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Education:
Grades 9-12

A primer on clouds and aerosols for grades 9 through 12.

Clouds on Earth

Clouds on Earth are formations in the atmosphere composed of water droplets or ice crystals suspended in the air. They originate from the evaporation of liquid water from Earth’s surface, which transforms into water vapor — a gas. As the warm, moist air rises and cools, the water vapor condenses around tiny particles called aerosols. These aerosols act as nuclei for cloud droplets to form. Over time, these droplets accumulate and become visible as clouds. When the droplets grow heavy enough, they fall to the ground as precipitation due to gravity. Clouds have a significant impact on Earth’s climate dynamics; they reflect incoming solar radiation back into space, which can cool the planet, and they absorb and re-radiate thermal radiation, contributing to the greenhouse effect.

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

Planetary clouds exhibit diverse compositions and behaviors due to varying atmospheric conditions:

Venus

Venusian clouds are primarily composed of sulfuric acid and cover the entire planet. These clouds reflect a substantial amount of sunlight, contributing to Venus’s high albedo and intense greenhouse effect.

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

Mars

Clouds on Mars consist mainly of ice water and carbon dioxide. They are often observed in regions with significant topographical features, particularly when Mars is farthest from the sun (aphelion).

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 in 1999.
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 complex cloud layers. Deeper clouds are formed of water ice, while higher layers consist of compounds like ammonium hydrosulfide and ammonia ice.

Jupiter
An enhanced color image of clouds on Jupiter taken from the Juno spacecraft in 2017. The white spots are storms called the “String of pearls”. The light and dark bands of clouds are wider than Earth. The lighter areas are regions where gas is rising, and the darker bands are regions where gas is sinking.
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)

Titan’s atmosphere features methane clouds in the troposphere.

5 Peering Through Titan's Haze
This image depicts Saturn’s moon Titan as seen by the Cassini spacecraft’s visual and infrared mapping spectrometer during a July flyby. The infrared view cuts through Titan’s cloud cover to pick up light and dark surface details.
Credit: NASA/JPL-Caltech/University of Arizona

Uranus and Neptune

These ice giants possess distinct cloud compositions at different atmospheric levels. Clouds are primarily composed of water ammonia solution at lower cloud layers and transition to water ice and methane ice clouds at higher altitudes.

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

Research Challenges and Future Endeavors

While our understanding of Earth’s clouds is extensive relative to clouds in other planetary systems, studying clouds on other planets remains challenging due to limited direct observations and remote sensing capabilities. Cloud chambers have been built to better understand cloud properties on Earth at several research organizations. The Planetary Cloud and Aerosol Research Facility aims to advance our knowledge by exploring aerosol-cloud interactions in diverse planetary atmospheres, contributing to our broader understanding of planetary climate systems.

References

  • Atreya, S. K., Wong, M. H., Owen, T. C., Mahaffy, P. R., Niemann, H. B., De Pater, I., … & Encrenaz, T. (1999). A comparison of the atmospheres of Jupiter and Saturn: deep atmospheric composition, cloud structure, vertical mixing, and origin. Planetary and Space Science, 47(10-11), 1243-1262.
  • Griffith, C. A., Penteado, P., Rodriguez, S., Le Mouélic, S., Baines, K. H., Buratti, B., … & Sotin, C. (2009). Characterization of clouds in Titan’s tropical atmosphere. The Astrophysical Journal, 702(2), L105.
  • Moses, J. I., Cavalié, T., Fletcher, L. N., & Roman, M. T. (2020). Atmospheric chemistry on Uranus and Neptune. Philosophical transactions of the royal society A, 378(2187), 20190477.
  • Ramanathan, V. L. R. D., Cess, R. D., Harrison, E. F., Minnis, P., Barkstrom, B. R., Ahmad, E., & Hartmann, D. (1989). Cloud-radiative forcing and climate: Results from the Earth Radiation Budget Experiment. Science, 243(4887), 57-63.
  • Read, P. L., Lewis, S. R., & Mulholland, D. P. (2015). The physics of Martian weather and climate: a review. Reports on Progress in Physics, 78(12), 125901.
  • Titov, D. V., Ignatiev, N. I., McGouldrick, K., Wilquet, V., & Wilson, C. F. (2018). Clouds and hazes of Venus. Space Science Reviews, 214, 1-61.