This is part two in our examination of the Jupiter mission that is being planned by the European Space Agency and NASA, with collaboration from Japan’s JAXA. The mission, which is called the Europa-Jupiter System Mission in the U.S. and the LaPlace Mission in Europe, is a huge project involving two separate space probes launched at different times and from different launch sites. One of these craft is NASA’s Jupiter Europa Orbiter (JEO), and the other is the European Space Agency’s Jupiter Ganymede Orbiter (JGO). These probes will arrive at the Jupiter system about a month apart, and will begin by working together on a survey of the giant planet and its moons as a system. Besides Europa and Ganymede, the JEO will study Jupiter’s moon Io during this time, and the JGO will study Callisto. After this, the probes will settle into their orbits around Europa and Ganymede, and subject those bodies to in-depth scrutiny. In this way, the mission will encompass the study of the four largest moons of Jupiter: Europa, Ganymede, Io and Callisto.
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