Passengers on Voyages of Exploration: the Beautiful and Surprising Work Amateurs Can Do with Raw Image Data from Planetary Missions

Preparing for the 2009 International Year of Astronomy ASP Conference Series, Vol. 400, c 2008 M. G. Gibbs, J. Barnes, J. G. Manning, and B. Partridge, eds.

Passengers on Voyages of Exploration: The Beautiful and Surprising Work Amateurs Can do with Raw Image Data from Planetary Missions

Emily Stewart Lakdawalla The Planetary Society, 65 North Catalina Avenue, Pasadena, California 91106, USA

Abstract. Many recent planetary science missions, including the Mars Ex- ploration Rovers, Cassini-Huygens, and New Horizons, have instituted a policy of the rapid release of “raw” images to the Internet within days or even hours of their acquisition. The availability of these data, along with the increasing power of home computers and availability of high-bandwidth Internet connec- tions, have stimulated the development of a worldwide community of armchair planetary scientists, who are able to participate in the everyday drama of ex- ploratory missions’ encounters with new worlds and new landscapes. Far from passive onlookers, many of these enthusiasts have taught themselves image pro- cessing techniques and have even written software to perform automated pro- cessing and mosaicking of these raw data sets. They rapidly produce stunning visualizations and then post them to their own blogs or online forums, where they also engage in discussing scientific observations and inferences about the data sets, broadening missions’ public outreach efforts beyond their direct reach. These amateur space scientists feel a deep sense of involvement in and connection to space missions, which makes them enthusiastic (and occasionally demanding) supporters of space exploration.

1. Introduction

It is a great time to be an armchair planetary explorer. As the Internet has developed, missions have expanded their outreach by providing rapid releases of raw image data for the public to download. And as people upgrade their homes to high-speed Internet service, more and more of them are developing the capability to consume the high volumes of image data being produced by active missions. At the same time, consumers are transitioning to the use of digital rather than film cameras, which means a large segment of the public is familiar with methods of digital image processing. And finally, the proliferation of sites that promote the sharing of user-generated content, places like online forums, per- sonal weblogs, Flickr, Picasso, and YouTube, means that people can share their work with other enthusiasts. They can comment on each other’s products, share information about data resources, learn image processing tricks from each other, and become inspired to teach themselves to do more. The end result is that there is now a thriving international community of amateur imagesmiths who actively follow every day of a space mission. This community doesn’t just consume data 436 Passengers on Voyages of Exploration 437 from space missions; they can make positive contributions to space science as well.

2. Where Amateurs Get the Data

Amateurs take advantage of two main types of data sources. First, some NASA missions have adopted policies of automatically spewing all the image data that they acquire onto special “raw” image websites. Currently, the three mis- sions that provide data in this way are the Mars Exploration Rovers,1 Cassini- Huygens,2 and Phoenix;3 recently, New Horizons4 did also. Typically, these data are sent to the Internet before flatfielding, dark current subtraction, and other basic calibration steps have been performed. The data also usually have an automatic contrast stretch applied that assigns the brightest and darkest few percent of the pixels in each image to extreme white and black values. Because of the lack of calibration and automatic contrast stretching, these images are not particularly useful for science. Instead, they provide snapshots of where a spacecraft has most recently been—a view out the porthole of a spaceship. These images allow the public to follow missions in “real time,” seeing the im- ages as quickly as the science teams do. Depending on the relative timing of downlink and the sleep cycles of science team members, the public may actually see the data first! What can amateurs do with such raw data? One popular activity is to make animations. For instance, one could follow the deployment of Phoenix’ robotic arm on the third day of its mission by taking the six images that were returned from Phoenix’ camera and assembling them into an animation. The rovers take many images with engineering cameras as they drive, which can be assembled into movies that show their motion across Mars. Cassini regularly captures time-series of motions in the rings and atmosphere of Saturn or ap- parent rotation or motion of moons during flybys, which make for enthralling animations. No unusual software is needed to do this. Many children are taught how to make slide presentations using Microsoft PowerPoint or similar software in the classroom; a simple animation can be made by dropping spacecraft im- ages onto separate slides in a presentation, and then rapidly advancing the slides. Alternatively, many pieces of home photo album software allow the creation of slideshows, which is a fine way to show an animation that has a small number of frames. Amateurs can also make mosaics, showing landscapes on Mars and Titan, or use right- and left-eye images to create anaglyphs, viewable with red-blue 3D glasses. They can even make three-filter color images, although producing

1Raw Images for Spirit and Opportunity: http://marsrovers.jpl.nasa.gov/gallery/all/ 2Cassini-Huygens Raw Images: http://saturn.jpl.nasa.gov/multimedia/images/raw/ index.cfm 3Phoenix Lander Raw Images: http://phoenix.lpl.arizona.edu/imageCategories lander. php 4New Horizons Science Operations Center Raw Images: http://pluto.jhuapl.edu/soc/ 438 Lakdawalla

approximate true-color views is made difficult by the automatic contrast stretch that has been applied.

