In our last article, we took a look at NASA’s JEO and the main object of its observations, the intriguing moon Europa.  In this article, we will look at the ESA’s JGO, which will orbit Jupiter’s largest moon, Ganymede.

As we said above, the opening of the mission, upon arrival at Jupiter, is a collaborative overview of the entire Jovian system.  Because of its enormous gravity pull and magnetic field, the great planet has a big influence over its satellites, and the system must be viewed as a whole.  In particular, the magnetic interaction between all of these bodies is very complex, and will be studied in great detail.

In connection with this, there will be a contribution from the Japan Aerospace Exploration Agency.  JAXA is designing and building a probe called the Jupiter Magnetospheric Orbiter (JMO), which will perform some stand-alone observations of the Jovian magnetic environment, as well as collaborating with the JGO and JEO on multi-point measurements of Jupiter’s magnetic field and its interaction with its satellites.

So far, we haven’t mentioned the JMO because it will travel onboard the JGO until insertion into Jupiter orbit.  At that time, it will be deployed from the JGO and enter a separate orbit.

The Jupiter Magnetospheric Orbiter will be a spinning probe weighing about 400 kg., and it will be carrying a scientific payload of 25 kg.  When it is deployed, the spin axis will be tilted toward Earth.  This craft will employ technology borrowed from three earlier missions: the Nozomi Mars probe, the BepiColombo Mercury probe and the Solar Sail project.  (The BepiColombo and Solar Sail missions were mentioned in earlier articles at this website.  Nozomi was a Japanese unmanned Mars probe which was unfortunately lost due to technical problems, but its failure had nothing to do with the technology that will be recycled for use on the JMO.)  For its post-deployment maneuvers, it will be carrying 60 kg. of propellant.  For all of its other functions, it will be powered by electricity from two “paddle-wheel” solar panels.

(This info comes from the original mission proposal, and may change before completion.  In particular, the proposal expressed the wish to increase the payload weight.  Hopefully they will be successful in this.)

The JMO has an ambitious schedule of observations to make after being deployed from the JGO.  It will perform the first complete survey of the Jovian magnetosphere, mapping lines of magnetic force which run from Jupiter to its moons.  It will also address various questions relating to the interaction of the solar wind with the Jovian magnetosphere, as well as the effects of these interactions on the atmosphere of Jupiter.  As mentioned above, there will be some studies which will be performed in coordination with the JGO and JEO.  The presence of a third point of observation will allow the construction of three-dimensional images of the magnetosphere.

After separating from the JMO, the JGO will first take part in an elaborate series of maneuvers in coordination with the JEO, in which they will conduct a large-scale survey of Jupiter and its moon system.  The JGO’s primary goal is to study the moon Ganymede, but there will also be observations of Callisto, Io and Europa, performed either alone or in cooperation with the JEO.  After that, the JGO will go into orbit around Ganymede for prolonged observations.  (This is a greatly simplified description.  The full itinerary will include an ambitious- and confusing- array of maneuvers, a full discussion of which is far beyond the scope of this humble article.  For those who want more details, the websites of all three space agencies offer fascinating reading.)

Ganymede is Jupiter’s largest moon.  In fact, if this body orbited the sun instead of Jupiter, it would be classified as a planet.  It is larger than either Mercury or Pluto, and is three-quarters of the size of Mars.  It actually has an oxygen atmosphere, though the pressure is too low to support any kind of life known on Earth.

One interesting point about Ganymede, and the subject of some of the study on this mission, is that it is the only moon in the solar system with an active magnetic field.  Like so many other things in the Jupiter system, Ganymede’s magnetism is a result of Jupiter’s gravity.  In our last article, we saw that the big planet’s gravity causes tidal heating in the interiors of its moons, especially the closer ones.  This is the reason why Europa almost certainly has a liquid ocean beneath its surface, and it is also the reason for Io’s excessive volcanic activity.  Here we see another example, for without Jupiter’s gravity, Ganymede would not have its magnetic field.

As we saw in our article on the BepiColombo Mercury probe a couple of weeks ago, a body can only have an active magnetic field if it has a solid inner core with a molten mantle above it.  The molten mantle contains iron, and the heat which keeps it molten causes it to move in convection currents.  The solid core contains iron, too, and the movement of the molten iron mantle around the solid iron core is what makes the electrical current that forms the magnetic field.  Without this movement of iron around iron, electricity will not be generated, and the body will not have a magnetic field.  In the case of Ganymede, it is the tidal heating caused by Jupiter’s gravity that keeps the moon’s mantle liquid, allowing the convection movement that makes the whole process work.

