Mercury with Mariner 10

Front:
MERCURY MARINER 10 29USA DASHGEM OCT S 1661 91109 CA

Back:
MERCURY WITH MARINER 10 First Day of Issue: October 1, 1991 First Issue Location: Pasadena, California Launched in November 1973, Mariner 10 approached Mercury on three separate occasions through March 1975, coming as close as 200 miles to the planet's surface and sending back data and photographs that show a world with amazing contrasts. Mercury has an ancient surface resembling the Earth's Moon, heavily scarred by meteor- ite impacts. One such crater is more than 500 miles across. The planet is also characterized by a feature unique to the Solar System — long, curved scarps (cliffs) that appear to be the result of compression on the planet's crust as it cooled. But on Mercury, cool is a relative term: the planet's surface temperature on the side facing the sun is 950°F. In contrast, Mercury's tenuous atmosphere of argon, neon and helium — a trillionth the density of Earth's atmosphere — retains virtually no heat on the planet's night side, with a resulting temperature of -350°F. Mariner 10 also revealed that Mercury has a weak mag- netic field, and that the small planet's core is likely comprised of iron. No. 91-78 ©1991 The Maximum Card Collection A division of Unicover Corporation • Cheyenne, WY 82008-0007 ® Artwork courtesy of NASA