Tag Archives: Jupiter

Cassini’s Solar System Scrapbook

Cassini has completed its second-to-last ring plane crossing.  There’s only one more left before the final and fatal atmospheric entry.  But before it goes, Cassini completed a sort of family scrapbook of the solar system, by adding Neptune.  Here are some highlights of Cassini’s solar system scrapbook (which skips Mercury because it’s far too close to the Sun for Cassini to photograph):

Venus, Earth, and Mars

Venus, Earth and Mars, the only rocky planets easily observable from Saturn, as seen during the equivalent of a total solar eclipse around Saturn — Saturn is backlit by the Sun here. This was captured July 19, 2013.

Earth (and Moon), closeup from last image

This is a mega huge zoom in on the picture above.

 

Captured just before an Earth gravity assist maneuver, this is the Moon as seen on August 17, 1999. The spacecraft did not attempt to photograph the Earth during closest approach.

It’s worth also adding this. It’s the last image Cassini will ever take of Earth, captured April 12, 2017.

Jupiter

This was captured on December 29, 2000, while Cassini was grabbing a gravity assist boost from the giant planet.

Saturn

There’s really no end of good Saturn pics, but I quite like this one, taken last year as Saturn approached the summer solstice in its northern hemisphere.

Uranus

This blue planet against Saturn’s rings is not Earth. That little blue dot is the larger of the two “ice giants”, Uranus. I sincerely hope this is not the closest we’ll get to it in the 21st Century; it’s an astonishingly bizarre world that would seriously test a lot of basic science about planetary formation, magnetospheres, and so forth. This was captured April 11, 2014.

Neptune

This is the most recent addition to the scrapbook, a zoom-in enhanced version of an image taken Aug. 10, 2017, commemorating Voyager 2’s flyby on August 25, 1989 and the 40th anniversary of the mission’s launch on August 20, 1977. This is Neptune and its largest moon, Triton.

Pluto

Call it a consolation for not nabbing Mercury; Cassini captured this image of the dwarf planet Pluto on July 14, 2015, just as New Horizons was making its closest approach. (Naturally, New Horizons got much better pictures!)

 

It’s bittersweet, waiting for the end, but it helps to remember the amazing things Cassini has been doing.  Like Voyager 1 before it, Cassini is leaving behind portraits of our solar system.

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The first Great Red Spot images are available!

The images and data from Perijove 7 have started coming down to Earth, and as they become available, the team is posting them in their gallery and inviting the public to process them — and the public, as always, is responding quickly.  This one, processed by Gerald Eichstädt and Seán Doran, is quite a striking view of the giant anticyclone, processed to bring a gloriously rich depth of color to it (the color is much paler in the unprocessed images).  This is closer than anyone has ever come before to the Great Red Spot, and the level of detail is breathtaking.  Go on, click to view it in full scale — you know you want to!

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Tomorrow: the Great Red Spot

The Juno spacecraft has been orbiting Jupiter for a year now (well, a year and four days — its anniversary was last Wednesday), making long, looping orbits with brief dives within a few thousand kilometers of Jupiter’s cloud tops, slipping through gaps in the intense radiation belts around the giant planet.  Its mission is to peer beneath the cloudy veils of Jupiter to better understand the processes that drive Jupiter.  So far, its data has been a treasure trove, revealing how little we really know about this planet.  We now know that the polar regions look completely different from the equatorial and mid-latitudes that we can see from terrestrial telescopes, and that its magnetic field is far more complex than we’d ever suspected, and that the atmosphere is not uniformly mixed like ours is; there is a band of ammonia in the equatorial cloud belts that extends at least as far into Jupiter as Juno’s instruments can reach — hundreds of kilometers.  It’s also studied Jupiter’s strange aurorae, which don’t behave in a manner consistent with the processes that drive aurorae on other worlds, and carry weird footprints of some of the Galilean satellites.

But there is one notable feature of Jupiter that has so far been completely untouched by Juno: the Great Red Spot.

The Great Red Spot, seen by Voyager 2 in 1979

Jupiter is famous for long-lived storms, but none is longer-lived (as far as we know) than the Great Red Spot.  It was first recorded in 1665, by Giovanni Cassini.  He observed it for the duration of his career, noting fluctuations in its visibility, and there are sporadic reports in the literature between then and the 19th Cnetury.  It has been systematically observed continuously since 1830, proving that it is stable for a remarkably long time, longer than any other known meteorological phenomenon, although that is not to say it is unchanging.  The color varies dramatically over time, usually in parallel with color shifts in its confining atmospheric band, and it has been seen to change particularly rapidly upon gobbling up a smaller storm.  Another oddity is that it doesn’t traverse the planet at the same rate as everything else — it moves around slightly more quickly, resulting it lapping the planet ten times since the start of continuous systematic observation in the nineteenth century.

