From Halopedia, the Halo wiki
Venus is the second planet in orbit around Sol, with no natural satellites. Though a terrestrial planet with a dense atmosphere largely composed of carbon dioxide, Venus was once a candidate for human colonization, and a terraforming project was initiated on the planet. However, as of some point during or after the late 23rd century, this project was considered a failure.[Note 1]
On March 7, 2526, when approached about taking part in Operation: SILENT STORM, Avery Johnson mused that if he turned down the assignment, his next one would likely be "guarding snowballs on Venus".
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