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What the Weather Is Like on Other Moons and Planets

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On Earth, we get snow, rain, fog, hail, and sleet, and all of them are basically the same thing: water. For a true change of weather, you need to go to other worlds. Here's a tour of what to expect on a trip through our solar system.

Mars: Dry Ice Snow

Scientists have known for years that the polar caps of Mars are made of a combination of water ice and dry ice (or frozen carbon dioxide—the same stuff that makes fog when you dump it into a pot of water). But how does it get there? The ice caps grow and recede with the seasons (in the Hubble images above, the carbon dioxide is receding with the onset of spring), so either the carbon dioxide is freezing directly out of the atmosphere, or it's snowing. Scientists working with data from Mars Reconnaissance Orbiter recently solved the puzzle: MRO detected clouds of carbon dioxide crystals, and clear evidence of snow falling out of them. The snow would not fall as flakes, but as tiny cuboctohedrons (which have eight triangular faces and six square faces). On the surface, Mars snow probably looks like granulated sugar.

Venus: Sulfuric Acid Rain

Once thought to be our sister planet, Venus is, in actuality, a hellhole. The surface is over 462 degrees C (864 degrees F)—easily hot enough to melt lead—and the atmospheric pressure is about 92 times the pressure on Earth at sea level. It's also bone dry (water is baked out of the soil). But high up above the slowly rotating surface, where the winds whip violently, Venus is enshrouded by clouds of sulfuric acid (shown here in ultraviolet light from the Hubble Telescope). When it rains, the acid falls down to about 25 km before evaporating—at these temperatures, even sulfuric acid can't stay liquid. The vapor rises back up to recondense as clouds, giving Venus a liquid cycle confined entirely to the upper atmosphere.

Io: Sulfur Dioxide Snow

Venus isn't the only hellhole in the solar system. Jupiter's moon Io would fit the bill pretty well, too. It's riddled with active volcanoes, covered in brimstone, and hiding a subsurface ocean of lava. And it snows the sort of snow you might get when Hell freezes over, because it too is made of brimstone: sulfur, and, more specifically, sulfur dioxide, which were detected when the Galileo orbiter flew through the volcanic plumes on its kamikaze mission in September 2003. Molten sulfur, heated to the boiling point below the surface of Io by torturous tidal flexing, sprays out of the volcanoes like a geyser would spray water on Earth. In the cold, airless void of space, the sulfur dioxide quickly crystalizes into tiny flakes; most of it falls back to the surface as a fluffy yellow snow. Galileo's sensors indicated that the particles were very small, perhaps 15-20 molecules apiece, so the snow would look extremely fine on the surface.  In the photo above, the broad white semi circle of material is sulfur dioxide snow from a plume called Amirani.

Titan: Methane Rain

Titan is Saturn's largest moon, and the pictures revealed by Cassini and the Huygens lander show a world that looks surprisingly Earthlike, with riverbeds, lakes, and clouds. (The radar image above shows the shores of Kraken Mare, the largest known lake on Titan, with rivers flowing into it.) But this is deceptive. Titan is much colder: What looks like rock is water ice, and what looks like water is natural gas. A methane cycle (much like the water cycle on Earth) exists on Titan, driving seasonal rains that follow patterns (much like the ones tropical monsoons follow on Earth). When the season is right, the rain falls, filling vast but shallow basins bigger than our Great Lakes. As the seasons change, the lakes slowly evaporate. The vapor makes its way up into the atmosphere and condenses into clouds; the clouds drift to the other hemisphere as the weather shifts, and when the rain falls, it starts the next loop of the cycle.

