Mars has always been visible to the unaided eye as a bright, reddish point of light. Its movement across the night sky has been tracked for millennia, making the true “discovery” not a single event but a long progression of observations. This history moved from ancient civilizations charting its path to the scientific revelation of its physical nature through advancing technology and changing astronomical insight.
Recognition in the Ancient World
Ancient civilizations across the globe meticulously tracked Mars, recognizing it as a “wandering star.” The Babylonians were among the earliest, beginning in the second millennium BCE, using arithmetic techniques to predict its positions. They named the object after Nergal, their deity of war, pestilence, and fire, likely due to its distinctive ruddy color.
The ancient Egyptians referred to it as “the red one” (Her Desher). The Greeks called it Pyroeis, meaning “fiery,” and associated it with their god of war, Ares. The Romans adopted this association, naming the planet Mars after their own god of war, a name that has endured.
Greek cosmology, formalized by Claudius Ptolemy in the second century CE, treated Mars as one of several celestial bodies orbiting the Earth in a geocentric model. This model accounted for the planet’s perplexing retrograde motion—the apparent backward loop it makes in the sky—by proposing it traveled on a small circle called an epicycle. For centuries, this complex geometric construction represented the highest level of understanding regarding Mars’s motion.
The First Telescopic Discoveries
The invention of the telescope in the early 17th century shifted observation from tracking movement to studying physical form. Galileo Galilei was among the first to observe Mars telescopically around 1609. Although his early instrument lacked the power to reveal surface details, Galileo confirmed that Mars was a spherical disc and not merely a point of light.
In 1659, Christiaan Huygens identified the first permanent surface feature on another planet: the prominent, dark, wedge-shaped region now known as Syrtis Major. By tracking the motion of this distinct marking, Huygens accurately calculated the planet’s rotation period. He found a Martian day to be approximately 24 hours, only slightly longer than Earth’s.
Further refinements came from Giovanni Cassini in the 1660s, who refined the Martian rotation period to twenty-four hours and forty minutes. Cassini is also credited with the earliest reliable observations of the polar ice caps, describing them as two whitish patches. These observations confirmed that Mars possessed features with Earth-like seasonal changes, as the size of the caps was noted to expand and contract annually.
Mapping the Surface and Finding the Moons
The 19th century brought a new era of detailed observation, fueled by improved telescopes and the planet’s close approach in 1877. During this favorable opposition, Italian astronomer Giovanni Schiaparelli produced the first detailed maps of the Martian surface. He observed a dense network of linear features, which he labeled canali, the Italian word for “channels.”
Schiaparelli’s term was mistranslated into English as “canals,” implying artificial construction. This linguistic error sparked a public sensation, amplified by American astronomer Percival Lowell. Lowell became the most fervent proponent of the idea that the “canals” were an irrigation system built by an advanced Martian civilization.
During the same 1877 opposition, American astronomer Asaph Hall used the powerful 26-inch refractor telescope to make a definitive discovery. After a deliberate search, he found two tiny, faint satellites orbiting the Red Planet: Phobos (fear) and Deimos (terror). The moons were extremely small and orbited close to Mars, explaining why they had eluded earlier searches. While the “canals” were later confirmed to be optical illusions, Hall’s discovery marked the last major telescopic finding before the space age began.