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Education:
Grades 5-8

A primer on clouds and aerosols for grades 5 through 8.

Clouds on Earth

Clouds on Earth are formations in the atmosphere consisting of numerous tiny water droplets or ice crystals suspended in the air. They form when water evaporates from oceans, lakes, and rivers, turning into water vapor. As the vapor rises and cools, it condenses around microscopic particles known as aerosols, which act as cloud condensation nuclei. These condensed droplets eventually gather to form visible clouds. When droplets grow too heavy, they fall as precipitation — rain or snow — under the influence of gravity. Clouds play a crucial role in Earth’s climate by reflecting sunlight back into space, which can cool the planet, or by trapping heat and radiating it back to the surface, contributing to warming.

Photo of clouds over the ocean taken from the space shuttle in 1982.
Clouds and open seas in the Bahamas as taken by the crew of the space shuttle Columbia in 1982.
Credit: NASA

Clouds on Other Planets

Clouds on planets beyond Earth exhibit diverse compositions due to varying atmospheric conditions:

Venus

The planet’s thick atmosphere is dominated by clouds of sulfuric acid, covering its entire surface. These clouds reflect a significant amount of sunlight away from Venus and contribute to its extreme heat by trapping heat below them.

Two views of the planet Venus from the Mariner 10 spacecraft.
Two photos of Venus clouds taken by the Mariner spacecraft that flew by the planet in 1974.
Credit: NASA

Mars

Clouds on Mars consist of ice crystals and carbon dioxide, observed mostly during specific seasons and in regions with significant topographical features. Water ice clouds are thin and patchy and usually observed in the winter season.

A photo of water ice clouds taken by a NASA satellite orbiting Mars.
Image of water ice clouds on Mars taken from the Mars Global Surveyor Orbiter.
Credit: NASA/JPL-Caltech
A photo of frozen carbon dioxide clouds on Mars taken by the NASA Mars Rover Curiosity.
A photo of frozen carbon dioxide clouds on Mars taken by the NASA Mars Rover Curiosity.
Credit: NASA/JPL-Caltech

Jupiter and Saturn

These gas giants have clouds composed of different substances at various atmospheric levels. Water ice clouds form at deeper levels, while higher up, clouds are made of compounds like ammonium hydrosulfide and ammonium ice.

Jupiter
An enhanced color image of clouds on Jupiter taken from the Juno spacecraft. The white spots are storms called the “String of pearls.”
Credits: Enhanced Image by Gerald Eichstädt and Sean Doran (CC BY-NC-SA) based on images provided Courtesy of NASA/JPL-Caltech/SwRI/MSSS

Titan (Saturn’s Moon)

Clouds on Titan are primarily methane-based, observed in the lower atmosphere (troposphere).

5 Peering Through Titan's Haze
A composite visible/infrared view of Titan shows a world with features strikingly like Earth.
Credit: NASA/JPL-Caltech

Uranus and Neptune

These ice giants also have complex cloud compositions. Near their surfaces, clouds are made of water ammonia solution and transition to water ice clouds. Higher up, clouds consist of compounds like ammonium hydrosulfide and methane ice.

Side-by-side photos of Uranus and Neptune, both taken by Voyager 2.
Left: The planet Uranus, as seen by NASA’s Voyager 2 spacecraft in January 1986. This close encounter was humankind’s first visit to the ice giant. Right: Image of Neptune with the Great Dark Spot and white high-altitude clouds from the Voyager 2 spacecraft in August 1989.
Credits: Left: NASA/JPL-Caltech; Right: NASA

Exploring Planetary Clouds

While we have extensive knowledge of Earth’s clouds compared to other planetary atmospheres, understanding planetary clouds beyond our planet presents challenges. Limited direct measurements and remote sensing techniques make studying these clouds difficult. Several research institutions have cloud chambers to study Earth clouds. The Planetary Cloud and Aerosol Research Facility aims to explore the role of aerosols and clouds in non-Earth planetary systems.