3. A Few Experts Open Access to Many Dabblers

Amateurs are also learning how to make use of calibrated data that has been archived to NASA’s Planetary Data System5 or their equivalents at ESA (the Planetary Science Archive6) and JAXA (Data Archives and Transmission Sys- tem7 and Hayabusa Project Science Data Archive8). These data are typically stored in formats that are difficult for the average user to search, open, and process. However, a few self-taught image experts have written software that enables the average user to access PDS-formatted data. For example, an Icelandic space artist named Bj¨orn J´onsson has developed a piece of command-line software titled IMG2PNG,9 which can batch-convert files stored in the Planetary Data System’s IMG format to losslessly compressed, 8- bit or 16-bit Portable Network Graphics (PNG) format, making them accessible to all. He has recently updated his software to open and convert New Horizons LORRI image data, stored in 32-bit FITS format. Another expert, Gordan Ugarkovic, from Croatia, has developed a similar piece of software, QUB2PNG,10 for converting Cassini’s VIMS image cubes into multiple PNG files. Probably the most impressive piece of amateur-produced software is the Midnight Mars Browser11 developed by an American programmer Michael Howard. Midnight Mars Browser automatically downloads all raw images from the Mars Exploration Rovers, produces RGB color composites and anaglyphs, and auto- mates the production of mosaics, which are displayed as virtual reality panora- mas that can be dynamically moved around the viewer (figure 1). Howard’s software also provides basic download capability for Phoenix images. Through the efforts of a few such experts, the vast catalogues of planetary data that have been returned from all space missions are being opened up to the regular Internet user. Thus amateurs are now increasingly capable of consuming image data from planetary missions. Amateurs can (and often do) produce more and prettier versions of images from active planetary missions than the science teams have time to do, and they can produce them very quickly; science teams should seriously consider offloading some tasks of creating presentation-quality images to the amateur community.

5Planetary Data System: http://pds.jpl.nasa.gov/ 6Planetary Science Archive: http://www.rssd.esa.int/index.php?project=PSA 7Data Archives and Transmission System: http://www.darts.isas.jaxa.jp/index.html.en 8Hayabusa Project Science Data Archive: http://hayabusa.sci.isas.jaxa.jp 9IMG2PNG: http://www.mmedia.is/bjj/utils/img2png/ 10QUB2PNG: http://www.unmannedspaceflight.com/index.php?showtopic=4759 11Midnight Mars Browser: http://midnightmarsbrowser.blogspot.com Passengers on Voyages of Exploration 439

Figure 1. Screen capture from Michael Howard’s Midnight Mars Browser (MMB) software showing a panoramic view from the Mars Exploration Rover Opportunity’s Navigational Camera (Navcam) on sols 1,327–1,329 (October 18–20, 2007), when the rover was sitting on the sloped surface of Duck Bay, looking in to Victoria Crater. MMB automatically downloads the component Navcam images (seven of which are tiled to create the view shown here) from the Jet Propulsion Laboratory or San Francisco Exploratorium websites, and displays images from selected time intervals in a virtual-reality panoramic view. By clicking and dragging with the mouse in the panorama window, a user can spin the rover’s 360-degree view around in azimuth and elevation; keystrokes advance the view forward and backward in time. Navcam images courtesy NASA/JPL-Caltech.

4. How Professionals Can Help Amateurs

The most direct way to encourage growth of the amateur community is to em- ulate the imaging teams on the Mars Exploration Rover, Cassini-Huygens, New Horizons, and Phoenix missions, and provide near-real-time access to raw ver- sions of the image data. The thrill of exploration that is generated by being allowed this glimpse into the everyday discoveries of active space missions is ad- dictive. In addition to the images themselves, it is helpful if associated metadata such as geometry, timing, and filter information is also provided, in straightfor- ward, simple-text format at a stable URL so that it can be automatically down- loaded and manipulated by the software being written by amateurs to handle the data. It is unnecessary to overdesign the interface through which the public can access the raw data. It can be tempting for mission outreach offices to create flashy, animation-heavy interfaces to raw data, but it is far more useful to the amateur community if a mission provides a lower-level product and allows the amateurs to make the most of it. (It also represents less work for the mission.) In general, the same types of planning and housekeeping documents that are 440 Lakdawalla

used internally by mission personnel are the types of information that are most valuable to the amateur community.

