Inner Planets Planet The International Astronomical Union IAU

Inner Planets

Planet The International Astronomical Union (IAU) defines a planet as a body that: �is in orbit around the sun �has sufficient mass for its self-gravity to assume nearly round shape, and �has cleared the neighborhood around its orbit. Source: IAU Resolution 5 B

Why should we study the planets? Learning about the other planets helps us understand a lot about Earth.

Inner Planets �Also called the terrestrial planets �Near to the sun �Small planets �Composed primarily of rocks and iron �Includes Mercury, Venus, Earth and Mars Source: Encarta encyclopedia 2009

Inner Planets (except Pluto)

Mercury

Mercury �Closest planet to the sun �Smallest planet in solar system �Has many craters and looks more like Earth’s moon �Has a very thin atmosphere �The temperature varies from 330°C to 750°C �Dry, hot and virtually airless.

Venus

Venus �Second planet from the sun �Known as Earth’s twin �One Venus day is longer than one Venus year �Hottest planet in the solar system with temperatures reaching 860°C �It’s atmosphere is composed mainly of carbon dioxide

Venus �Appears to have phases like the moon and Mercury �The “morning and evening star” �Third brightest object in the sky

Venus

Earth �Third planet from the sun �The only planet known to support life �Atmosphere is composed of 78% nitrogen, 21% oxygen �The surface is about 70% water

Earth

Mars

Mars �Also known as the “red planet” �Has polar ice caps that vary during seasons �Has many craters �Has the largest volcano, the Olympus Mons �Atmosphere consists predominantly of carbon dioxide

Mars

That’s all for now! Source of planetary images: www. nasa. gov