Update – Sept. 11, 2017: This feature (originally published on April 25, 2017) has been updated to reflect Cassini's current mission status, as well as new lessons and activities.


In the News

After almost 20 years in space, NASA's Cassini spacecraft has begun the final chapter of its remarkable story of exploration. This last phase of the mission has delivered unprecedented views of Saturn and taken Cassini where no spacecraft has been before – all the way between the planet and its rings. On Friday, Sept. 15 Cassini will perform its Grand Finale: a farewell dive into Saturn’s atmosphere to protect the environments of Saturn’s moons, including the potentially habitable Enceladus.

Animation of Cassini Pi in the Sky 4 math problem

Lessons All About Saturn

Explore our collection of standards-aligned lessons about NASA's Cassini mission.

How It Works

On April 22, Cassini flew within 608 miles (979 km) of Saturn’s giant moon Titan, using the moon’s gravity to place the spacecraft on its path for the ring-gap orbits. Without this gravity assist from Titan, the daring, science-rich mission ending would not be possible.

Cassini is almost out of the propellant that fuels its main engine, which is used to make large course adjustments. A course adjustment requires energy. Because the spacecraft does not have enough rocket fuel on board, Cassini engineers have used an external energy source to set the spacecraft on its new trajectory: the gravity of Saturn’s moon Titan. (The engineers have often used Titan to make major shifts in Cassini’s flight plan.)

Titan is a massive moon and thus has a significant amount of gravity. As Cassini comes near Titan, the spacecraft is affected by this gravity – and can use it to its advantage. Often referred to as a “slingshot maneuver,” a gravity assist is a powerful tool, which uses the gravity of another body to speed up, slow down or otherwise alter the orbital path of a spacecraft.

In this installment of the "Crazy Engineering" video series from NASA's Jet Propulsion Laboratory, host Mike Meacham talks to a Cassini engineer about astrodynamics and how it was used to design the Saturn mission's Grand Finale.

When Cassini passed close by Titan on April 22, the moon’s gravity pulled strongly on the spacecraft. The flyby gave Cassini a change in velocity of about 1,800 mph (800 meters per second) that sent the spacecraft into its first of the ring-gap orbits on April 23. On April 26, Cassini made its first of 22 daring plunges between the planet and its mighty rings.

Cassini final orbits petal plot

This graphic illustrates Cassini's trajectory, or flight path, during the final two phases of its mission. The 20 Ring-Grazing Orbits that Cassini made between November and April 2017 are shown in gray; the 22 Grand Finale Orbits are shown in blue. The final partial orbit is colored orange. + Enlarge image

Up-close image of Saturn's clouds from Cassini

Clouds on Saturn take on the appearance of strokes from a cosmic brush thanks to the wavy way that fluids interact in Saturn's atmosphere. This images used in this false-color view were taken with the Cassini spacecraft narrow-angle camera on May 18, 2017. Image credit: NASA-JPL/Caltech/SSI | › Full image and caption

Animated image of Saturn's moon Enceladus from Cassini

This animated image of Saturn's moon Enceladus is a composite of six images taken by the Cassini spacecraft on Aug. 1, 2017. Image credit: NASA-JPL/Caltech/SSI | › Full image and caption

Up-close image of Saturn's rings from Cassini

These are the highest-resolution color images of any part of Saturn's rings, to date, showing a portion of the inner-central part of the planet's B Ring. The view is a mosaic of two images that show a region that lies between 61,300 and 65,600 miles (98,600 and 105,500 kilometers) from Saturn's center. Image credit: NASA-JPL/Caltech/SSI | › Full image and caption

As Kepler’s third law indicates, Cassini traveled faster than ever before during these final smaller orbits. Cassini's orbit continued to cross the orbit of Titan during these ring-gap orbits. And every couple of orbits, Titan passed near enough to give the spacecraft a nudge. One last nudge occured on September 11, placing the spacecraft on its final, half-orbit, impact trajectory toward Saturn.

Because a few hardy microbes from Earth might have survived onboard Cassini all these years, NASA has chosen to safely dispose of the spacecraft in the atmosphere of Saturn to avoid the possibility of Cassini someday colliding with and contaminating moons such as Enceladus and Titan that may hold the potential for life. Cassini will continue to send back science measurements as long as it is able to transmit during its final dive into Saturn.

Why It’s Important

Flying closer than ever before to Saturn and its rings has provided an unprecedented opportunity for science. During these orbits, Cassini’s cameras have captured ultra-close images of the planet’s clouds and the mysterious north polar hexagon, helping us to learn more about Saturn’s atmosphere and turbulent storms.

