Scientists detect salts and carbon-based molecules on Ganymede

Ganymede as seen by Juno
A close-up image taken during the June 7, 2021
Juno fly-by of Ganymede Click for original image.

Using data obtained during a close fly-by of Ganymede by Juno in June 2021, scientists have detected evidence of salts and organic carbon-based molecules.

On June 7, 2021, Juno flew over Ganymede at a minimum altitude of 650 miles (1,046 kilometers). Shortly after the time of closest approach, the JIRAM instrument acquired infrared images and infrared spectra (essentially the chemical fingerprints of materials, based on how they reflect light) of the moon’s surface. Built by the Italian Space Agency, Agenzia Spaziale Italiana, JIRAM was designed to capture the infrared light (invisible to the naked eye) that emerges from deep inside Jupiter, probing the weather layer down to 30 to 45 miles (50 to 70 kilometers) below the gas giant’s cloud tops. But the instrument has also been used to offer insights into the terrain of moons Io, Europa, Ganymede, and Callisto (known collectively as the Galilean moons for their discoverer, Galileo).

The JIRAM data of Ganymede obtained during the flyby achieved an unprecedented spatial resolution for infrared spectroscopy – better than 0.62 miles (1 kilometer) per pixel. With it, Juno scientists were able to detect and analyze the unique spectral features of non-water-ice materials, including hydrated sodium chloride, ammonium chloride, sodium bicarbonate, and possibly aliphatic aldehydes.

The data indicated that the salts and organics were most concentrated in Ganymede’s equatorial regions, which are less impacted by Jupiter’s strong magnetic field. The scientists think these materials originally came from the brine of an underground ocean that somehow reached the surface, though this hypothesis remains unconfirmed.

The grooved surface of Ganymede

The grooves of Ganymede
Click for original image.

Cool image time! The picture to the right, reduced to post here, was taken on June 7, 2021 when the Jupiter orbiter Juno did a close flyby of the moon Ganymede, taking four pictures.

Citizen scientists Gerald Eichstädt and Thomas Thomopoulos have now reprocessed parts of those images to bring out the details more clearly (the other new versions available here, and here).

I have chosen to highlight the picture to the right however because it so clearly shows the puzzling grooves that cover much of Ganymede’s surface. While these parallel grooves in many ways mimic the grooves often seen on top of valley glaciers on Earth and Mars, on Ganymede they do not follow any valley floor. Instead, they form patches of parallel grooves that travel in completely different directions, depending on the patch. At the moment their origin is not understood.

These grooves are one of the mysteries that Europe’s Juice probe will attempt to solve when it arrives in orbit around Jupiter in 2031.

Arianespace launches JUICE mission to Jupiter

Arianespace early today used its Ariane-5 rocket, on its next-to-last launch, to send the European Space Agency’s (ESA) JUICE mission on its way to Jupiter to study its large moons.

It will take eight years for JUICE to get to Jupiter, using flybys of the Earth, Moon, and Venus along the way. This journey might also include a flyby of an asteroid, depending on orbital mechanics and the spacecraft’s condition.

Once at Jupiter it will, from ’31 to ’34, do thirty-five flybys of the Ganymede, Callisto, and Europa, and then enter orbit around Ganymede for most of 2035, before being sent to crash onto the planet to end its mission.

Ariane-5 meanwhile has one more launch, in June. After this Arianespace will not at present have an active large rocket, as its Ariane-6 replacement is not yet flying, its maiden flight presently scheduled for the fourth quarter of this year.

This was also Europe’s first launch in 2023, so it does not get listed on the leader board. The leaders of the 2023 launch race are as follows:

23 SpaceX (with a launch scheduled for tonight)
15 China (with a launch scheduled for tomorrow)
6 Russia
3 Rocket Lab

American private enterprise still leads China 26 to 15, but is now tied with the entire world combined 26 all.

Using reflected light from Jupiter to photograph Ganymede’s night side

Ganymede as seen in the reflected light of Jupiter
Click for full image.

During Juno’s June 7, 2021 close fly-by of Ganymede, scientists used its instruments to obtain the first good image of a part of this Jupiter moon. What made the achievement especially amazing was that the area photographed was only lit by the reflected light from Jupiter, the equivalent of its “earthshine.” From the paper’s abstract:

On 7 June 2021, the Juno spacecraft flew within about 1,000 km of the surface of Jupiter’s largest moon, Ganymede. The Mission used their sensitive navigation camera to photograph the moon’s dark side where it was lit only by scattered sunlight from Jupiter. This new imaging approach revealed multiple surface features, including a patchwork of different surface textures (such as grooved terrain), several craters, and ejecta deposits. These features had not been visible in images collected by previous spacecraft.

