Monday, July 13, 2015

Reflections on a flyby: My personal journey to Pluto



As a ten year old, I would take daily breaks from a long summer of yard baseball and building trails through the woods to go to the public library and that of a local college, hoping to spot the latest Voyager image of Neptune and Triton, its planet-sized moon.  I would scour every newspaper, magazine, CD-ROM – anything that came in, hoping to see a slightly sharper view of these mysterious worlds.  

Of course many days ended in disappointment.  When that happened, or when I had some extra time after seeing the latest from Neptune, I would seek out what else I could find.  Via NASA publications, books, and especially back issues of periodicals, I was able to relive a whole history that I had missed.  I rode around the far side of the moon with Luna 3.  I saw our view of Mars evolve from Christian Huygens first spotting of dark markings and polar caps to our first glimpse of Martian craters from Mariner 4 (incidentally, 50 years to the day before the New Horizons Pluto flyby).  I got to ride along with Mariner 6 and 7 as they zoomed in on Mars and Mariner 9 as it watched dust clouds abate and the surface reveal itself on a global scale

I would set out book and compare how worlds looked as different spacecraft approached.
Mariner-10 brought us the cloud covers of Venus and the cratered surface of Mercury, and the Venera and Viking landers took us to the surfaces of Venus and Mars.  The Pioneers gave us glimpses that were enough to tell us that the Jovian and Saturnian systems were far more complex and interesting than we thought from our earthbound view, but while they were very good at studying other things such as magnetic fields, they were small spacecraft designed to pave the way for the follow on, Voyager.  

While the previous missions revealed a world (or, in the case of Mariner 10, two worlds but separated by years), the Voyagers visited planets with planet-sized moons as well as a retinue of smaller companions.  From the volcanoes of Io to Titan’s thick atmosphere, from Europa the billiard ball with a hint of a global ocean to Miranda with its jigsaw puzzle surface, each encounter was a grand tour of a mini solar system. 

August 25 - encounter day - finally came and I was glued to the coverage on PBS.  Neptune and its great dark spot created a lot of buzz, and Triton looked like, well, a cantaloupe (at least in places).  I didn’t get to watch all the coverage – my mother made me go to bed, telling me I’d thank her for it someday (still hasn’t happened).  I remember after much arguing, responding, “OK, but I’ll be there next time.”

Next time.  There was much to do about Voyager 2 reaching the edge of the solar system, exploring its most distant planet and its moons.  That was technically true at the time – from 1979 to 1989, Pluto was inside Neptune’s orbit.   But the proclamation that we had completed the initial reconnaissance of the solar system felt hollow, because there was one major world that hadn’t received a visit – Pluto.  But the Voyagers, speeding out of the solar system, could not help us anymore.  

It would take great effort by people such as Principle Investigator Alan Stern, to finally get humanity on its way to filling this gap with the launch of New Horizons in 2006, 17 years after Voyager visited Neptune.  In the intervening years, three things changed our view of Pluto.  From ground based and Hubble Space Telescope observations, we produced our first crude maps, revealing Pluto to be one of the most high contrast objects in the solar system.  This indicated that it isn’t simply a carbon-copy of Triton, which is thought to be a captured satellite and is similar in size and mass to Pluto.  


Second, the Kuiper Belt of distant worlds beyond Neptune, predicted a half a century earlier, became real to us, transforming Pluto from an oddball to the largest of these outer worlds that we can only faintly see from earth.  Pluto remains the largest, and is the only one to have a moon so big that it could be a planet in its own right (technically, Pluto and Charon form a double planet).  Two more small moons were found, a number which has since risen to four.   

The Plutonian system is the last menagerie of worlds on the scale reminiscent of the ones surrounding the giant planets that we have yet to visit, albeit without the giant planet.  It is the only unexplored household name in the solar system.  It is the only remaining world that humanity had in mind when it reached out into the solar system with the Mariners, Lunas, and Pioneers.  

The experience of seeing the new images as they come down and the reactions of scientists in real time has been a priceless experience – much different from scrounging around at the local library – oh, and Mom, told you I’d be here.  There are plenty of small worlds left to explore and our studies of even much-visited Mars are far from complete – this is the end of the beginning, by no means the actual end, if one even exists.  But will be no single unexplored target that stands tall above the others.  There will be no great region of the solar system taunting us.  The initial reconnaissance will be complete.  Some people have gotten to live the whole journey - 66 years since Luna 3.  The rest of us have joined it in progress.  July 14, 2015 will be the last opportunity to live it as it happens.  It is truly a special time to be alive.  