The cameras have been taking high-resolution images of the rings, and to improve our knowledge of how much material is in the rings, Cassini has also been conducting gravitational measurements. Cassini's particle detectors have sampled icy ring particles being funneled into the atmosphere by Saturn's magnetic field. Data and images from these observations are helping bring us closer to understanding the origins of Saturn’s massive ring system.

Cassini has also been making detailed maps of Saturn's gravity and magnetic fields to reveal how the planet is structured internally, which could help solve the great mystery of just how fast Saturn is rotating.

On its first pass through the unexplored 1,500-mile-wide (2,400-kilometer) space between the rings and the planet, Cassini was oriented so that its high-gain antenna faced forward, shielding the delicate scientific instruments from potential impacts by ring particles. After this first ring crossing informed scientists about the low number of particles at that particular point in the gap, the spacecraft was oriented differently for the next four orbits, providing the science instruments unique observing angles. For ring crossings 6, 7 and 12, the spacecraft was again oriented so that its high-gain antenna faced forward.

Fittingly, Cassini's final moments will be spent doing what it does best, returning data on never-before-observed regions of the Saturnian system. On September 15, just hours before Cassini enters Saturn's atmosphere for its Grand Finale dive, it will collect and transmit its final images back to Earth. During its fateful dive, Cassini will be sending home new data in real time informing us about Saturn’s atmospheric composition. It's our last chance to gather intimate data about Saturn and its rings – until another spacecraft journeys to this distant planet.

Explore the many discoveries made by Cassini and the story of the mission on the Cassini website.

Teach It

Use these standards-aligned lessons to get your students excited about the science we have learned and have yet to learn about the Saturnian system.

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TAGS: Saturn, Titan, Cassini, Grand Finale, Teachable Moments, Kepler's Laws, K-12, Lessons,

  • Ota Lutz
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Adopt the Planet campaign from NASA Earth

In the News

Earth Day, the day set aside each year to celebrate our planet and bring attention to the natural world, is on April 22, 2017. More than one billion people are expected to participate in Earth Day events around the globe that will draw attention to what we know about Earth, how it is changing and how we can be kind to our home planet.

One of the ways that NASA participates – not just on Earth Day, but also year-round – is by collecting and analyzing science data from sensors on Earth and satellites. These data allow us to monitor the health of our planet and better understand how and why it is changing.

Visualizing global data trends – Earth Science – NASA/JPL Education

Earth Day Resources for Educators

Explore our collection of standards-aligned Earth science lessons – plus this new lesson about reading NASA data visualizations and heat maps.

› Explore Earth science lessons from NASA!

This year, to highlight the importance of these data, NASA is inviting people to “adopt” a portion of Earth’s surface and obtain a snapshot of some of the satellite data available for their adopted location. Even though you’ll have no legal or ownership rights to this region, it will be fun to learn about the various types of data available for different locations on Earth. Find out how you can participate.

How It Works

NASA’s fleet of Earth-observing satellites and airborne sensors provides us with data about such vital information as carbon dioxide, carbon monoxide, global land and sea temperature, ice, sea surface salinity, and chlorophyll – just to name a few. The satellites and sensors collect these data over time and from as many perspectives as possible, allowing us to discern trends in the data.

Learn about the fleet of NASA satellites and instruments studying Earth. › Watch NASA's Earth Minute series

A snapshot of data is just one piece of a much larger puzzle because it only gives us an indication of what was happening at the exact moment that data was captured. Even data collected over a year has its limitations because local conditions may ebb and flow over longer time periods. Collecting data about multiple elements of the Earth system over decades or centuries enables us to develop correlation and causation models, powerful indicators of why trends are developing as they are. And using multiple platforms (satellite, aerial, Earth-based) to measure data enables us to validate our data sets.

Why It’s Important

Humans are dependent on a healthy and functioning Earth to survive, which means we need to keep a close eye on all Earth systems and our impacts on those systems. This process of collecting data over time from multiple perspectives, discerning trends and validating the data is crucial to understanding our planet and helping policymakers formulate actions we can take to preserve Earth for future generations.