The picture to the right is from figure 2 of the paper, cropped and reduced to post here. It shows a region on Ganymede that in the earlier images had shown few details because the lighting was poor and thus features were not easily discerned (as can be seen by the inset in the lower right). In the new picture, the only light was reflected from Jupiter, and its low angle brings out the surface topography.

The same region on Ganymede, as seen by Voyager-1 in 1979 and Juno in 2021

Ganymede compared between Voyager-1 and Juno
Click for full image.

When the Jupiter orbiter Juno did a close pass of the moon Ganymede on June 7, 2021, it took four pictures, covering regions mostly photographed for the first time by Voyager-1 in its close fly-by in 1979.

Scientists have now published the data from this new fly-by. Though Juno’s higher resolution pictures revealed many new details when compared with the Voyager-1 images from four decades earlier, the scientists found no changes. The comparison image, figure 2 of their paper, is to the right, reduced and sharpened to post here.

A flicker comparison between the registered JunoCam and Voyager reprojected mosaics revealed no apparent new impact features. Given the high albedo of fresh craters on Ganymede, with high albedo ejecta deposits two or three times the diameter of the craters themselves, we argue that new craters as small as 250 m diameter would be detectable in images at these 1 km per pixel scales. Extrapolating Ganymede cratering rates from Zahnle et al. (2003) below 1 km, the probability of JunoCam observing a new crater over 12.2 million km2 in 42 years is 1 in 1500, consistent with none being observed.

In other words, at these resolutions finding no new impacts is not a surprise.

Of the new features detected, the Juno images could see more details in the bright rays emanating from the crater Tros (in the lower center of both images), and thus found “…terrain boundaries previously mapped as ‘undivided’ or as ‘approximate’, several large craters, and 12 paterae newly identified in this region.”

Paterae resemble craters but are thought to be a some form of volcanic caldera. Their geological origin however is not yet completely understood.

The paper’s conclusion is actually the most exciting:

The insight gained from this handful of images makes it likely in our opinion that new observations from the upcoming JUICE and Europa Clipper missions will revolutionize our understanding of Ganymede.

Ganymede as seen by Juno

Ganymede as seen by Juno
Click to see full image.

Cool image time! The picture to the right, cropped and reduced to post here, was taken on June 7, 2021 when Juno made a close fly-by of Jupiter’s moon Ganymede. It has been reprocessed to bring out the details by citizen scientist Brian Swift.

Note the bands and parallel light and dark ridges that criss-cross the planet. Scientist as yet do not understand what caused them. Note also the bright impact craters, suggesting the release of water ice from below.

This image anticipates Juno’s upcoming September 29, 2022 fly-by of Europa, one of Jupiter’s other Galilean moons. The orbiter will pass only 221 miles above its surface, and get the best images in decades, since the Galileo mission in the 1990s.

1st water vapor in Ganymede’s atmosphere, detected using data from Hubble

Using Hubble data, astronomers have detected the first evidence of water vapor in the atmosphere of Jupiter’s largest moon, Ganymede.

Though larger than the blistering planet Mercury, the Jovian moon Ganymede is no place to go sunbathing. Located ½-billion miles from the Sun, the water ice on its surface is frozen solid in frigid temperatures as low as minus 300 degrees Fahrenheit. This makes the ice as hard as rock. Still, a rain of charged particles from the Sun is enough to turn the ice into water vapor at high noon on Ganymede.

This is the first time such evidence has been found, courtesy of the Hubble Space Telescope’s spectroscopic observations of aurora on Ganymede spanning two decades. The auroras are used to trace the presence of oxygen, which then is linked to the presence of water molecules sputtering off the surface. Ganymede has a deep ocean located an estimated 100 miles below the surface. That’s too deep for water vapor to be leaking out.

This detection has a margin of uncertainty, but it provides a baseline for the up close observations planned for Europe’s JUICE orbiter, set to launch in ’22 and arrive in Jupiter orbit in ’29. JUICE’s study focus will be the three Galilean moons that appear to have lots of ice, Ganymede, Calisto, and Europa.

Juno team creates dramatic animation of Ganymede/Jupiter fly-by

Using images from Juno’s fly-by of both Ganymede and Jupiter on June 7th and 8th, the science team has produced a dramatic animation, with background music, showing that fly-by from the point of view of the spacecraft.

I have embedded it below the fold.

The 3:30-minute-long animation begins with Juno approaching Ganymede, passing within 645 miles (1,038 kilometers) of the surface at a relative velocity of 41,600 mph (67,000 kph). The imagery shows several of the moon’s dark and light regions (darker regions are believed to result from ice sublimating into the surrounding vacuum, leaving behind darkened residue) as well as the crater Tros, which is among the largest and brightest crater scars on Ganymede.

