In ancient times, this star rose at dawn during the hottest time of summer, thus the "dog days of summer"
(Sarah of the Clue Crew reports from beside a replica rover at the Adler Planeterium in Chicago, IL.) This is a replica of both the Mars exploration rover Spirit and this companion, who came knocking in January 2004
Add this letter to Earth & you get a scarcity
Add this letter to Mars & you get a fen
Add this letter to Jupiter's moon Io & you get an acronym that's a ground-floor stock offer for regular guys
Add this letter to star & get something harsh or grim
Add this letter to Saturn's moon Titan & you get a Renaissance guy who liked to paint Venus