Earth is a complex, dynamic system we do not fully understand. To learn more about it, NASA, as the agency with access to space, was tasked with launching the first weather satellite back in 1960. Today, NASA uses satellites, aircraft and even an occasional boat to study our planet's air, land and water. It's called "Earth System Science" and we are trying to answer some big questions: How is the global Earth system changing? What causes these changes? How will Earth change in the future? And what we learn benefits society through applications such as weather forecasting, freshwater availability and disaster response. › Watch NASA's Earth Minute series

Teach It

First, introduce students to the kinds of data scientists use to study Earth. Participate in NASA’s Adopt the Planet campaign to receive a snapshot of Earth science data for one patch of Earth. Then encourage students to dig deeper with these standards-aligned lessons:

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TAGS: Earth Day, Climate Change, Earth Science, Lessons, Activities, K-12, Teaching

  • Ota Lutz
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Brightened processed image of Saturn from Cassini to highlight the F ring

Update – Feb. 24, 2017: The deadline for the Cassini Scientist for a Day Essay Contest has passed. The winners will be announced in May 2017.


In the News

Next week, NASA’s Cassini spacecraft will go where no spacecraft has gone before when it flies just past the edge of Saturn’s main rings. The maneuver is a first for the spacecraft, which has spent more than 12 years orbiting the ringed giant planet. And it’s part of a lead-up to a series of increasingly awesome feats that make up the mission’s “Grand Finale” ending with Cassini’s plunge into Saturn on Sept. 15, 2017.

How They’ll Do It

graphic showing Cassini's orbits

Cassini's ring-grazing orbits, which will take place from late Novemeber 2016 through April 2017, are shown here in tan. The blue lines represent the path that Cassini took in the time leading up to the new orbits during its extended solstice mission. Image credit: NASA/JPL-Caltech/Space Science Institute | › Larger image

To prepare for the so-called “ring-grazing orbits,” which will bring the spacecraft within 56,000 miles (90,000 km) of Saturn, Cassini engineers have been slowly adjusting the spacecraft’s orbit since January. They do this by flying Cassini near Saturn’s large moon Titan. The moon’s gravity pulls on the spacecraft, changing its direction and speed.

On November 29, Cassini will use a big gravitational pull from Titan to get into an orbit that is closer to perpendicular with respect to the rings of Saturn and its equator. This orbit will send the spacecraft slightly higher above and below Saturn’s north and south poles, and allow it to get as close as the outer edge of the main rings – a region as of yet unexplored by Cassini.

This diagram shows Saturns ring-grazing and planet-grazing orbits

This graphic illustrates the Cassini spacecraft's trajectory, or flight path, during the final two phases of its mission. The view is toward Saturn as seen from Earth. The 20 ring-grazing orbits are shown in gray; the 22 grand finale orbits are shown in blue. The final partial orbit is colored orange. Image credit: NASA/JPL-Caltech/Space Science Institute | › Larger image

Why It’s Important

Cassini’s ring-grazing orbits will allow scientists to see features in Saturn's rings, up close, that they’ve only been able to observe from afar. The spacecraft will get so close to the rings, in fact, that it will pass through the dusty edges of the F ring, Saturn’s narrow, outermost ring. At that distance, Cassini will be able to study the rings like never before.

Among the firsts will be a “taste test” of Saturn’s rings from the inside out, during which Cassini will sample the faint gases surrounding the rings as well as the particles that make up the F ring. Cassini will also capture some of the best high-resolution images of the rings, and our best views of the small moons Atlas, Pan, Daphnis and Pandora, which orbit near the rings' outer edges. Finally, the spacecraft will do reconnaissance work needed to safely carry out its next planned maneuver in April 2017, when Cassini is scheduled to fly through the 1,500-mile (2,350-kilometer) gap between Saturn and its rings.

› Read more about what we might learn from Cassini's ring-grazing orbits.

These orbits are a great example of scientific research in action. Much of what scientists will be seeing in detail during these ring-grazing orbits are features that, despite Cassini’s 12 years at Saturn, have remained a mystery. These new perspectives could help answer questions scientists have long puzzled over, but they will also certainly lead to new questions to add to our ongoing exploration of the ringed giant.

Teach It

Cassini Scientist for a Day Essay Contest 2016 graphic

As part of the Cassini Scientist for a Day Essay Contest, students in grades 5-12 will write an essay describing which of these three targets would provide the most interesting scientific results. › Learn more and enter

What better way to share in the excitement of Cassini’s exploration than to get students thinking like NASA scientists and writing about their own questions and curiosities?

NASA’s Cassini Scientist for a Day Essay Contest, open to students in grades 5-12, encourages students to do just that. Participants research three science and imaging targets and then write an essay on which target would provide the most interesting scientific results, explaining what they hope to learn from the selected target. Winners of the contest will be featured on NASA’s Solar System Exploration website and get an opportunity to speak with Cassini scientists and engineers via video conference in the spring.

