New Horizons Journey into Space and Its Findings on the Pluto System
Launch and First Encounter
After all the years of preparation and planning that go into a new space probe, New Horizons finally launched on January 19, 2006 aboard an Atlas V rocket with a Boeing STAR 48B solid rocket motor. Just 45 seconds after liftoff, New Horizons separated from the rocket. It easily became the fastest space probe ever launched, making it to the moon in hours. It even reached faster velocities (up to 35,800 mph!) after its Jupiter gravity assist, but before that occurred New Horizons passed by 2002 JF56, a 4 kilometer-diameter asteroid, on June 13, 2006. NASA took the opportunity to test out some of New Horizons instruments (Stern "The New" 11, Dunbar “NASA," Stern "NASA" 24)
On February 28, 2007, New Horizons finally encountered Jupiter 13 months after its launch. This was incredibly fast - 5 times sooner than Galileo and 3 times sooner than Cassini. NASA turned on New Horizons instruments and began to look at Jupiter and its moons while taking pictures as well. Even though the gravity assist occurred the next day, New Horizons continued to observe Jupiter until June of 2007. After the assist, New Horizons now travels 35,000 miles per hour on its 3 billion mile trip (Stern "The New" 1, 11; Dunbar “NASA," Stern "NASA" 24).
Only 2 months of every year saw New Horizons turn on its instruments to ensure that they were operational as it moved to Pluto. Because it took 9 hours for signals to travel from New Horizons to us and back, the probe had to do most of the science automatically. The actual flyby was quick, and the total amount of observational time amounted to a few months. Also, because New Horizons transmited data at 1000 bits (not bytes!) per second, it took over a year for the full results to even reach NASA (Stern "The New" 11, Fountain 2, Guterl 55).
Arrival At Pluto and the Flyby
In January of 2015, New Horizons was woken up to begin its 6-month long mission on Pluto, which was 135 million miles away when the probe was turned on. Using its LORRI equipment, New Horizons began taking pictures of Pluto to help triangulate its position and maintain its course. As the probe neared Pluto, it was also taking data telemetry on particles including solar wind and interstellar dust and taking additional pictures of Pluto. Pictures from mid-April of 2015 began to show surface details, including a potential polar ice cap. The resolution improved and improved until the best pictures of Pluto ever were taken during the flyby (Johns Hopkins 16 Jan). A brief scare was encountered by all when the probe entered safe mode 9 days before the flyby, preventing science from being collected. Fortunately, the problem (a timing error in preparation of the flyby) was resolved quickly and everything was back on track (Thompson "New Horizons Enters").
The days passed by quickly and New Horizons was already beginning to see features which would not be visible as the flyby occurred due to the hemisphere proximity. This included four spots which seem to be connected to each other and spaced at a seemingly regular manner. They are about 300 miles wide all together and have sharply defined boundaries of light and dark, according to New Horizons program scientists Curt Niebur. Another interesting find prior to the flyby was the size of Pluto was finally determined to be 1,474 plus or minus 4 miles wide. Previous efforts had been thwarted because of Pluto's atmosphere obstructing a definite reading. The official Mission specialist Bill McKinnon of the Washington University in St. Louis and the team came to this conclusion based off readings from the LORRI instrument which were also looking out for Nix and Hydra. This makes it the largest KBO known to scientists at this time and also revises its volume and therefore density, having further implications as to its composition. The official value is now 1.86 +/- 0.01 grams per cubic centimeter., pointing to a 60% rock, 40% ice make-up. And if this wasn't exciting enough more details emerged about the side that New Horizons would get to image in high-resolution, including what seemed to be a giant heart! The anticipation was killer (John Hopkins 11 Jul, John Hopkins 13 Jul, Chang, Stern "The Pluto" 26).
As New Horizons flew past Pluto and Charon at 30,800 miles per hour on July 14, 2015, its closest approach was at 7:49 am eastern time at 7,690 miles, just 74 seconds early and only 45 miles off! New Horizon's trajectory took it behind both Pluto and Charon, falling into their shadows. This allowed New Horizons to potentially see any atmosphere on each body and to analyze the sunlight going through it by making use of ALICE. Also, by passing behind Charon, the LORRI instrument was hoping to see Charon-glow on Pluto, allowing mapping of the night side of Pluto to occur. But all in good time. As Alan Stern put it, "Right now, we're just standing under the waterfall and enjoying it" (Howard).
