Juno: Journey to Jupiter

Next Friday, the 5th of August, all things going as planned, I will be watching NASA’s latest scientific planetary mission launch into space, aboard at Atlas V rocket, from Kennedy Space Center Florida. The mission, named Juno, is a spacecraft bound for Jupiter, the largest planet in our solar system and the fifth planet from our Sun.

Juno is the second mission of NASA’s New Frontiers program, with the first being the New Horizons probe launched in 2006 and headed to Pluto. The program focuses on exploring the solar system with frequent (approximately one every 36 months) spacecraft missions that will conduct focused scientific investigations designed to enhance our understanding of the solar system.

Juno will take five years to reach Jupiter – arriving there in 2016. Even though it is “only” 2 planets over from Earth, Jupiter is far enough away (400 million miles from us) to be considered in the “outer” solar system. Once it reaches Jupiter, Juno will enter a polar  orbit and at its closest will be a mere 3,100 miles (5000 km) above the colorful clouds. Its orbital journey will be harrowing to say the least. In a highly elliptical orbit, Juno will race by the equator at a rate of 60 km/s (37 miles/s) threading a narrow gap between Jupiter and it’s hazardous “radiation belts” before swinging out further into space and returning. In total, Juno will complete 37 orbits in its 20-month long mission.

Juno mission insignis/patch
The Juno mission insignia

Juno will be only the second spacecraft to ever orbit Jupiter (the last being Galileo in 1995) – which makes this mission particularly exciting. Although eight probes have passed by the gas giant planet, they have not been close enough to Jupiter for long enough to give us the answers to the big questions that still remain about the planet. Shrouded by clouds, astronomers have been able to study only the very outer layers. The images of giant storms across reddish bands stretching around Jupiter are familiar to most. Even with a small telescope it is possible to make out the parallel light bands (called zones) and darker stripes of cloud (called bands). The oft-observed “Great Red spot” is also popular with observers and is actually a “hurricane” bigger than our Earth that has been swirling across Jupiter’s surface for hundreds of years!

Close-up image of Jupiter and the Great Red Spot taken by Voyager I in 1979. Credit: NASA

“Our knowledge of Jupiter is truly skin deep,” said Juno’s principal investigator, Scott Bolton of the Southwest Research Institute (SwRI) in San Antonio, TX

What we can’t see is what is happening beneath Jupiter’s clouds. The Juno science team believes the answers to many perplexing questions lie hidden here. They want to know what exactly makes up the atmosphere of Jupiter, how Jupiter was formed and, ultimately, how  solar systems and planets form in general.

Juno’s name, which comes from Roman mythology, seems particularly apt. In the myth, the god Jupiter would hide behind clouds. But his wife, the goddess Juno could see through them.

Why Jupiter?

Despite the fact that Jupiter is by far the largest planet in our solar system (in fact it could easily hold every other body in our solar system excluding our Sun) we still know surprisingly little about its composition, atmosphere and the physical processes that occur there. Composed predominantly of hydrogen and helium like our Sun, scientists believe Jupiter was the first planet in our solar system to form from the “leftovers” of the Sun’s creation. So in studying Jupiter we can also test theories related to the formation and evolution of our entire planetary system, and answer the question: “how did our solar system come to be?”

As we have also started to discover many Jupiter-massed planets orbiting in distant solar systems, understanding Jupiter and how it was formed becomes more relevant.

NASA Juno spacecraft
Artists impression of the NASA Juno spacecraft — credit:NASA

As Bolton puts it, “If we want to go back in time and understand where we came from and how the planets were made, Jupiter holds this secret, because it got most of the leftovers after the sun formed, and we want to know that ingredient list. What we’re really after is discovering the recipe for making planets.”

The science

The Juno mission will gather data that will help in completing several scientific goals.

One of the first goals is to measure how much water and oxygen are present inside Jupiter. Since oxygen is “locked-up” in the atmosphere as water vapour, we can use water vapour measurements to tell us how much oxygen is present

“Understanding the history of water across the early Solar System is a fundamental question, and Jupiter is going to give you the first clue,” says Bolton

You might wonder if the previous Galileo mission had already done this – well, yes and no. When the Galileo orbiter dropped a probe into the atmosphere of Jupiter in 1995, scientists were surprised by what they found. The probe reached about 97 miles below the outer cloud cover and showed that there was far less water present than expected. This indicated that scientific theories of Jupiter’s formation were incorrect.