Enceladus: Water and Ammonia Snow

Enceladus is one of the most active moons of Saturn. The south polar region especially is riddled with geysers that shoot water and ammonia hundreds of miles into space. Most of that leaves Enceladus altogether, forming Saturn's E ring. The rest falls back down, forming deep, powdery snow that would put the best "white smoke" of the Rockies to shame. But the snow falls very slowly. By mapping the snowdrifts, scientists have found that although the snow barely accumulates over the course of a year, the snow has been falling on some spots for tens of millions of years. Because of this, the snowpack is over 100 meters deep. And it's all light, fluffy snow; an unwary skier might disappear into the powder if he hit a particularly deep patch. This photo above shows Cairo Sulcus, a grooved feature in Encealdus' active south, its sharp edges softened by millenia of gentle snowfall.

Triton: Nitrogen and Methane Snow

Titan is cold enough to liquify methane, but Neptune's moon Triton is colder still. Voyager 2 discovered that Triton's surface is suspiciously new, and it's not just from volcanic resurfacing; the southern polar region also appears to be covered partially in a light, fluffy material that could only be snow. But while our snow is white and Io's snow is yellow, Triton's snow is pink. It's made of a mixture of nitrogen and methane. Like Io and Enceladus, the snow comes from geysers that blast liquid high up into space, where it freezes into fine particles that fall down as snow onto a terrain pockmarked by nitrogen/methane permafrost. Because of its color and the curious texture of the southern polar region, scientists call it "cantaloupe terrain."

Pluto: Nitrogen, Methane, and Carbon Monoxide Snow

Pluto has an awful lot in common with Triton, and apparently that includes snow. Although Pluto has never been seen close-up, careful observations with the Hubble Space Telescope suggest that it experiences snows of nitrogen, methane, and possibly carbon monoxide. Like Triton, this makes its surface very pinkish. Depending on the process that desposits it (geysers or frost or "diamond dust" snowfall, where the stuff just freezes straight out of the air and falls), this could be a fine powder or big, spiky piles of frost. We'll know more when NASA's New Horizons spacecraft visits; right now, it's about halfway there.

Jupiter: Liquid Helium Rain

The environments on gas giant planets are extreme in many ways; one is that there is a depth within them at which the atmospheric pressure is so great that exotic forms of matter appear, such as metallic helium and hydrogen. If the models are correct, above Jupiter's rocky core lies a deep ocean of liquid metallic hydrogen. Helium is a little harder to compress into a metallic form, so it doesn't mix with this ocean. It is heavier than hydrogen, though; scientists believe it falls through the metallic hydrogen ocean like droplets falling through the atmosphere, until it gets deep enough to become metallic.

Uranus and Neptune: Diamond Rain

Uranus and Neptune aren't really Jovian worlds; they're much colder than Jupiter or Saturn, and contain high fractions of water, leading some to call them ice giants. Another thing they contain is methane—lots of it, pressurized into a liquid state inside the giant planets. Methane is a hydrocarbon; under the right conditions (and models predict such conditions on Uranus and Neptune), the carbon within it can crystallize out as tiny diamonds. On Earth, "diamond dust" means superfine particles of ice suspended in the atmosphere on very cold days, but the phrase might be more literally true on Uranus and Neptune. The diamonds aren't accessible; they continually rain down towards the interior of the planets to be lost forever in a vast diamond ocean.  Fans of Arthur C. Clarke may recognize this idea as part of the inspiration for "2061."

Bonus — The Sun: Plasma Rain

The Sun represents 99 percent of the mass in our solar system, so fittingly, it has what may be the most extreme precipitation in the solar system: plasma rain. Unlike the others on this list, you can actually see it from Earth. Huge loops of plasma are lifted up into space above the photosphere (what is generally considered the "surface" of the Sun) and suspended by magnetism, until finally something snaps and material is hurled violently into space in a coronal mass ejection. Not all of the material escapes, however; a lot of it falls back down as coronal rain. The video above, from June 7, 2011, was a particularly big and dramatic coronal mass ejection; look for the bright flashes as material impacts the photosphere.

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Courtesy Murdoch University
Australian Scientists Discover First New Species of Sunfish in 125 Years
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Courtesy Murdoch University

Scientists have pinpointed a whole new species of the largest bony fish in the world, the massive sunfish, as we learned from Smithsonian magazine. It's the first new species of sunfish proposed in more than 125 years.