It takes just 14 hours, 50 minutes for Juno to travel the 735,000 miles (1.18 million kilometers) between Ganymede and Jupiter, and the viewer is transported to within just 2,100 miles (3,400 kilometers) above Jupiter’s spectacular cloud tops. By that point, Jupiter’s powerful gravity has accelerated the spacecraft to almost 130,000 mph (210,000 kph) relative to the planet.

Among the Jovian atmospheric features that can be seen are the circumpolar cyclones at the north pole and five of the gas giant’s “string of pearls” – eight massive storms rotating counterclockwise in the southern hemisphere that appear as white ovals. Using information that Juno has learned from studying Jupiter’s atmosphere, the animation team simulated lightning one might see as we pass over Jupiter’s giant thunderstorms.

The lightning shown on Jupiter, while entertaining, is a complete fantasy. The flashes are much too bright and large. At the scale created, some would cover the Earth. In reality, that lightning wouldn’t be visible until you are very very close, and even then probably difficult to spot in the vastness of Jupiter.

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Craters on Ganymede’s striped surface

Craters on Ganymede
Click for full image.

Cool image time! The photo to the right, cropped to post here, is a color enhanced section taken from of one of the images taken by Juno when it did a close fly-by of the Jupiter moon Ganymede back on June 7, 2021.

The enhancement was done by citizen scientist Navaneeth Krishnan, using a wider Juno image of Ganymeded enhanced by citizen scientist Kevin Gill. That wider image is below, and marks the area covered by this first image with a white box.

In this one picture we can see many of the geological mysteries that have puzzled scientists since the Galileo orbiter first took close-up images back in the 1990s. We can see patches of grooved terrain with the grooves in the different patches often oriented differently. We can also see bright and dark patches that while they overlay the grooved terrain they bear no correspondence to those grooved patches. And on top of it all are these small craters, impacts that obviously occurred after the formation of the grooves.
» Read more

Juno takes first close-up images of Ganymede since 2000

Ganymede as seen by Juno
Click for full image.

Ganymede as seen by Juno
Click for full image.

On June 7th the Jupiter orbiter Juno made its first close fly-by of Ganymede, taking the first close-up images of this Jupiter moon since the orbiter Galileo flew past in 2000.

The first two images from NASA Juno’s June 7, 2021, flyby of Jupiter’s giant moon Ganymede have been received on Earth. The photos – one from the Jupiter orbiter’s JunoCam imager and the other from its Stellar Reference Unit star camera – show the surface in remarkable detail, including craters, clearly distinct dark and bright terrain, and long structural features possibly linked to tectonic faults.

…Using its green filter, the spacecraft’s JunoCam visible-light imager captured almost an entire side of the water-ice-encrusted moon. Later, when versions of the same image come down incorporating the camera’s red and blue filters, imaging experts will be able to provide a color portrait of Ganymede. Image resolution is about 0.6 miles (1 kilometer) per pixel.

In addition, Juno’s Stellar Reference Unit, a navigation camera that keeps the spacecraft on course, provided a black-and-white picture of Ganymede’s dark side (the side opposite the Sun) bathed in dim light scattered off Jupiter. Image resolution is between 0.37 to 0.56 miles (600 to 900 meters) per pixel.

Both images are to the right, each slightly reduced to post here. These images of this moon of Jupiter, the largest moon in the solar system and about 26% larger than the planet Mercury, reveal many of the same unsolved geological mysteries uncovered when the Galileo orbiter photographed it two decades ago. As I wrote in my Chronological Encyclopedia

Closer inspection of Ganymede revealed a strange topography, including patches of grooved terrain (not unlike the surface of a vinyl record) overlaying other patches of grooved terrain, the different patches oriented in random and totally unrelated directions. Moreover, the surface is overlain by bright and dark patches (the bright patches thought to be caused by water frost) that often had no apparent correspondence to topographical features. Planetary geologists could only scratch their heads in wonderment.

NASA extends mission of Juno and InSight probes

NASA has decided to extend the missions of Juno and InSight probes, giving both several more years to gather data.

InSight main goal for the two-year extension will be to gather more seismic data of Mars. They will also continue their efforts to get the heat sensor into the ground, but that will have a lower priority.

Juno will be able to slowly adjust its orbit to better study Jupiter’s north polar regions, thus developing a more complete first rough map of the gas giant’s internal structure and atmosphere. The changing orbit will also allow the first close fly-bys of some of Jupiter’s moons, the first in more than twenty years.

