Jump to content

235 Years Ago: Herschel Discovers Saturn’s Moon Enceladus


Recommended Posts

  • Publishers
Posted

On Aug. 29, 1789, German-born British astronomer William Herschel observed a tiny bright dot orbiting around Saturn. His son later named the object Enceladus. Because of its distance from Earth and proximity to bright Saturn, for the next two centuries little remained known about Enceladus other than its size, orbital parameters, and that it held the honor as the most reflective body in the solar system. It took the Voyager flybys through the Saturn system in the early 1980s and especially the detailed observations between 2005 and 2015 by the Saturn orbiter Cassini to reveal Enceladus as a truly remarkable world, interacting with Saturn and its rings. Harboring a subsurface ocean of salty water, Enceladus may possibly be hospitable to some forms of life.

Portrait (1785) of William Herschel by Lemuel Francis Abbott Drawing of Herschel’s 40-foot telescope Portrait (1867) of John Herschel by Julia Margaret Cameron
Left: Portrait (1785) of William Herschel by Lemuel Francis Abbott. Image credit: courtesy National Portrait Gallery, London. Middle: Drawing of Herschel’s 40-foot telescope. Right: Portrait (1867) of John Herschel by Julia Margaret Cameron. Image credit: Metropolitan Museum of Art.

Herschel’s previous astronomical accomplishments include the discovery of Uranus in 1781 and two of its moons, Oberon and Titania, in 1787. He also catalogued numerous objects he termed nebulae, but remained frustrated by the limitations of telescopes of his age. He began to build ever larger instruments, finally building the world’s largest reflecting telescope of its time. At 40 feet long, and with a 49-inch diameter primary mirror weighing a ton, it looked impressive although its optical characteristics did not advance the field as much as he had hoped. Nevertheless, Herschel used this telescope to observe Saturn and its five known moons, looking for others. On Aug. 28, 1789, he observed a bright point orbiting the planet and believed he had discovered a sixth moon. On Sept. 17, he discovered a seventh moon orbiting the ringed planet. He did not name these moons, that task fell to his son John who believed Saturn’s moons should be named after the Titans of Greek mythology. He named the first moon Enceladus and the second Mimas.

Relative sizes of Earth, Earth’s Moon, and Enceladus Best Voyager 2 image of Enceladus
Left: Relative sizes of Earth, Earth’s Moon, and Enceladus. Right: Best Voyager 2 image of Enceladus.

For nearly two centuries, Enceladus remained not much more than a point of light orbiting Saturn, just another icy moon in the outer solar system. Astronomers estimated its diameter at around 310 miles and its orbital period around Saturn at 1.4 days, with a mean distance from the planet’s center of 148,000 miles. Enceladus has the distinction as one of the brightest objects in the solar system, reflecting almost 100 percent of the Sun’s light. Unusual telescope observations during the 20th century showed an increase in brightness on its trailing side, with no known explanation at the time. In 1966, astronomers discovered a diffuse ring around Saturn, the E-ring, and found in 1980 that its density peaked near Enceladus. The Voyager 1 spacecraft flew within 125,570 miles of Enceladus during its passage through the Saturn system on Nov. 12, 1980. Its twin Voyager 2 came within 54,000 miles on Aug. 26, 1981, during its flyby. These close encounters enabled the spacecraft to return the first detailed images of the moon, showing various terrains, including heavily cratered areas as well as smooth crater-free areas, indicating a very young surface.

False color image of Enceladus from Cassini showing the tiger stripes at bottom Limb view of Enceladus showing plumes of material emanating from its surface Cassini image of Enceladus backlit by the Sun showing the fountain-like plumes of material
Left: False color image of Enceladus from Cassini showing the tiger stripes at bottom. Middle: Limb view of Enceladus showing plumes of material emanating from its surface. Right: Cassini image of Enceladus backlit by the Sun showing the fountain-like plumes of material.