Tuesday, May 26, 2015

Kanehekili Patera from Galileo

Due to the nature of its orbit, although Galileo made several close approaches to Io, some parts of its surface were never seen except from a great distance.  Some of these areas were covered by Voyager 1's close flyby, but others were not.  The are centered around Kanehekili, the volcano which can be seen erupting above the limb at about four o'clock, is one such place. A major eruption was seen here earlier this year.  Hopefully a new mission will be able to fill in this gap.



This image was taken on May 6, 1997, during Galileo's eighth orbit around Jupiter.

Processed image Copyright Ted Stryk, Raw Data Courtesy NASA/JPL

Sunday, May 10, 2015

Nereid from Voyager

When planning began for Voyager 2's 1989 encounter with Neptune, the planet had two known moons - Triton and little Nereid, a small, distant moon that, like Triton, is likely captured.  The flyby didn't go well for little Nereid.  First, it takes nearly 360 days to orbit Neptune - almost a year! - and was not in a convenient place for Voyager to meet it (unless Neptune itself and Triton were sacrificed).  Second, it would be dethroned as Neptune's second largest moon by Proteus, a newly discovered moon that would receive much better coverage. 

Voyager 2 came no closer than 4.7 million kilometers from Nereid.  All that could be made out is that it is a somewhat spherical (if a bit lumpy), 340-km in diameter little world with a relatively low albedo -15%.  It rotates in 11 hours, as determined by light curve data, further supporting the idea that it is captured (not being tidally locked is unusual for a moon). 

Here are Voyager 2's two best views.  The first shows the lumpy little world in a gibbous phase as Voyager approached on August 21, 1989, and the second shows a crescent on August 24 - Nereid was "in front" of Neptune, so closest approach was earlier than the August 25 closest approach of Neptune.
 

Yet another world cries out for exploration!

Processed images Copyright Ted Stryk, Raw Data Courtesy NASA/JPL

Tuesday, April 28, 2015

Looking Down On Jupiter's North Pole.

In December 1974, Pioneer 11 became the second emissary of humanity to visit Jupiter.   Being a spin stabilized spacecraft with essentially no onboard memory and only able to transmit at 2048 bits per second, it carried no real camera, but it did carry the Imaging Photopolarimeter, basically a scanning one-pixel photometer which scanned along with the spacecraft's spin.  By doing this, it could, over time, develop crude pictures.  In high resolution mode, the images were at most 14 degrees wide and 466 pixels across (although in practice most were much smaller.  And given that the spacecraft was moving quickly and these scans took around half an hour, the ones near closest approach are, in addition to being frustratingly small, badly distorted.  Although attempts were made to correct for this, they were made with 1970s computing power, so they are limited, and since the digital data is missing (perhaps forever), all we have to work with are scans of these attempts. 

Pioneer 11's dataset is unique in that after passing Jupiter, it looked down on its north pole as it headed off across the solar system toward Saturn.  No other spacecraft has gotten such a direct angle on a Jovian pole (although Juno will do so next year), but the global images are frustratingly small.  In this view, I have combined the best six pictures (12 if you count the color pairs as individual pictures) to make a mosaic of Jupiter looking down on the pole soon after closest approach.  I think I can improve on it, but having tinkered with it a year, I am ready to share the image as it stands now.


Processed Image Copyright Ted Stryk, Data Courtesy NASA/Ames Research Center.  A special thanks to the Ames Research Center history office for helping me find the data used in making this. 

Thursday, March 05, 2015

Venus from 33 years ago, and why we need to explore.

Thirty-three years ago today, Venera 14 plunged down through the thick Venusian atmosphere to the surface, where it successfully operated for 57 minutes.  Like the three imaging landers before it, its cameras scanned back and forth across the surface while other instruments took measurements.  The cameras would touch the horizon at either end of the panorama and dip down to the foot of the lander in the middle, a compromise which allowed images to be returned showing both the foreground and the horizon while having adequate resolution to be interpretable and to still be returnable during the short surface mission.  Venera 14, as it happened, landed a very rocky site.  Being tipped a bit, one of its cameras barely touched the horizon, while one side of the other camera gave the most sweeping view of the Venusian horizon we have. 


On the opposite side, the landing managed to dislodge a piece of the rocky surface.


Venera 14 showed a rocky, harsh surface with little regolith/soil compared to the other landing sites.  This brought to mind a talk I heard last fall, in which Victor Baker criticized the vain attempts to find a single site to send a rover where it could tell the whole story of Mars.  As Baker said, imagine finding a site where the story of Earth could be told by roving a few kilometers!  The Martian three sites we've sent stationary landers and four sites we've sent rovers are grossly inadequate.  That despite the fact that we have sub 10-meter coverage of nearly the whole planet and resolution of a few tens of centimeters over great swaths of the planet.

