The Geeky Geological Features of Charon

As talked about in a previous post, Charon was named after the wife if the discoverer James Christy. Since then the New Horizons probe has visited and taken some amazing pictures of the surface. As part of the mapping they have also started naming some of the craters and other geological features found on the surface, and they all have very fictional culture names. Although some have been accepted but he International Astronomical Union, there are still many that haven’t. As of April 2018 they have set out an agreed naming convention and set of rules for the names. They should conform to one of the following:

  • Destinations or milestones of fictional space and other exploration.
  • Fictional and mythological vessels of space or other exploration.
  • Fictional and mythological voyagers, travelers and explorers.
  • Authors and artists associated with space exploration, especially Pluto and the Kuiper Belt.

So far there have been many provisional names given by the New Horizons team based on mostly science fiction franchises such as Star Wars, Star Trek, Doctor Who and Firefly. Most are still provisional, but some have been accepted

Charon Enhanced
An enhanced colour version of Charon taken by New horizons space probe. It is enhanced to show the differences in surface composition. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

A Terra is a large landmass or highland, and there is only one highland region on Charon. It was named Oz Terra after the Wonderful Wizard of Oz children’s novel by L. Frank Baum. The dark spots on the surface are called maculae in planetary science. The first is named Gallifrey Macula after the home planet of Doctor Who (Gallifrey). The second is the Mordor Macula after the base of Sauron in the Lord of the rings books by J.R.R. Tolkien. A planum is a scientific name for a plateau (elevated plain) and Charon only has one. Named Vulcan Planum after the home planet of Spock in the Star Trek Series. Terrae, Maculae and Plana are all being named after fictional destinations. A Mons is a planetary mountain, you may have heard of some of the Mons currently being explored by NASA rovers on Mars. Charon has three major mountains and are named after authors and artists. Butler Mons is named after Octavia E. Butler, an american science fiction author. Clarke Montes is named after Arthur C. Clarke, a famous English science fiction author who wrote 2001: A Space Odyssey. Kubrick Mons is named after Stanley Kubrick, a film director of films such as the shining and clockwork Orange. All three of the Mons names are accepted by the IAU.

Mordor Macula is located at Charon. A large dark area about 475 km in diameter near the north pole of Charon, Pluto’s largest moon. It is named after the shadow lands in J.R.R. Tolkien’s The Lord of the Rings.  It is not currently known what Mordor is. It may be frozen gases captured from Pluto’s escaping atmosphere, a large impact basin, or both. Credit: NASA

A chasma is a deep steep sided depression (a chasm), and are being named after fictional vessels. Argo Chasma is named after a ship in the Greek myth of Jason and the Argonauts, it is also the spaceship in the English translation of the Space Battleship Yamato anime series. Caleuche Chasma is named after the mythological ghost ship that travels the seas around Chiloé Island off the coast of Chile, collecting dead who then forever live aboard (much like Davy Jones). Mandjet Chasma is named after the solar boat of the ancient Egyptian God Ra. All three of the above Chasmas are recognised by the IAU. Macross Chasma is named after the SDF-1 spaceship in the Macross anime series. Nostromo Chasma should be known to most as the spaceship in the Alien films. Serenity Chasma is from the spaceship used in the Firefly series. Tardis Chasma is named after the infamous blue box flown by Doctor Who.

Annotated map of Charon, with provisional names for features. Credit: NASA/JPL.

There are 16 notable craters found on Charon’s surface, of which six have officially recognised names. They have all been named after characters associated with science fiction and fantasy. Dorothy Crater is named after the main character is the Wizard of Oz, also naming the only terra on Charon. Nasreddin crater is a sufi traveler from folklore. Nemo is after Captain Nemo from novels by Jules Verne. Pirx crater is the main character from the short stories by Stanislaw Lem. Revati Crater is named after the main character in the Hindu epic narrative Mahabharata. Sadako Crater is the adventurer who traveled to the bottom of the sea in the medieval Russian epic Bylina. All of the above craters have been officially recognised by the IAU. Alice Crater is named after the main character of the Lewis Carroll novels. Kaguyahime Crater is named after the princess of the Moon in Japanese folklore. Organa Crater is named after princess Leia in the Star wars films, along with Vader Crater, and Skywalker crater. Ripley Crater is one of the more studied craters and is named after the main character in the Alien films. Kirk Crater, Spock Crater, Sulu Crater, and Uhura Crater are all named after main characters in the Star Trek TV franchise.