However the Galileo probe is thought to have possibly plunged through a rare “dry spot” in Jupiter’s atmosphere, which may have affected results.

Juno will see beneath Jupiter’s clouds to its internal structure. Credit: NASA/SwRI

This time Juno will try to measure water content by detecting microwaves emitted by Jupiter’s atmosphere. The amount of water present at different depths in the atmosphere alters the strength of the emission at different frequencies. Knowing the amount of water and oxygen can give us an idea of whether Jupiter formed close to its position today or alternatively whether it formed further away and “migrated in” toward the Sun. These questions form the basis of planetary formation theory.

Another key question Juno will try to answer is “what is the structure inside Jupiter?” Juno’s Microwave radiometer (MWR) will probe beneath the visible cloud tops to provide data on the structure, movement and chemical composition to a depth of up to 342 miles (550km). This will be especially important in understanding those “zones and belts” – for example, are the zones and belts just surface features or does the structure go down deeper? Are they showing us how Jupiter is structured internally perhaps? Also, just how deep are the roots to the Great red Spot (GRS) and how has it maintained itself for so long?

When we consider Jupiter’s structure, we also want to know about its gravitational and magnetic fields. The gravitational field is measured by way of the “Doppler shift” effect so as the spacecraft flies – we watch how Jupiter pushes and pulls at the spacecraft’s velocity. This can tell us how the mass is distributed within Jupiter and also how the planet is rotating – for instance, whether it is rotating as a solid body or a series of concentric shells.

Part of the way down into Jupiter’s depths, the hydrogen that we are familiar with on Earth comes under so much pressure that it actually becomes “metallic” and starts behaving like a fluid (a little like mercury in some thermometers). This metallic substance starts to conduct electricity and the result is the production of a magnetic field. Investigators are very interested in understanding this field and that is why Juno includes a magnetometer (MAG), which will measure the strength and direction of Jupiter’s magnetic field lines.

Theories for Jupiter’s internal structure vary. Credit: NASA/SwRI

Jupiter has the 2nd strongest magnetic field in the solar system (after the Sun). Juno will study Jupiter’s magnetosphere and because it is in a polar orbit it has the distinct advantage of being able to observe the polar magnetosphere where the phenomenon known as the “great aurora” occurs. Jupiter has the brightest aurora in the solar system: almost 100 times brighter than those on Earth. Juno can detect high-energy particles coming down into Jupiter’s magnetosphere and forming aurora. Scientists can then compare these with the aurora that occur on Earth, and also those on Saturn (which are being studied now with the Cassini space probe) giving us a much better understanding of the auroral processes.

Juno will also tackle the question as to whether  the center of  Jupiter is solid.  And if so, how large is it?  Currently, scientists do not know if there is an ice and rock core beneath the metallic hydrogen region under incredibly high (40Mbar) pressure. The atmospheric pressure at sea level on Earth is, by comparison, a meager 1 bar – so at 40MBar or 40 million times this pressure, it is almost impossible to imagine what form this solid “rock” substance may take.

Finding evidence of a core made of heavy elements would suggest that that these elements were made in rocks early in solar system before Jupiter formed. This would constrain how and when the planet formed and give us more of a picture of what the early solar system was like. While some believe the existence of a solid core of roughly ten Earth masses would have been necessary to allow the runaway accretion of the hydrogen and helium gases that make up most of the planet, other models can explain the formation of the gas giant without the presence of a solid core.

Will Juno be able to definitively tell us the story of Jupiter’s formation and evolution? Possibly not, but it will help to constrain different theoretical models being proposed.

The Spacecraft

The Juno spacecraft in itself is extremely interesting.

One of Juno’s massive solar panels. Credit: NASA JPL

The $1.1 billion dollar craft consists of a “vault” measuring 11.5 feet high and 11.5 feet wide and it weighs about 8000 pounds. Outstretched from this vault are three enormous solar panels, which will help to power the spacecraft. Juno is the first solar powered spacecraft designed to operate as far away as Jupiter.  Since Jupiter receives about 25 times less sunlight that Earth, the panels need to be extremely efficient and extremely large. Each solar panel wing measures about 9ft by 29ft, so about the size of a tractor-trailer. With solar panels extended the craft spans more than 66 feet (20m). These panels will be unfurled shortly after the deployment of Juno in space.  At Jupiter’s distance the panels generate the power equivalent of four 100 watt light bulbs; half goes to powering the instruments and the other half to engineering systems like heaters to warm equipment in harsh cold conditions of space.

