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This image has been shared hundreds of thousands of times on social media channels (especially facebook and tumblr), but is it really like this? Sure, it rains water on Earth… but can it really rain methane? Or iron… or diamonds? Let’s find out.

Does it rain sulfuric acid on Venus?

Venus is the second planet from the Sun, and in many ways, it is just like Earth. It’s pretty similar in size, mass, composition and even proximity to the Sun. But that’s where the similarities end. The atmosphere of Venus is composed of carbon dioxide, 96.5% by volume. Most of the remaining 3.5% is nitrogen. Its atmosphere is extremely dense, and it’s estimated that the atmospheric mass is 93 times that of Earth’s atmosphere, whereas the pressure at the planet’s surface is about 92 times that at Earth’s surface. Early evidence pointed to the sulfuric acid content in the atmosphere, but we now know that that is a rather minor constituent of the atmosphere.

The atmosphere on Venus is mostly made of Carbon Dioxide, with small quantities of sulfuric acid. Image via Daily Galaxy.

The atmosphere on Venus is mostly made of Carbon Dioxide, with small quantities of sulfuric acid. Image via Daily Galaxy.

Because CO2 is a greenhouse gas, the temperature on Venus is at least 462 °C – much higher than that of Mercury, which is much closer to the Sun. The surface of Venus can be accurately described as hellish. Venus has clouds which may extend from about 50 to 70 km; beneath the clouds, there is a layer of haze down to about 30 km and below that it is clear. Above the dense CO2 layer there are thick clouds consisting mainly of sulfur dioxide and sulfuric acid droplets.

The thing is, there is no rainfall on the surface of Venus – while sulfuric acid rain falls in the upper atmosphere, it evaporates around 25 km above the surface. Also, sulfur dioxide concentrations in the atmosphere, which dropped by a factor of 10 between 1978 and 1986, which suggests that the sulfur in the atmosphere actually comes from volcanic eruptions. The clouds are also extremely acidic and there is also lightning on Venus. The sulphuric acid droplets can be highly electrically charged, and so they offer the potential for lightning. The European Space Agency has a mission (Venus Express) studying the clouds and atmosphere on Venus

Verdict: It does rain sulfuric acid on Venus, but not on the surface, 25 km high in the atmosphere. The sulfur may come from volcanic eruptions.

Does it rain Glass on HD 189733b?

PHOTO: Turbulent alien world: An illustration depicting HD 189733b (AFP: ESA/NASA)

HD 189733b is an extrasolar planet approximately 63 light-years away from the Solar System. The planet was discovered in 2005. With a mass 13% higher than that of Jupiter, HD 189733 b orbits its host star once every 2.2 days, making it a so-called hot Jupiter. Hot Jupiters are a class of extrasolar planets whose characteristics are similar to Jupiter, but that have high surface temperatures because they orbit very close to their star.

Diagram showing how a smaller object (such as an extrasolar planet) orbiting a larger object (such as a star) could produce changes in position and velocity of the latter as they orbit their common center of mass (red cross).

The planet was discovered using Doppler spectroscopy – an indirect method for detecting extrasolar planets. Basically, you don’t observe the planet itself, you study its stars and notice any tiny wobbles in it with Doppler shifts. In 2008, a team of astrophysicists managed to detect and monitor the planet’s visible lightthe first such success in history. This result was further improved by the same team in 2011. They found that the planet albedo is significantly larger in blue light than in the red. But the blue doesn’t come from an ocean or some watery surface – it comes from a hazy, turbulent atmosphere believed to be laced with silicate particles – the stuff of which natural glass is made.

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The planet has incredibly fast winds and the estimated temperature of over 1000 degrees Celsius, so the rain is likely more horizontal than vertical.

“It rains glass, sideways, in howling 7,000 kilometre-per-hour winds,” Frederic Pont of the University of Exeter.

Verdict: We don’t know for sure, but it likely rains silicate particles (you can consider them glass) on the planet we call HD 189733b.