Download and Be Amazed
Of course, to ensure that the flyby was a maximum gain event the New Horizons probe did not transmit any data until the flyby was well over. Scientists like Alan Stern had to wait over 13 hours post-Pluto flyby to know if New Horizons had even survived or had fallen victim to a possible space collision. But it had indeed made it through and started to send some amazing pictures that blew scientists away. A heart-shape feature was indeed on Pluto and Charon did have a dark red pole, just as preliminary data suggested (Boyle "Its", Chang).
Despite the long download time for the data, scientists have had plenty to sink their teeth into. Within the initial download on the same day as the flyby many discoveries were made. The 3-filter color images that the RALPH instrument was able to capture shows differentiations in the surfaces not visible in the visible spectrum. Interestingly it shows that Pluto's "heart" is not a whole feature but rather two distinct halves made of different materials with one side being smooth and made of carbon monoxide ice (possibly indicating a young age) and the other full of craters (possibly indicating an old age). The red pole of Charon, named Mordor, is either a result of UV light reducing material falling down on it (likely from Pluto) to tholins, a type of carbon compound, or the aftermath of an impact. The region has a darker inner zone of 170 miles with an outer zone of 280 miles (Stern "The Pluto" 25, Boyle "New From," Talcott "Pluto", Hupres).
The next day offered even more surprises, including mountains. Located along the western edge of the heart-shape feature on Pluto (informally known as the Tombaugh Regio), they offered some tantalizing and shocking clues about what does on geologically. Some of them are higher than the Himilayas at over 11,000 feet and instead of being made of rock are composed of water ice. The images showed no signs of impact craters, leading scientists to think that the mountains are young, probably no more than 100 million years old. But as to what could have allowed much of Pluto to have this youthful appearance was unknown but the best theory was radiological decay causing the interior to be warm enough for resurfacing, Tidal heating caused by gravitational pull cannot be occurring here because nothing is pulling hard enough. There simply isn't enough mass. Small pits next to mountains in Sputnik Planum seem to have arisen from sublimation of carbon monoxide/nitrogen ice of the plain into gas (Freeman, Yuhas, Stromberg, Calderone "The Biggest", Thompson "First," Powell).
Norgay Montes and the Hillary Montes
Also found on the surface of Pluto were these huge mountains named the Norgay Montes and the Hillary Montes. As tall as the American Rockies, they are too big for them to be made of the ice seen in Tombaugh, for that material is weak on Pluto and cannot withstand the 0.06 g environment. So what can it be made of? Maybe if it were composed of water ice, we would be in luck. If true, it would hint at a water ice mantle with a rocky core, based on those density readings (Stern "The Pluto" 27).
Moon and Methane Madness
The first picture of Hydra was also released. Though highly pixilated it does reveal the irregular shape of the moon to be 20 by 27 miles and that it is made of mostly water ice. Charon got a high resolution release that day also. Amongst the interesting findings was canyons that are 4 to 6 miles deep and cliffs which go on for over 600 miles. But even more bizarre was how smooth it is. Pluto is considered to be too small for geological activity, so how could Charon be? Maybe a collision in the past caused it to be partially molten again, erasing any craters from the surface. Finally, a methane map of Pluto was displayed from infrared measurements. The different colors refer to the different types of methane ice present on the dwarf planet. Other surface measurements indicate that it is all ice and is 90% nitrogen and 10% methane. The different colors seen could be due to particulates like tholin (which absorb blue light and reflect red like most organic materials), age of the ice, or concentrations of the nitrogen and methane (Freeman, Yuhas, Stromberg, Betz "Pluto's Bright", Thompson "First," Hupres).
Scientists have known about the atmosphere of Pluto thanks to many occultations but the size of it was unknown until now. Measuring in at 1,650 miles above the surface, it was not only larger than expected but also colder and more dense than anticipated. But what was even more surprising was what the SWAP instrument detected behind Pluto: a comet-like tail spanning 48,000 to 68,000 miles! The low gravity of Pluto means it cannot hang onto any gases for long so its escapes the surface, being deflected by the solar wind into a tail. It is made of ionized nitrogen and forms a plasma which allows the solar wind to carry away up to 500 tons of it each hour. Despite all of this, Pluto maintains a 7-10 microbar surface pressure (about 0.001% that of Earth's) and only has lost half a foot of total atmosphere depth to space since the formation of the solar system (as opposed to the old-school though of a half mile) (Thompson "First," Calderone "NASA," Betz "Pluto's Icy," Stern "The Pluto" 26, Talcott "New").