The inner vault is made of titanium, houses delicate instruments and acts as armour for Juno to protect it from hazardous “radiation belts” which encircle Jupiter’s equator. In these regions the magnetic field traps and whips up electrons to almost the speed of light. The belts are similar to the “Van Allen” belts that exist around Earth but are many millions of times more intense. Without the armoured tank design of Juno, sensitive instruments and detectors would not survive the spacecraft’s very first pass by Jupiter.

Juno’s orbit (in green) has it dipping beneath dangerous radiation bands that surround Jupiter. Credit: NASA

Juno is a “rotating spacecraft”. Essentially this means that the spacecraft is spinning as it moves through space. Why? Because this spinning action makes the direction of pointing (where Juno is looking) extremely stable and easy to control (it has a gyroscopic action). During science operations Juno will spin at a rate of two revolutions per minute (RPM).

All instruments within Juno are fixed, so as Juno cartwheels past Jupiter the spacecraft will sweep the fields of view of each instrument. In fact, at 2RPM the instruments’ fields of view sweep across Jupiter about 400 times in the 2 hours it takes Juno to fly from one pole to the other.

The scientific payload consists of 9 instruments fed by 29 sensors. One of these instruments, “JunoCam” is simply designed to take images of Jupiter – especially the never before seen poles: to be used for public outreach and education.

“JunoCam will show us what you would see if you were an astronaut orbiting Jupiter,” said Bolton. “I am looking forward to that.”

Me too, Dr Bolton. Me too.

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ESA’s Mars Express provides video of the week!

On June 1st of this year, the European Space Agency’s (ESA) Mars Express spacecraft was able to capture images of an unusual alignment as Mars’ moon Phobos passed in front of Jupiter (seen in background). The images were put together to form this amazing animation.

Mars has two moons – Phobos and Deimos. The origins of these names are a bit gloomy : Phobos, named after a Greek God, means “fear” and Deimos is a figure representing “dread” in Greek mythology. Phobos is the largest of the two, and the closest moon to Mars.

You can see quite clearly that Phobos has an irregular shape – it’s mean radius is only  of 11.1 km (6.9 mi). Compare that with our Moon with its mean radius of approximately 1737.5 km (1079 miles). And that seemingly small object behind Phobos is of course Jupiter with a mean radius of (a not so small) 69,911 km (or 43440 miles).

This was a unique opportunity for the Mars Express spacecraft which performed a special maneuver to capture the alignment.  At the time these images were taken, there was a distance of 11,389 km (7076 miles) between the spacecraft and Phobos with Jupiter a further 529 million km away.

The Mars Express spacecraft was launched in 2003 and consisted of two parts – the Mars Express orbiter reponsible for the images in the animation above and the Beagle 2 – which was to land on the Martian surface and study the planet’s geochemistry.  Sadly the ill-fated Beagle 2 failed to make a safe landing (reminding us that planetary exploration is not easy!).  The Mars Express, however, has been collecting valuable data since 2004.  In particular, experiments are looking at the atmospheric environment, studying the distribution of water vapour, imaging and analysing the surface composition of Mars and searching for possible ice below the planet’s surface.

The science return and flexibility of the Mars Express  has earned it significant mission extensions – in fact it was initially planned to have a mission length of one Martian year (that’s 687 days for we earthlings).  It is now expected to continue its operations until December 2012.  Find out more about the mission at ESA’s site http://www.esa.int/SPECIALS/Mars_Express/index.html.

 


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Fermi’s bubble find baffles astronomers

This week NASA’s Fermi space telescope made a discovery that is perplexing scientists around the world.  Fermi is a space telescope which detects gamma ray radiation – the most energetic form of electromagnetic radiation. In fact it is billions of times more energetic than the type of light visible to our eyes.

Electromagentic spectrum gamma rays fermi
The Electromagnetic Spectrum.

