E6 Solar System

Topic

The Solar System formed approximately 4.6 billion years ago from the collapse of a cloud of gas and dust; since then, its eight planets have been divided into rocky planets—located closer to the Sun—and gas or ice giants, situated further away.

The equilibrium temperature of each planet—resulting from the balance between the solar energy received and the energy radiated back into space—decreases with distance from the Sun and rises as the planet's surface becomes less reflective (i.e., has a lower albedo).

However, the greenhouse effect can raise a planet's actual temperature well above this equilibrium level—as seen on Venus, where the actual temperature exceeds the value predicted by a simple radiative balance by several hundred degrees; this discrepancy illustrates how a planet's atmosphere can trap energy far beyond what a simple radiative balance would predict.

The Solar System's minor bodies—such as main-belt asteroids and comets from the Kuiper Belt and Oort Cloud—are relics that have survived since the system's original formation.

In practice, exploring the Solar System relies on the principles governing space propulsion: the change in velocity a rocket can achieve increases with the speed at which it expels its exhaust gases, but only logarithmically with the ratio of its initial to final mass; consequently, gaining each additional increment of speed requires an ever-larger fraction of fuel, yielding diminishing returns. Thus, from the formation of the Solar System—with which this document begins—to the diminishing returns of space propulsion—with which it concludes—and encompassing everything from the equilibrium temperature of each planet to the greenhouse effect and minor bodies, the Solar System is such that fully understanding it requires both studying the planets that comprise it and solving the problem of how to reach them.

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