Nix and Hydra Revealed
A few days later saw the release of better resolution pictures of Nix and Hydra. The picture of Nix was taken at a distance of 102,000 miles and shows details as small as 2 miles including in interesting red area against the predominant grey. Based on the shape of it, the red area could be an impact crater. We also now know that Nix is 22 miles in diameter, spins 10% faster than it did 3 years ago, and reflects 43-50% of the light that hits it, pointing to the presence of water ice. The picture of Hydra was taken from 143,000 miles away and shows details as small as 0.7 miles. Based on the LORRI data, Hydra is about 27 by 21 miles in size, reflects 51% of the light hitting it (again hinting at ice), completes 89 revolutions per orbit around Pluto, has two possible impact craters and a possibly dark half. This indicates a likely change in composition of materials (NASA "New Horizons Captures," Thompson "New Horizons Data," Talcott "New").
Compounds in the Atmosphere
July 24 of that year, just 10 days post flyby, saw NASA release a picture of Pluto backlit by the Sun. The outlined dwarf planet shows two haze layers with one 30 miles above the surface and the other 50 miles above, going up to 80 miles high. The production of the haze is a little complicated, so buckle up. Methane gases in the atmosphere of Pluto get broken down by UV light and converts it to ethylene, acetylene, and other complex hydrocarbons called tholins which are red in color, producing a blue appearance similar to what nitrogen and oxygen in our atmosphere scatters. They settle to the lower levels of the atmosphere where they freeze into icy particles and become haze. It is possible that these can be broken down further by UV light into even more tholins which help give a red tint to the dwarf planet (NASA "New Horizons Finds," Thompson "New Horizons Data," Powell, Betz "Pluto Surprises," Stern "The Pluto" 26).
Also released that day was evidence of ice flows on the surface of Pluto. Located in Sputnik Planum, the image shows nitrogen ice and the possible migration it makes through the soft ice, like glaciers on Earth. It is another sign of a geologically active world despite the -390 degree Fahrenheit temperature found there. In fact, images of the lower portion of the Tombaugh Regio possible show ice moving over into the dark area known as the Cthulhu Regio. Images of both of these along with other newly named features are on the right (NASA "New Horizons Team," Thompson "New Horizons Data," Stern "The Pluto" 27).
Alright, so what is the deal with all this nitrogen? Where does it come from? Comets are unlikely to collide enough to constantly replenish the 100's of tons lost hourly. It seems as though the geologically active dwarf planet viewpoint has gained more ground. Somehow, an internal mechanism is bringing nitrogen to the surface. Stern thinks that cryovolcanoes could be a possible delivery system. He also pointed out that for Pluto to be pumping as much nitrogen as it currently is suggests that it is much younger than anyone thought it was, possibly denting Kuiper Belt theories (Lewin).
Meanwhile, Charon continues to be a source of intrigue as the time passes from the flyby. The giant canyon seen on images may extend further around the moon than previously thought, over a 1000 miles. It seems to point to a violent collision with the moon which fractured the surface! Indeed, many cracks and chasms such as the Macross Chasma (which is 650 miles long and many miles deep) are present on the moon. And the southern hemisphere of the moon is smoother than the north, indicating it is a newer surface. Most scientists seem to think that cryovolcanism is the likely reason, which would be huge especially because the moon shouldn't be geologically active, considering its small size and lack of internal heat. A comparison of Skywalker and Organa, two craters near each other, seems to point to this as well. When examining the ammonia levels of the two, one was off the charts comparatively to the other. How could two structures close together differ so much? If the moon was cyrovolcanically active with ammonia as magma then perhaps one shows subsurface content seeping through (NASA "Pluto's Big Moon," Timmer "Pluto's Moon", NASA "The Youngest," Stern "The Pluto" 28, Hupres).
The talk of cyrovolcanoes in the Pluto system heated up when Wright Mons, Kubrick Mons and Piccard Mons on Pluto were identified as being similar to shield volcano-like structures on Mars and Earth. The 100 kilometer wide rim around shallow but gentle depression slopes points to a collapse of the surface once material from below vacated it. The likely material of the cryovolcano would be a mix of nitrogen (as theorized before), ammonia, methane, or even water ice. And with a lack of craters in Sputnik Planum and a general lack of old craters anywhere on Pluto hints at both an active surface but also at a lack of small objects colliding with the dwarf planet. In fact, the Tombaugh Regio seems to be 1 billion years old while Sputnik Planum is less than 10 million years old! It hints at a shocking picture: that KBO's did not form through accumulation of smaller objects but rather formed as large objects near their current orbit. Solar system formation theories will need potential revising if further data confirms this (NASA "Pluto May Have," Berger "Volcanoes," Talcott "New").