After the Cassini spacecraft entered orbit around Saturn in July 2004, our understanding of Enceladus increased tremendously, and of course raised new questions. Between 2005 and 2015, Cassini encountered Enceladus 22 times, turning its various instruments on the moon to unravel its secrets. It noted early on that the moon emitted gas and dust or ice particles and that they interacted with the E-ring. Images of the moon’s south polar region revealed cracks on the surface and other instruments detected a huge cloud of water vapor over the area. The moon likely had a liquid subsurface and some of this material reached the outside through these cracks. Scientists named the most prominent of these areas “tiger stripes” and later observations confirmed them as the source of the most prominent jets. During the most daring encounter in October 2015, Cassini came within 30 miles of the Enceladus’ surface, flying through the plume of material emanating from the moon. Analysis of the plumes revealed an organic brew of volatile gases, water vapor, ammonia, sodium salts, carbon dioxide, and carbon monoxide. These plumes replenish Saturn’s E-ring, and some of this material enters Saturn’s upper atmosphere, an interaction unique in the solar system. More recently, the James Webb Space Telescope imaged the water vapor plume emanating from Enceladus’ south pole, extending out 40 times the size of the moon itself. The confirmation of a subsurface ocean of salty water has led some scientists to postulate that Enceladus may be hospitable to some forms of life, making it a potential target for future exploration. Enceladus may yet have more surprises, even as scientists continue to pore over the data returned by Cassini.

James Webb Space Telescope image of a water vapor plume emanating from Enceladus Illustration of the interaction of Enceladus and Saturn’s E-ring
Left: James Webb Space Telescope image of a water vapor plume emanating from Enceladus. Right: Illustration of the interaction of Enceladus and Saturn’s E-ring.

Map of Enceladus based on imagery from Cassini, turning our view of Enceladus from a small point of light into a unique world with its own topography
Map of Enceladus based on imagery from Cassini, turning our view of Enceladus from a small point of light into a unique world with its own topography.

Events in world history in 1789:

January 29 – Vietnamese emperor Quang Trung defeats Chinese Qing forces at Ngọc Hồi-Đống Đa in one of the greatest military victories in Vietnamese history.

March 10 – In Japan, the Menashi-Kunashir rebellion begins between the Ainu people and the Japanese.

April 7 – Selim III succeeds Abdul Hamid I as Sultan of the Ottoman Empire.

April 28 – Aboard the HMS Bounty in the Pacific Ocean, Fletcher Christian leads the mutiny against Captain William Bligh.

April 30 – Inauguration of George Washington as the first President of the United States of America.

July 14 – Citizens storm The Bastille fortress in Paris during the French Revolution.

September 15 – Birth of American writer James Fenimore Cooper in Burlington, New Jersey.

December 11 – Founding of the University of North Carolina, the oldest public university in the United States.

