Jupiter is a great big question mark.  Like the king of the gods for whom it is named, the giant planet dominates the solar system, surrounding itself with an entourage of moons and other attendants.  The region of space all around Jupiter is filled with its gravitational field, its magnetic field and its zones of intense radiation.  Its nearer moons are heated by the tidal force of its gravity, allowing them to have inner oceans of water (probably) and sometimes active volcanoes.  Jupiter is our biggest gas giant planet, but we know from our observations of other planetary systems that  there are others that are much bigger.  These enormous planets, Jupiter and its big cousins, are really the main product of planet formation.  They suck up most of the matter that surrounds a planet-forming star, and the crumbs that are left over form the lesser planets.   Jupiter and its cloud of satellites are often called a mini-solar system, with good reason.

One of the main questions that Juno will attempt to answer is, exactly what is Jupiter?  Is there a solid planet down there, or is it just a globe of gas?  You will sometimes hear TV science programs saying that Jupiter has no solid body at its core, but the truth is, we just don’t know.  Understanding that will tell us how the planet formed in the first place.

In its most basic form, the question we’re asking is this: did a rocky core form first, and then attract the rest of the matter around it to form the planet, or did an unstable region of the solar nebula collapse and trigger the planet’s formation?  In the first case, the rocky core should still be there.  In the second case, there will only be gas all the way through, and while it will be extremely compressed at the center of the planet, there will be no rocky core there.

And that’s only one of the topics Juno will be investigating.  In the old myth, Jupiter made a cloud around himself to hide his misdeeds, but Juno was able to pull it aside and see within.  Hopefully, the analogy will prove to be appropriate.

(Just a few days ago, NASA made an announcement that points out our lack of understanding of Jupiter and its atmosphere: one of the iconic stripes has disappeared from the lower hemisphere of the planet.  Scientists confess that they are completely baffled by this event.  When Juno gets there, perhaps it can suggest an explanation of how a feature that has “always” been there can suddenly disappear.)

The Juno probe will be launched in August, 2011, aboard an Atlas V-551 rocket from Cape Canaveral.  The journey will take about five years, with the craft arriving at Jupiter in July of 2016.  The projected mission time (which may be changed, as we know) is one Earth year.  During that time, Juno will orbit Jupiter 32 times in a highly elliptical orbit that will bring it to within 3,000 miles of the planet at closest approach.

The specific goals of the Juno mission are:

1. Measure the amount of water in Jupiter’s atmosphere, which will help us figure out which theory of planetary formation is right, or if we need new theories.

2. Conduct in-depth study of Jupiter’s atmosphere, measuring composition, temperature, cloud motion, etc.

3. Make the first map of Jupiter’s gravity and magnetic fields, which should reveal the planet’s internal structure.

4. Specifically investigate Jupiter’s magnetosphere near the north and south poles, where enormous auroras occur that will hopefully give us new insights into how the planet’s magnetic field interacts with its atmosphere.

Like NASA’s previous Pioneer probes, Juno will spin on its axis to ensure stability and make aiming the craft easier.  Immediately after launch, Juno will be spun up by the rocket motors of its second-stage booster, to which it will still be attached.  When it enters Jupiter orbit, the spinning satellite will sweep space with its instruments once in each rotation.  At three rotations per minute, this means that Juno’s instruments will sweep Jupiter 400 times in the two hours it takes the craft to circle from pole to pole.

Juno will be the first solar-powered satellite made to operate so far from the sun.  Since Jupiter receives 25 times less sunlight than Earth, Juno will need three extra-large solar panels to provide sufficient energy.  These panels will be folded flat against the sides of the probe during launch.  When deployed, they will extend outward from the hexagonal body, giving the craft a span of more than 20 meters.

Thanks to recent technological advances in the field of solar power, Juno’s panels will be 50 percent more efficient and radiation tolerant than solar panels that were used just 20 years ago.  The mission needs only small amounts of electricity, since it will only be in use for about six hours out of each 11-day orbit of Jupiter.  (Juno will be in a highly elliptical orbit, and will only be observing the planet during its closest approach.)  Once it is in its working orbit, Juno will be in total sunlight for the duration of the mission; there will be no time when it is in Jupiter’s shadow.

There are zones of intense radiation around Jupiter which could easily fry the electronics of a space probe, so Juno will have all of its sensitive innards in a shielded vault. Juno is the first space probe to use such heavy shielding, and scientists will be watching carefully to see how well it works.  This line of research is relevant to future missions, since the harsh radiation of space is potentially harmful both to unmanned probes, and to the human crews that will eventually follow them.  To hedge its bets, Juno will try to avoid the worst areas of radiation by making its approaches to Jupiter over the planet’s north pole, dropping below the radiation belts, and then exiting over the south pole.

