the cloud collapses, the material within it gets pulled closer together, causing the density and temperature to increase. This process can lead to the formation of a protostar at the center of the collapsing cloud. The surrounding material will continue to collapse towards the center, feeding into the growing star.

Following the initial collapse, the material in the collapsing cloud does not just fall straight into the center. Due to the conservation of angular momentum, the cloud begins to spin faster as it collapses. This process leads to the formation of a rotating disk of gas and dust around the protostar.
The spinning motion causes the collapsing material to flatten into a disk shape, known as a protoplanetary disk. This disk is where planets will eventually form. The protoplanetary disk is composed of gas, dust, and other debris, all rotating around the newly formed protostar.
This disk will provide the material needed for the formation of planets, moons, and other celestial bodies.

In the protoplanetary disk, small dust grains begin to stick together by static electricity. This initial coalescence forms larger and larger particles, eventually leading to the creation of planetesimals, which are small bodies that can be a few kilometers in size.
Planetesimals act as the building blocks of planets. As they collide and stick together, they gradually form even larger bodies. This process is driven by gravity and can take millions of years. The larger these bodies become, the more they can attract additional material through gravitational forces, speeding up their growth.
The eventual result is the formation of protoplanets, which are larger bodies that will become planets.

Once the newly formed star becomes active, it starts to emit a stellar wind, which is a stream of charged particles emitted by the star. This stellar wind plays a critical role in shaping the planetary system.
The stellar wind sweeps away the remaining gas and dust from the protoplanetary disk. This clearing of material is crucial for the development of the planetary system because it halts the accretion of gas onto forming planets and helps in defining the final planetary orbits.
Without the influence of stellar wind, the gas and dust would continue to interfere with the formation of planets, potentially leading to a very different planetary system.

As planetesimals continue to grow and become protoplanets, they begin to capture gas from their surroundings, forming primary atmospheres. These atmospheres are typically composed of hydrogen and helium, the main components of the protoplanetary disk.
However, primary atmospheres are often lost due to the intense stellar wind and radiation from the active young star. This loss can be significant, particularly for smaller planets. Once the primary atmospheres are stripped away, the protoplanets can develop secondary atmospheres.
Secondary atmospheres are formed from volcanic outgassing, impacts from comets and asteroids, and other geological processes. These atmospheres are typically more complex and can include a variety of gases like carbon dioxide, water vapor, and nitrogen. The development of secondary atmospheres is crucial for the potential habitability of planets, as seen with Earth.