Studying the Planets and Moons

The Planets

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  Capturing the Aftermath of Impacts on Jupiter

  In 1994, just four years into its long tenure of collecting data, Hubble watched as 21 fragments of Comet Shoemaker-Levy 9 (SL9) bombarded the giant planet Jupiter with a sequential train of impacts. Each fragment left a temporary black scar that revealed deeper layers of the planet’s atmosphere. It was the first time astronomers witnessed such an event. Hubble observed another impact in 2009, when a suspected asteroid plunged into Jupiter’s atmosphere and left a temporary dark feature the size of the Pacific Ocean.  

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  Monitoring Jupiter’s Shrinking Red Spot

  Using Hubble, astronomers tracked Jupiter’s Great Red Spot, a giant swirling storm slightly larger than Earth, and found that it is shrinking and jiggling. The spot’s outer winds are speeding up while moving significantly more slowly toward its center.

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  Studying Auroras

  Hubble captured brilliant curtains of light, called auroras, on Jupiter, Saturn, and Uranus. Auroras develop when electrically charged particles trapped in a planet’s magnetic field spiral inward at high speeds toward the north and south magnetic poles. When these particles hit the upper atmosphere, they excite atoms and molecules there, causing them to glow in a similar process to that of a neon light.

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  Discovering a Link Between Neptune’s Clouds and the Sun

  Hubble expanded upon the NASA Voyagers’ observations of Neptune and Uranus. It found that Neptune’s southern hemisphere ‘Great Dark Spot’ vanished in 1994, then spotted another dark storm in Neptune’s northern hemisphere a year later. Hubble’s decades of observations revealed that Neptune’s storms last for a few years before vanishing or fading away and that this cycle correlates to the Sun’s cycle of activity.

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  Saturn's Rings Heating Its Atmosphere

  Hubble also helped astronomers calibrate archival Saturn data from four separate missions. The precision of Hubble's Space Telescope Imaging Spectrograph (STIS) and its ability to see ultraviolet light, allowed researchers to compare STIS UV observations of Saturn to 40 years of UV data from the Voyager and Cassini missions, and the International Ultraviolet Explorer. They discovered that icy ring particles raining on Saturn’s atmosphere at specific latitudes and seasonal effects cause atmospheric heating. Researchers are testing to see if this unexpected interaction can help define new ways of examining distant exoplanets for extended Saturn-like ring systems.

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  Studying the Dynamic Martian Atmosphere

  Hubble offers planetary astronomers the opportunity to studying global Martian weather. Hubble has charted the evolution of Martian sandstorms, the waxing and waning the planet's polar ice caps, and seasonal changes in the planet's cloud cover and atmospheric composition.

Their Moons

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  Finding Water on Jupiter’s Moons

  Hubble found the best evidence yet for an ocean of liquid under an ice crust on Jupiter’s moon Ganymede, the largest moon in the solar system. This ocean may have more water than all of Earth’s surface. Hubble also recorded evidence of short-lived changes in the atmosphere above the surface of Jupiter’s moon Europa – the likely result of gas plumes expelled from a subsurface ocean.

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  Finding New Moons

  In 2003, astronomers using Hubble discovered two small moons around Uranus, called Cupid and Mab. The moons are about 8 to 10 miles across (12-16 km), or roughly the size of San Francisco. Hubble also detected two large outer rings around Uranus.
  Ten years later researchers found a small, faint moon called Hippocamp in images Hubble took of Neptune between 2004 and 2009. Astronomers discovered the moon while studying faint ring-arcs around the planet. Then they combed through 150 archived Hubble images of Neptune looking for the moon. Using those Hubble images, they were able to plot Hippocamp’s 23-hour orbit around Neptune.