Views of Our Planets USPS Forever Postage Stamps Sheet of 16 Self-Adhesive 1 Sheet of 16 Stamps New Sheet of (16) Self Adhesive forever stamps issued by USPS Forever stamps, always valid for 1 ounce first class postage May 31, 2016 (Pre Order for May 31 shipping date) Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.