There are so many questions about the Great Red Spot it’s hard to know where to begin.  There are as many theories as there are questions, and so far, very little means of testing most of them.  But tomorrow, that may change.  Until now, the only data we’ve had on the Great Red Spot has been photographic and spectroscopic, revealing only the very surface details.  Tomorrow, Juno’s periapsis will have precessed just enough around Jupiter to put it directly over the Great Red Spot.  What will it learn?

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Juno’s perijove trove

Juno has completed yet another perijove, the fifth in the science phase of the mission, and NASA has released the first batch of findings from the mission.  Some of the findings are no surprise, while others show there’s a lot still to learn about the giant of the solar system:

  • The planet’s enormous and powerful magnetic field is surprisingly lumpy, suggesting it may not be generated in the core after all, but rather closer to the surface or even throughout the planet, above the core that is presumed to be made of liquid metallic hydrogen.
  • Also, the field is a great deal stronger than previously estimated — 7.766 Gauss, ten times stronger than the strongest naturally-occuring field found on Earth.
  • The two poles of Jupiter look very different.  This echoes what Cassini found on Saturn, except that Jupiter’s poles not only look dissimilar to each other, they also look dissimilar to Saturn — four poles that look nothing alike.  One feature the two poles have in common is that they are densely peppered with cyclonic storms bigger than the Earth, so close they sometimes appear to be rubbing against one another.  It is unclear how stable these are; they have never before been visible to a camera.
  • The equatorial belt appears to extend deep into Jupiter, making it exceptionally stable over long periods of time — but the same is not true of some of the other bands, where storms appear to be more dynamic and the belts themselves can evolve into other structures.
  • Jupiter’s auroras remain mysterious — although the basic process that causes them is the same as on Earth (charged particles slamming into the atmosphere), it doesn’t appear to have the same origin as auroras on Earth.  One longstanding mystery is why they seem to track the Galilean satellites around; so far, this remains unanswered.

The next pass is particularly exciting — it will be the first to give Juno a good look at the Great Red Spot.  The microwave sounder on board has revealed some intriguing things about the cloud bands; hopefully we will soon have answers to basic questions such as how deep the Great Red Spot goes.  It has been raging on Jupiter for at least three centuries, having been first observed in 1665 (and continuously monitored since 1830).  Other storms come and go, but that one stays, and it’s one of Jupiter’s oldest and most enduring mysteries.

In the meantime, enjoy this gorgeous time-lapse showing the view from JunoCam during the fifth science pass (sixth orbit, seventh perijove if you count the original orbital capture):

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Juno returns more awesome images

The Juno probe has completed another perijove, and returned some more truly sublime photography.  The spacecraft is going to remain in its initial orbit rather than the originally planned science orbit, due to concerns about its main engine following the failure of a very similar engine from the same manufacturer on a commercial satellite.  This will make the mission take longer, but will have about the same overall radiation exposure (since it will make the same number of perijoves) and can still be completed before Juno’s orbit precesses to where it will go into Jupiter’s shadow.  Juno is solar powered and Jupiter’s shadow is very large; going into that shadow will be a dicey proposition when the time inevitably comes.  But until then, it’s returning images like these:

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Europa is Erupting

Europa’s fascinated scientists for a long time as a possible home for extra-terrestrial life.  When the Voyager mission returned the first pictures, it was clearly a geologically active world — there were few craters, and the surface was covered in striations that looked like obvious signs of a crust shifting over a molten subsurface.  The spectroscopy indicated a surface of water ice, and the density (determined from careful measures of Europa’s deflection of Voyagers 1 and 2) was pretty consistent with water ice as well.  Plus, just doing the math tells us that it experiences enormous tidal strain.  This was so compelling, it became a major feature of Arthur C. Clarke’s novel “2010: The Year We Made Contact”, his long-awaited sequel to “2001: A Space Odyssey”.

Then, the Galileo probe arrived at Jupiter, after a much longer cruise than originally intended.  Unlike the Voyagers, Galileo was to slip into orbit around the giant planet, allowing it to linger and study the moons in far greater detail than had ever been possible before.  Although the mission was marred by a crippled high gain antenna, it nevertheless returned a gigantic wealth of data, including magnetometer readings proving what had already been suspected from Voyager data: Europa has its own magnetic field.