More information, contest rules and videos can be found here.

The deadline to enter is Feb. 24, 2017.

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TAGS: Cassini, Saturn's Rings, Saturn, Grand Finale, Spacecraft, Missions, K-12, Lessons, Activities, Language Arts, Science, Essay Contest

  • Lyle Tavernier
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This summer, while many of us were sleeping in and avoiding heavy school work, lots of exciting things were happening in and around our solar system! Here's a guide to launching the 2016 school year right and turning those stellar events into educational connections from NASA. 

Science on Fire

An image of the Soberanes fire, in northern California near Big Sur
This false-color image of the Soberanes fire in Northern California, near Big Sur, was captured by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on NASA's Terra spacecraft on July 28, 2016.

Here at home, on Earth, it is fire season in many places in the Northern Hemisphere. Fire season comes about with warmer temperatures, dry air, and dry brush. Once a fire gets started in these conditions, it can rapidly spread and become out of control, especially when high winds are involved. This summer has already witnessed some dangerous fires including the Sand Fire in Southern California and the Soberanes Fire near Big Sur on the Central California coast. Beyond the immediate threat from flames, smoke degrades air quality and burn scars leave hillsides vulnerable to rain-induced mudslides.

NASA satellites and airborne instruments are helping scientists better understand wildfires and their impacts on our changing climate. And in the immediate term, they are helping firefighters track wildfires and respond to people and structures in risk areas.

Check out JPL's latest Teachable Moment to find out more about how scientists are studying wildfires, what they're learning and why it's important. And get links to two new lessons for students in grades 3-12 that have students use NASA data, algebra and geometry to approximate burn areas, fire-spread rate and fire intensity. (You can also go straight to the new lessons at: Fired Up Over Math: Studying Wildfires from Space and Pixels on Fire)

And speaking of Earth science, find out how you can get a free bulletin board featuring posters and lithographs about NASA Earth science and missions for your classroom!

Greetings from Jupiter

Watch a recap of the July 4 excitement as NASA's Juno spacecraft entered orbit around Jupiter.

On July 4, just in time for a fireworks spectacle, the Juno spacecraft went into orbit around Jupiter. Juno launched from Earth aboard a huge rocket and had been hurtling toward Jupiter for nearly five years. Getting into orbit around Jupiter was a real nail-biter here at NASA's Jet Propulsion Laboratory (which helps manage the mission) and we are all very happy everything went as planned. Juno’s mission is to study the origin, core and magnetic fields of our solar system’s largest planet. Juno will orbit Jupiter for only about 20 months before Jupiter’s intense radiation environment takes a toll on the spacecraft.

Communicating with a spacecraft as far away as Juno is a challenge that involves a lot of planning and teamwork. Try out this new lesson for young learners that demonstrates this process and provides practice with number concepts, counting and geometry, and data collection in a concrete, active manner. 

Wish you had your very own Juno spacecraft you could use to uncover secrets beneath Jupiter? Check out this easy-to-build Juno model that uses household objects and can be used in a game with friends and family!

Explore more about Juno with these related lessons and videos: 


TAGS: Back-to-School, Juno, Wildfires, Bulletin Board, Lessons, Activities, DIY

  • NASA/JPL Edu
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UPDATE - May 9, 2016: NASA's Solar Dynamics Observatory, or SDO, spacecraft captured stunning images of the May 9, 2016 transit of Mercury. Visit the mission's Transit of Mercury page to see a collection of videos of the transit compiled using SDO images. And have students play "Can You Spot Mercury?" in our educational slideshow. 


In the News

It only happens about 13 times per century and hasn’t happened in nearly a decade, but on Monday, May 9, Mercury will transit the sun. A transit happens when a planet crosses in front of a star. From our perspective on Earth, we only ever see two planets transit the sun: Mercury and Venus. (Transits of Venus are even more rare. The next one won't happen until 2117!) On May 9, as Mercury passes in front of the sun, viewers around Earth (using the proper safety equipment) will be able to see a tiny dark spot moving slowly across the disk of the sun.

CAUTION: Looking directly at the sun can cause permanent vision damage – see below for tips on how to safely view the transit.

Why It's Important

Then and Now

In the early 1600s, Johannes Kepler discovered that both Mercury and Venus would transit the sun in 1631. It was fortunate timing: The telescope had been invented just 23 years earlier and the transits wouldn’t happen in the same year again until 13425. Kepler didn’t survive to see the transits, but French astronomer Pierre Gassendi became the first person to see the transit of Mercury (the transit of Venus wasn’t visible from Europe). It was soon understood that transits could be used as an opportunity to measure the apparent diameter – how large a planet appears from Earth – with great accuracy.

