Which of the following planets is often referred to as Earths twin because of its similar size and mass?

Introduction / Context:

This question assesses basic planetary science or astronomy knowledge, focusing on the planet that is commonly called Earths twin. The nickname reflects similarity in certain physical characteristics, mainly size and mass, rather than an identical environment. Knowing such comparisons between planets is a frequent requirement in general science sections.

Given Data / Assumptions:

• Several planets in the solar system have been compared with Earth for size, mass or conditions.
• The term Earths twin is used in textbooks for one specific planet.
• The options list inner planets like Mercury, Venus and Mars, as well as gas giants Jupiter and Saturn.
• The comparison is based mainly on radius and mass, not on habitability.

Concept / Approach:

Venus has a radius and mass that are very close to those of Earth. Its diameter is only slightly smaller and its mass is about 80 percent of Earth mass. Because of this similarity, many books call Venus Earths twin or Earths sister planet. However, surface conditions on Venus are extremely hostile, with very high temperatures and dense carbon dioxide atmosphere, so the twin concept applies to size and mass, not environment. No other planet in the options matches Earth physical size as closely as Venus does.

Step-by-Step Solution:

Verification / Alternative check:

Standard astronomical data show Earth radius at about 6371 km and Venus radius at about 6052 km, a relatively small difference. Their densities and compositions are also broadly similar, both being rocky terrestrial planets. In contrast, Mercury radius is only about 2440 km and Mars radius about 3390 km, which are significantly smaller. Textbooks and exam guides consistently label Venus as the twin of Earth in terms of size and mass, confirming the answer.

Why Other Options Are Wrong:

Mercury is far too small and lacks a significant atmosphere, so it does not earn the twin description. Jupiter and Saturn are gas giants with diameters and masses many times that of Earth, making them very different in structure and composition. Mars is sometimes described as a potential host for past or future life, but its size is much smaller than Earth and it is not usually called Earths twin. Therefore only Venus matches the usual textbook description.

Common Pitfalls:

Candidates sometimes confuse the idea of similarity in life supporting conditions with similarity in size. Mars is often in the news for exploration, which may cause some to mistakenly think it is the twin of Earth. Others may not focus on the specific wording about size and mass. Remembering that Venus is physically very similar in size but very different in climate helps keep the comparison clear.

Final Answer:

The planet commonly called Earths twin due to its similar size and mass is Venus.