When the Sky Falls: Extraordinary Precipitation Across Our Solar System 🌧️
Earth: The Water World's Perfect Balance 🌍
Water vapor rises from oceans covering 71 percent of our surface, condenses around microscopic particles of dust and salt, and falls in drops ranging from fine drizzle at 0.02 inches (0.5 millimeters) to tropical downpours exceeding 0.24 inches (6 millimeters) in diameter. This perpetual cycle shapes continents, fills rivers, and sustains every ecosystem from rainforests to deserts. Earth experiences the solar system's most diverse precipitation, from snow and sleet to hail and freezing rain, each form revealing atmospheric conditions at different altitudes. This cycle has persisted for billions of years, with geological evidence of water-mediated processes extending back at least 3.8 billion years, making it one of our planet's most enduring features.
Mercury: The Sun-Scorched World Without Weather 🌡️
Mercury demonstrates the fundamental impossibility of precipitation without atmosphere. As the closest planet to our Sun, Mercury possesses only an exosphere so tenuous that molecules rarely collide, with a surface pressure less than 10⁻¹² bar, effectively a perfect vacuum. Without atmospheric pressure to support phase transitions or temperature moderation, Mercury experiences the solar system's most extreme temperature swings: 800 degrees Fahrenheit (430 degrees Celsius) in sunlight and minus 290 degrees Fahrenheit (minus 180 degrees Celsius) in darkness.Paradoxically, this airless world hosts water ice in permanently shadowed polar craters, delivered by impacts from comets and other volatile-bearing bodies and preserved for millions to billions of years. However, this ice cannot participate in any precipitation cycle. On Mercury, materials either sublimate directly to space or remain frozen in eternal shadow. The MESSENGER spacecraft (2011-2015) confirmed these ice deposits while mapping a world where the absence of weather has preserved impact craters billions of years old. Mercury stands as the solar system's starkest example of why precipitation requires not just volatile compounds, but atmospheric pressure to enable their transformation between states.
Venus: Where Acid Rain Vanishes Mid-Flight ☁️
Venus demonstrates how a planet can have rain that never reaches its surface. High in the Venusian atmosphere, specifically between 30 and 37 miles (48 to 60 kilometers) altitude where temperatures range from 32 to 140 degrees Fahrenheit (0 to 60 degrees Celsius), sulfuric acid forms through photochemical reactions when solar ultraviolet radiation breaks down sulfur dioxide and water vapor molecules. These acid droplets, concentrated at about 75 percent sulfuric acid, begin their descent through the dense carbon dioxide atmosphere, creating virga-like features interpreted as evaporating droplets beneath the cloud deck.However, this rain faces an impossible journey. As droplets fall into increasingly hot atmospheric layers, they evaporate completely before descending even halfway to the surface, creating virga that maintains a constant cycle of condensation and evaporation. Venus's surface remains the hottest in our solar system at 864 degrees Fahrenheit (462 degrees Celsius), hot enough to melt lead, due to an extreme greenhouse effect caused by its dense carbon dioxide atmosphere and heat-trapping cloud layers. The sulfuric acid cycle has likely operated for hundreds of millions of years, creating one of the solar system's most stable yet hostile precipitation systems.
Mars: The Planet That Lost Its Rain 🔴
Mars tells a story written in ancient riverbeds and mineral deposits formed by water interaction. Between 4.1 and 3.5 billion years ago, when Mars possessed a thicker atmosphere whose pressure remains debated among scientists, liquid water rain carved valley networks still visible today. These channels form extensive networks, with recent studies documenting over 9,300 miles (15,000 kilometers) of ancient riverbeds in regions like Noachis Terra, speaking of a warmer, wetter world where rain shaped landscapes for hundreds of millions of years.Modern Mars experiences only frozen precipitation in its thin atmosphere of 0.006 bar pressure. During winter, carbon dioxide freezes from the atmosphere at minus 195 degrees Fahrenheit (minus 125 degrees Celsius) and falls as dry ice snow at the poles, creating seasonal caps that advance and retreat. Water ice clouds form in the thin atmosphere, occasionally producing snow that sublimates before reaching the surface. The Phoenix Lander observed water ice snow falling through the Martian atmosphere in 2008, confirming theoretical predictions. Mars lost its precipitation through a complex process of atmospheric escape driven by solar wind, with the weakening of its magnetic field between roughly 4.1 and 3.5 billion years ago being one significant contributing factor.
