The Pluto—Explored! souvenir sheet contains two stamp designs, an artist’s rendering of the New Horizons spacecraft, and the spacecraft’s image of Pluto taken at its closest approach.
Honoring Pluto with its own stamp helps skate around sentimental attachments to the former ninth planet, now reclassified, which might have prevented some fans from enjoying the Views of Our Planets stamp set, with just eight planets…. *sniff*
Your average science fiction reader probably includes Mercury, planet closest to the Sun, on the list of places where having “a snowman’s chance” is a bad thing. However, that depends where the snowman is standing. If it’s in a crater near Mercury’s north pole, he may be quite comfortable.
Two decades ago, Earth-based radar images of Mercury showed polar deposits that were predicted to consist of water ice. That was confirmed by NASA’s Mercury Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft through instrument measurements. Now MESSENGER also also provided optical images of the ice and other frozen volatile materials within the permanently shadowed craters around the planet’s north pole.
Nancy Chabot, the Instrument Scientist for MESSENGER’s Mercury Dual Imaging System (MDIS) and a planetary scientist at the Johns Hopkins University Applied Physics Laboratory is on her way to unraveling the next mystery:
“One of the big questions we’ve been grappling with is ‘When did Mercury’s water ice deposits show up?’ Are they billions of years old, or were they emplaced only recently?” Chabot said. “Understanding the age of these deposits has implications for understanding the delivery of water to all the terrestrial planets, including Earth.”
Overall, the images indicate that Mercury’s polar deposits either were delivered to the planet recently or are regularly restored at the surface through an ongoing process.