The given sentences are related to the topic of Mars and its water history. Four sentences can be logically grouped to form a coherent paragraph discussing how water was lost and where it might still exist, while one sentence directly states that ancient water was lost. The sentences can be analyzed as follows:
Sentence 1: Most of the planet's remaining water is now frozen or buried, but clues over the past decade suggested that some liquid water, a presumed necessity for life, might survive in underground aquifers.
Sentence 2: Data from NASA's MAVEN orbiter show that solar storms stripped away most of Mars's once-thick atmosphere.
Sentence 3: Particles from the Sun collided with molecules in the atmosphere, knocking them into space or giving them an electric charge that caused them to be swept away by the solar wind.
Sentence 4: A recent study reveals how Mars lost much of its early water, while another indicates that some liquid water remains.
Sentence 5: The water that made up ancient lakes and perhaps an ocean was lost.
Sentences 1, 2, 3, and 4 collectively describe the mechanisms for water loss and hint at remaining water, suggesting causes and potential reservoirs. Sentence 5 merely states water loss, without connecting it to a detailed explanation or current state. Hence, Sentence 5 is the odd one out.