Jupiter and Saturn: Giants with Complex Atmospheric Cycles 🪐
Within the vast atmospheres of our gas giants, precipitation occurs at multiple levels with different compositions. Both Jupiter and Saturn experience ammonia ice crystal formation in their upper atmospheres at pressure-dependent altitudes where temperatures reach approximately 150 Kelvin (minus 189 degrees Fahrenheit or minus 123 degrees Celsius). Lightning detected by the Galileo, Juno, and Cassini spacecraft confirms active storm systems where these crystals form clouds and likely fall as ammonia snow through progressively warmer layers until they evaporate and recycle.Deeper within these atmospheres, at pressures of tens of bars, water clouds are expected to form and potentially create water rain. The Galileo atmospheric probe reached pressures of about 22 bars in 1995 but descended through an unusually dry region, providing limited data about typical water cloud formation. At even greater depths, some models suggest conditions might allow carbon from decomposed methane to form diamonds, though this remains more speculative than in the ice giants.
Saturn adds a unique phenomenon directly measured during Cassini's Grand Finale orbits in 2017: ring rain. Charged water particles from the innermost rings follow magnetic field lines down to the planet's atmosphere at rates up to 22,000 pounds (10,000 kilograms) per second. This process has likely operated for millions of years and current models suggest it could eventually erode the rings entirely, though timescales remain uncertain, with estimates ranging from 100 million to 300 million years.
Uranus and Neptune: Where Diamonds May Fall 💎
If similar processes occur within these planets, diamonds could theoretically range from nanometer-scale to several centimeters in diameter based on formation time and conditions, sinking through approximately 5,000 miles (8,000 kilometers) of the planets' mantles before potentially settling into diamond-enriched layers. On Neptune, this hypothetical diamond precipitation represents one possible explanation for the planet's anomalous heat output of 2.6 times the energy it receives from the Sun, as gravitational energy would convert to heat during diamond descent, though primordial heat and slow atmospheric cooling likely contribute more significantly. While laboratory experiments confirm diamond formation is possible under the extreme conditions found within ice giants, the actual precipitation of diamonds through their atmospheres remains a compelling theoretical model rather than confirmed observation.
Pluto and the Dwarf Planets: Precipitation on Geological Timescales ❄️
Pluto, visited by New Horizons in July 2015, showcases precipitation operating on timescales that dwarf human comprehension. Over its 248-Earth-year orbit, nitrogen ice sublimates from regions receiving more sunlight and redeposits in colder areas, creating the bright heart-shaped plain of Sputnik Planitia. This nitrogen migration represents precipitation in extreme slow motion, with volatile ices flowing like glaciers at rates of centimeters per year.The spacecraft revealed that methane ice preferentially deposits on mountain peaks above 11,000 feet (3,350 meters), reversing Earth's altitude relationships due to atmospheric dynamics unique to Pluto. New Horizons measured Pluto's surface pressure at approximately 10 microbars, though this varies significantly with seasonal cycles and orbital position. Some models suggest that during periods of thicker atmosphere, conditions might theoretically support very tenuous nitrogen condensation, though this remains speculative.
Ceres, the asteroid belt's lone dwarf planet, exhibits minimal precipitation phenomena. The Dawn spacecraft (2015-2018) revealed bright spots of sodium carbonate and ammonium chloride in Occator Crater, likely deposited when subsurface brines reached the surface through cryovolcanism, immediately boiled in the vacuum, and redeposited as salts, creating bright crystalline deposits that coat the crater floor like cosmic sea salt. Eris and Makemake, more distant dwarf planets, likely experience methane and nitrogen frost cycles similar to Pluto, though no spacecraft has visited them.
