1. Solar System Inventory
Unit 5.1

2. Solar System Inventory
The Greeks and other astronomers of old were aware of the Moon, the stars and 5 planets in the night sky – Mercury, Venus, Mars, Jupiter, and Saturn.

3. Solar System Inventory
They also knew of 2 other types of heavenly objects that were clearly neither stars or planets.

4. Solar System Inventory
Comets appear as long, wispy strands of light in the night sky that remain visible for periods of up to several weeks and then slowly fade from view.

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Meteors, or “shooting stars,” are sudden bright streaks of light that flash across the sky, usually vanishing less than a second after they first appear.

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These transient phenomena must have been familiar to ancient astronomers, but their role in the “big picture” of the solar system was not understood until much later.

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Human knowledge of the basic content of the solar system remained largely unchanged from ancient times until the early 17th century, when the invention of the telescope made more detailed observations as possible.

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Galileo Galilei was the first to capitalize on this new technology.

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Galileo’s discovery of the phases of Venus and of the 4 moons orbiting Jupiter early in the 17th century helped forever change our vision on the universe.

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As technological advances continued, knowledge of the solar system improved rapidly as astronomers were now able to see what was one invisible to the naked eye.

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By the end of the 19th century, astronomers had found Saturn’s rings, the planets Uranus and Neptune, many planetary moons, and the first asteroids.

12. Solar System Inventory
Asteroids are “minor planets” orbiting the Sun, mostly in a broad band called the Asteroid belt lying between Mars and Jupiter.

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Ceres, the largest asteroid and the first to be sighted, was discovered in 1801.

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During the 20th century, Pluto (now downgraded to a planetoid) along with 3 planetary rings systems, dozens of moons, and thousands of asteroids were discovered.

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Due to the advances in technology regarding telescopes and in spectroscopy, more information has been in attained in the past century than in all history.

16. Solar System Inventory
Astronauts have carried out experiments on the Moon and numerous unmanned probes have left Earth and traveled to all of the planets.

17. Solar System Inventory
As currently explored, our solar system consists of 1 star (Sun), 8 planets, 150 moons orbiting planets (confirmed), 5 dwarf planets (Pluto, Ceres, Eris, Haumea, Makemake), tens of thousands of asteroids, and countless comets, meteors and meteriods.

18. Solar System Inventory
Also in our solar system are the asteroid belt, the Kuiper Belt and the Oort Cloud.

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As we proceed through the solar system over the next few chapters, we will seek to understand how each planet compares with our own and what each contributes to our knowledge of the solar system as a whole.

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We will use the powerful perspective of comparative planetology to understand better the conditions under which planets form and evolve.

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Our goal will be to develop a comprehensive theory of the origin and evolution of our planetary system - a theory that explains most (or all) of the solar system’s observed properties.

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We will find many similarities and common features among planets. Each planet will also present new questions and afford unique insights into the ways planets work.

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As we unravel the origin of our solar system, we may hope to learn something about planetary systems beyond our own.

24. Solar System Inventory
Since 2017, a total of 3545 confirmed exoplanets – planets orbiting stars other than our own Sun - have been detected.

25. Solar System Inventory
Before the discovery of exoplanets, those theories have been based on our own solar system.

26. Solar System Inventory
Current data suggests that many of the newly discovered systems have properties different from our own.

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This fact has added fuel to the debate of the possibility of planets like Earth and the life elsewhere in the Universe.