This means that Fermi sees the immense energy of the most exotic and energetic phenomenon in our Universe: super massive black holes,  pulsars and streams of hot gas travelling at close to the speed of light.   This week Fermi and the astronomers at the Harvard -Smithsonian Center for Astrophysics discovered an astounding structure right in our own Galactic back yard.  They discovered huge gamma ray emitting “bubbles” which can best be shown in this image:

gamma ray galaztic bubbles
Galactic Gamma ray "bubbles"

The purple bubbles show this incredible and unexpected structure in our Galaxy. Here we are looking at our Milky Way Galaxy edge-on with the “bubbles” emanating from the center. The structures extend 25,000 light years (see box below) to the North and South of the center of our Galaxy. That is quite a significant structure not to have been aware of, but many astronomical phenomenon do not show themselves unless we use the right wavelength of light to detect them – in this case: gamma rays.

A light year is the distance that light travels in one year. One light year is 5,865,696,000,000 miles or 9,460,800,000,000 kilometers.

In total the two bubbles span 50,000 light years or half the diameter of our Galaxy.  They have well defined edges and are expanding at a rate of about 2.2 million miles per hour.  As mentioned already, gamma rays are emitted from the most energetic things in the universe and here we are looking at structures that hold the energy of about 100,000 supernovae.  Earlier surveys aimed at detecting X-ray emission gave a hint to some sort of structure which astrophysicists assumed may also emit gamma rays. They did not however expect anything like the scale of these huge bubbles.

So what in the world (or more aptly, Galaxy) could possibly have produced so much energy?

So far astronomers are considering two possible explanations.

One explanation suggests that at some time there was a “burst” of star formation occurring near the center of the Galaxy which may have produced massive short-lived stars which in turn produced energetic winds (like a much stronger version of our Sun’s “solar wind”) capable of blasting high energy particles out into space and forming these gamma ray bubbles.

black hole jets engine accretion disk Fermi
The black hole engine: powerful jets carry ejected material away

Doug Finkbeiner, an astronomer with the Harvard Smithsonian Center for Astrophysics and part of the team that made the discovery, suggests another option may be more plausible. This one is even wilder – and involves an outburst from the supermassive black hole that lives at the center of our own Milky Way. Most if not all, galaxies are thought to harbor a black hole at their center and many of these black holes are associated with high energy “jets” which eject material out of the black hole.  This illustration (left) shows the concept of a black hole where there is a spinning disk of material being drawn into the black hole (the accretion disk) and at the same time powerful jets shooting high energy particles out of the back hole in opposite directions.

There is a catch – our Galaxy’s black hole is not see to possess these high energy jets. But at 400 million times the mass of the Sun, our own “local” black hole has probably been very active in its past.

In fact, these bubbles may be the first real “evidence” of an outburst at some time in the past where the black hole was accreting material at such a rate that it was spewing high energy particles back out in the form of jets which formed the structures we are now seeing – these so-called  “Fermi bubbles”.  Estimates suggest it would only take a period of 10,000 to 100,000 years to produce enough energy to create these structures.  (Our Galaxy is about 13.2 billion years old!)

At any rate, it is exciting to have Fermi reveal to us such enormous structures which may have been part of our Galaxy for millions of years.

Sometimes, all you need is a fresh set of  (gamma ray sensing) eyes.

NASA’s Fermi is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States. Read more about Fermi at: http://fermi.gsfc.nasa.gov/

The research discussed has been accepted for publication in The Astrophysical Journal

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How to Catch a Comet

There is plenty of excitement for NASA this week with both manned and unmanned missions sharing the limelight.  Avid shuttle watchers are eagerly awaiting this week’s scheduled launch of Space Shuttle Discovery’s final mission to the International Space Station now scheduled for Nov.5th at the earliest.

Nov. 4th held a real treat: NASA’s  EPOXI mission made a very successful close encounter with a comet known as Hartley 2.  In fact this encounter is the closest a  man-made object has ever come to any comet – coming within 435 miles/700 km.  This is only the fifth time a spacecraft has “visited” a comet in this way.  Many may recall the “Deep Impact” mission which launched in 2005 and aimed to rendezvouz with comet Tempel 1. It did just that on July 4th, 2005. That mission involved the spectacular release of  a washing machine-size probe, known as the “impactor,” which collided with the comet, releasing material which was imaged by the Deep Impact spacecraft (which is, in comparison approx the size of a VW beetle).

Scientists used the data and spectra they observed as a means of better understanding the nature and composition of the comet.  Although the Deep Impact spacecraft had completed its mission, NASA scientists saw potential for continuing to use the still functioning craft and set about determining a new scientific adventure for the probe.  After realizing that a new mission could be accomplished using the same imaging equipment, scientists decided on a new target – the comet Hartley 2.