View the full article

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Similar Topics

    • By NASA
      NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker This image, taken by NASA’s New Horizons spacecraft on July 14, 2015, is the most accurate natural color image of Pluto. This natural-color image results from refined calibration of data gathered by New Horizons’ color Multispectral Visible Imaging Camera (MVIC). The processing creates images that would approximate the colors that the human eye would perceive, bringing them closer to “true color” than the images released near the encounter. This single color MVIC scan includes no data from other New Horizons imagers or instruments added. The striking features on Pluto are clearly visible, including the bright expanse of Pluto’s icy, nitrogen-and-methane rich “heart,” Sputnik Planitia.
      Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker
      View the full article
    • By NASA
      As Hubble marks three and a half decades of scientific breakthroughs and technical resilience, the “Hubble at 35 Years” symposium offers a platform to reflect on the mission’s historical, operational, and scientific legacy. Hubble’s trajectory—from early challenges to becoming a symbol of American scientific ingenuity—presents valuable lessons in innovation, collaboration, and crisis response. Bringing together scientists, engineers, and historians at NASA Headquarters ensures that this legacy informs current and future mission planning, including operations for the James Webb Space Telescope, Roman Space Telescope, and other next-generation observatories. The symposium not only honors Hubble’s transformative contributions but also reinforces NASA’s commitment to learning from the past to shape a more effective and ambitious future for space science.
      Hubble at 35 Years
      Lessons Learned in Scientific Discovery and NASA Flagship Mission Operations
      October 16–17, 2025
      James Webb Auditorium, NASA HQ, Washington, D.C.
      The giant Hubble Space Telescope (HST) can be seen as it is suspended in space by Discovery’s Remote Manipulator System (RMS) following the deployment of part of its solar panels and antennae on April 25, 1990.NASA The story of the Hubble Space Telescope confirms its place as the most transformative and significant astronomical observatory in history. Once called “the eighth wonder of the world” by a former NASA administrator, Hubble’s development since its genesis in the early 1970s and its launch, repair, and ultimate impact since 1990 provide ample opportunity to apply insights from its legacy. Scientists and engineers associated with groundbreaking discoveries have always operated within contexts shaped by forces including the government, private industry, the military, and the public at large. The purpose of this symposium is to explore the insights from Hubble’s past and draw connections that can inform the development of mission work today and for the future.
      Contact the Organizer Keep Exploring Discover More Topics From NASA
      Hubble’s 35th Anniversary
      Universe
      Humans In Space
      NASA History

