Much of astronomy is motivated by the desire to understand the origin of things: to find at least partial answers to old questions about where the universe, the sun, the earth and ourselves come from. Each planet and moon is a fascinating place that can spark our imaginations as we try to imagine what the visit would be like. Together, the members of the solar system keep patterns that can tell us about the formation of the entire system. At the beginning of our exploration of the planets we would like to present our picture of the formation of the entire solar system.
The recent discovery of hundreds of planets orbiting other stars has shown astronomers that many Exoplanetary systems can be very different from our own solar system. For example, it is common for these systems to contain planets that are between our terrestrial and giant planets. These are often referred to as superstars. Some exoplanet systems even have huge planets near the star. Reversal of the order we see in our system. In The Birth of Stars and the Discovery of Planets Outside the Solar System, we will look at these exoplanet systems. But now let’s focus on the theories about how our own particular system was formed and evolved.
Looking For Patterns
One way to approach our original question is to look for regularities between the planets. We find, for example, that all planets lie almost in the same plane and rotate in the same direction around the sun together formed from a rotating cloud of gas and dust that we call a solar nebula. The composition of the planets gives a further indication of the origins. Spectroscopic analysis enables us to determine which elements are present in the sun and planets.The sun has the same hydrogen dominance composition as Jupiter and Saturn and therefore appears to have formed from the same deposit of material. In comparison, the terrestrial planets and our moon have a relatively limited in light gases and the various types of ice that are formed from the common elements oxygen, carbon & nitrogen. Instead, we mainly see the rarer heavy elements such as iron and silicon on earth and its neighbors. This pattern suggests that the processes that led to the formation of planets in the inner solar system must have somehow excluded much of the lighter materials common elsewhere. These lighter materials must have escaped and left a heavy residue.
The reason for this is not difficult to guess, bearing in mind heat of the sun: the inner planets and most asteroids are made of rocks and metal that can survive heat but contain very little ice or gas that evaporates at temperatures. (To see what we mean, just compare how long a stone and an ice cube survive when they’re in sunlight.) In the outer solar system, where it’s always been colder, the planets and their moons exist, as well as icy dwarf planets and Comets mostly made up of ice and gas.
Evidence From Far Away
A second approach to understanding the origins of the solar system is to look outside for evidence that other planetary systems are forming elsewhere. We cannot look back in time to see our own system formed, but many stars in space are much younger than the sun, and in these systems the planet formation processes may still be amenable to direct observation. We observe that there are many other “solar nebulae” or circumstellar disks, flattened and spinning clouds of gas and dust that surround young stars. These disks resemble the initial stages of our own solar system. Formed billions of years ago.
Circumstellar disks are common in very young stars, suggesting that the disks and stars are formed together. With theoretical calculations, astronomers can see how solid bodies can form from gas and dust in these disks when they cool down. These models show that the material begins to fuse first. form small objects, precursors to planets that we call planetesimals.
Today’s fast computers can simulate how millions of planetesimals, probably no more than 100 kilometers in diameter, could gather together under their mutual gravity to form the planets we see today. understand that this process was violent, with planetesimals colliding with each other & sometimes even disturb the growing planets themselves. As a result of these violent impacts (and the heat from the radioactive elements within them), all of the planets warmed until they became liquid and gaseous and therefore differentiated, which explains their current internal structures.
The process of impacts and collisions in the early solar system was complex and often seemingly random. The solar nebula model can explain many of the regularities we find in the solar system, but for some it could be due to accidental collisions of massive clusters of planetesimals. Exceptions to the “rules” of the behavior of the solar system. For example, why do the planets Uranus and Pluto spin on their sides? Why is Venus spin slowly and in the opposite direction to the other planets? Why is the composition of the moon similar to the earth in many ways? and yet they show considerable differences? The answers to such questions are likely to be found in huge collisions in the solar system long before life began on Earth. Today, about 4.5 billion years after its origin, the solar system is thankfully a much less violent place. We see, however, that some planetesimals continue to interact and collide, with their fragments moving through the solar system as roving “transients” that can cause problems for established members of the Sun family, such as our own earth.