Why we explore Mars—and what decades of missions have revealed

When scientists view the Martian surface, they see branching streams, river valleys, basins, and deltas, suggesting that the planet may have once had a vast ocean covering its northern hemisphere. It was likely wrapped in a thick atmosphere able to maintain liquid water.

But somehow, the planet went through a dramatic transformation. Exploring Mars can help scientists learn about climate change that can alter planets. Learning more about Mars may equip us to someday make a living there.

Since 1960, dozens of spacecraft have been sent to Mars. It is difficult to send a spacecraft to Mars and even harder to land on the planet because of the thin atmosphere.

Data revealed the largest volcanoes in the solar system and one of the largest canyons yet discovered. Dust storms regularly sweep over the plains. Several spacecraft orbiting Mars shows an active planet rich in ingredients needed for life - water, organic carbon, and an energy source.

Once every 26 months, Earth and Mars are aligned to enable spacecraft to reach it in about half a year. Space agencies launch probes during these conjunctions.

• The most recent launches were the Hope spacecraft of the United Arab Emirates, to study its atmosphere and weather patterns.
• China launched its Tianwen-1.
• The United States launched its Perseverance rover to study Martian climate and weather, test technologies that could help humans survive, and collect samples from rocks.

The robotic activity is laying the groundwork for sending humans to Mars.