Table of Contents
Very few questions are asked in prelims [time to benefit ratio is too low] from this section. You can ignore these concepts if you found them too scientific.
- The nebula from which our Solar system is supposed to have been formed, started its collapse and core formation some time 5-5.6 billion years ago and the planets were formed about 4.6 billion years ago.
- Our solar system consists of the sun (the star), planets, satellites, millions of smaller bodies like asteroids, meteorites and comets and huge quantity of dust-grains and gases.
- Out of the nine planets, Mercury, Venus, Earth and Mars are called as the inner planets as they lie between the sun and the belt of asteroids the other five planets are called the outer planets.
- Alternatively, the first four are called Terrestrial, meaning earth-like as they are made up of rock and metals, and have relatively high densities.
- The rest five are called Jovian or Gas Giant planets.
- Jovian means Jupiter-like. Most of them are much larger than the terrestrial planets and have thick atmosphere, mostly of helium and hydrogen.
- The orbits of the planets are nearly circular, but many comets, asteroids, and Kuiper belt objects follow highly elliptical orbits
Why are the inner planets rocky while others are mostly in gaseous form?
- The terrestrial planets were formed in the close vicinity of the parent star where it was too warm for gases to condense to solid particles. Jovian planets were formed at quite a distant location.
- The solar wind was most intense nearer the sun; so, it blew off lots of gas and dust from the terrestrial planets. The solar winds were not all that intense to cause similar removal of gases from the Jovian planets.
- The terrestrial planets are smaller and their lower gravity could not hold the escaping gases.
Components of the Solar System
- Eight major planets,
- Dwarf planets (Pluto, Ceres, Eris etc.),
- Satellites and countless minor planets
- Meteors, and
- Debris etc….
Nicolaus Copernicus was the first to develop a mathematically predictive heliocentric system (Sun at the center). [Geocentric: Earth at the center]
- Age => 4.6 billion years
- Diameter => 13,91,785 km (~1.3 million km)
- Temperature => 6000 C on surface and 16 million C in core
- Density => 1.41 times that of water…[Density of water = 999.97 kg/m³; Density of Iron = 7870 kg/m³] => Iron is (7870/999.97) = 7.87 times denser than water
- Period of rotation => 25 days 9 hrs
- Speed of rotation => 7179.73 km/hr (Earth’s rotational velocity => 1675Km/hr)
- Equivalent to 3,32,900 Earth masses.
- Compared to the majority of stars in the Milky Way, the Sun is rather large and bright.
- Sun are rare, whereas substantially dimmer and cooler stars, known as red dwarfs, are common, making up 85% of the stars in the galaxy.
- Sun is located in Orion arm of Milky Way galaxy.
- The vast majority of the system’s mass is in the Sun, with most of the remaining mass contained in Jupiter and Saturn.
- Sun is rotating (counter-clockwise, as viewed from a long way above Earth’s north pole).
- Kepler’s laws of planetary motion describe the orbits of objects about the Sun.
- A body’s closest approach to the Sun is called its perihelion, whereas its most distant point from the Sun is called its aphelion.
- Although the Sun dominates the system by mass, it accounts for only about 2% of the angular momentum due to the differential rotation within the gaseous Sun.
- The Sun, which comprises nearly all the matter in the Solar System, is composed of roughly 98% hydrogen and helium. Jupiter and Saturn, which comprise nearly all the remaining matter, possess atmospheres composed of roughly 99% of these elements.
- Those objects closer to the Sun, which are more affected by heat and light pressure, are composed of elements with high melting points.
- Objects farther from the Sun are composed largely of materials with lower melting points.
- A celestial body moving in an elliptical orbit round a star, the Earth is known as planet.
- Planets are generally divided into:
- the Inner Planets (Mercury, Venus, Earth and Mars), and
- the Outer Planets (Jupiter, Saturn, Uranus, Neptune, and Pluto-dwarf planet).
- The inner Solar System is the traditional name for the region comprising the terrestrial planets and asteroids.
- Composed mainly of silicates and metals.
- The four inner or terrestrial planets have dense, rocky compositions, few or no moons, and no ring systems.
- They are composed largely of refractory minerals, such as the silicates, which form their crusts and mantles, and metals, such as iron and nickel, which form their cores.
- Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to generate weather; all have impact craters and tectonic surface features, such as rift valleys and volcanoes.
- The term inner planet should not be confused with inferior planet, which designates those planets that are closer to the Sun than Earth is (i.e. Mercury and Venus).
- Surface gravity: 1kg = 0.38 kg
- Mercury is similar to the Moon with a surface dominated by craters and a younger area of dark plains presumably made from floods of lava.
- Surface gravity: 1kg = 0.88 kg
- Venus is often considered to be the Earth’s twin, but the two planets are not identical.
- Venus has high plateaus, folded mountain belts, numerous volcanoes, and relatively smooth volcanic plains.
- The surface of Venus is totally obscured by a thick atmosphere composed mostly of carbon dioxide, with clouds of sulfuric acid.
- It is much drier than Earth, and its atmosphere is ninety times as dense.
- Surface gravity: 1 kg =1 kg
- The force of the Earth’s rotation makes the world bulge very slightly at the equator and go a little flat at the North and the South poles. So the Earth is actually a flattened sphere, or a ‘geoid’.
- It is large enough to develop and retain an atmosphere and a hydrosphere.
- The Pacific Ocean contains the deepest places on the Earth’s surface-the ocean trenches.
- The very deepest is the Challenger Deep in the Mariana Trench which plunges 11022 m into the Earth’s crust.
- A ray of light from the sun takes about eight minutes to reach the earth. Light takes only a second to reach us from the moon.
- Surface gravity: 1 kg = 0.38 kg.
- Surface has been dynamic. Almost every geologic feature is gigantic. Three huge volcanoes, one more than 28 km high exists at Mars.
- There is evidence not only of stream action, but of catastrophic flooding .
- Wind action is also an important process on Mars.
- In addition polar regions are covered with alternating layers of ice and windblown sediment.
- It possesses an atmosphere of mostly carbon dioxide.
- Its surface, peppered with vast volcanoes, such as Olympus Mons, and rift valleys, such as Valles Marineris, shows geological activity that may have persisted until as recently as 2 million years ago.
- Its red colour comes from iron oxide (rust) in its soil.
- Mars has two tiny natural satellites (Deimos and Phobos) thought to be captured asteroids.
- Millions of objects, remnants of planetary formation, circle the Sun in a zone lying between Mars and Jupiter. They are known as asteroids.
- Fragments of asteroids break off to form meteoroids, which can reach the Earth’s surface.
- Asteroids are small Solar System bodies composed mainly of refractory rocky and metallic minerals, with some ice.
- The asteroid belt occupies the orbit between Mars and Jupiter, between 2.3 and 3.3 AU from the Sun.
- It is thought to be remnants from the Solar System’s formation that failed to coalesce because of the gravitational interference of Jupiter.
- Asteroids range in size from hundreds of kilometres across to microscopic.
- All asteroids except the largest, Ceres, are classified as small Solar System bodies.
- Ceres (2.77 AU) is the largest asteroid, a protoplanet, and a dwarf planet.
- It has a diameter of slightly under 1,000 km, and a mass large enough for its own gravity to pull it into a spherical shape.