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Epic storms, new moons and worlds that might host life: Here are Cassini's greatest discoveries

Cassini arrived at Saturn in 2004, and it wasted no time making scientific discoveries.

The NASA spacecraft witnessed epic storms and discovered new moons. Most importantly, its observations of Enceladus upended scientists’ ideas of where life might exist in the solar system.

Here are some highlights from Cassini’s 13 years at Saturn:

May 31, 2004

Cassini spies two new moons

From its close-in vantage point, the Cassini spacecraft spies two tiny moons that were previously unknown to science. Methone is an egg-shaped moon that speeds around the planet once every 24 hours. Pallene completes an orbit in under 28 hours. Scientists now think particles from both moons help form Saturn’s E ring. Discovery of Methone and Pallene brings the total number of Saturnian moons to 60.

Cassini's view of Methone from about 2,500 miles away.
Cassini's view of Methone from about 2,500 miles away. (NASA)

Jan. 14, 2005

Historic Huygens landing

About three weeks after detaching from Cassini, the European Space Agency’s Huygens probe lands on Titan, Saturn’s largest moon. It survives for 72 minutes on the frozen surface and reveals that Titan has a lot in common with Earth in terms of meteorology and geology. Huygens is the only spacecraft to land on a world in the outer solar system.

Huygens' views of Titan during its 147-minute descent to the moon's surface.
Huygens' views of Titan during its 147-minute descent to the moon's surface. (NASA)

July 14, 2005

Active Enceladus

Cassini detects a cloud of water vapor and ice emanating from the southern pole of Enceladus — a discovery that astonishes scientists. The spacecraft also reveals that the moon’s surface is young, complex and has many fewer craters than expected. Discoveries from Enceladus are some of the most significant of the entire Cassini mission.

Cassini's view of the southern polar region of Saturn's moon Enceladus.
Cassini's view of the southern polar region of Saturn's moon Enceladus. (NASA)

March 9, 2006

A watery world

After analyzing Cassini’s detailed images of Enceladus and its plumes, scientists conclude that reservoirs of liquid water are hidden just beneath the moon’s icy surface. That water escapes into space from fractures that resemble a tiger’s stripes. Scientists had considered the possibility that the plumes were fed by surface ice, but they ultimately decided that wasn’t the case.

This color-coded image reveals an extended plume emanating from Enceladus's south polar region
This color-coded image reveals an extended plume emanating from Enceladus's south polar region (NASA)

July 22, 2006

Titanic lakes

Cassini’s radar spots dozens of liquid lakes on Titan, including some that measure nearly 20 miles across. That makes Titan the only other place in the solar system with a stable liquid on its surface. The lakes aren’t made of water as they are on Earth; instead, they probably contain liquid methane or a methane-ethane combination. Scientists say the hydrocarbons in Titan’s smoggy atmosphere can probably be traced to these lakes.

This colorized mosaic image using radar data gathered by Cassini shows Titan's northern land of lakes.
This colorized mosaic image using radar data gathered by Cassini shows Titan's northern land of lakes. (NASA)

Sept. 15, 2006

Put a ring on it

A mosaic of 165 images taken by Cassini over a three-hour period revealed rings made of microscopic particles that were previously unknown to exist. The faint rings were visible because the sun, Saturn and Cassini were aligned in such a way that the planet shielded the spacecraft from the sun. The newly discovered rings lie just beyond the bright rings but inside the more distant G and E rings.

With Saturn blocking the sun, Cassini was able to see faint rings that were previously unknown to science.
With Saturn blocking the sun, Cassini was able to see faint rings that were previously unknown to science. (NASA)

Oct. 10, 2007

Tiger-stripe jets

Scientists report in the journal Nature that they have traced the source of eight jets on Enceladus. All of them emanate from the moon’s “tiger stripe” fractures. The jets release water vapor, ice particles and trace amounts of organic compounds.