The smaller planets of the solar system have all seen extensive changes to their atmospheres during their lifetimes.  For instance, we now know that the atmospheres of both Mars and Venus were very different in their early days.  (See our articles on the Mars Express and Venus Express missions.)  But Jupiter, with its enormous gravity, has probably held onto all of the gas that it had at its formation. Planetary scientists will be very interested in studying the big planet’s atmosphere to see what it can tell us about the matter that was around in the solar system’s youth.  Juno will be able to observe that atmosphere in greater detail than ever before, seeing the global structure and motion of gases below the cloud tops for the first time, and mapping variations in the composition, temperature and patterns of motion down to unprecedented depths.

Jupiter has the brightest auroras in the solar system, and Juno will actually take samples of charged particles as it flies over the poles.  Its study of the auroras and the magnetic fields that produce them should increase our understanding of Jupiter and of all other powerful sources of magnetism, such as young stars with their own planetary systems.

So, those are some of the things that Juno will tell us about Jupiter.  This is really basic science, the kind of preliminary investigation that should pave the way for more complex enterprises in the future.  In fact, the mission overview at the NASA website points out that no new technology had to be invented for this mission.  It uses tried-and-true instruments that gather basic information- the kind of stuff that can tell us fundamental things about this giant planet, and about the beginnings of our solar system.

Juno will be launched in August of next year- and of course, you can read all about it here.

Sources:

“Juno: Unlocking Jupiter’s Mysteries” at the NASA website:  nasa.gov/mission_pages/juno/main/index.html

“Juno Mission Overview” at the NASA website:  nasa.gov/mission_pages/juno/overview/index.html

“Juno: Spacecraft and Instruments” at the NASA website: nasa.gov/mission_pages/juno/spacecraft/index.html

“Juno Mission News: Juno Taking Shape in Denver” at the NASA website:

nasa.gov/mission_pages/juno/news/juno20100405.html

The New Frontiers program came about following a study in 2001 which was conducted to look at the state of solar system exploration at that time and identify priorities for continued exploration during the 10 year period 2003 to 2013. The study identified five medium class missions that were considered of importance and the New Frontiers program was set up to examine and implement these.

The first mission launched was named New Horizons and its goal is to visit and explore Pluto. It will also visit one or more Kuiper Belt objects during the mission. New Horizons was launched in January 2006 and is scheduled to reach its destination by July 2015. The second New Frontiers mission is named Juno and has been designed to conduct an in-depth study of Jupiter. It is currently scheduled for launch in August 2011. At the end of December 2009 NASA announced that three candidates had been chosen for the third New Frontiers program and these include some exciting possibilities for solar system exploration.

The first potential candidate is named the Sunrise and Atmosphere Geochemical Explorer (SAGE) and would comprise a mission to Venus. On arrival it would release a probe into the atmosphere of the planet which would undertake extensive measurements as it descended to the surface of Venus. Upon landing the probe would conduct studies to assess the composition and mineralogy of the surface material.

The second candidate is called the Origins Spectral Interpretation Resource Identification Security Regolith Explorer or Osiris-Rex for short. This mission would be designed to travel to and orbit an asteroid. Extensive measurements of the asteroid would be taken while the spacecraft was in orbit around it. Samples would then be collected from the surface of the asteroid and these would be returned to Earth. These samples would be used to assist in the study of the formation of the solar system and the origins of the molecules necessary for life.

The third candidate would send a spacecraft to land in an area near the south pole of the moon which would collect lunar material and return it to Earth. This mission is known as Moonrise: Lunar South Pole – Aitken Basin Sample Return Mission. The returned lunar sample would be used to help gain an insight into the early history of the Earth-moon system.

Each of the candidates will now have around a year to complete a detailed concept study which is required to consider the feasibility of implementation, the costs involved and technical plans for carrying out and completing the mission. The teams will receive approximately $3.3 million to undertake the concept study and it is currently proposed that selection of the winning candidate will be made in mid 2011. Planning and preparation for the chosen mission would then take around seven years and the spacecraft has to be ready for launch by no later than the end of December 2018.

Each of the missions represents an opportunity for further study of a celestial body and the winning candidate is sure to advance our knowledge of the solar system. All three are potentially exciting opportunities to learn something new and any one of them would provide scientists with a rich source of data. Only time will tell which of the candidates will be successful and for now the three teams have a year of hard work ahead of them.