During the time when the JGO is orbiting Ganymede, there will be times when the JEO is also passing close enough to allow coordinated observations involving both probes.  This will allow detailed study, with the JGO performing close study while the JEO observes from farther away.  In this way, it is hoped that they will be able to do precise mapping of the Ganymedan magnetic field.

We already know that Ganymede’s history has been long and complicated.  About forty percent of its surface is highly cratered, darker areas, while the other sixty percent is lighter in color, and is covered by an elaborate pattern of grooves.  The surface of Ganymede is mostly water ice, and these grooves are thought to be caused by tensional faulting of this ice, or by liquid water flowing up from below the surface.  Here, as on Europa, we have the near certainty of large amounts of liquid water beneath the surface.   The presence of liquid water always raises the possibility of life, and here again we get back to the main goal of the entire EJSM/LaPlace mission,  to search for habitable worlds.  This actually encompasses two separate questions: do these worlds have life now, and could they support human beings in the future?

The fourth moon to be examined will be Callisto, and these observations will be conducted primarily by the JGO, though the JEO will take part in some of them.  Callisto is the third largest moon in the solar system, and is almost as big as Mercury.  The unique and interesting thing about Callisto is that it seems to be a geologically dead world, with no visible seismic activity, vulcanism, or anything else to alter its surface.   Unlike the three other moons we have looked at, this one orbits much farther from Jupiter, so the kind of volcanic activity that we saw on Io, for example, is absent here.  Because of this, it is thought that Callisto has the oldest landscape in the solar system, preserving impact craters from the very early history of planetary formation.  All of the other bodies in the solar system have changed since then, but Callisto remains as a snapshot of the system’s childhood.  As you can imagine, this moon will be the subject of much study in the future, and the work that will be done by this mission will pave the way for that research by giving us our first close-up view of the body.

The EJSM/LaPlace mission is a huge undertaking which promises to yield a staggering amount of data.  Even if some of the science doesn’t come off as planned, this project will undoubtedly be one of the most productive and thorough space projects ever.  For years to come, we will be poring over the information that this project will give us.

We have always had our eyes on the moons of Jupiter.  Ever since Galileo looked through his homemade telescope and drew his first crude pictures of them, we have wanted to visit them.  The more we learn about them, the more interesting they get.  These are real worlds, with atmospheres, heat and water.  They may have life, and they certainly will have it in the future, for we will visit these bodies in person someday.  While it is unlikely that hellish Io will ever be settled by humans, it certainly makes an interesting place to study, and the other three Galilean moons will almost certainly feel the tread of human feet someday.  When that happens, it will be a direct result of the knowledge we gain from this mission.

Sources:

Solar System Exploration: Moons and Planets of the Solar System at NASA website:  solarsystem.jpl.nasa.gov/planets/

OPFM: Outer Planet Flagship Mission at website of Jet Propulsion Laboratory, California Institute of Technology:  opfm.jpl.nasa.gov/europajupitersystemmissionejsm/

OPFM: Outer Planet Flagship Mission- Jupiter Ganymede Orbiter (JGO) Concept at website of Jet Propulsion Laboratory, California Institute of Technology:  opfm.jpl.nasa.gov/europajupitersystemmissionejsm/jupiterganymedeorbiterjgoconcept/

Synergy Between JMO, JGO, and JMO at ISAS/JAXA website:  sprg.isas.jaxa.jp/jupiter/pukiwiki/index.php?Synergy%20between%20JMO%2C%20JGO%2C%20and%20JEO

Scope and Purpose: The Europa Jupiter System Mission (EJSM) at ISAS/JAXA website:  sprg.isas.jaxa.jp/jupiter/pukiwiki/index.php?I.%20SCOPE%20and%20PURPOSE

III “The Spacecraft” and III.1: “Current Plan” at ISAS/JAXA website:  sprg.isas.jaxa.jp/jupiter/pukiwiki/index.php?III.%20Spacecraft

II.2.1 “Main Objectives” at ISAS/JAXA website:  sprg.isas.jaxa.jp/jupiter/pukiwiki/index.php?II.2%20Magnetospheric%20and%20Space%20Sciences