      View the full article
    • By NASA
      Explore Webb Webb News Latest News Latest Images Webb’s Blog Awards X (offsite – login reqd) Instagram (offsite – login reqd) Facebook (offsite- login reqd) Youtube (offsite) Overview About Who is James Webb? Fact Sheet Impacts+Benefits FAQ Science Overview and Goals Early Universe Galaxies Over Time Star Lifecycle Other Worlds Observatory Overview Launch Deployment Orbit Mirrors Sunshield Instrument: NIRCam Instrument: MIRI Instrument: NIRSpec Instrument: FGS/NIRISS Optical Telescope Element Backplane Spacecraft Bus Instrument Module Multimedia About Webb Images Images Videos What is Webb Observing? 3d Webb in 3d Solar System Podcasts Webb Image Sonifications Webb’s First Images Team International Team People Of Webb More For the Media For Scientists For Educators For Fun/Learning Since July 2022, NASA’s James Webb Space Telescope has been unwaveringly focused on our universe. With its unprecedented power to detect and analyze otherwise invisible infrared light, Webb is making observations that were once impossible, changing our view of the cosmos from the most distant galaxies to our own solar system.
      Webb was built with the promise of revolutionizing astronomy, of rewriting the textbooks. And by any measure, it has more than lived up to the hype — exceeding expectations to a degree that scientists had not dared imagine. Since science operations began, Webb has completed more than 860 scientific programs, with one-quarter of its time dedicated to imaging and three-quarters to spectroscopy. In just three years, it has collected nearly 550 terabytes of data, yielding more than 1,600 research papers, with intriguing results too numerous to list and a host of new questions to answer.
      Here are just a few noteworthy examples.
      1. The universe evolved significantly faster than we previously thought.
      Webb was specifically designed to observe “cosmic dawn,” a time during the first billion years of the universe when the first stars and galaxies were forming. What we expected to see were a few faint galaxies, hints of what would become the galaxies we see nearby.
      Instead, Webb has revealed surprisingly bright galaxies that developed within 300 million years of the big bang; galaxies with black holes that seem far too massive for their age; and an infant Milky Way-type galaxy that existed when the universe was just 600 million years old. Webb has observed galaxies that already “turned off” and stopped forming stars within a billion years of the big bang, as well as those that developed quickly into modern-looking “grand design” spirals within 1.5 billion years.
      Hundreds of millions of years might not seem quick for a growth spurt, but keep in mind that the universe formed in the big bang roughly 13.8 billion years ago. If you were to cram all of cosmic time into one year, the most distant of these galaxies would have matured within the first couple of weeks, rapidly forming multiple generations of stars and enriching the universe with the elements we see today.
      Image: JADES deep field
      A near-infrared image from NASA’s James Webb Space Telescope shows a region known as the JADES Deep Field. Tens of thousands of galaxies are visible in this tiny patch of sky, including Little Red Dots and hundreds of galaxies that existed more than 13.2 billion years ago, when the universe was less than 600 million years old. Webb also spotted roughly 80 ancient supernovae, many of which exploded when the universe was less than 2 billion years old. This is ten times more supernovae than had ever been discovered before in the early universe. Comparing these supernovae from the distant past with those in the more recent, nearby universe helps us understand how stars in these early times formed, lived, and died, seeding space with the elements for new generations of stars and their planets. NASA, ESA, CSA, STScI, JADES Collaboration 2. Deep space is scattered with enigmatic “Little Red Dots.”
      Webb has revealed a new type of galaxy: a distant population of mysteriously compact, bright, red galaxies dubbed Little Red Dots. What makes Little Red Dots so bright and so red? Are they lit up by dense groupings of unusually bright stars or by gas spiraling into a supermassive black hole, or both? And whatever happened to them? Little Red Dots seem to have appeared in the universe around 600 million years after the big bang (13.2 billion years ago), and rapidly declined in number less than a billion years later. Did they evolve into something else? If so, how? Webb is probing Little Red Dots in more detail to answer these questions.
      3. Pulsating stars and a triply lensed supernova are further evidence that the “Hubble Tension” is real.
      How fast is the universe expanding? It’s hard to say because different ways of calculating the current expansion rate yield different results — a dilemma known as the Hubble Tension. Are these differences just a result of measurement errors, or is there something weird going on in the universe? So far, Webb data indicates that the Hubble Tension is not caused by measurement errors. Webb was able to distinguish pulsating stars from nearby stars in a crowded field, ensuring that the measurements weren’t contaminated by extra light. Webb also discovered a distant, gravitationally lensed supernova whose image appears in three different locations and at three different times during its explosion. Calculating the expansion rate based on the brightness of the supernova at these three different times provides an independent check on measurements made using other techniques. Until the matter of the Hubble Tension is settled, Webb will continue measuring different objects and exploring new methods.