And while it may have taken a while, Mid-October of 2015 found us seeing the first images of Kerberos, meaning that all the moons of Pluto had finally been seen. According to the data, the moon is not only smaller than expected but also more reflective as well and is shaped as if two objects collided and merged together. One of these lobes is 5 miles in diameter while the other is 3 miles in diameter. The reflective nature of the surface of the moon hints at a surface of water ice, something that becomes more of a theme for the Pluto system as time continues on (NASA "Last of," Hupres).
December of 2015 saw more information being released as well as new images. Amongst the findings released as continuing evidence for past and present geological activity on Pluto and with this the formation of interesting valleys that result from erosion. Sputnik Planum had its temperature readings released also, and they paint a picture for the nitrogen ices seen there. The way the heat flows in the 620-mile wide region causes the interesting polygon formations seen, and also how certain features travel around. Based on the heat, the plain is likely a few miles deep. Also mentioned was the lack of any new moons despite New Horizons looking for objects 20-30 times fainter than Nix (NASA "New Findings," Stern "The Pluto" 28).
Also discussed during these findings was the nature of the atmosphere surrounding Charon. LEISA found that all over the surface of Charon is a low-level absorption of ammonia. This seems to point to a possible link to the concentrated, high areas seen elsewhere on the moon, but whether it is internal or external is not known (Ibid).
Near the end of January 2016, the New Horizons team released a false-color map of Pluto's surface uncovered by LEISA to show how water is distributed. The image on the right shows all the water on the surface while the map on the left shows where the water is from bedrock, known due to the gases like methane obscuring material. While the map shows more water than scientists suspected there was, it also points out an interesting absence of the material in Sputnik Planum and Lowell Regio, perhaps indicating how their age plays a role in the surface of Pluto. Also, water levels on this map corresponded to the red areas on the dwarf planet, perhaps indicating a correspondence to tholins and water production (NASA "Pluto's Widespread," Betz "Pluto Surprises").
A month later, scientists announced that Charon's fractured surface might hint at a subsurface ocean that has long since vanished. When Charon formed, radioactive material would have heated water to a liquid phase. But eventually that fuel ran out, and the ice froze and expanded, pushing the surface of Charon outward and therefore fracturing it. Surface spectrometric data shows that water is on the surface of that moon, and many of the ridges on Charon point to a stretch (for they line up nicely, similar to the coast of South America and Africa) (Berger "Far," NASA "Pluto's Largest").
In March of 2016, a connection was found between the mountains of Pluto and its atmosphere. Turns out the dwarf planet has another parallel to Earth: snow on mountains. Yes, mountains in the Cthulhu region seem to have brighter tops than the rest of the tholin-covered terrain. And when we compare these tips to methane ice distributions around the mountains, we have a match. And where does that methane come from? The atmosphere, where the methane condensed and fell back to the surface. At the altitudes of the mountains it remains in its frozen form (Berger "NASA May").
Remember those nitrogen ice flows in Sputnik Planum? Scientists suspect that it acts like a giant "lava lamp." In a June 2016 press release, William B. McKinnon (from Washington University in St. Louis) and colleagues laid out their theory, which was based off imagery and computer simulations. Whatever is heating Pluto internally (likely a radioactive material) gets things hot enough to melt the nitrogen (which normally would be at 35 K) into a liquid, which rises because of buyoncy. As it nears the surface, it cools off until becoming solid again and sinking back down. In addition, this ice easily changes shape because of the lack of strong bonds between nitrogen atoms. All of this creates flow patterns like an uprising convection cell, which matches what images we have of up to 50 meter height differences between cells. But according to the simulations, the flow is slow, about a few centimeters a year. That means it would take over 500,000 years to fully circulate the surface and explain its youthful appearance. But as for why most of the nitrogen on Pluto exists solely in this region, the simulations offer no answers. Simply amazing (John Hopkins 02 Jun, Timmer "Pluto's Sputnik").
