CREATE TABLE table_44983 ("Name" TEXT, "Latitude" TEXT, "Longitude" TEXT, "Diameter  ( km ) " FLOAT, "Year named" FLOAT)

Which Diameter (km) has a Name of alma-merghen planitia, and a Year named smaller than 1997?
SELECT MAX("Diameter (km)") FROM table_44983 WHERE "Name" = 'alma-merghen planitia' AND "Year named" < '1997'
SELECT MAX("Diameter (km)") FROM "table_44983" WHERE "Name" = 'alma-merghen planitia' AND "Year named" < '1997'