Photo of Charon centered on Ripley Crater. Nostromo Chasma crosses Ripley vertically. Vader is the dark crater at 12:00, Organa Crater is at 9:00, Skywalker Crater at 8:00, Gallifrey Macula and Tardis Chasma at 4:00. Credit: NASA/JPL

Thank You for reading, take a look at my other posts if you are interested in space or electronics, or follow me on Twitter to get updates on projects I am currently working on.

Follow @TheIndieG
Tweet to @TheIndieG

The Dawn of Ion Engines

Ion thrusters are becoming a bigger and bigger part of modern satellite design. Over 100 geosynchronous Earth Orbit communication satellites are being kept in the desired locations in orbit using this revolutionary technology. This post is about its most amazing achievement to date, the Dawn Spacecraft. Just reported that it is at the end of its second extension of the mission it has a few records under its belt. It is the first spacecraft to orbit two different celestial bodies, and the first to orbit any object in the main asteroid belt between Mars and Jupiter. It is also a record breaker for electric speed. Travelling over 25,700 mph it is 2.7x faster than the previous fastest electric thrusted spacecraft. That is a comparable speed to the Delta 2 launch vehicle that got it to space in the first place.

Delta 2 launch
The Dawn spacecraft launching on a Delta 2 rocket from Cape Canaveral Air Force Station SLC 17 on Sept 27th, 2007. Credit: NASA/Tony Gray & Robert Murra

The Dawn mission was designed to study two large bodies in the main asteroid belt. This is to get a deeper insight into the formation of the solar system . It also has the added benefit of testing the ion drive in deep space for much longer than previous spacecraft. Ceres and Vesta are the two most massive bodies in the belt, and are also very useful protoplanets from a scientific standpoint. Ceres is an icy and cold dwarf planet whereas Vesta is a rocky and dry asteroid. Understanding these bodies can bridge the understanding of how the rocky planets and icy bodies of the solar system form. It could also show how some of the rocky planets can hold water/ice. In 2006 the International Astronomical Union (IAU) changed the definition of what a planet is, and introduced the term “dwarf planet”. This is the change that downgraded Pluto from its planet status, although that has been argued to be wrong by Dr. Phil Metzger in a recent paper. Ceres is classified as a dwarf planet. As Dawn arrived at Ceres a few months before New Horizons reached Pluto, Dawn was the first to study a dwarf planet.

Dawn prior to encapsulation at its launch pad on July 1, 2007. Credit: NASA/Amanda Diller

The ion engine is so efficient that without them a trip to just Vesta would need 10 times more propellant, a much larger spacecraft, and therefore a much larger launch vehicle (making it much more expensive). The ion propulsion system that it uses was first proven by Deep Space Mission 1, along with 11 other technologies. Dawn has three 30 cm diameter (12 inch) ion thrust units. They can move in two axis to allow for migration of the center of mass as the mission progresses. The attitude control system can also use the movable ion thrusters to control the attitude. The mission only needs two of the thrusters to complete the mission, the third being a spare. All three have been used at some point during the mission, one at a time. As of September 7th 2018 the spacecraft has spent 5.9 years with the ion thrusters on, which is about 54% of its total time in space. The thrust to its first orbit took 979 days, with the entire mission being over 2000 days. Deep Space 1’s mission in contrast lasted 678 days before the fuel ran out.

