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Hello. I am Rebecca Barnes. And, welcome to the [email protected] Vodcast. In this episode, I will journey through the wonders of modern astronomy, because, it's closer to home. As we begin to explore the Solar System, we discover the scale and structure of the Solar System, find out why we explore it, and introduce to you the European missions launched on a quest to further investigate our local celestial neighbourhood. Ancient astronomers observed points of light in the night sky that appeared to wander across the fixed background stars. These five wandering stars, or planets as they came to be called, along with the Moon and Sun, are Earth's closest cosmic neighbours. Until about 400 or so years ago, a limited view and understanding of our Solar System, let astronomers to believe that our world was at the center of the Universe, and, that the Sun, stars and the planets, orbited the Earth. At that time, astronomers only knew about the five planets closest to Earth, those that are visible from Earth, to the unaided eye. Over time, our view of our local cosmic neighbourhood has changed, and evolved, as technology and scientific thinking has progressed. Nicolaus Copernicus was the first to realize that the Sun was the center of the Solar System. Johannes Kepler discovered that the planets moved in an ellipse-shaped orbits. And, Galileo Galilei was the first to use a telescope to observe four tiny moons orbiting the giant planet Jupiter, showing that more than one center of motion existed in the Solar System. The invention of the astronomical telescope provided the ultimate tool for astronomers to observe the Solar System in more detail. In addition to facilitating the discovery of two more giant planets, telescopes also allowed scientists to see the surface of the planets for the first time. Continued study of the heavens over the past few hundred years, has completely changed our perspective of our place in the Universe. The Solar System, a tiny region of our galaxy, is dynamic and is in constant motion, and evolving. Although small in size, compared to the Milky Way, the Solar System is actually very large. Our Solar System formed from a large cloud or nebula of gas and dust, about 4.6 billion years ago. This cloud mostly consisted of hydrogen and helium that formed in previous generations of stars. This pre-solar nebula was a rotating sphere of dust and gas. Slowly, the dust settled around the center of plane to form a disk. At the center of the nebula, a protostar formed. Further contraction in the heart of the protostar caused the temperature and pressure to increase, until they were high enough, for nuclear fusion to ignite in the disc of debris, surrounding the very young Sun, Heavier elements remained closer to the central star, whereas lighter elements were pushed by the Solar Wind to the outer regions. The dust and gas was settling into a disc. It started to create. Some material was broken down into smaller pieces and others began to cluster together and stick. As these clusters grew larger and larger, they attracted even more material, and eventually formed the planets, observed today. The Sun is the central engine of the Solar System. It is by far the largest body providing light and energy to all other objects that lie within the system, and, that are held in orbit by strong gravitational influence. Closest to the Sun, is a group of our terrestrial planets with solid rocky surfaces. Mercury, Venus, Earth and Mars. Beyond the orbit of Mars, lies the main asteroid belt containing thousands of chunks of rock that vary in size and tend to be irregular in shape. Traveling even farther from the Sun, we'll reach a group of four giant planets which have no solid surface. These are the gas giants, Jupiter, Saturn, Uranus, and Neptune. Past Neptune, hugging the plane of the Solar System, is the Kuiper belt. The thousands of objects here, so far away from the Sun, contain much colder material, and are predominantly made of ices and rock. These are comets. The Kuiper belt is also home to three dwarf planets, Pluto, Eris and Makemake. Even further away from the Sun, the Oort cloud forms a halo, surrounding the entire Solar System. The Oort cloud is home to millions of comets. The outer boundary of the Solar System is called the Heliopause. This is where the Solar Wind, energetic charged particles emitted by the Sun in all directions, collides from incoming particles from interstellar space. Many of the planets have moons orbiting them. And, the entire Solar System is filled with microscopic particles of dust. So, why do astronomers and scientists want to explore the Solar System. It's human nature to seek knowledge of the world around us. The Solar System can be considered as a laboratory that allows scientists to explore physical processes seen elsewhere in the Universe. For example, the Sun is the only star that can be studied close up. It was much as possible is learnt about the siblings of the Earth, such as Mercury, Venus, Mars and the Moon. Thus, scientists can build up a deeper comprehension of the history of our own planet, and, what might be in store for its future. For example, on Earth, processes such as water flow, plate tectonics, and the growth of vegetation, have constantly changed the landscape, and, hidden a lot of its geological past. Whereas these processes are not active on Mercury, Mars or the Moon. So, that preserves a record of the Solar System's history. Ultimately, scientists want to explore in depth, and compare the properties of all Solar System bodies, including the Sun, in order to reveal and understand their composition and the processes at play, together with how the system formed and evolved into its present day state, and how it will continue to evolve in the future. I am Rebecca Barnes. Thank you for watching the [email protected] Vodcast.