      4. Webb has found surprisingly rich and varied atmospheres on gas giants orbiting distant stars.
      While NASA’s Hubble Space Telescope made the first detection of gases in the atmosphere of a gas giant exoplanet (a planet outside our solar system), Webb has taken studies to an entirely new level. Webb has revealed a rich cocktail of chemicals, including hydrogen sulfide, ammonia, carbon dioxide, methane, and sulfur dioxide — none of which had been clearly detected in an atmosphere outside our solar system before. Webb has also been able to examine exotic climates of gas giants as never before, detecting flakes of silica “snow” in the skies of the puffy, searing-hot gas giant WASP-17 b, for example, and measuring differences in temperature and cloud cover between the permanent morning and evening skies of WASP-39 b.
      Image: Spectrum of WASP-107 b
      A transmission spectrum of the “warm Neptune” exoplanet WASP-107 b captured by NASA’s Hubble and Webb space telescopes, shows clear evidence for water, carbon dioxide, carbon monoxide, methane, sulfur dioxide, and ammonia in the planet’s atmosphere. These measurements allowed researchers to estimate the interior temperature and mass of the core of the planet, as well as understand the chemistry and dynamics of the atmosphere. NASA, ESA, CSA, Ralf Crawford (STScI) 5. A rocky planet 40 light-years from Earth may have an atmosphere fed by gas bubbling up from its lava-covered surface.
      Detecting, let alone analyzing, a thin layer of gas surrounding a small rocky planet is no easy feat, but Webb’s extraordinary ability to measure extremely subtle changes in the brightness of infrared light makes it possible. So far, Webb has been able to rule out significant atmosphere on a number of rocky planets, and has found tantalizing signs of carbon monoxide or carbon dioxide on 55 Cancri e, a lava world that orbits a Sun-like star. With findings like these, Webb is laying the groundwork for NASA’s future Habitable Worlds Observatory, which will be the first mission purpose-built to directly image and search for life on Earth-like planets around Sun-like stars.
      6. Webb exposes the skeletal structure of nearby spiral galaxies in mesmerizing detail.
      We already knew that galaxies are collections of stars, planets, dust, gas, dark matter, and black holes: cosmic cities where stars form, live, die, and are recycled into the next generation. But we had never been able to see the structure of a galaxy and the interactions between stars and their environment in such detail. Webb’s infrared vision reveals filaments of dust that trace the spiral arms, old star clusters that make up galactic cores, newly forming stars still encased in dense cocoons of glowing dust and gas, and clusters of hot young stars carving enormous cavities in the dust. It also elucidates how stellar winds and explosions actively reshape their galactic homes.
      Image: PHANGS Phantom Galaxy (M74/NGC 628)
      A near- to mid-infrared image from NASA’s James Webb Space Telescope highlights details in the complex structure of a nearby galaxy that are invisible to other telescopes. The image of NGC 628, also known as the Phantom Galaxy, shows spiral arms with lanes of warm dust (represented in red), knots of glowing gas (orange-yellow), and giant bubbles (black) carved by hot, young stars. The dust-free core of the galaxy is filled with older, cooler stars (blue). NASA, ESA, CSA, STScI, Janice Lee (STScI), Thomas Williams (Oxford), PHANGS team 7. It can be hard to tell the difference between a brown dwarf and a rogue planet.
      Brown dwarfs form like stars, but are not dense or hot enough to fuse hydrogen in their cores like stars do. Rogue planets form like other planets, but have been ejected from their system and no longer orbit a star. Webb has spotted hundreds of brown-dwarf-like objects in the Milky Way, and has even detected some candidates in a neighboring galaxy. But some of these objects are so small — just a few times the mass of Jupiter — that it is hard to figure out how they formed. Are they free-floating gas giant planets instead? What is the least amount of material needed to form a brown dwarf or a star? We’re not sure yet, but thanks to three years of Webb observations, we now know there is a continuum of objects from planets to brown dwarfs to stars.
      8. Some planets might be able to survive the death of their star.
      When a star like our Sun dies, it swells up to form a red giant large enough to engulf nearby planets. It then sheds its outer layers, leaving behind a super-hot core known as a white dwarf. Is there a safe distance that planets can survive this process? Webb might have found some planets orbiting white dwarfs. If these candidates are confirmed, it would mean that it is possible for planets to survive the death of their star, remaining in orbit around the slowly cooling stellar ember.
