Question

Which is the ninth planet from the Sun? A. Earth C. Jupiter B. Mars D. Pluto

Short answer

D. Pluto

Step-by-step solution

Identify the Planet Order

First, we need to list the planets in order from the sun to understand the sequence. Starting with Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and historically, Pluto was considered the ninth planet.

Match the Choices to the Order

Next, compare each option to the list of planets in order from the Sun. Earth is the 3rd planet, Mars is the 4th, Jupiter is the 5th, and Pluto was historically known as the 9th.

Determine the Correct Answer

Since the question asks for the ninth planet from the Sun and you have matched the options to the order, identify that historically, Pluto is the ninth planet.

Key concepts

Planetary Order

Understanding the order of planets in our solar system is vital for answering any question related to their sequence. The planets close to the Sun are warmer and generally smaller. As we move further out, the planets tend to be larger and often have multiple moons.

Here's a quick guide to the planetary order from the Sun:

• Mercury - the closest to the Sun and the smallest planet.
• Venus - similar in size to Earth and often called Earth's "sister planet."
• Earth - our home planet, known for its life-sustaining atmosphere.
• Mars - the red planet, famous for its dusty landscape.
• Jupiter - the largest planet, with a massive storm known as the Great Red Spot.
• Saturn - distinguished by its extensive ring system.
• Uranus - known for its unique blue color due to methane in its atmosphere.
• Neptune - has strong winds and a dark spot similar to Jupiter's Great Red Spot.
• Pluto - was historically the ninth planet.

By memorizing these planets in their order, it becomes easier to understand and answer such questions.

Pluto

Pluto has a fascinating and somewhat controversial history in the solar system. Discovered in 1930 by Clyde Tombaugh, it was initially hailed as the ninth planet of the solar system. For decades, students learned about the nine planets with Pluto rounding out the list.

However, in 2006, the International Astronomical Union (IAU) changed Pluto's designation from a planet to a "dwarf planet." This decision was based on new rules that required a planet to clear its orbit of other debris, which Pluto does not do. Therefore, while it is no longer classified as a planet, Pluto remains an object of interest and study due to its unique characteristics, such as its icy surface and its five known moons, the largest of which is Charon.

Planet Classification

Understanding how planets are classified helps in comprehending their order and characteristics. When scientists classify planets, they use certain criteria that differentiate them from other objects in space. There are a few key categories to consider:

• Terrestrial planets: These are closer to the Sun and have solid, rocky surfaces. This group includes Mercury, Venus, Earth, and Mars.
• Gas giants: These are larger planets that lack a solid surface and are composed mainly of hydrogen and helium. Jupiter and Saturn are considered gas giants.
• Ice giants: Neptune and Uranus fall into this category. Unlike gas giants, they contain icy materials such as water, ammonia, and methane beneath their thick atmospheres.
• Dwarf planets: These objects, like Pluto, share characteristics with planets but don't meet all the criteria set by the IAU for full planet status.

Understanding these classifications clarifies why Pluto was reclassified and helps us appreciate the incredible diversity within our solar system.