An artist’s impression of Dawn with its ion thrusters on. Credit: NASA

The thrusters work by using electrical charge to accelerate ions from xenon fuel to speeds 7-10 times that of chemical engines. The power level and the fuel feed can be adjusted to act like a throttle. The thruster is very thrifty with its fuel, using a minor 3.25 milligrams of xenon per second, roughly 280g per day, at maximum thrust. The spacecraft carried 425 kg (937 pounds) of xenon propellant at launch. Xenon is a great fuel source because it is chemically inert, easily stored in compact form. Plus the atoms are very heavy so they provide large thrust compared to other comparable candidate propellants. At launch on Earth the xenon was 1.5 times the density of water. At full thrust the ion engines produce a thrust of 91 mN, which is roughly the force needed to hold a small sheet of paper. Over time these minute forces add up and over the course of years can produce very large speeds. The electrical power is produced by two 8.3 m (27 ft) x 2.3 m (7.7 ft) solar arrays. Each 18 meter squared (25 yard squared) array is covered in 5,740 individual photo voltaic cells. They can convert 28% of the sun’s energy into useful electricity. If these panels were on Earth they would produce 10 kW of energy. Each of the panels are on gimbals that mean they can turn any time to face the sun. The spacecraft uses a nickel-hydrogen battery to charge up and power during dark points in the mission.

The dawn mission patch.  This logo represents the mission of the Dawn spacecraft. During its nearly decade-long mission, Dawn will study the asteroid Vesta and dwarf planet Ceres Credit: NASA.

Vesta was discovered on March 29th 1807 by astronomer Heinrich Wilhelm Olbers, and is named after the Roman virgin goddess of home and hearth. The Dawn mission uncovered many unique surface features of the protoplanet ,twice the area of California, that have intrigued scientists. Two colossal impact craters were found in the southern hemisphere, the 500 km (310 miles) wide Rheasilvia basin, and the older 400 km (250 miles) wide Veneneia crater. The combined view of these craters was apparent even to the Hubble telescope. Dawn showed that the Rheasilvia crater’s width is 95% of the width of Vesta (it’s not perfectly spherical) and is roughly 19 km (12 miles) deep. The central peak of the crater rises to 19-25 km (12-16 miles) high, and being more that 160 km (100 miles) wide, it competes with Mars’ Olympus Mons as the largest mountain in the solar system. The debris that was propelled away from Vesta during the impacts made up 1% of its mass, and is now beginning its journey through the solar system. These are known as Vestoids, ranging from sand and gravel all the way up to boulders and smaller asteroids. About 6% of all meteorites that land on Earth are a result of this impact.


The brave new world of 4 Vesta, courtesy of NASA’s Dawn spacecraft. Credit: NASA/JPL-Caltech/UCAL/MPS/DLR/IDA

Dawn mapped Vesta’s geology, composition, cratering record and more during its orbit. It also managed to determine the inner structure by measuring its gravitational field. The measurements were consistent with the presence of an iron core of around 225 km (140 miles), in agreement with the size predicted by
howardite-eucrite-diogenite (HED)-based differentiation models. The Dawn mission confirmed that Vesta is the parent body of the HED meteorites, by matching them with lab based measurements. These experiments measured the elemental composition of Vesta’s surface and its specific mineralogy. These results confirm that Vesta experienced pervasive, maybe even global melting, implying that differentiation may be a common history for large planetesimals that condensed before short-lived heat-producing radioactive elements decayed away. The pitted terrains and gullies were found in several young craters. This could be interpreted as evidence of volatile releases and transient water flow. Vesta’s composition is volatile-depleted, so these hydrated materials are likely exogenic (formed on the surface).

A colour coded topographic map from the Dawn mission of the giant asteroid Vesta. Credit: NASA/JPL

The first object ever discovered in the main asteroid belt was Ceres. Named after the Roman goddess of corn and harvest, it was discovered by Italian astronomer Father Giuseppe Piazzi in 1801. Initially classified as a planet, it was later classified as an asteroid as more objects were found in the same region. In recognition of its planet like properties (being very spherical) it was designated a dwarf planet in 2006 along with Pluto and Eris. Observed by the Hubble telescope between 2003 and 2004, it was shown to be nearly spherical, and approximately 940 km (585 miles) wide. Ceres makes up 35% of the mass of the main asteroid belt. Before Dawn there were plenty of signs of water on Ceres. First, its low density indicates that it is 25% ice by mass, which makes it the most water rich body in the inner solar system after Earth (in absolute amount of water). Also, using Hershel in 2012 and 2013, evidence of water vapor, probably produced by ice near the surface transforming from solid to gas (known as sublimating).