IV.1 “The Current JAXA Plan” at ISAS/JAXA website:  sprg.isas.jaxa.jp/jupiter/pukiwiki/index.php?IV.%20Orbit%20and%20Operation

The Jupiter flyby was a huge success, allowing observations of the giant planet and its moons in unprecedented detail.  Among other things, information was gathered about the atmosphere and weather of Jupiter.  Data on cloud composition was collected by the visible light, infrared and ultraviolet remote sensing devices, and ammonia was observed welling up from the lower atmosphere to form clouds.  Lightning strikes were observed at the poles, the first polar lightning ever seen off Earth, and from this it was learned that heat moves evenly through water clouds at all latitudes across Jupiter.  New Horizons also made size and speed measurements of waves in the Jovian atmosphere, indicating strong storm activity beneath, and obtained close-up images of the Little Red Spot, a smaller version of the Great Red Spot.  The smaller feature is about half the size of the bigger one, or about 70 per cent of Earth’s diameter.

New Horizons obtained the clearest images yet of the tenuous Jovian rings.  Here clumps of material were observed that may be from a recent impact within the ring system.  The probe got a detailed view of the ring dynamics involved here, with moons Metis and Adrastea shepherding the materials around the rings.  A search for small moons within the rings yielded negative results.

The probe performed observations of Jupiter’s four largest moons, focusing especially on Io, closest to Jupiter and volcanically active.  Eleven volcanic plumes of varying size were seen, three for the first time.  One of these, a 200-mile-high eruption from the volcano Tvashtar, offered a chance to see the structure and motion of the plume as it condensed and fell back to the surface.  Instruments picked up infrared radiation from at least 36 volcanoes on Io with lava temperatures about 1900 degrees Fahrenheit, which is comparable to volcanoes on Earth.  Io is the most active body in the solar system, and more than 20 geological changes had occurred since the Galileo Jupiter orbiter was there in 2001.  Observations of Io while in Jupiter’s shadow showed glowing clouds over many of the volcanoes, a possible source of gas for Io’s atmosphere.

The probe passed down Jupiter’s magnetotail and got the closest-ever look at this region.  Particle detectors indicated that volcanic material from Io moves down the tail in slow-moving blobs.  Scientists are hoping to learn how these gases are ionized, trapped and energized by Jupiter’s magnetic field, and then finally ejected from the system.

New Horizons left Cape Canaveral in January, 2006.  It is the fastest spacecraft ever built, reaching Jupiter in only 13 months.  It is now about halfway between the orbits of Jupiter and Saturn, more than 743 million miles from Earth, and it will fly past Pluto and its moons Charon, Nix and Hydra in July 2015 before going deeper into the Kuiper Belt.

At present, the mission continues to go well.  In November of 2009, the probe was brought out of hibernation to repoint the communications dish antenna in order to keep up with the changing position of Earth around the sun.  This wake-up also provided an opportunity to download several months of stored data, correct a minor bug in the fault protection system software, perform adjustments to refine the craft’s trajectory, and upload instructions for the running of the craft from now until its next scheduled wake up in January 2010.

While New Horizons will not reach its destination until 2015, it will be able to perform some observations of Pluto and its largest moon, Charon, about a year earlier.  It will be taking pictures of the two at that point, and a few months later, it will be able to generate a map of Pluto.

The long approach will give an opportunity to watch seasonal changes in Pluto’s atmosphere.    Since 1989, Pluto has been heading away from the sun.  In 1999, it crossed the orbit of Neptune, once again becoming the outermost of the nine traditional planets.  It is now heading into its 200-year winter, when its atmosphere is expected to freeze and fall to the surface as snow, and because of this, the New Horizons mission will be the last chance to study the atmosphere of Pluto.  The probe will obtain information about its chemical composition, and also allow observations of cloud formation.  Clouds, probably composed of nitrogen or carbon monoxide, have already been observed in the thin atmosphere of Pluto.

Once New Horizons has passed Pluto, it will head out into the Kuiper Belt to find and study some of the mysterious bodies that exist there, which are thought to be icy and comet-like.  The probe will conduct a search for Kuiper Belt bodies, and when it finds them, will modify its own course to approach and observe them.  It is hoped that New Horizons will find six to ten of these bodies to study.

The outermost region of the solar system is a vast, dark area that is only beginning to reveal its secrets.   What else is out there?  Over the next few years, we will begin to find out.