Posted on by Nancy Atkinson

Amateur Astronomer Creates Detailed Map of Ganymede

The original observations (top) and interpretations (bottom) of the first ever amateur albedo map of Ganymede. Credit: Manos Kardasis.

As our frequent “Astrophoto” posts from amateur astronomers and photographers attest – as well as the rise of citizen science — , the latest technology allows amatuers to make significant contributions to the field of astronomy. Case in point: Emmanuel I. Kardasis of the Hellenic Amateur Astronomy Association has produced the first amateur albedo map of Jupiter’s moon Ganymede. He used an off-the-shelf telescope, camera and computer equipment, but put his experienced observing skills to the test.

“Ganymede has a tiny disk as seen from Earth so was a good test for my techniques,” said Kardasis. “If the same methods were applied to other worlds, perhaps the volcanic moon Io, we could capture surface fluctuations. Professional observatories may create better images but they cannot monitor our rapidly and ever-changing Universe.”

Albedo maps of Ganymede (left) and how they relate to known surface features (right). Credit: Manos Kardasis.

Like many amateurs, Kardasis attached a camera to his telescope and recorded a video of Ganymede. Selecting only the sharpest frames of the video allowed him to obtain a series of images when the atmospheric conditions – known as ‘seeing’ – were most favorable. These best images were then stacked and aligned, before being enhanced through photo-editing software.

An albedo map details higher areas of reflectivity on an object’s surface recording where material is brighter or darker. Kardasis’ albedo map closely aligns with professional images of Ganymede’s surface, indicating features such as Phrygia Sulcus (furrows and ridges 3,700 km across) and the Nicholson region (a low-lying darker area).

Amateur photographs of Jupiter and Ganymede, accompanied with a professionally-obtained labeled map (bottom right). Credit: Manos Kardasis.

“Creating useful images of planets requires a telescope with a diameter of at least eight inches, said Kardasis. “For tiny discs, such as the moons of Jupiter, bigger is definitely better. My Ganymede images were made using an 11-inch telescope. You also need a good motor drive on your tripod, a sensitive camera, some freely-available software, and lots of patience!”

Kardasis presented his images at the European Planetary Science Congress this week in Madrid, Spain. He suggests that future amateur programs could monitor both surface and atmospheric changes on worlds as varied as Uranus, Neptune and Titan, complementing more detailed but far less regular observations made by professionals. Kardasis says, “I hope my work will inspire anyone interested in astronomy to use whatever equipment they have to make useful observations.”

Source: EPSC

Posted on by Jason Major

ESA Turns On The JUICE For New Jupiter Mission

Galileo image of Ganymede, Jupiter's - and the Solar System's - largest moon. (Ted Stryk)

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The European Space Agency has given the go-ahead for an exciting mission to explore the icy moons of Jupiter, as well as the giant planet itself.

JUICE — JUpiter ICy moons Explorer — will consist of a solar-powered spacecraft that will spend 3.5 years within the Jovian system, investigating Ganymede, Europa and the upper atmosphere of Jupiter. Anticipated to launch in June 2022, JUICE would arrive at Jupiter in early 2030.

As its name implies, JUICE’s main targets are Jupiter’s largest icy moons — Ganymede and Europa — which are thought to have liquid oceans concealed beneath their frozen surfaces.

The largest moon in the Solar System, Ganymede is also thought to have a molten iron core generating a magnetic field much like Earth’s. The internal heat from this core may help keep Ganymede’s underground ocean liquid, but the dynamics of how it all works are not quite understood.

JUICE will also study the ice-coated Europa, whose cueball-smooth surface lined with cracks and jumbled mounds of frozen material seem to be sure indicators of a subsurface ocean, although how deep and how extensive is might be are still unknown — not to mention its composition and whether or not it could be hospitable to life.

The rust-colored cracks lining Europa's otherwise smooth surface hint at a subsurface ocean. (Ted Stryk)

“JUICE will give us better insight into how gas giants and their orbiting worlds form, and their potential for hosting life,” said Professor Alvaro Giménez Cañete, ESA’s Director of Science and Robotic Exploration.

The JUICE spacecraft was originally supposed to join a NASA mission dedicated to the investigation of Europa, but NASA deemed their proposed mission too costly and it was cancelled. According to Robert Pappalardo, study scientist for the Europa mission based at JPL, NASA may still supply some instruments for the spacecraft “assuming that the funding situation in the United States can bear it.”

Artist's rendering of JUICE at Jupiter. (ESA/AOES)

JUICE will also capture images of Jupiter’s moon Callisto and search for aurorae in the gas giant’s upper atmosphere, as well as measure the planet’s powerful magnetic field. Once arriving in 2030, it will spend at least three years exploring the Jovian worlds.

Read more in today’s news release from Nature, and stay tuned to ESA’s JUICE mission page here.

Recalibrated Galileo images © Ted Stryk. See more of Ted’s excellent work on his site Planetary Images From Then And Now.

Posted on by Nancy Atkinson

One of Jupiter’s Moons is Melted!

The two outer moons of Jupiter, with the cutaway showing the extent of melting caused by an astroid/comet bombardment. Credit: Amy Barr, SWRI

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Jupiter’s two moons Ganymede and Callisto could be considered fraternal twins. They have a similar composition and size, but visually, they are different. Also, data from the Galileo and Voyager spacecraft reveal the two moons’ interiors are very dissimilar, as well. The reasons for the differences have eluded scientists for 30 years, but a new study provides an explanation. During the Late Heavy Bombardment, Callisto escaped relatively unscathed, while Ganymede was a battered child; so much so that the later moon melted. “Impacts during this period melted Ganymede so thoroughly and deeply that the heat could not be quickly removed,” said Dr. Amy Barr of the Southwest Research Institute. “All of Ganymede’s rock sank to its center the same way that all the chocolate chips sink to the bottom of a melted carton of ice cream. Callisto received fewer impacts at lower velocities and avoided complete melting.”

Barr and and Dr. Robin Canup created a model showing how Jupiter’s strong gravity focused cometary impactors onto Ganymede and Callisto 3.8 billion years ago, during the LHB period. Each impact onto Ganymede or Callisto’s mixed ice and rock surface creates a pool of liquid water, allowing rock in the melt pool to sink to the moon’s center.

But Ganymede is closer to Jupiter and therefore was hit by twice as many icy impactors as Callisto. Additionally, the impactors hitting Ganymede had a higher average velocity. Modeling by Barr and Canup shows that core formation begun during the late heavy bombardment becomes energetically self-sustaining in Ganymede but not Callisto.

Interior density structures created by an outer solar system late heavy bombardment onto Ganymede (top row) and Callisto (bottom row). Credit: SwRI

Watch a movie that shows the effect of an outer solar system late heavy bombardment on the interior structure of Callisto (top model in the movie) and Ganymede (bottom).

“Similar to Earth and Venus, Ganymede and Callisto are twins, and understanding how they were born the same and grew up to be so different is of tremendous interest to planetary scientists,” explains Barr. “Our study shows that Ganymede and Callisto record the fingerprints of the early evolution of the solar system, which is very exciting and not at all expected.”

The “Ganymede-Callisto dichotomy,” has been a classical problem in comparative planetology, a field of study that seeks to explain why some solar system objects with similar bulk characteristics have radically different appearances. The study by Barr and Canup also links the evolution of Jupiter’s moons to the orbital migration of the outer planets and the bombardment history of Earth’s moon.

Their article, “Origin of the Ganymede-Callisto dichotomy by impacts during the late heavy bombardment,” by Barr and Canup, appears online in Nature Geoscience on Jan. 24, 2010.

Source: SwRI