Does it rain Diamonds on Neptune?

Neptune is the eighth and farthest planet from the Sun in the Solar System (sorry Pluto). Neptune’s composition is similar to that of Uranus and different to that of gas giants like Saturn and Jupiter. Neptune’s atmosphere, like Jupiter’s and Saturn’s, is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen; however, it contains a higher proportion of “ices” such as water, ammonia, and methane.

Neptune,_Earth_size_comparison

Image via Wiki Commons.

Neptune’s weather is characterized by extremely dynamic storm systems, with winds reaching speeds of almost 600 m/s (2160 km/h). The abundance of methane, ethane, and ethyne at Neptune’s equator is 10–100 times greater than at the poles. It has been theorized that Uranus and Neptune actually crush methane into diamonds, and lab experiments seemed to confirm that this is possible. However, you need significant pressures to do that, and you need to go some 7000 km inside the planet – but keep in mind, the planet is made out of gas (grossly 80% hydrogen, 19% helium and 1% methane).

“Once these diamonds form, they fall like raindrops or hailstones toward the center of the planet,” said Laura Robin Benedetti, a graduate student in physics at UC Berkeley.

It’s estimated that at a depth of 7000 km, the conditions may be such that methane decomposes into diamond crystals that rain downwards like hailstones.

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Verdict: It likely rains diamonds on Neptune, but not on the surface, but 7000 km deep in the gas planet.

Does it rain Iron on OGLE-TR-56b?

Size comparison of OGLE-TR-56b with Jupiter. Image via Wiki Commons.

Out of all the planets here, we know the least about OGLE-TR-56b. Astronomers from the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge detected it back in 2003. At the time, it was the farthest planet ever discovered.

It’s estimated that the temperature on the surface of the planet is almost 2000 degrees Celsius, which is theoretically just right to form clouds, not of water vapor, but of iron atoms. We have no direct information to confirm this… but it is possible – it’s a theory just as good as any.

Verdict: We don’t know if it rains iron on OGLE-TR-56b… but it’s certainly possible. 

Does it rain Methane on Titan?

Titan is he largest moon of Saturn. It is the only natural satellite known to have a dense atmosphere, and the only object other than Earth where clear evidence of stable bodies of surface liquid has been found. Titan has seas made of hydrocarbon, lakes, mountains, fog, underground water oceans and yes, it does rain methane on Titan. In fact, Earth and Titan are the only worlds in the Solar System where liquid rains on a solid surface – though on Titan, the rain is methane.

Titan globe. Image via Wiki Commons.

Interestingly enough, in many ways, the weather on Titan is similar to that on Earth. The climate—including wind and rain—creates surface features similar to those of Earth, such as dunes, rivers, lakes, seas (probably of liquid methane and ethane), and deltas, and is dominated by seasonal weather patterns as on Earth. With its liquids (both surface and subsurface) and robust nitrogen atmosphere, Titan’s methane cycle is viewed as an analogy to Earth’s water cycle, although at a much lower temperature. Titan gets 100 times less solar radiation than Earth, so the average surface temperature is about −179 °C. At this temperature water ice has an extremely low vapor pressure, so the atmosphere is nearly free of water vapor. However, the methane in the atmosphere causes a substantial greenhouse effect which keeps the surface of Titan at a much higher temperature than would happen otherwise.

The terrain on Titan is likely not made up of small grains of silicates like the sand on Earth, but rather might have formed when liquid methane rained and eroded the ice bedrock, possibly in the form of flash floods. The satellite even has dunes, much like Earth’s own deserts.

Titan’s internal structure. Image via NASA.

Clouds typically cover 1% of Titan’s disk, though outburst events have been observed in which the cloud cover rapidly expands to as much as 8%. The weather on Titan is dominated by Saturn; it was summer in Titan’s southern hemisphere until 2010, when Saturn’s orbit, which governs Titan’s motion, moved Titan’s northern hemisphere into the sunlight.

Verdict: It does rain methane on Titan.

 

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