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Venus snow is a brightening of the radar reflection from the surface of
Venus
Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
at high elevations. The "snow" appears to be a mineral condensate of
lead sulfide Lead sulfide refers to two compounds containing lead and sulfur:
*Lead(II) sulfide
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is s ...
and
bismuth sulfide
Bismuth(III) sulfide () is a chemical compound of bismuth and sulfur. It occurs in nature as the mineral bismuthinite.
Synthesis
Bismuth(III) sulfide can be prepared by reacting a bismuth(III) salt with hydrogen sulfide:
: 2 Bi3+ + 3 H2S → Bi2S ...
precipitated from the atmosphere at altitudes above .
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The nature of the "snow" was initially unknown. In radar images, smooth surfaces such as lava plains generally appear dark, while rough surfaces such as impact debris appear bright. The composition of the rock also alters the radar return: conductive material, or material with a high
dielectric constant
The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulat ...
, appears brighter. It was therefore initially difficult to determine whether the high-altitude areas of Venus were different from the lowlands in chemical composition or in texture. Possible explanations included loose soil, different rates of weathering at high and low elevations, and chemical deposition at high elevation.
It could not be
water ice Water ice could refer to:
*Ice formed by water (as opposed to other substances)
*The alternate term for various similar frozen fruit-flavoured desserts:
**Italian ice primarily in Philadelphia and the Delaware Valley
**Sorbet
Sorbet (), also c ...
, which cannot exist in the extremely hot, dry conditions of the Venusian surface.
Data from the radar mapper on the
Pioneer Venus
The Pioneer Venus project was part of the Pioneer program consisting of two spacecraft, the Pioneer Venus Orbiter and the Pioneer Venus Multiprobe, launched to Venus in 1978. The program was managed by NASA's Ames Research Center.
The Pione ...
orbiter suggested an explanation in terms of chemical composition. It was hypothesized that the underlying rock contained
iron pyrite
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic luster and pale brass-yellow hue giv ...
or other metallic inclusions that would be very reflective. At the high temperatures found on the surface of Venus, these minerals would gradually evaporate. Faster
weathering
Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), ...
at high elevation might continually expose new material, causing the highlands to appear brighter than lowlands.
High-resolution radar observations by the
Magellan probe
The ''Magellan'' spacecraft was a robotic space probe launched by NASA of the United States, on May 4, 1989, to map the surface of Venus by using synthetic-aperture radar and to measure the planetary gravitational field.
The ''Magellan'' pro ...
by 1995 began to favor the hypothesis that metallic compounds sublimate in lower, warmer altitudes and deposit in higher, cooler areas.
Candidates included
tellurium
Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally fou ...
, pyrite, and other metal
sulfide
Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...
s.
External links
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References
{{Venus
Geology of Venus
Surface features of Venus