Images such as this helped scientists pinpoint the source of the jets on Enceladus.
Images such as this helped scientists pinpoint the source of the jets on Enceladus. (NASA)

March 13, 2008

Plume sample

Cassini flies through an Enceladus plume, coming within 120 miles of the moon’s surface as it was spraying its brew at speeds of about 800 mph. Instruments aboard Cassini sampled the plume and detected water vapor, carbon dioxide, carbon monoxide, volatile gasses and organic materials. The tiger-stripe fissures from which the plumes emanate were found to be hotter than the surrounding area.

Cassini detected heat radiating from the "tiger stripe" fissures on Enceladus. The warmest areas coincided with the locations of plume jets.
Cassini detected heat radiating from the "tiger stripe" fissures on Enceladus. The warmest areas coincided with the locations of plume jets. (NASA)

March 3, 2009

Another moon

Cassini discovers the moon Aegaeon, the smallest of the many moons in orbit around Saturn. Aegaeon is nearly hidden in Saturn’s G ring. Shaped like a football, its average radius is only 0.2 miles.

The moon Aegaeon appears as a small streak of light within Saturn's G ring.
The moon Aegaeon appears as a small streak of light within Saturn's G ring. (NASA)

July 22, 2009

Finding ammonia in the Enceladus plume

Cassini scientists announce that ammonia is one of the chemicals in the Enceladus plume. This is a very strong sign that there is liquid water beneath the moon’s frozen crust. When mixed with ammonia, water is able to stay in liquid form at temperatures as low as -143 degrees Fahrenheit. With liquid water and organic materials present on Enceladus, the possibility for life becomes more intriguing.

One of Cassini's many shots of Enceladus and its jets. Instruments aboard the spacecraft detected ammonia in the plume.
One of Cassini's many shots of Enceladus and its jets. Instruments aboard the spacecraft detected ammonia in the plume. (NASA)

Sept. 14, 2009

The Dione Belt

Cassini scientists discover a temporary magnetosphere around Saturn. Since it is near the orbit of the moon Dione, scientists dub it the “Dione Belt.” The belt itself was detectable by Cassini’s instruments for only a few weeks in 2005. The charged particles that made up the belt were probably absorbed by Dione and another moon, Tethys.

The moon Dione may have absorbed the particles that formed a temporary magnetosphere around Saturn.
The moon Dione may have absorbed the particles that formed a temporary magnetosphere around Saturn. (NASA)

Nov. 29, 2010

Another atmosphere with oxygen

Cassini finds a very thin atmosphere, called an exosphere, surrounding Saturn’s icy moon Rhea. What’s more, the exosphere contains molecules of oxygen and carbon dioxide. Scientists think the oxygen travels from the surface to the exosphere under the influence of Saturn’s magnetic field. Rhea joins Earth as the only bodies known to have oxygen in their atmospheres.

Rhea's thin atmosphere contains oxygen, giving it something in common with Earth.
Rhea's thin atmosphere contains oxygen, giving it something in common with Earth. (NASA)

Dec. 5, 2010

Monster storm on Saturn

Cassini spies a monster storm on Saturn’s northern hemisphere. It measured about 9,000 miles from north to south and about 190,000 miles from east to west. It also churned up material from 100 miles below the surface. About 12 weeks in, the storm had wrapped itself around the entire planet.

This is how a monster storm appeared on Saturn 12 weeks after it began.
This is how a monster storm appeared on Saturn 12 weeks after it began. (NASA)

June 22, 2011

A hidden ocean

After studying the ice grains shooting out of Enceladus, scientists determine that the ones closer to the moon’s surface are rich in sodium and potassium salts. Their make-up indicates they evaporated from liquid salt water, suggesting that a hidden ocean lies beneath the Enceladus surface. The finding is reported in the journal Nature.

