Short answers, pulled from the story.
Olympus Mons rises over 21 kilometers from the foot of its cliffs to its peak, and the total climb from the plains of Amazonis Planitia to the summit approaches 26 kilometers, roughly three times the height of Mount Everest. The volcano is over 600 kilometers wide and is either the tallest or second-tallest mountain in the Solar System.
The atmosphere of Mars is about 96 percent carbon dioxide, with roughly 1.93 percent argon and 1.89 percent nitrogen plus traces of oxygen and water. Surface pressure averages around 600 pascals, only about 0.6 percent of Earth's.
Mars has two moons, Phobos and Deimos, discovered in 1877 by Asaph Hall and named for the Greek deities of panic and terror. Phobos is about 22 kilometers across and Deimos about 12 kilometers across.
Landforms and minerals strongly suggest liquid water once flowed on Mars, including outflow channels in about 25 places and water-formed minerals like jarosite and gypsum found by the Opportunity rover. Most Martian water now exists as ice, including the south polar cap, which if melted could cover most of the planet to a depth of 11 meters.
Mars is called the Red Planet for its orange-red appearance, which is caused by iron oxide dust on its surface and in its atmosphere. The fine dust tints the Martian sky a tawny color when seen from the ground.
Spacecraft have visited Mars since the Soviet Mars 1 in 1963, with NASA's Mariner 4 transmitting the first images of another planet from deep space in 1965. Today Mars hosts ten functioning spacecraft, eight in orbit and two on the surface, the Curiosity and Perseverance rovers.
The Martian canals began as features called canali that Giovanni Schiaparelli mapped in 1877 using a 22-centimeter telescope in Milan, a term mistranslated from channels into canals. They were later shown to be largely an optical illusion, though they fueled widespread belief in Martian civilizations promoted by Percival Lowell.