Our Moon: The Absence That Defines Precipitation 🌙
While dwarf planets at the solar system's edge showcase precipitation operating over geological timescales, our own Moon, remarkably close yet utterly dry, offers essential perspective through absence. Earth's Moon exemplifies why precipitation remains rare in our solar system. Without atmosphere to support clouds or rain, the Moon experiences only molecular-scale water migration discovered through observations by multiple spacecraft including NASA's Lunar Reconnaissance Orbiter, Chandrayaan-1, and ground-based telescopes. Solar wind protons interact with oxygen in lunar minerals to create hydroxyl and water molecules at parts-per-million concentrations. These molecules hop across the surface with temperature swings between minus 280 degrees Fahrenheit (minus 173 degrees Celsius) at night and 260 degrees Fahrenheit (127 degrees Celsius) in sunlight.This molecular migration, while not precipitation, demonstrates water movement even on airless worlds. The absence of weather means the lunar surface consists entirely of regolith, a powdery layer of impact-shattered rock untouched by rain or wind erosion. Permanently shadowed polar craters trap migrating molecules as ice deposits potentially billions of years old. As we observe the Moon through its phases from Earth (related article), or watch Earth's shadow cross its surface during a lunar eclipse, we witness a world frozen in time. The complete absence of weather helps us appreciate how special precipitation is, requiring the precise combination of atmosphere, temperature variations, and volatile compounds that most worlds lack.
Titan: Where Methane Falls Like Earthly Rain 🌊
Saturn's moon Titan stands alone with its thick atmosphere of 1.5 bar pressure and complete methane precipitation cycle. Operating at minus 290 degrees Fahrenheit (minus 179 degrees Celsius), methane on Titan behaves like water on Earth. Cassini radar data from 2004 to 2017 revealed extensive methane lakes and channels, while atmospheric models suggest methane rain falls in drops approximately 0.37 inches (9.5 millimeters) in diameter at just 5.2 feet per second (1.6 meters per second), creating an almost dreamlike descent through the orange haze.During Titan's seasons, each lasting 7.5 Earth years, intense storms can release decades worth of precipitation within hours. The Huygens probe, landing in January 2005, detected methane moisture in the soil and photographed rounded cobbles shaped by liquid flow. Cassini observed large storm systems carving channels and filling lakes that shift with seasons. The Dragonfly rotorcraft mission, launching in July 2028 and arriving in 2034, will directly sample this precipitation cycle.
Europa and Ganymede: Hidden Ocean Dynamics 🧊
Jupiter's large icy moons likely host subsurface precipitation invisible from space. Europa's global ocean lies beneath an ice shell often estimated at roughly 9 to 16 miles (15 to 25 kilometers) thick, with some analyses allowing thicknesses approaching 19 miles (30 kilometers). Models published in 2022 suggest that when ice forms on the ocean ceiling, salt exclusion creates fresher ice that's less dense than the salty water below, causing it to "snow" upward through the ocean. This process could transport nutrients and energy between ocean layers.Ganymede, the solar system's largest moon, likely hosts similar processes in its subsurface ocean beneath ice estimated at tens to over 100 miles (tens to over 150 kilometers) thick in many models. Hubble Space Telescope observations have detected water vapor around Europa, though the existence and nature of plumes remains contested among scientists. At Ganymede, detected water vapor appears linked to ice sublimation from the surface rather than erupting plumes. The Europa Clipper mission, arriving in 2030, will investigate these processes in detail.
