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Telling Pluto’s Story, One Fragment at a Time

The Pluto System

Pluto and Charon are in the middle, orbiting around their common center of mass. The four smaller moons orbit around them.

When you begin a new research project, you usually have expectations about where it will lead. Most projects take you or less to the expected destination. Some go nowhere. However, every now and then a project picks you up and makes you feel like you’re just coming along for the ride.

Today, in the journal Nature, we have published the results of a research project that fits solidly into the third category.

Our original plan was straightforward. We had recently discovered two small moons of Pluto, now known as Kerberos and Styx. We wanted to publish a short discovery paper that would just cover the basics: How did we find the moons? What are their orbits? How big are they? What are the implications of the discovery?

The Pluto system had other ideas.

Pluto also has two much brighter moons nearby, Nix and Hydra. They had been discovered years earlier and much had been written about them. I had no reason to think there was anything new to be said about either of them. For me, they could just be my “reality checks” to confirm that I was obtaining valid results.

However, my early efforts to determine the size–or at least the brightness–of each moon took a very strange turn. Most moons in the Solar System are in “synchronous rotation”, meaning that they rotate once about their own axis every time they circle the planet. This is why we only ever see one face of our own Moon. The “de-spinning” of a moon happens very quickly, because the gravity of the central planet creates tides, which dissipate energy inside the moon as it rotates. The dissipation can only end when the moon reaches synchronous lock.

If Nix and Hydra were in synchronous lock, we would have seen a distinct relationship between how bright they appear and where they fall along their orbits. We didn’t. There was no pattern at all. Neither moon is in synchronous rotation! The same is probably true of Styx and Kerberos, but it has been harder for us to get good measurements of these dim points of light.

It finally dawned on me to start thinking about the double-planet in the middle of the system. The moons orbit not one object but two. Pluto has a very large, close moon called Charon, and the two orbit around each other like two unequal weights at the ends of a dumbbell. I could imagine that this might prevent the moons from ever reaching synchronous lock.

Imagining it and proving it are two different things. Most orbit simulators track the position but not the orientation of the bodies in the system. I had to re-learn the physics of rigid body rotation and build my own simulator. The movie published today shows the results of that study. Caution: May cause vertigo.

After that, I knew this was not going to be just a short discovery paper. I also knew that I had better check every other detail of the system just in case the Pluto system held more surprises. I was not disappointed.

For example, we have determined that Kerberos is an oddball–an extremely dark object in the midst of much brighter moons–a charcoal briquette surrounded by dirty snowballs. Hypothesis #1: A snowman broke apart and Kerberos was one of the eyes. Hypothesis #2: Kerberos is a monolith. Seriously, we don’t know what to make of this result. If the moons all formed at the same time, then we would have expected them to look alike. They don’t.

In the end, the paper is sort of a grab-bag of strange results about the Pluto system. The best I can do to summarize it is to make an analogy. Imagine that you are an archeologist and have just recovered a few fragments of an ancient scroll. The pieces themselves are hard to interpret, but you know they have to fit together in some way that tells a bigger story. In this case, the story is how the Pluto system formed. The full story remains to be told, but now we know that it will have at least a few very interesting paragraphs.

Small dunes on Mars

ESP_041089_1980_0.75xA piece of Mars: These dunes are some of the smallest on Mars. The smallest in this frame is ~150 m long (492 ft). But the smallest Earth dunes are ~20 m across. Why are they so much bigger on Mars? The air is thinner, so the wind has to blow stronger to lift sand grains. So once the sand is moving, it goes fast – and therefore goes farther before it lands. This makes for a bigger dune. (HiRISE ESP_41809_1890, NASA/JPL/Univ. of Arizona)

The looming dune

ESP_027432_1350_1.0xA piece of Mars: this 0.96×0.54 km (0.6×0.33 mi) scene shows a large, rippled dune that is slowly marching towards the upper right. The smooth striped band running from upper left to lower right is the slip face, where sand pushed by the wind eventually avalanches. Smaller scars show where slope failures (little landslides) have formed. (HiRISE ESP_027432_1350, NASA/JPL/Univ. of Arizona)

Windblown or not?