5. How Amateurs Can Help Professionals

The amateur community can be demanding. However, they can also contribute positively to the scientific exploration of our solar system and its promotion to the wider public. Consider two examples: New Horizons Jupiter imaging. Only a year after New Horizons launched, it was scheduled for a gravity-assist flyby of Jupiter. The goal of the Jupiter encounter was to speed the spacecraft onward to Pluto, but the science team desired to use the opportunity to test out their instruments and systems and do some valuable Jupiter system science. The tight schedule allowed very lit- tle time for planning, however. One activity that seemed to be falling by the wayside was the task of examining the encounter geometry for opportunities to take photographs that might have exceptional outreach value because of their beautiful composition. In February 2006, a member of the imaging team, John Spencer, posted a notice to the online forum unmannedspaceflight.com12 invit- ing forum participants to search for so-called “Kodak moments,” opportunities to take aesthetically pleasing photos. Within 24 hours, forum member Richard Hendricks had posted a list of possibilities, two of which eventually entered the New Horizons science plan (figure 2). The experiment was considered a suc- cess, and Spencer has now issued a call to the amateur community for “Kodak moment” proposals for the Pluto encounter.13 Mining Old Data Sets. Many of the most dramatic images in the history of space exploration were taken during a time when manipulating even half- megapixel images was computationally challenging. With the image-crunching power of modern home computers, amateurs can wring amazing images out of old mission data sets, such as the Rangers, Lunar Orbiters, Mariners, Pioneers, and Voyagers. For example, consider the departing mosaic of Mercury captured by Mariner 10 on March 29, 1974. The most-published version of this mosaic, taken from JPL’s Planetary Photojournal, contains obvious seams from the more than 100 individual images that compose it. A new version produced by an amateur, Tennessee English professor Ted Stryk, contains none of these seams, revealing the subtle variations of albedo across the disk (figure 3). Stryk has also worked on newly calibrated images of the moons of the outer solar system from the Voyager missions. While working on Voyager 2 images of the Uranian satellites he noticed that the nighttime hemispheres of two of the moons, Ariel and Miranda, were faintly illuminated by sunlight reflected off of Uranus. Because it was summer in the Uranian system during the Voy- ager 2 encounter, the nightsides of these moons included nearly all of their northern hemispheres, and these regions were previously thought to be invisible to Voyager. However, Stryk’s processing revealed previously unseen details in these dark regions, particularly on Ariel, where the long rift zone called Kachina

12http://www.unmannedspaceflight.com/index.php?showtopic=2088 13http://www.unmannedspaceflight.com/index.php?showtopic=5061 Passengers on Voyages of Exploration 441

Figure 2. Two “Kodak moments” from the New Horizons Jupiter flyby, views chosen for aesthetic beauty rather than scientific value. These two views were proposed by unmannedspaceflight.com forum contributor Richard Hendricks, and incorporated into the spacecraft’s encounter plan by imaging team member John Spencer. Both were taken after the spacecraft’s closest approach to Jupiter, on February 28, 2007. Top image: two of the Galilean moons, Europa (lower left) and Io (upper right) cluster close together in New Horizons’ view. Europa is much closer to the spacecraft so appears the same size as Io even though Io is significantly larger than Europa. Io’s crescent and volcanic Tvashtar plume are lit from behind by the Sun, while its nightside is lit by reflected light from Jupiter. By contrast, no Jupiter light reaches the dark side of Europa, so only its s unlit crescent is visible. Bottom image: the ice-covered moon Europa, smallest of the Galilean satellites, rises from behind Jupiter’s limb. Images courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute. 442 Lakdawalla

Figure 3. Two versions of the highest-resolution full-globe mosaic of Mer- cury captured by Mariner 10 in March of 1974. The version on the left is the one available from NASA’s Planetary Photojournal and is often reproduced in museum displays, publications, and websites. The version on the right was created by an amateur, Ted Stryk, from the individual Mariner 10 image frames archived at the Planetary Data System. His processing has removed the distracting seams between adjacent frames, revealing subtle albedo varia- tions across Mercury’s disk. For example, the dark rim surrounding the large southern hemisphere crater Tolstoj is readily visible in Stryk’s version of the image, but not in the Photojournal version. Images courtesy Ted Stryk and NASA/JPL.

Chasmata—which spans 1,200 kilometers across the portion of the disk that was sunlit to Voyager—can be seen to extend 500 to 800 kilometers into the moon’s nightside, making Kachina Chasmata rival Ithaca Chasma on Saturn’s moon Tethys for scale. Stryk then crossed the boundary between amateur and profes- sional when he collaborated with a geologist to present the results of his image processing at the Lunar and Planetary Science Conference (Stryk and Stooke, 2008). More generally, amateurs help professionals by proselytizing about the thrill and excitement of space exploration to the wider public. Through their efforts either to create software to help other people visualize other worlds, or through speeches, articles, blogs, and other public communication activities, they mas- sively expand a mission’s public outreach efforts. The professional community would be wise to take note of the amateur community, help to nourish its devel- Passengers on Voyages of Exploration 443 opment, and take advantage of it by using them to produce artistic, publication- quality graphics from past and present mission data sets.

References

Stryk, T., and P. J. Stooke 2008, http://www.lpi.usra.edu/meetings/lpsc2008/ pdf/1362.pdf