Enceladus: Cryovolcanic Snow Globe ⛲
Saturn's small moon Enceladus demonstrates the most visually spectacular extraterrestrial precipitation. Through four tiger stripe fractures at the south pole, tidal heating drives water geysers that shoot ice particles up to 300 miles (500 kilometers) into space. Cassini flew through these plumes multiple times between 2005 and 2017, directly sampling the precipitation that continuously deposits fresh ice on the surface.The erupted material ranges from nanometer-sized ice crystals to millimeter-scale particles, falling back at various rates depending on size and ejection velocity. Estimates place Enceladus's plume output at roughly hundreds of kilograms per second, with only a fraction escaping to supply Saturn's E ring, while the rest falls back as snowfall that gradually accumulates on the surface. This process maintains Enceladus as one of the most reflective objects in our solar system with a Bond albedo around 0.8, giving it a brilliant white appearance.
Io and Callisto: Extremes of Volcanic and Ancient Surfaces 🌋
Io showcases frequent sulfur dioxide precipitation driven by extreme volcanism. With over 400 active volcanoes launching SO₂ up to 300 miles (500 kilometers) high, this compound freezes in space and falls back as yellow-white snow, particularly on the night side where temperatures drop to minus 230 degrees Fahrenheit (minus 145 degrees Celsius). This creates a regular cycle of sublimation and deposition that can resurface areas within years. For a deeper exploration of Io's volcanic activity and its role in shaping this remarkable moon, see our related article: 🌋 Io: Jupiter’s Volcanic MoonCallisto, by contrast, preserves an ancient surface largely unchanged for billions of years, serving as a geological time capsule with no active precipitation. As Jupiter's outermost large moon, it lacks the tidal heating that drives activity on other Galilean satellites. Its heavily cratered surface has remained largely unchanged for billions of years, preserving a record of the early solar system when impact bombardment, not precipitation, shaped worlds.
Triton: Neptune's Captured World 🎇
Triton exhibits nitrogen geyser-driven precipitation unique in the outer solar system. Dark streaks first observed by Voyager 2 in 1989 result from nitrogen geysers powered by faint solar heating through transparent nitrogen ice. These eruptions carry dark organic particles up to 5 miles (8 kilometers) high, where Triton's tenuous winds at 5-10 meters per second carry them downwind before deposition.This exotic precipitation occurs at minus 391 degrees Fahrenheit (minus 235 degrees Celsius), where seasonal solar heating drives sublimation and venting processes. The deposits create wind streaks up to 95 miles (150 kilometers) long, representing precipitation at the edge of thermodynamic possibility in the outer solar system.
When Every World Weeps Differently 🌌
From Earth's life-sustaining water cycle to the methane rains of Titan, from Venus's vanishing acid droplets to Neptune's hypothetical diamond precipitation, each world in our solar system tells its own story through the materials that fall from its skies. These diverse forms of precipitation reveal fundamental principles of planetary science: phase transitions, atmospheric dynamics, and the interplay between temperature, pressure, and chemistry. Understanding these alien weather systems deepens our appreciation for the delicate balance that makes Earth's familiar rain possible, while expanding our perspective on the remarkable processes shaping worlds throughout the cosmos.Share the Wonder 🌟
Let these stories of distant rains inspire conversations about the magnificent diversity of our cosmic neighborhood.We kindly invite you to share and spread the word. Your support in sharing this journey through the extraordinary weather of other worlds helps more people discover the wonders that lie beyond our blue skies. Together, we can inspire curiosity about the remarkable phenomena occurring throughout our solar system.
💡 Did You Know?
🌡️ Earth's Goldilocks Zone: Our planet remains the only known world where water naturally cycles through solid, liquid, and gas phases at temperatures life can tolerate, a range of just 32 to 212 degrees Fahrenheit (0 to 100 degrees Celsius).
💎 Neptune's Energy Puzzle: Diamond precipitation is one hypothesis for why Neptune emits 2.6 times more energy than it receives from the Sun, as falling diamonds would convert gravitational potential to heat.
