Mars

Mars (火星) is the fourth planet from the Sun, named after the Roman god of war, and nicknamed the "Red Planet" because of its red soil. Mars is mentioned frequently or offhandedly throughout the series.

Background
Mars is one of the planets traditionally used in astrology along with Mercury, Venus, Jupiter and Saturn, together with the Sun and Moon.

Toaru Majutsu no Index: Mars SS
Planet Mars first introduced in the series in this short story. The Martian Microbes are supposedly a life form native to the planet Mars, an intelligent species speaking Japanese.

Toaru Majutsu to Kagaku no Ensemble
Indian astrology, also referred as Vedic and Navagraha Astrology, tells fortunes through the positions of 9 Navagraha; the Sun, the Moon, Mercury, Venus, Mars, Jupiter, Saturn, Rahu, and Ketu, as well as the angles of the constellations.

Baggage City Arc
Shar Berylan mentioned Natural Selector participant who claims to talk with a mass of bacteria collected from Mars. It is unknown if the 'mass of bacteria collected from Mars' is related to the Martian Microbes.

Agitate Halation Arc
Cp-191 is a hibernation drug originally developed for a manned Mars investigation project.

VS The World
The Space Save Supply Shoot System (軌道上防衛兵站輸送システム) also known as the S5 is a terraforming device meant to send a massive amount of water mixed with nutrients to other celestial bodies like the Moon or Mars.