Analysis of ice grains in the Enceladus plume strengthens the case for a salt-rich ocean beneath the surface.
Analysis of ice grains in the Enceladus plume strengthens the case for a salt-rich ocean beneath the surface. (NASA)

March 2, 2012

Dione joins the oxygen club

Scientists didn’t know whether Dione even had an exosphere, but Cassini detected a sparse exosphere with one oxygen ion per 11 cubic centimeters of space. The exosphere is so thin that its density at the moon’s surface is the same as Earth’s atmosphere 300 miles up. Scientists think the oxygen comes from water ice on Dione’s surface, which is released by photons from the sun or other energetic particles.

Cassini detects minute amounts of oxygen in Dione's thin exosphere.
Cassini detects minute amounts of oxygen in Dione's thin exosphere. (NASA)

April 23, 2012

Punching through Saturn’s F ring

Cassini spots an object about half a mile wide punching through Saturn’s F ring, leaving a trail of icy particles in its wake. The length of the trail ranges from about 47 miles to 155 miles over the 11 hours and 5 minutes of elapsed time captured in the movie below. Cassini scientists think the objects penetrating the ring are icy ring particles pushed together by the moon Prometheus. They call the trails “mini-jets”

A tiny object punches through Saturn's F ring, leaving a trail of icy particles in its wake. (NASA)

July 19, 2013

Wave at Saturn

Cassini takes Earth’s picture from 898 million miles away. Both Earth and the moon are visible to the right of Saturn’s south pole, below the rings. Cassini’s home planet is visible because Saturn was blocking the sun. When mission managers realized this would be the case, they kicked off the “Wave at Saturn” campaign to encourage Earthlings to smile for Cassini’s camera.

Cassini's photo of Earth, taken from 898 million miles away.
Cassini's photo of Earth, taken from 898 million miles away. (NASA)
A mosaic image of Earthlings waving at Saturn.
A mosaic image of Earthlings waving at Saturn. (NASA)

Dec. 4, 2013

Hexagonal storm in motion

Saturn’s north pole has a six-sided jet stream, and Cassini captures all of it for the first time in a high-resolution movie. The weather feature spans about 20,000 miles and is powered by 200-mph winds. The storm, known as the hexagon, has been active for decades (if not centuries) and is thought to be unique in the solar system. The version below uses color filters to distinguish between different types of particles in the atmosphere.

Cassini captures Saturn's six-sided jet stream in motion.
Cassini captures Saturn's six-sided jet stream in motion. (NASA)

Jan. 28, 2015

New view of Titan

In December 2013, Cassini visited Titan while it was outside of Saturn’s protective magnetosphere, a situation that occurs only 5% of the time. In January 2015, scientists reported that the solar wind enveloped the unprotected moon, creating a shock wave when it slammed into Titan’s atmosphere. This is similar to the way the solar wind interacts with Venus or Mars, two planets that lack a magnetic field.

How Cassini came to view Titan when it was outside Saturn's magnetosphere.
How Cassini came to view Titan when it was outside Saturn's magnetosphere. (NASA)

Aug. 28, 2017

Last view of Enceladus’s plume

Cassini conducts its last observation of the jets spraying out of Enceladus’ south pole. The movie below was captured over a period of about 14 hours as the moon goes from being partially lit by Saturn into complete darkness. NASA scientists are now contemplating a follow-up mission to Enceladus, which they have dubbed Enceladus Life Finder.

This movie of Enceladus and its jets is made of images captured by Cassini over a 14-hour period.
This movie of Enceladus and its jets is made of images captured by Cassini over a 14-hour period. (NASA)

Sept. 11, 2017

Kissing Titan goodbye

Cassini gives Titan a “goodbye kiss” during its final flyby of the giant moon. Although the spacecraft remained rather distant, it came close enough for Titan’s gravity to slow it down. That will ensure Cassini enters Saturn’s atmosphere at an angle that causes it to incinerate. Although it sounds harsh, the mission managers decided to destroy Cassini to protect Saturn’s moons from possible contamination.

Cassini's final Titan flyby, which puts the spacecraft on a crash course for Saturn.
Cassini's final Titan flyby, which puts the spacecraft on a crash course for Saturn. (NASA)

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karen.kaplan@latimes.com

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