🐌 Titan's Dreamlike Descent: Methane raindrops on Titan fall approximately six times slower than Earth rain due to low gravity and high atmospheric density, creating an ethereal precipitation experience.
🙃 Europa's Inverted Blizzard: Salt-depleted ice in Europa's ocean becomes buoyant and snows upward, potentially creating inverted blizzards beneath the ice shell.
🏔️ Pluto's Altitude Reversal: Methane frost coats Pluto's mountain peaks while valleys remain bare because atmospheric dynamics at extremely low pressure reverse Earth's elevation patterns.
⏰ Saturn's Ring Rain Intensity: Cassini measured up to 22,000 pounds (10,000 kilograms) of water falling from Saturn's rings every second, enough to fill an Olympic swimming pool in half an hour.
🌍 Mars's Lost Ocean: Evidence suggests ancient Mars had enough water for a global ocean 450 feet (137 meters) deep, lost through complex atmospheric escape processes including solar wind stripping.
🎨 Io's Volcanic Canvas: Sulfur dioxide snow constantly repaints Io's surface, with dramatic changes occurring within days near active volcanic regions.
🔬 Diamond Formation Validated: Scientists created nanodiamonds in 2017 laboratories by replicating ice giant interior conditions, supporting theoretical models of diamond precipitation.
📏 Cassini's Final Gift: During its 2017 Grand Finale, Cassini discovered Saturn's ring rain by diving between the planet and rings 22 times before its planned destruction.
❓ FAQ
How do scientists know about rain on other planets without direct observation?
Scientists combine multiple lines of evidence including spectroscopic analysis that identifies chemical compositions, spacecraft imaging of surface features and atmospheric phenomena, laboratory experiments recreating planetary conditions, and computer models based on known physics. For example, Cassini's radar penetrated Titan's haze to map methane lakes and channels, while spectroscopy confirmed their methane composition. Mars rovers analyzed minerals that only form through water interaction, while Venus Express measured sulfuric acid concentrations in clouds.
Which world has the most Earth-like rain?
Titan claims this distinction despite using methane instead of water. Its complete hydrological cycle includes evaporation from lakes, cloud formation at 10-30 miles (16-48 kilometers) altitude, rainfall that carves channels, and surface collection in seas. The timescales and patterns mirror Earth's water cycle remarkably, just occurring at much colder temperatures with different chemistry.
Could these exotic rains support life?
Titan's methane cycle might support hypothetical hydrocarbon-based life, though none has been detected. Ancient Mars likely had habitable conditions during its wet period 3.5-4 billion years ago. Europa and Enceladus have subsurface water cycles that could potentially support microbial life. Even Venus's upper atmosphere where sulfuric acid droplets form has been proposed as potentially habitable for acid-resistant microbes, though this remains highly speculative.
What determines whether a world can have precipitation?
Three key requirements must align: sufficient pressure and temperature conditions for phase transitions (varying widely by substance, as water needs different conditions than methane or nitrogen), volatile materials that can cycle between states, and a mechanism to drive that cycling. Earth, Venus, and Titan meet these criteria with different chemicals and pressure-temperature regimes. Mars once supported liquid water precipitation under thicker atmospheric conditions but lost that capability. Most moons lack sufficient atmosphere for traditional precipitation, though some exhibit alternative mechanisms like Enceladus's geyser-driven ice precipitation or Europa's theorized underwater snow, demonstrating that phase transitions can occur through various energy sources beyond atmospheric cycles.
How long do these precipitation cycles last?
Duration varies dramatically across worlds. Earth's water cycle has persisted nearly 4 billion years. Titan's methane cycle operates on seasonal timescales of 29.5 Earth years. Venus's sulfuric acid cycle has likely continued for hundreds of millions of years. Mars experienced liquid water rain for hundreds of millions of years before atmospheric loss, though the precise duration remains debated. The theoretical diamond rain on ice giants would be ongoing processes lasting billions of years. Pluto's nitrogen cycle operates over its 248-year orbit.