Next Target: MU69
At the end of August of 2015 NASA announced that the follow-up to Pluto would be 2014 MU69, an object over 1 billion miles past Pluto, so long as it passed inspection and review. That was achieved on July 1, 2016. At a little under 30 miles long, it was one of 5 objects spotted by Hubble in 2014 as the New Horizons team was searching for the next phase of the mission. Targeted fuel burns should get New Horizons to MU69 by January 1, 2019. Then another window into the mysterious Kuiper Belt will hopefully be revealed (NASA "New Horizons Selects").
So many have been released that I could overflow this hub! Check out the link below for even more exciting pictures of Pluto:
Berger, Eric. "Far-distant Charon May Have Once Has a Large Subsurface Ocean." arstechnica.com. Conte Nast, 19 Feb. 2016. Web. 13 Jul. 2016.
---. "NASA may have found snow-covered mountains on Pluto." arstechnica.com. Conte Nast, 03 Mar. 2016. Web. 05 Aug. 2016.
---. "Volcanoes on Pluto Look a Lot Like Those On Earth and Mars." arstechnia.com. Conte Nast, 09 Nov. 2015. Web. 19 Dec. 2015.
Betz, Eric. "Pluto’s bright heart and Charon’s dark spot revealed in HD." Astronomy.com. Kalmbach Publishing Co., 15 Jul. 2015. Web. 18 Aug. 2015.
---. "Pluto’s icy plains, pits, and mountains take shape in Tombaugh Regio." Astronomy.com. Kalmbach Publishing Co., 17 Jul. 2015. Web. 19 Aug. 2015.
---. "Pluto Surprises With Blue Skies, Red Water." Astronomy Jan. 2016: 16. Print.
Boyle, Alan. "It's Pluto Flyby Day! Get In on the Climax of NASA's New Horizons Mission." NBCNews.com. NBC Universal, 14 Jul. 2015. Web. 17 Aug. 2015.
---. "New From New Horizons: 5 Things We Just Found Out About Pluto and Charon." NBCNews.com. NBC Universal, 14 Jul. 2015. Web. 18 Aug. 2015.
Calderone, Julia. "NASA just found something big hiding out behind Pluto." BusinessInsider.com. Business Insider Inc., 17 Jul. 2015. Web. 19 Aug. 2015.
---. "The biggest discovery in new images of Pluto is what scientists didn't see." BusinessInsider.com. Business Insider Inc., 15 Jul. 2015. Web. 18 Aug. 2015.
Chang, Kenneth. "NASA’s New Horizons Spacecraft Zips Past Pluto in Flyby." TheNewYorkTimes.com. The New York Times Company, 14 Jul. 2015. Web. 17 Aug. 2015.
Dunbar, Brian. "NASA's Pluto Mission Launched Toward New Horizons." NASA. NASA, 19 Jan. 2006. Web. 07 Aug. 2014.
Fountain, Glen H., David Y. Kusnierkiewicz, Christopher B. Hersman, Timothy S. Herder, Coughlin, Thomas B., William T. Gibson, Deborah A. Clancy, Christopher C. DeBoy, T. Adrian Hill, James D. Kinnison, Douglas S. Mehoke, Geffrey K. Ottman, Gabe D. Rogers, S. Alan Stern, James M. Stratton, Steven R. Vernon, Stephen P. Williams. “The New Horizons Spacecraft.” arXiv:astro-phys/07094288.
Freeman, David and Eliza Sankar. "Dazzling New Pluto Photos Are The Best Ever Taken Of The Icy Dwarf Planet." HuffingtonPost.com. Huffington Post, 15 Jul. 2015. Web. 18 Aug. 2015.
Guterl, Fred. “Journey to the Outer Limits.” Discover: March 2006: 53-5. Print.
Howard, Jacqueline. "NASA's New Horizons Spacecraft Takes Closest Look Yet At Dwarf Planet Pluto." HuffingtonPost.com. Huffington Post, 14 Jul. 2015. Web. 17 Aug. 2015.
Hupres, Korey. "Pluto's Moons Revealed." Astronomy Feb. 2016: 12. Print.
Johns Hopkins University Applied Physics Lab. "How Big Is Pluto? New Horizons Settles Decades-Long Debate." Astronomy.com. Kalmbach Publishing Co, 13 Jul. 2015. Web. 17 Aug. 2015
---. "New Horizons begins first stages of Pluto encounter." Astronomy.com. Kalmbach Publishing Co., 16 Jan. 2015. Web. 08 Feb. 2015.
---. "New Horizons' last portrait of Pluto's puzzling spots." Astronomy.com. Kalmbach Publishing Co., 11 Jul. 2015. Web. 17 Aug. 2015.
