Mädler is a crater on Mars named in honor of the German astronomer Johann Heinrich Mädler. It is located at 2.7°E 10.7°S.
Mädler and collaborator Wilhelm Beer produced the first reasonably good maps of Mars in the early 1830s. When doing so, they selected a particular feature for the prime meridian of their charts. Their choice was strengthened when Giovanni Schiaparelli used the same location in 1877 for his more famous maps of Mars. The feature was later called Sinus Meridiani ("Middle Bay" or "Bay of the Meridian"), but following the landing of the NASA probe MER-B Opportunity in 2004 is perhaps better known as Meridiani Planum.
Mädler lies in the south of Meridiani Planum, close to the prime meridian and about 10° east of Beer. Schiaparelli is also in the region.
Eroded rim of Madler Crater, as seen by MRO's CTX.