Is the diamond rain on Neptune and Uranus valuable?
While these diamonds might range from microscopic to potentially boulder-sized given billions of years of accumulation, their inaccessibility makes them economically meaningless. Located thousands of miles deep at pressures exceeding 1.5 million atmospheres and temperatures around 8,500 degrees Fahrenheit (4,700 degrees Celsius), they remain forever beyond reach. The energy required to reach and return from these planets would exceed Earth's entire economic output by orders of magnitude.
What future missions will study precipitation on other worlds?
NASA's Dragonfly will launch in July 2028 and arrive at Titan in 2034 to directly study methane rain effects. Europa Clipper, arriving in 2030, will investigate water plumes and subsurface ocean dynamics. Proposed Venus balloon missions could sample cloud-level chemistry where acid rain forms. The Uranus Orbiter and Probe, under consideration for the 2030s, could study ice giant atmospheres where diamond rain occurs. VERITAS is currently planned to launch no earlier than 2031, with ESA's EnVision also targeting November 2031.
How does studying rain on other worlds help us understand Earth?
Comparative planetology reveals universal versus unique aspects of precipitation. Venus demonstrates runaway greenhouse effects that inform climate science. Mars shows consequences of atmospheric and magnetic field loss. Titan provides insights into organic chemistry in a reducing atmosphere similar to early Earth. These studies improve our climate models, weather prediction capabilities, and understanding of habitability conditions.
Could humans ever witness these phenomena safely?
Only from within heavily protected environments. Every non-Earth precipitation would prove fatal: Titan's minus 290 degrees Fahrenheit (minus 179 degrees Celsius) methane rain, Venus's concentrated sulfuric acid, the extreme pressures where diamond rain occurs, or Io's radiation-bathed sulfur snow. Future explorers might observe these phenomena through specialized spacecraft windows or experience them through virtual reality based on robotic probe data.
What role does magnetism play in precipitation?
Magnetic fields dramatically influence certain precipitation types. Saturn's ring rain follows magnetic field lines, creating concentrated fall zones at specific latitudes. Jupiter and Saturn's powerful magnetic fields affect charged particles in storms, influencing lightning and precipitation patterns. Mars lost its protective magnetic field between roughly 4.1 and 3.5 billion years ago, allowing solar wind to strip its atmosphere and end its precipitation cycles.
How do scientists detect chemical compositions of distant rain?
Spectroscopy serves as the primary tool, analyzing how molecules absorb and emit light at specific wavelengths. Each chemical has unique spectral fingerprints: methane shows strong absorption at 2.3 micrometers, while sulfuric acid has distinctive features at 11.2 micrometers. Ground-based telescopes, space telescopes, and spacecraft instruments combine to identify atmospheric compositions. Laboratory experiments then recreate conditions to verify how these chemicals behave.
Do any worlds have seasonal precipitation like Earth?
Titan exhibits the most Earth-like seasonal precipitation, with methane storms intensifying during its 7.5-year seasons. Mars's polar regions show seasonal carbon dioxide snow accumulation and sublimation. Pluto experiences extreme 124-year seasons driving nitrogen migration between hemispheres. However, no world matches Earth's complex monsoons and regional patterns driven by ocean-atmosphere interactions and continental geography.
How fast does rain fall on different worlds?
Terminal velocity depends on gravity, atmospheric density, and droplet size. Earth rain falls at 6.5-30 feet per second (2-9 meters per second) depending on drop size. Titan's methane rain descends at just 5.2 feet per second (1.6 meters per second) due to low gravity and thick atmosphere. On Venus, sulfuric acid droplets never reach terminal velocity before evaporating. Any hypothetical rain on Mars would fall faster than Earth's despite lower gravity due to the thin atmosphere.
Could comets be considered a form of cosmic precipitation?