---. "Pluto's Heart Like a Cosmic Lava Lamp. Astronomy.com. Kalmbach Publishing Co., 02 Jun. 2016. Web. 14 Jul. 2016.
Lewin, Sarah. "If Pluto Keeps Spewing Nitrogen, Why Is It Still Full of It?" Space.com. Space.com, 17 Aug. 2015. Web. 09 Sept. 2015.
NASA. "Last of Pluto’s moons — mysterious Kerberos — revealed by New Horizons." Astronomy.com. Kalmbach Publishing Co., 23 Oct. 2015. Web. 04 Nov. 2015.
---. "New Findings From New Horizons Shape Understanding of Pluto and its Moons." Astronomy.com. Kalmbach Publishing Co., 21 Dec 2015. Web. 10 Mar. 2016.
---. "New Horizons captures two of Pluto's smaller moons." Astronomy.com. Kalmbach Publishing Co., 21 Jul. 2015. Web. 19 Aug. 2015.
---. "New Horizons selects Kuiper Belt target." Astronomy.com. Kalmbach Publishing Co., 31 Aug. 2015. Web. 09 Sept. 2015.
---. "New Horizons team finds haze, flowing ice on Pluto." Astronomy.com. Kalmbach Publishing Co., 01 Oct. 2015. Web. 04 Nov. 2015.
---. "Pluto's Big Moon Charon Reveals a Colorful and Violent History." Astronomy.com. Kalmbach Publishing Co., 24 Jul. 2015. Web. 19 Aug. 2015.
---. "Pluto's Largest Moon May Have Once Had An Ocean." Astronomy.com. Kalmbach Publishing Co., 19 Feb. 2016. Web. 13 Jul. 2016.
---. "Pluto May Have Ammonia Fueled Ice Volcanoes." Astronomy.com. Kalmbach Publishing Co., 09 Nov. 2015. Web. 19 Dec. 2015.
---. "Pluto's Widespread Water Ice." Astronomy.com. Kalmbach Publishing Co., 29 Jan. 2016. Web. 10 Mar. 2016.
---. "The Youngest Crater on Charon?" Astronomy.com. Kalmbach Publishing Co., 02 Nov. 2015. Web. 19 Dec. 2015.
Powell, Corey S. "The Passion of the Pluto-Philes." Discover Dec. 2015: 71. Print.
Stern, Alan. "NASA Sets Its Sights on Pluto." Astronomy: Feb. 2015: 24-5. Print.
---. "The New Horizons Pluto Kuiper Belt Mission: An Overview with Historical Context." Space Science Reviews 140.1-4 (2008): 3-21. Web. 07 Aug 2014.
---. "The Pluto System Explored." Astronomy Nov. 2015: 25-9. Print.
Stromberg, Joseph. "New Horizons' photos from the Pluto flyby are finally here — and they're amazing." Vox.com. Vox Media, 15 Jul. 2015. Web. 18 Aug. 2015.
Talcott, Richard. "New Horizons Unleashes Torrent of Pluto Science." Astronomy Mar. 2016: 15. Print.
---. "Pluto and Charon show craters, dark spots, and even signs of snow as New Horizons flies by." Astronomy.com. 14 Jul. 2015. Web. 18 Aug. 2015.
Thompson, Amy. "First Pluto data reveals lots of terrain that is “not easy to explain” ars technica. Conte Nast., 17 Jul. 2015. Web. 19 Aug. 2015.
---. "New Horizons data shows Pluto’s atmosphere, surface features." ars technica. Conte Nast, 27 Jul. 2015. Web. 19 Aug. 2015.
---. "New Horizons enters safe mode 9 days before Pluto rendezvous." ars technica. Conte Nast., 05 Jul. 2015. Web. 17 Aug. 2015.
Timmer, John. "Pluto’s moon Charon shows fractured surface, signs of recent activity." ars technica. Conte Nast., 02 Oct. 2015. Web. 04 Nov. 2015.
---. "Pluto's Sputnik Planum is an Ocean of Slowly Shifting Nitrogen Ice." ars technica. Conte Nast, 02 Jun. 2016. Web. 14 Jul. 2016.
Yuhas, Alan. "Nasa unveils 'surprise' Pluto photos and New Horizons discoveries – as it happened." TheGuardian.com. Guardian News, 15 Jul. 2015. Web. 18 Aug. 2015.
© 2015 Leonard Kelley
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