As the researchers report in the Zoological Journal of the Linnean Society, the genetic differences between the newly named hoodwinker sunfish (Mola tecta) and its other sunfish brethren was confirmed by data on 27 different samples of the species collected over the course of three years. Since sunfish are so massive—the biggest can weigh as much as 5000 pounds—they pose a challenge to preserve and store, even for museums with large research collections. Lead author Marianne Nyegaard of Murdoch University in Australia traveled thousands of miles to find and collected genetic data on sunfish stranded on beaches. At one point, she was asked if she would be bringing her own crane to collect one.

Nyegaard also went back through scientific literature dating back to the 1500s, sorting through descriptions of sea monsters and mermen to see if any of the documentation sounded like observations of the hoodwinker. "We retraced the steps of early naturalists and taxonomists to understand how such a large fish could have evaded discovery all this time," she said in a press statement. "Overall, we felt science had been repeatedly tricked by this cheeky species, which is why we named it the 'hoodwinker.'"

Japanese researchers first detected genetic differences between previously known sunfish and a new, unknown species 10 years ago, and this confirms the existence of a whole different type from species like the Mola mola or Mola ramsayi.

Mola tecta looks a little different from other sunfish, with a more slender body. As it grows, it doesn't develop the protruding snout or bumps that other sunfish exhibit. Similarly to the others, though, it can reach a length of 8 feet or more. 

Based on the stomach contents of some of the specimens studied, the hoodwinker likely feeds on salps, a jellyfish-like creature that it probably chomps on (yes, sunfish have teeth) during deep dives. The species has been found near New Zealand, Australia, South Africa, and southern Chile.

[h/t Smithsonian]

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Gregory H. Revera, Wikimedia Commons // CC BY-SA 3.0
Study Suggests There's Water Beneath the Moon's Surface
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Gregory H. Revera, Wikimedia Commons // CC BY-SA 3.0

Astronauts may not need to go far to find water outside Earth. As CNN reports, Brown University scientists Ralph E. Milliken and Shuai Li suspect there are significant amounts of water churning within the Moon’s interior.

Their findings, published in the journal Nature Geoscience, lean on the discovery of glass beads encased in the Moon’s volcanic rock deposits. As recently as 100 million years ago, the Earth’s moon was a hotbed of volcanic activity. Evidence of that volatile time can still be found in the ancient ash and volcanic rock that’s scattered across the surface.

Using satellite imagery, the researchers identified tiny water droplets preserved inside glass beads that formed in the volcanic deposits. While water makes up a small fraction of each bead, its presence suggests there’s significantly more of it making up the Moon’s mantle.

Milliken and Li aren't the first scientists to notice water in lunar rocks. In 2008, volcanic materials collected from the Moon during the Apollo missions of 1971 and 1972 were revealed to contain the same water-flecked glass beads that the Brown scientists made the basis of their recent study. They took their research further by analyzing images captured across the face of the Moon and quickly saw the Apollo rocks represented a larger trend. "The distribution of these water-rich deposits is the key thing," Milliken said in a press statement. "They're spread across the surface, which tells us that the water found in the Apollo samples isn't a one-off. Lunar pyroclastics seem to be universally water-rich, which suggests the same may be true of the mantle."

The study challenges what we know about the Moon's formation, which scientists think occurred when a planet-sized object slammed into the Earth 4.5 billion years ago. "The growing evidence for water inside the Moon suggests that water did somehow survive, or that it was brought in shortly after the impact by asteroids or comets before the Moon had completely solidified," Li said. "The exact origin of water in the lunar interior is still a big question."

The findings also hold exciting possibilities for the future of space travel. NASA scientists have already considered turning the Moon into a water station for astronauts on their way to Mars. If water on the celestial body is really as abundant as the evidence may suggest, figuring out how to access that resource will definitely be on NASA's agenda.

[h/t CNN]


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