While not atmospheric precipitation, cometary impacts represent material transfer between celestial bodies. Earth's water arrived through various sources including cometary bombardment during the Late Heavy Bombardment 3.8-4.1 billion years ago. Comets continue delivering water ice to airless bodies like the Moon and Mercury, creating temporary atmospheres and frost deposits. In the outer solar system, cometary impacts on icy moons might trigger localized geyser activity.
Can precipitation occur without an atmosphere?
Yes, as several moons demonstrate alternative precipitation mechanisms. Enceladus's geysers create ice crystal precipitation in near-vacuum conditions. Europa's subsurface ocean likely has underwater snow. Io's volcanic plumes generate localized sulfur precipitation despite minimal atmosphere. These examples show phase transitions creating precipitation can occur through volcanic, tidal, or other energy sources beyond traditional atmospheric cycles.
What would be needed to terraform a planet for Earth-like rain?
Creating Earth-like precipitation requires precise conditions: atmospheric pressure between 0.5-2 bar, temperatures permitting liquid water (32-212 degrees Fahrenheit or 0-100 degrees Celsius), and abundant water vapor. Mars would need massive atmospheric thickening through releasing polar CO₂ and importing volatiles. Venus requires cooling by 750 degrees Fahrenheit (400 degrees Celsius) and removing 90 bars of CO₂ atmosphere. These challenges remain beyond any conceivable technology for centuries or millennia.
How do ring systems create precipitation?
Saturn demonstrates the most dramatic ring precipitation. Micrometeorite impacts and solar radiation charge ring particles, which then follow magnetic field lines spiraling into the atmosphere. Cassini's 2017 observations revealed this "ring rain" deposits up to 22,000 pounds (10,000 kilograms) per second of water onto Saturn. Jupiter's faint rings contribute minimal material. The process requires both substantial rings and strong magnetic fields.
What can ancient Earth teach us about rain on other worlds?
Early Earth's dramatically different atmosphere provides templates for understanding other worlds. Before the Great Oxidation Event 2.4 billion years ago, Earth's reducing atmosphere resembled modern Titan more than today's Earth. Studying banded iron formations and other geological evidence reveals how precipitation chemistry evolved with atmospheric composition. The transition from a methane-rich to oxygen-rich atmosphere shows how worlds can fundamentally transform their precipitation. Early Earth may have experienced methane rain similar to Titan, while Venus potentially represents what happens when greenhouse effects eliminate water-based precipitation entirely.
Have we directly sampled precipitation from any world besides Earth?
Yes, though limited. The Huygens probe detected methane moisture when landing on Titan in 2005 and analyzed surface evidence consistent with recent rainfall. Cassini flew through Enceladus's water ice geysers multiple times, directly sampling the plume particles that fall back as snow. Various Mars rovers have analyzed water ice frost that forms overnight. The Stardust mission collected comet particles that represent the primordial materials from which planetary precipitation ultimately derives. However, we have not returned a captured sample of liquid rain from another world.
What are the most extreme precipitation conditions in our solar system?
Diamond rain on Neptune and Uranus would occur at the most extreme hypothesized conditions: 1.5 million atmospheres pressure and 8,500 degrees Fahrenheit (4,700 degrees Celsius). For accessible precipitation, Titan's methane rain at minus 290 degrees Fahrenheit (minus 179 degrees Celsius) represents the coldest liquid precipitation. Venus's sulfuric acid rain is the most corrosive. Io experiences the most rapid surface changes from precipitation, with sulfur compounds capable of resurfacing areas within days near active volcanoes.
How might precipitation differ on exoplanets?
Exoplanets likely host precipitation beyond our solar system's examples. Hot Jupiters like WASP-76b may experience iron rain, with vaporized iron on the day side condensing on the cooler night side. Super-Earths in habitable zones might have water rain with droplet sizes and fall rates unlike Earth's due to different gravities and atmospheric densities. Tidally locked planets could have permanent precipitation zones at the day-night boundary. Brown dwarfs might experience silicate or salt rain at various atmospheric levels.
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