The moon flybys could begin in mid-2021 with an encounter with Ganymede, Jupiter’s largest moon, at a distance of roughly 600 miles (1,000 kilometers), Bolton said last year.

After a series of distant passes, Juno will swoop just 200 miles (320 kilometers) above Europa in late 2022 for a high-speed flyby. Only NASA’s Galileo spacecraft, which ended its mission in 2003, has come closer to Europa.

There are two encounters with Jupiter’s volcanic moon Io planned in 2024 at distances of about 900 miles (1,500 kilometers), according to the flight plan presented by Bolton last year. Juno will be able to look for changes on the surfaces of Jupiter’s moons since they were last seen up close by NASA’s Voyager and Galileo probes.

While it will take images, Juno’s camera is not particularly high resolution. The main effort will be to use its instruments to study the surface make-up of the moons.

Giant impact covered almost half of Gandymede’s surface

Artist's illustration of Ganydmede
Click for full illustration.

The uncertainty of science: Computer modeling and a review of images taken by Voyager 1 and 2 and the Galileo orbiter of Jupiter’s moon Ganymede now suggest the existence of a giant impact so large that it covers almost half the moon’s surface.

The artist’s illustration of Ganymede on the right, based on our presently incomplete set of global images, shows this impact area as the circular dark region.

Many furrows, or trough formations, have been observed on the surface of Ganymede, one of the Jovian moons. This research group comprehensively reanalyzed image data of Ganymede obtained by NASA’s Voyager 1, Voyager 2, and Galileo spacecrafts. The results revealed that almost all of these furrows appear to be arranged in concentric rings centered around a single point, indicating that this global multiring structure may be the remains of a giant crater. The radial extent of the multiring structures measured along Ganymede’s surface is 7800 km. For comparison, the mean circumference of Ganymede is only 16,530 km. If correct, this is the largest crater yet identified in the Solar System. The previous record holder with a 1900 km radius is on Calisto, another Jovian moon.

The conclusion reached here is very uncertain, since we really do not have a high resolution global map of Ganymede. All three spacecraft were only able to send back a scattering of high resolution images. The global map is based on Earth observations and images from the Hubble Space Telescope.

First image of Ganymede’s north pole

Ganymede's north polar region

During Juno’s 24th close approach to Jupiter the spacecraft was able to take the first images ever of the north pole of Ganymede, the largest moon in the solar system. The image to the right was processed by citizen scientist Roman Tkacenko, and shows a variety of light and dark features.

The Juno science team decided for some reason to highlight a different set of images processed by citizen scientist Gerald Eichstädt, using the same data. I prefer Tkacenko’s version, because he focused in on the planet itself, making it easier to see what’s there.

In either case, however, the fuzziness of the image reminds me of planetary astronomy in my early childhood. Images like this, taken by telescopes on Earth, were the best we had of any planet beyond the Moon. Made it very hard to understand what was there, or what it meant.

Ganymede’s underground salt water ocean

By measuring the interaction of Jupiter and Ganymede’s magnetic fields, scientists have been able to estimate the size of the salt water ocean in Ganymede’s interior.

A team of scientists led by Joachim Saur of the University of Cologne in Germany came up with the idea of using Hubble to learn more about the inside of the moon. “I was always brainstorming how we could use a telescope in other ways,” said Saur. “Is there a way you could use a telescope to look inside a planetary body? Then I thought, the aurorae! Because aurorae are controlled by the magnetic field, if you observe the aurorae in an appropriate way, you learn something about the magnetic field. If you know the magnetic field, then you know something about the moon’s interior.”

If a saltwater ocean were present, Jupiter’s magnetic field would create a secondary magnetic field in the ocean that would counter Jupiter’s field. This “magnetic friction” would suppress the rocking of the aurorae. This ocean fights Jupiter’s magnetic field so strongly that it reduces the rocking of the aurorae to 2 degrees, instead of 6 degrees if the ocean were not present. Scientists estimate the ocean is 60 miles (100 kilometers) thick — 10 times deeper than Earth’s oceans — and is buried under a 95-mile (150-kilometer) crust of mostly ice.

That’s more water than contained in all of Earth’s oceans.

Europe has decided to build a probe, dubbed JUICE, to study Ganymede, Callisto and Europa, Jupiter’s big icy moons.

Europe has decided to build a probe to study Ganymede, Callisto and Europa, Jupiter’s big icy moons.

Known as JUICE, the Jupiter Icy Moons Explorer, the probe will enter orbit around the gas giant planet in 2030 for a series of flybys of Ganymede, Callisto and Europa. JUICE will brake into orbit around Ganymede, Jupiter’s largest moon, in 2032 for at least one year of close-up research.