A piece of Mars: The surface in this 960×540 m (0.6×0.34 mi) scene has a distinct fabric to it that runs from the upper left to lower right. Are these old lithified dunes? And what makes the tiny filamentary lines that run from upper right to lower left, are those ripples? I’m not convinced either way, but I suspect the wind has had a hand in shaping them, one way or another. (HiRISE ESP_040297_1605, NASA/JPL/Univ. of Arizona)

Wind stripes

ESP_039581_1520_1.0xA piece of Mars: Yes, I post a lot of pictures of martian dunes with striped patterns. They’re all distinct and beautiful. So here’s another one, 480×270 m (0.3×0.17 mi) in size. These beasts moved from right to left across the scene, some of them leaving behind some stripey deposits in their wake. (HiRISE ESP_039581_1520, NASA/JPL/Univ. of Arizona)

Martian lace

ESP_040776_2115_1.0xA piece of Mars: This 300×300 m (984×984 ft) scene shows bright windblown dunes or ripples arrayed in a lacy pattern (the biggest ones are about 5 m, or 16 ft, across). This is near the landing site of Ares 3, a science fiction book called “The Martian”, by Andy Weir that’s being made into a movie. I’m betting these beauties won’t make an appearance in the movie, though… (HiRISE ESP_040776_2115, NASA/JPL/Univ. of Arizona)


ESP_039902_1965_0.724xA piece of Mars: Below this ~550 m (0.3 mi) wide crater lies a ~1.3 km (0.8 mi) long “beard”, the wake of an ancient flow around the crater. Based on its location on Mars, I’m guessing the fluid flowing was lava. Inside the (interestingly dual) crater are bedforms, the remnants of more recent fluid flow – but in this case, the fluid is air. (HiRISE ESP_039902_1965, NASA/JPL/Univ. of Arizona)

New Explorers on the OurPluto Ballot, April 2

We have added three new historic explorers to the OurPluto ballot today. Keep those great ideas coming in! I have been learning so much.

Map of Europe, Asia and North Africa by Al-IdrisiSeveral people nominated the renowned 10th-century explorer and cartographer Muhammad al-Idrisi. He traveled as far west as Ireland and as far east as China, mapping much of the known world in the process. His exquisite maps were still being used centuries later. The title of his compendium of geographic information roughly translates from the Arabic as The Pleasure of Him Who Longs to Cross the Horizons. How appropriate it will be for a spacecraft named New Horizons to memorialize his work!

We also learned about for Hyecho, a Korean Buddhist monk who lived in the 8th century. The nomination from East Asia reads as follows: Hyecho was the first man to travel across the Asian continent, from far east to far west, by sea and land and to record his journey. He wrote a travelogue, consisting of originally 11,300 characters, called Memoir of the pilgrimage to the five kingdoms of India during his journey. The work of Hyecho offers a full account of a long journey that lasted four years spanning 9,000 kilometers in distance by ship, and 11,000 kilometers by land. To this day, It is praised as a valuable archeological and anthropological reference for its unprecedentedly comprehensive scope and depth.

Looking back to the way home under the reflection of moonlight
I see only the clouds floating
Though a letter was sent on a cloud
a gusty wind blows away its answer
-Hyecho (704-787 CE)

Isabella BirdFinally, this is the nomination for a remarkable woman named Isabella Bird: Born in Yorkshire England in 1831 she holds a special place in history. Isabella was the first woman to be elected Fellow of the Royal Geographical Society. Isabella battled with ill health all her life. However this did not stop her traveling the world and writing many incredible books about her travels. She visited Australia, Hawaii, America (where she traveled over 800 miles on horseback and met some very interesting characters including one-eyed outlaw Jim Nugent “Rocky Mountain Jim”). Battling ill health she went traveling to Asia: Japan, China, Vietnam, Singapore and Malaysia. At nearly 60 years of age she set off for India covering Ladakh on the borders of Tibet, and then travelled in Persia, Kurdistan and Turkey. In India, she worked with Fanny Jane Butler to found the John Bishop Memorial Hospital in memory of her recently deceased husband. The following year she joined a group of British soldiers traveling between Baghdad and Tehran. She remained with the unit’s commanding officer during his survey work in the region, armed with her revolver and a medicine chest supplied – in possibly an early example of corporate sponsorship – by Henry Wellcome’s company in London. By now Isabella was a household name in the Royal Geographical Society. Her final great journey took place in 1897 where she travelled up the Yangtze and Han rivers which are in China and Korea, respectively. Later still, she went to Morocco, where she travelled among the Berbers and had to use a ladder to mount her black stallion, a gift from the Sultan. She died in Edinburgh within a few months of her return in 1904, just shy of her seventy-third birthday. She was still planning another trip to China. What an amazing achievement for a person who battled with severe illness her entire life. Horizons exploration of Pluto should give credit to this amazing explorer by having a piece of Pluto named after her.

