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Frosty Worlds

by Perry Pezzolanella

The days are getting shorter and a chill hangs in the air as the nights and frosty mornings return creating a fantasy-like world with white on everything. Especially beautiful is when the sun's first rays light up objects under a deep blue sky and rosy-rimmed horizon. Everything glitters like millions of diamonds, but nothing lasts forever, and soon the beauty is gone. Earth is blessed with a unique environment where water can co-exist as a solid, liquid, and vapor. Frost is common everywhere in the Solar System from frigid Pluto, to the moons of the outer planets, Mars, and even the torrid surfaces of Venus and Mercury. It may seem strange to consider frost in odd places, but frost does not have to be made of water.

Mercury: It is known that there are frost deposits in the deep and perpetually dark craters near the poles where the temperature always hovers around -300 degree F. MESSENGER confirmed in late 2012 that the frost is made of water. A future orbiter, BepiColombo, will further determine the extent and volume of the ice sometime in the early 2020's and a future lander may directly sample and analyze the ice. In spite of the 800 degree F heat, comets impacting Mercury could deliver water vapor to the surface where some of it could freeze near the poles.

Venus: Is it really possible to have frost on a world where the average surface temperature is 870 degree F day and night? The highest mountain peaks are as chilly as 650 degree F to 750 degree F and may be cool enough where certain metallic compounds such as lead sulfide and bismuth sulfide, cooked out of the rocks in the hotter lowlands, condense as a thin layer of frost. Radar images of the surface show the high peaks being unusually reflective indicating something is condensing at the cooler, higher elevations. The intense heat, pressure, and sulfuric acid mist all conspire to create some rapid and nasty chemical reactions; metal frost could be a byproduct.

Earth and Moon: Water rules on a world ranging from -130 degree F to 130 degree F and frost is entirely made of water. It has been confirmed that the perpetually dark, deep craters at the Moon's poles have frosty deposits of water ice where it is always colder than -250 degree F.

Mars: Carbon dioxide is the key ingredient on a world that averages -64 degree F and is as cold as -190 degree F. Carbon dioxide and water vapor freeze out of the atmosphere and are visible as white polar ice caps. The frost is actually a crushing layer that was thick enough to collapse the solar panels on the Phoenix lander long after it ceased functioning. Due to the low atmospheric pressure of 1/100th Earth's, the frost sublimates instead of melting with warmer weather, and returns to the atmosphere as gas once again.

Jupiter: Jupiter has no solid surface and neither do Saturn, Uranus, and Neptune so it would be the moons of these worlds that would have frost. Vapor from Io's volcanoes freeze in the -200 degree F cold to form a deposit of fresh white sulfur dioxide ice on this pizza-colored world. Europa has deposits of water ice and sulfur dioxide ice near many of the cracks on its smooth surface. Ganymede has slight but obvious polar ice caps of water ice. Callisto has patches of water ice and carbon dioxide ice on it surface.

Saturn: Ice abounds on all its moons with water ice dominating most. Enceladus is the gem with active geysers spewing true water ice hundreds of miles into the sky and coating the surface with highly reflective frost. Enceladus is the most reflective world of all with 95% of the sunlight being reflected and makes it an unusually cold world at -330 degree F. Titan is a little warmer at -290 degree F thanks to a thick atmosphere of nitrogen, methane, and hydrocarbons and has lakes and seas of methane, ethane, and other hydrocarbons. The frigid highlands could be covered with frosts of water ice and methane or other compounds. Iapetus is a strange moon with one side as bright as snow and the other as dark as coal. Water ice is the key player that produces the strange appearance of this odd moon.

Uranus: It is brutally cold, nearly -350 degree F and the Sun is no brighter than twilight on Earth so ice abounds and is as hard as rock. The frost that prevails is methane. Umbriel has a few impact craters that have bright splotches of methane ice or frost. Oberon, Titania, and Ariel also appear to have frosty deposits of methane, but a future spacecraft, preferably a dedicated Uranus orbiter, will be needed to determine the composition, amount, and extent of the frost and ice on these moons along with Miranda.

Neptune: Nitrogen is the dominant frost on Triton with an ice cap of nitrogen frost that evaporates from the summer pole and condenses on the winter pole. Methane frost also covers Triton and the ultraviolet radiation from the sun damages the frost and reddens it giving Triton a pinkish tint. It is a brutally cold world at -392 degree F.

Pluto: This is an odd world because the highly elliptical orbit creates a range in temperature from -380 degree F to -420 degree F, which causes the atmosphere to freeze out onto the surface when it moves to the most distant part of its orbit where it is the coldest. Nitrogen and methane frost are dominant but there may be vast frosty deposits of carbon dioxide, carbon monoxide, oxygen, and even argon. New Horizons will finally determine the extent of the frost and its composition when it flies by on July 14, 2015.

The vistas from the surfaces of these worlds with peaks and plains covered with exotic frost in environments from lead-melting heat to bone-shattering cold are fascinating and unlike anything we could ever comprehend. Proof is as close as our own backyard on a chilly autumn morning if we take a moment to appreciate the beauty of frost through the magic of the miracle, life-essential liquid known as water.