      9. Saturn’s water supply is fed by a giant fountain of vapor spewing from Enceladus.
      Among the icy “ocean worlds” of our solar system, Saturn’s moon Enceladus might be the most intriguing. NASA’s Cassini mission first detected water plumes coming out of its southern pole. But only Webb could reveal the plume’s true scale as a vast cloud spanning more than 6,000 miles, about 20 times wider than Enceladus itself. This water spreads out into a donut-shaped torus encircling Saturn beyond the rings that are visible in backyard telescopes. While a fraction of the water stays in that ring, the majority of it spreads throughout the Saturnian system, even raining down onto the planet itself. Webb’s unique observations of rings, auroras, clouds, winds, ices, gases, and other materials and phenomena in the solar system are helping us better understand what our cosmic neighborhood is made of and how it has changed over time.
      Video: Water plume and torus from Enceladus
      A combination of images and spectra captured by NASA’s James Webb Space Telescope show a giant plume of water jetting out from the south pole of Saturn’s moon Enceladus, creating a donut-shaped ring of water around the planet.
      Credit: NASA, ESA, CSA, G. Villanueva (NASA’s Goddard Space Flight Center), A. Pagan (STScI), L. Hustak (STScI) 10. Webb can size up asteroids that may be headed for Earth.
      In 2024 astronomers discovered an asteroid that, based on preliminary calculations, had a chance of hitting Earth. Such potentially hazardous asteroids become an immediate focus of attention, and Webb was uniquely able to measure the object, which turned out to be the size of a 15-story building. While this particular asteroid is no longer considered a threat to Earth, the study demonstrated Webb’s ability to assess the hazard.
      Webb also provided support for NASA’s Double Asteroid Redirection Test (DART) mission, which deliberately smashed into the Didymos binary asteroid system, showing that a planned impact could deflect an asteroid on a collision course with Earth. Both Webb and Hubble observed the impact, serving witness to the resulting spray of material that was ejected. Webb’s spectroscopic observations of the system confirmed that the composition of the asteroids is probably typical of those that could threaten Earth.
      —-
      In just three years of operations, Webb has brought the distant universe into focus, revealing unexpectedly bright and numerous galaxies. It has unveiled new stars in their dusty cocoons, remains of exploded stars, and skeletons of entire galaxies. It has studied weather on gas giants, and hunted for atmospheres on rocky planets. And it has provided new insights into the residents of our own solar system.
      But this is only the beginning. Engineers estimate that Webb has enough fuel to continue observing for at least 20 more years, giving us the opportunity to answer additional questions, pursue new mysteries, and put together more pieces of the cosmic puzzle.
      For example: What were the very first stars like? Did stars form differently in the early universe? Do we even know how galaxies form? How do stars, dust, and supermassive black holes affect each other? What can merging galaxy clusters tell us about the nature of dark matter? How do collisions, bursts of stellar radiation, and migration of icy pebbles affect planet-forming disks? Can atmospheres survive on rocky worlds orbiting active red dwarf stars? Is Uranus’s moon Ariel an ocean world?
      As with any scientific endeavor, every answer raises more questions, and Webb has shown that its investigative power is unmatched. Demand for observing time on Webb is at an all-time high, greater than any other telescope in history, on the ground or in space. What new findings await?
      By Dr. Macarena Garcia Marin and Margaret W. Carruthers, Space Telescope Science Institute, Baltimore, Maryland
      Media Contacts
      Laura Betz – laura.e.betz@nasa.gov
      NASA’s Goddard Space Flight Center, Greenbelt, Md.
      Christine Pulliam – cpulliam@stsci.edu
      Space Telescope Science Institute, Baltimore, Md.
      Related Information
      More Webb News
      More Webb Images
      Webb Science Themes
      Webb Mission Page
      Related For Kids
      What is the Webb Telescope?
      SpacePlace for Kids
      En Español
      Ciencia de la NASA
      NASA en español 
      Space Place para niños
      Keep Exploring Related Topics
      James Webb Space Telescope


      Webb is the premier observatory of the next decade, serving thousands of astronomers worldwide. It studies every phase in the…


      Galaxies



      Exoplanets



      Universe


      Share








      Details
      Last Updated Jul 02, 2025 Editor Marty McCoy Contact Laura Betz laura.e.betz@nasa.gov Related Terms
      James Webb Space Telescope (JWST) Astrophysics Black Holes Brown Dwarfs Exoplanet Science Exoplanets Galaxies Galaxies, Stars, & Black Holes Goddard Space Flight Center Nebulae Science & Research Star-forming Nebulae Stars Studying Exoplanets The Universe View the full article
    • By Amazing Space
      Backyard Astronomy: LIVE Streaming the Moon 1st July
    • By Amazing Space
      Backyard Astronomy: LIVE Streaming the Moon 1st July
  • Check out these Videos

×
×
  • Create New...