To produce a magnetic field, a celestial body requires electrically conductive material that is in motion.  On Earth, this is our molten iron core.  On the Sun, it’s the seething mass of unfathomable megatons (exatons, even!) of  roiling plasma.  On Jupiter, it’s believed to be an exotic, super-compressed form of liquid metallic hydrogen, which would be superconductive in that environment.  But what could it be on Europa?

Observations of Europa by Galileo revealed that the linea (the striations across the surface) are indeed cracks where material has welled up from beneath, and frozen, and many clear geological features have been seen that show the crust is floating on a liquid or semi-liquid material.  (Our own crust floats on the mantle, which is actually not truly liquid, but does still flow.  So this doesn’t prove Europa has a liquid ocean, in and of itself.)  And they revealed the presence of interesting contaminants on the surface. This image of the sub-Jupiter point on Europa contains an inset from Galileo’s mapping spectrometer.  There is still debate over the exact composition of the mottled surface, but the most likely explanations are sulfuric acid or mineral salts that have welled up from below.  Saltwater, if there are enough electrolytes in it, is famously conductive, and a deep subsurface ocean would definitely account for Europa’s magnetic field.

Then, in 2005, Cassini arrived in the Saturn system.  Saturn has another moon with haunting similarities to Europa: Enceladus.  Enceladus also has a density consistent with water ice, a surface spectrum also consistent with water ice, and a suspiciously young surface.  But Cassini found something more: its particle sensors picked up saltwater as it flew past the cracked southern hemisphere of Enceladus, directly detecting geysers erupting from the moon and marking the first direct observation of liquid water elsewhere in the solar system.  Subsequent observations were able to photograph Enceladus’ faint plumes, which, rather like Io’s volcanoes, extend hundreds of kilometers into space.  So that raised the question: could the same thing be found on Europa?

It would be years before a new spacecraft could be sent to Jupiter.  That spacecraft, Juno, has now arrived, but has only just barely begun its mission.  So scientists have been working instead with the Hubble Space Telescope.  Although Hubble has been orbiting since just six months after Galileo was launched, it has benefitted enormously from crewed servicing missions to upgrade its sensors.  Today, it is capable of work far beyond its original design.  Using this instrumentation, scientists have detected water vapor near the south pole of Europa.  This graphic indicates the apparent position of the vapor; note, however, that the image of Europa is a simulation.  The vapor cloud is not visible to the eye.

The next step is to rule out other explanations.  They haven’t proven that the plume is actually associated with Europa.  one problem with observing from Earth is that it can be difficult to tell whether something is actually on the object you’re looking at, or just floating right in between you and the target.  They have conclusively determined it *is* water vapor, but more work is needed to prove for certain that it is a plume from Europan geysers.

Perhaps soon we will get a better answer.  The Juno spacecraft newly arrived at Jupiter isn’t well equipped to answer the question, as it carries equipment better suited to studying the giant planet itself.  But ESA’s planned JUICE mission (JUpiter ICy moons Explorer — yeah, scientists can get a little desperate in their acronyms sometimes) would definitely be able to answer the question. Planned for launch in 2022, this mission would be dedicated entirely to Jupiter’s large icy moons: Europa, Ganymede, and Callisto.  And for good reason: while Europa definitely has a large subsurface ocean, and copious energy sources in the form of Jovian tides and radiation, it isn’t alone.  Ganymede and Callisto have older, more battered surfaces, but they too are made mostly of ice, and they too have magnetic fields.  They may not be as active as Europa, but there’s something going on there too.

Oceans may be more common than we know.

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Jupiter’s poles look nothing like its equator

Juno has returned the rest of its images from its recent perijove, and Jupiter’s south pole looks amazing.  It’s not entirely a surprise; images from previous probes, the Hubble Space Telescope, and ground observatories show that the colorful bands which characterize the mid and low latitudes disappear at higher latitudes.  What’s stunning is just how complete the effect is:

pia21032_4_south_polar_full_disk_c

The north pole was also imaged, and it looks a lot like the south pole:

pia21031_3_figb_north_pole_close-ups1_figb

 

The team was hoping to see if Jupiter sports a hexagon like Saturn does — and interestingly, the answer is that it does not.  However, it does have a great many small storms (well, “small” by Jupiter’s standards) and a surprising blue tint that suggests that whatever’s going on at Jupiter, Juno will have plenty to keep itself busy.

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