Question

Imagine Earth and Mars start off with the same ratio of deuterium to hydrogen (D/H). Which of the following best explains why Mars' ratio will increase over time, relative to Earth's?

a) Mars loses D more easily than Earth does.
b) Both planets lose some D, but Mars loses much more H than Earth does.
c) Earth can hold onto all of its supply of both D and H.
d) Both planets hold all of their H, but Mars gains D.
e) Earth loses D much more easily than Mars does.

Answer 1

Mars' lower mass and gravity allow hydrogen to escape more readily than deuterium, leading to an increased deuterium to hydrogen (D/H) ratio over time compared to Earth.

Step-by-step explanation:

The correct explanation for why Mars' deuterium to hydrogen (D/H) ratio will increase over time, relative to Earth's, is because both planets lose some D, but Mars loses much more hydrogen (H) than Earth does (Option b). Mars, having a smaller mass and weaker gravity compared to Earth, allows atmospheric gases to escape more easily. Since hydrogen is lighter than deuterium, it escapes into space more readily.

Mars' thin atmosphere exacerbates this loss, especially when compared with Earth's thicker and more protective atmosphere. Over time, this leads to a higher concentration of deuterium relative to hydrogen on Mars than on Earth.