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 two main spacecraft in the mission are NASA’s Jupiter Europa Orbiter (JEO) and the European Space Agency’s Jupiter-Ganymede Orbiter (JGO).  While the exact timeline has yet to be released, tentative plans would have the two crafts being launched about a month apart.  They will travel for about six years, and for a while after reaching Jupiter, they will work together.  The first part of the mission is an elaborate dance through the Jupiter system, collaborating on an overview of the giant planet and its system of satellites, which has been called a mini-solar system because of its size and complexity.   After that, the probes will go into their separate orbits around Europa and Ganymede for in-depth study.  During the course of the mission, there will also be flybys of Io and Callisto.

Because this mission is so big, and since it involves two spacecraft, we will divide it into two segments.  In this part, we will look at NASA’s Jupiter Europa Orbiter.  As the plan stands now, this probe will launch in February 2020 aboard an Atlas V 551 rocket.   The course that it will follow will be called the VEEGA course, since it involves one gravity assist maneuver at Venus and two at Earth.  On this trajectory, it will arrive at the Jupiter system in December 2025.  (Dates may change slightly as plans become firmer.)  After entering orbit around Jupiter, it will undertake a 30-month tour of the Jovian system, which will be followed by Europa Orbital Insertion (EOI) for a nine-month science mapping phase.  There will be several highlights in this tour:

1. Four encounters with the moon Io, with a possible volcanic plume flythrough.

2.  Six Europa encounters before the actual insertion into orbit around that moon.

3. Six encounters with Ganymede, to study that moon’s magnetosphere.

4.  Nine encounters with Callisto.

5.  Continuous monitoring of Jupiter and Io’s atmospheres.

After this, the probe will enter a 200 km. orbit around Europa, conduct a one-month mapping survey, then move to a 100 km. orbit for further observations.

The data collected by the JEO will add to the basic information we already know about this body.  Europa is a little smaller than Earth’s moon.  Like Earth, it is thought to have an iron core, a rocky mantle and an ocean of salt water.  However, this ocean is deep enough to cover the entire surface, and the top layer is frozen solid.  Europa is an ice world, its surface riddled with countless cracks.

When we look at Europa, we see evidence of the dominant theme of the Jupiter system: Jupiter.  The enormous planet influences everything here with its gravity.  It is tidal heating which causes Europa’s inner ocean to be liquid instead of solid, and it is Jupiter’s constant tugging on this water that causes the ice above it to be covered with an elaborate pattern of cracks.

Within that inner ocean, there may be life.  Nature has created a perfect environment for it here, containing both water and heat.  Of course, we won’t really know what’s in there until we can put landers down and take some samples, but the JEO will be doing the basic groundwork that will lead to that.  Using the information that comes from this mission, future missions will know where to go on Europa, and what to look for.  Someday a lander will reach this little world, put a periscope down through the ice, and have a look around.  When that happens, will something be looking back?  We won’t know until we try.

The investigation of Europa will follow the overall purpose of the entire EJSM mission: to assess habitability.  Specifically, does Europa support life, or could it in the future?  To simply ask this question is exciting.  We’re talking about exploration, future colonies and the possibility of extraterrestrial life.  The future is here.

But for now, we’re just trying to get a better idea of all the parts involved, and their relationship to each other.  How big is this layer of liquid water, and how big is the solid core beneath it?  How thick is the ice layer above it, and what are the variations in thickness and composition of this ice over the entire moon?  What is the nature of the surface-ice-ocean exchange?  What are the surface features?  How quickly are they changing?  What are the possible sites for future landings?  These are some of the questions that will be addressed by the JEO.

In addition to its ongoing survey of Europa, the JEO will also perform observations of Io, one of Jupiter’s other moons.  In contrast to Europa, Io is a fire world.  It is the most volcanically active body in the solar system, its surface constantly erupting in an ever-changing array of volcanoes, some of which hurl plumes of matter far into space.  Just as Europa’s inner ocean is the result of Jupiter’s gravity, so is Io’s volcanic activity.  The same tidal heating which melts Europa’s ice is more extreme here, generating enough heat to melt magma.  If there is a volcano conveniently erupting in the right direction when JEO flies by, the probe may be able to fly through the plume and take samples.   Even failing that, we should be able to get some spectrographic data from starlight shining through some of the plumes, and we can expect some wonderful pictures of a world that is about as close to Hell as we’ll ever find.

The lifespan of the JEO is uncertain.  It will eventually impact on Europa when it finally succumbs to radiation damage, or when it runs out of fuel for maneuvers.  By that time, it will have added volumes to our knowledge of the solar system’s biggest planet and its moons.

In our next article, we’ll take a look at the other half of the EJSM/LaPlace mission, the European Space Agency’s Jupiter Ganymede Orbiter.  As we said earlier, this probe will be performing some observations in coordination with the JEO, and will also do some “stand alone” science of its own, orbiting Jupiter’s largest moon while the JEO is orbiting Europa.   Watch for part two!

Sources:

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

Mission News: NASA and ESA Prioritize Outer Planets Missions at NASA website:  nasa.gov/topics/solarsystem/features/20090218.html

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/Europa Orbiter (JEO) Concept at website of Jet Propulsion Laboratory, California Institute of Technology:  http://opfm.jpl.nasa.gov/europajupitersystemmissionejsm/jupitereuropaorbiterconcept/

News: LaPlace, Studying the Jovian System at website of the European Space Agency:  esa.int/esaSC/SEMPHEWX3RF_index_0.html

Jupiter: Moons: Europa at website of Jet Propulsion Laboratory, California Institute of Technology:  solarsystem.jpl.nasa.gov/planets/profile.cfm?Object=Jup_Europa