We agree.

More Nominations for OurPluto

We continue to receive a fascinating collection of nominees for the OurPluto campaign. Here are a few that we recently added to the ballot.

doreSeveral wrote to remind us of the iconic prints by Gustav Doré, a French artist from the 19th century who illustrated an 1861 edition of Dante’s Inferno.




In the category of historical explorers, we learned about Michał Boym: “He is notable as one of the first westerners to travel within the Chinese mainland and his Flora Sinensis was the first description of an ecosystem of the Far East published in Europe. Boym also published the first dictionary to translate between Chinese and European languages.

1024px-AltamiraBisonAnother historic explorer reminds of the roles that serendipity and patience play in all of science: Marcelino Sanz de Sautuola, who discovered the first prehistoric cave paintings known to the modern world. “He was a Spanish amateur archaeologist and explorer of the Cave of Altamira. These caves provide a window into human development, much as Pluto provides a window into Solar System development. Although Sautuola’s discoveries were discredited by experts early on, he was later completely vindicated and his discoveries appreciated, albeit after his death.”

Finally, a New Jersey professor provided a very good reason for his endorsement of Krun, a monster of the darkness. “I’m trying to raise awareness of the Mandaean community of Iraq and Iran. They are one of the few communities from the Middle East that still preserve the ancient Babylonian tradition of divination by the stars and heavenly bodies (astrology), directly from the source (they even retain the traditional Akkadian names for the stars and the visible planets). [….] Unfortunately, with the Second Gulf War, their community (a minority faith in both Iraq and Iran) has become progressively endangered, and much of it has gone into a global diaspora. The lives of those that remain and their ancient culture are threatened by religious extremists, such as ISIS, who seek to eliminate anything pre-Islamic in the Middle East. I hope that OurPluto can establish a monument to them in the heavens, where these extremists cannot reach them.”

OurPluto Campaign, Day 6

The OurPluto naming campaign has been an exhilarating experience for me so far. The amount of thought that our site visitors have been putting into their nominations astounds me. You can visit the Site News page for regular updates. Today I would just like to highlight a few of the new names that we added to the ballot last night.

640px-Lowell_blink_comparatorOn the list of scientists and engineers, we have added Carl Pulfrich, 1858-1927. Although he died before the 1930 discovery of Pluto, he contributed in a critical way—he invented the blink comparator. This is a device that lets you switch back and forth between two sky plates, looking for subtle changes. Clyde Tombaugh discovered Pluto using a blink comparator. The discovery would not have been possible without the device.



From Europe, we were reminded of the importance of the Soviet The Luna Program: “Luna was a series of robotic spacecraft missions sent to the Moon by the Soviet Union between 1959 and 1976. Fifteen were successful, each designed as either an orbiter or lander, and accomplished many firsts in space exploration. They also performed many experiments, studying the Moon’s chemical composition, gravity, temperature, and radiation. Twenty-four spacecraft were formally given the Luna designation, although more were launched.”

Two prominent women explorers were also nominated. For Alexandrine Tinné, who explored the Nile and the Sahara in the 1860s, the nomination reads, “It is rare that we take the opportunity to praise some of the women who have contributed to the exploration of our world. Ms. Tinné was courageous, dedicated, and passed on a legacy of adventure for today’s women to aspire to.”

Jeanne_BarreWe also learned about Jeanne Baré who, a century earlier, became the first woman to circumnavigate the globe. She was naturalist studying the world’s plants. However, times being what they were, she had to impersonate a man for the journey.



Our fictional explorers now include several popular nominees. Among others, we include a pair of the great travelers in literature, Don Quijote and his patient squire Sancho Panza.


In the category of Underworld beings, we learned that the King of the Underworld in Vietnam has a Pluto connection. “Diem Vuong is the King of Hades. Demons obey and serve him. He is the ruler of the underworld and the judge of the bad souls after death. Diem Vuong once upon a time has been added to form “Diem Vuong Tinh” to name for Pluto in Vietnamese.”

In Inuit mythology, we learned that the realm of the dead has an astronomical connection. The souls of the dead first spend time under ground in Adlivun, but later ascend to a permanent home in Quidlivun, on the Moon.