Venus is much larger than Mars - nearly the size of earth! Yet we have only landed in four places and done very limited imaging and surface science at those sites.  We have, granted, landed at four more sites where imagery was not taken, but less than half a day, collectively, has been spent operating on the surface, while the shortest-lived Mars landers had lifespans measured in months, most lasted years, and one has lasted more than a decade.  And many of them roved the surface, covering multiple terrain types.  Beyond the four Venera sites that were imaged, the next best images we have are radar images taken at a scale of 70-100 meters per pixel, the size of a football field!   And despite the fact that all four landers landed in roughly the same area of the planet, the terrain at each site was markedly different.  The above images were balanced to better bring out detail, these balanced (or in some cases colorized)to be more along the lines of how I think the surface might actually look.

(Clockwise from the upper left:  Venera 13, Venera 10, Venera 14, Venera 9 - order chosen for aesthetic purposes)
 
Here is the same set, tipped upright:


  This is the tip of the iceberg when ti comes to terrain types, and even these landscapes were barely touched.  Below is the widest panorama that can be made by combining the panoramas, and even it is patchy and of poor resolution.


Sadly, other than orbiters that primarily studied the atmosphere, Venus has been left alone since the end of the Magellan radar mapping mission in the early 90s.  The final lander accomplished its mission, albeit with no camera, on June 15, 1985.  We need to go back!

Around 6:00 UTC on March 5, 1984, this picture was being returned by Venera 14 as it fell silent forever.  It remains humanity's last view from the surface of Venus.

________________________
 Edit:  Here is a second interpretation of the color for the combined set, with an attempt to improve the balance. I can't decide which one i think is more accurate.



Data Courtesy the Russian Academy of Sciences, Processed Images Copyright Ted Stryk

Sunday, November 23, 2014

Some Recent Views of Mars from Hubble

During the 1990s and the early 2000s, the Hubble Space Telescope served in some respects as a Mars mission, checking in frequently to monitor seasonal changes and to study the surface at wavelengths unavailable from earth and/or with higher spatial resolution than could be obtained from earth's surface.  After 2003, when Mars received a lot of attention due to the unusually close approach, priorities changed.   Mars had and has a flotilla of spacecraft studying it that leave a lot of what Hubble used to do redundant, or at least relatively redundant.  After all, there are four planets in our solar system without a spacecraft currently present, not to mention countless other worlds, plus three with only one spacecraft present. So Hubble, for the most part, has focused its time elsewhere.

The exception is in the ultraviolet.  At least until MAVEN's arrival, the ultraviolet capabilities of the fleet at Mars were very limited.  Thus Hubble periodically checks in with the Space Telescope Imaging Spectrograph (STIS) and with the Advanced Camera for Surveys Solar Blind Channel (ACS/SBC). 

Below is the most recent view available from STIS, taken on April 26, 2012.  Several observations have been taken this year but  none have yet been released.


This year, ACS/SBC has also had some looks, some of which have been released.  One dataset was obtained on May 30, 2014, for the purpose of preparing for MAVEN, providing a baseline for its observations to be compared with Hubble's past observations.


Hubble was again called into service when Comet C/2013 A1 Siding Spring flew by Mars on October 19.  Hubble of course looked on with the STIS and ACS/SBC, and one of the SBC datasets has been released.  I have no idea if it shows any effects of the comet, but it definitely show the atmosphere.



Hubble also took a look with its Wide Field Camera 3 (WFC3), the successor to its old workhorse, the Wide Field/Planetary Camera 2 (WFPC2). This was during the closest approach, when the orbiters were hiding behind Mars relative to the comet.  The primary purpose was to provide a picture for posterity, covering closest approach, but given that many of the exposures overexposed much of the disk, I do wonder if they were trying to study the terminator region.  However, Mars was quite distant during the comet flyby.  As a result, its apparent diameter was less than six arc seconds, much farther away than it has been during most previous Hubble observations.  For a comparison, I have put a WFPC2 image of Mars from the 2003 close approach next to an image from October 19, 2014.  And, given that the pixel scale was somewhat coarser on WFPC2 compared to WFC3, the actual apparent size different is slightly greater. 


A rough RGB process didn't offer much.

  
 
I stacked all available frames and produced the best image I could.  I even mixed in the ACS/SBC image which had higher spacial resolution, then combining it with a color overlay.  The result gives us a good idea of what Mars looked like as the orbiters were hiding behind it for protection from the comet and many around the world were trying to catch a glimpse of this historic event (well, those of us not clouded out, sniff sniff). 


Processed Images Copyright Ted Stryk
Raw Hubble Data Courtesy NASA/STScI