Hence the EPOXI mission was born. Same spacecraft, different set of of targets – which is why you may be hearing the term “Deep Impact” frequently when listening to coverage of the mission.  EPOXI is actually a combination of two scientific investigations.   The new mission name “EPOXI” comes from combining two scientific investigations being undertaken by the spacecraft:

EPOCH: Extrasolar Planet Observation and CHaracterization

Deep Impact spacecraft

DIXI: the Deep Impact eXtended Investigation of comets

So it came to be that the original $252 million dollar spacecraft was to fly an additional 2.9 billion miles (4.6 billion Km) to hunt down Hartley 2 arriving 5 years later on Nov. 4th 2010. During it’s time cruising between these comets, the Deep Impact spacecraft completed the  Extrasolar Planet Observation and Characterization part of it’s mission objective: primarily a search and study of extrasolar planets and moons.

Catching comet Hartley 2 was to be significantly more challenging than the approach to Tempel-1 because it is about a seventh of the size at roughly 1.25 miles across (2 km) and yet still releases about the same amount of material into space. This makes the comet “flit around the sky” according to mission navigator Shyam Bhaskaran of NASA’s Jet Propulsion  Laboratory.  In fact the comet moves so much that three maneuvers were needed to adjust the spacecraft’s course – the latest last minute maneuver was 2 days ago!

Finally, yesterday at 10:10am EDT, the EPOXI spacecraft reached it’s goal, flying past Hartley 2 at a distance of 435 miles.  The comet came by the EPOXI craft at 12.3 km/s or more than 27, 000 miles per hour.

The flyby went off without a hitch and within an hour 5 spectacular high resolution images arrived at Earth:

The initial data suggests the comet's nucleus, or main body, approximately 2 kilometers (1.2 miles) long and .4 kilometers (.25 miles) at the "neck," or most narrow portion. Jets can be seen streaming out of the nucleus
Scientists plan to use the extensive data they will receive from its imagers ( two operating at visible wavelengths and one in the infrared) to study the structure of the nucleus and compare it with observations of other comets. Other important questions include what makes this comet so active? Which parts of the comet are emitting gas and what is the nature of these chemicals? With such detailed imagery we may be able to link the activity we observe (jets of gas being emitted) to distinct structures of the nucleus.

The excitement in being able to answer such questions relates to our desire to better understand our Solar System.  Since comets are leftovers from the solar system’s early days, this knowledge could reveal a great deal about how our cosmic neighborhood came to be.
Hartley 2 nucleus
The unusual rough, peanut shaped nucleus with "jets" emitting material

Expect more- much more in the coming months. Today’s flyby and the approach leading up to it have already provided a mountain of data for scientists and by Thanksgiving when EPOXI will shift it’s gaze from Hartley 2, scientists expect around 120,000 comet images to have been downloaded to the scientists computers.

NASA scientists have said that they feel that by reusing the Deep Impact spacecraft in this extended mission they have succeeded in getting a very good deal.  Although extending the mission into EPOXI has cost an additional $45 million,  Ed Weiler, associate administrator at NASA’s Science Mission Directorate has said that this amounts to about 10 percent of what it would have cost to launch a whole new mission. In his words:  “The spacecraft has provided the most extensive observations of a comet in history.” “Scientists and engineers have successfully squeezed world class science from a re-purposed spacecraft at a fraction of the cost to taxpayers of a new science project.”

So what is next for Deep Impact and EPOXI? Sadly the Deep Impact spacecraft is running out of fuel, so whether it will remain as a stationary observing platform or set it’s sights on another comet is unknown at this time.  As for comet Hartley 2, its days are numbered too. Although it will continue to zip around the Sun for a while longer, (it orbits the Sun once every 6.5 years) it seems the sun is “cooking”  3 to 5 feet (1 to 1.5 meters) of material off the comet’s surface on each orbit.   With its smallest side measuring about 1650 feet (500 m), Hartley 2 will not be around for very much longer.

Whatever the future holds the Deep Space/EPOXI mission has certainly shown us a new way to think about “recycling”, NASA style. Rethinking and repurposing missions to get the most science for our buck – that’s something I think we can all get behind.

Read more about past spacecraft-comet rendezvous:  http://www.space.com/scienceastronomy/comet-close-encounters-history-101103.html
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