First in the system and first to face the full might of a recovered and ascendant Humanity.
Mercury is small. Very small. The planet itself, when compared to its seven siblings, and the community living there, even in comparison to Saturn's hab-networks. Mercury is a port world, a well tuned, tight knit community of laborers, each with wide ranges of responsibilities and skills all focused on two things: the barrel and the
Once the final ships from Earth were safely aground on the hastily assembled dome cities on Mars, Ceres, Ganymede and Europa, the scientific community had their leash loosened. No longer enlisted to save the species, they were given vast power to explore what use could be made of technologies originally developed for survival. A plan was made for each of the notable inner system bodies, with a Conglomerate given executive power over each. These conglomerates were made of pre-exodus powerhouses in science, energetics and engineering, vying for power in what was essentially a post-war boom. Plans were submitted during the Second Congress of Sol, and approved by a majority vote held in each of the one hundred thousand exodus ships. (Election systems in Post-Exodus Humanity are more broadly explored in databases focused on the history of the Exodus and Humanity) The Calliope Group laid claim to Venus first, being the most powerful energetics foundation in pre-exodus Earth meant its leaders were especially keen to explore the planet on which Manifest events were first observed. Mars was already serving as the make-shift home for roughly 9 billion humans, arriving over the course of just ten years, and Earth was under the strict supervision of the United Nations and its one long term aim; eventual revival. Its moon had already been set aside by the impressively forward thinking 20th century superpowers, its success as a multinational treaty being a foundation upon which the UN intended on building during the start of a interplanetary humanity.
That left Mercury, a small world with a massively fluctuating temperature, and a 3:2 tidal synchronicity with the sun. The first planet will rotate only once every two revolutions around the sun, so the entire surface is vulnerable to the largest temperature ranges in the entire solar system, and a magnetic field weak enough to allow solar winds to leak down to its surface and scar it. The planet wasn't particularly rich in inorganic materials, so not even a single-minded mining cooperative would propose plans for its terraformation, let alone for its inhabitance by humans. Smaller energetics teams, some bitter from the instantly approved Venusian plan which vested power only in the Calliope group, sent probes to monitor any energetic properties, materials, or manifest, but Mercury was a dead world, bereft of even traces of even simple energetic compounds.