In 1677, Edmond Halley observed the transit of Mercury and realized that the parallax shift of the planet – the variation in Mercury’s apparent position against the disk of the sun as seen by observers at distant points on Earth – could be used to accurately measure the distance between the sun and Earth, which wasn’t known at the time.

Today, radar is used to measure the distance between Earth and the sun with greater precision than can be found using transit observations, but the transit of Mercury still provides scientists with opportunities for scientific investigation in two important areas: exospheres and exoplanets.

Exosphere Science

Some objects, like the moon and Mercury, were originally thought to have no atmosphere. But scientists have discovered that these bodies are actually surrounded in an ultra-thin atmosphere of gases called an exosphere. Scientists want to better understand the composition and density of the gases that make up Mercury’s exosphere and transits make that possible.

“When Mercury is in front of the sun, we can study the exosphere close to the planet,” said NASA scientist Rosemary Killen. “Sodium in the exosphere absorbs and re-emits a yellow-orange color from sunlight, and by measuring that absorption, we can learn about the density of gas there.”

Mercury transits the sun in 2006
This image of Mercury passing in front of the sun was captured on Nov. 8, 2006 by the Solar Optical Telescope, one of three primary instruments on the Hinode spacecraft. Image credit: Hinode JAXA/NASA/PPARC

Exoplanet Discoveries

When Mercury transits the sun, it causes a slight dip in the sun’s brightness as it blocks a tiny portion of the sun's light. Scientists discovered they could use that phenomenon to search for planets orbiting distant stars, called exoplanets, that are otherwise obscured from view by the light of the star. When measuring the brightness of far-off stars, a slight recurring dip in the light curve (a graph of light intensity) could indicate an exoplanet orbiting and transiting its star. NASA’s Kepler mission has found more than 1,000 exoplanets by looking for this telltale drop in brightness.

illustration of how transits are used to find exoplanets
This diagram shows how scientists use the light curves of distant stars to search for planets outside our solar system. A drop in the light curve, as illustrated here, is a good indication that there's a planet orbiting the observed star. Credit: NASA Ames

The Kepler mission measures the brightness of stars. The data will look like an EKG showing the heart beat. Whenever a planet passes in front of its parent star as viewed from the spacecraft, a tiny pulse or beat is produced. From the repeated beats, we can detect and verify the existence of Earth-size planets and learn about the orbit and size of the planet. Video credit: NASA Ames and Dana Berry

Additionally, scientists have begun exploring the exospheres of exoplanets. By observing the spectra of the light that passes through an exosphere – similar to how we study Mercury’s exosphere – scientists are beginning to understand the evolution of exoplanet atmospheres as well as the influence of stellar wind and magnetic fields.

Watch It

Mercury will appear as a tiny dot on the sun’s surface and will require a telescope or binoculars with a special solar filter to see. Looking at the sun directly or through a telescope without proper protection can lead to serious and permanent vision damage. Do not look directly at the sun without a solar filter.

The transit of Mercury will begin at 4:12 a.m. PDT, meaning by the time the sun rises on the West Coast, Mercury will have been transiting the sun for nearly two hours. Fortunately, it will take seven and a half hours for Mercury to completely cross the sun’s face, so there will be plenty of time for West Coast viewers to witness this event. See the transit map to learn when and where the transit will be visible.

Don’t have access to a telescope, binoculars or a solar filter? Visit the Night Sky Network website for the location of events near you where amateur astronomers will have viewing opportunities available.

NASA also will stream a live program on NASA TV and the agency’s Facebook page from 7:30 to 8:30 a.m. PDT (10:30 to 11:30 a.m. EDT) -- an informal roundtable during which experts representing planetary, heliophysics and astrophysics will discuss the science behind the Mercury transit. Viewers can ask questions via Facebook and Twitter using #AskNASA.

Teach It

Here are two ways to turn the transit of Mercury into a lesson for students.

  • Exploring Exoplanets with Kepler - Students use math concepts related to transits to discover real-world data about Mercury, Venus and planets outside our solar system.
  • Pi in the Sky 3 - Try the "Sun Screen" problem on this illustrated math problem set that has students calculate the percentage drop in sunlight reaching Earth when Mercury transits.

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Transit Resources:

Exoplanet Resources:

TAGS: Transit, Transit of Mercury, Mercury, Venus, Sun, Exoplanets, Teach, Classroom Activities, Lessons,

  • Lyle Tavernier
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