Dwarf planet Ceres is shown in these false-color renderings, which highlight differences in surface materials. Credit: NASA/JPL-CalTech/UCLA/MPS/DLR/IDA

Acquiring all the data it needed by the middle of 2016, Dawn measured its global shape, mean density, surface morphology, mineralogy, elemental composition, regional gravity and topography at exceeded resolutions. The imaging from the mission showed a heavily cratered surface with bright features. Often referred to as “bright spots” they are deposits of carbonates and other salts. Multiple measurements showed an abundance of ice at higher latitudes. However the retention of craters up to 275 km (170 miles) in diameter argue for a strong crust, with lots of hydrated salts, rocks and clathrates (molecules trapped in a cage of water molecules). Gravity and topography data also indicated that that Ceres’ internal density increases with depth. This is evidence for internal differentiation resulting from the separation of the dense rock from the low density water-rich phases in Ceres history. The rock settled to form an inner mantle overlain with a water-rich crust. This internal differentiation is typical of small planets like Ceres and Vesta that Sets them apart from asteroids.

Thank you for reading, take a look at my other posts if you are interested in space, electronics, or military history. If you are interested, follow me on Twitter to get updates on projects I am currently working on.

Follow @TheIndieG
Tweet to @TheIndieG

Charon: The Man Who Gave His Wife a Moon

Charon Enhanced
An enhanced colour version of Charon taken by New horizons space probe. It is enhanced to show the differences in surface composition. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

On June 22nd, 1978 James Christy was trying to refine the orbit of Pluto when he noticed something odd about the images. Going straight to Robert Harrington, his supervisor at the U.S. Naval Observatory in Flagstaff, Arizona, together they concluded that they had found what we now know as Pluto’s largest moon Charon. Discovered just 6 miles away from where pluto itself was found (Lowell Observatory), discovering Charon began a journey from Pluto being a dot on a telescope to its own planetary system. With some amazing images coming from a probe NASA sent there, we have a glimpse of the edge of our solar system. The best part of the story, Charon is named after Christy’s wife.

40 years after christy
40 years on, Christy shows the images he used to discover Charon, and now one of the New Horizons images is his PC wallpaper. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Art Howard/GHSPi

In 1930, Clyde Tombaugh discovered Pluto, and although famous in itself, there was limited study on this dot in the far reaches of the solar system. So on the fateful day James Christy asked his supervisor Bob Harrington for something to do, Harrington pulled some telescope plates of Pluto from the Naval Observatory at Flagstaff to look over. Christy looked over them for some time under a microscope and noticed some inconsistencies with the images, with the asymmetry being different between them. In simple terms he noticed a bump on the side of Pluto that seemed to move over time. Although at first he thought he might be seeing things, when he took it to Harrington he agreed with the findings.

Jim Christy points
Jim Christy pointing to the photographic plate that he used to discover that Pluto has a moon. Credit: U.S. Naval Observatory

When  looking at other images of Pluto, the bump was constantly moving from one side to the other. Further examination showed the bump moved around Pluto at the same own rotational period, 6.39 days. There were two potential theories as to what it was, either Pluto had a mountain thousands of miles high (meaning Pluto was not very spherical) or it has a satellite in synchronous orbit. In the 48 years since Pluto’s discovery at Lovell Observatory in 1930, there had never been any evidence spotted that Pluto had a moon. The next steps included scouring the archives for more cases of an elongated looking Pluto.

The Charon images
The discovery at the US Naval Observatory, Flagstaff was seen as a time varying bulge on the image of Pluto. This is a negative version of the one Christy looked at. Credit: US Naval Observatory.

Christy measured the angle from the north where the strange elongation was. At the same time Robert Harrington calculated what the answer would be if the elongation was from a satellite. They then compared their results, and they were the same. To be sure they waited for the Observatories 61 inch telescope to make a final confirmation on the matter. On the 2nd of July 1978 new images showed an elongation exactly where they expected it to be. Five days later they announced the discovery to the world. Pluto’s first satellite had been discovered.

40 years difference
The difference of 40 years, top left is one of the images Christy used to discover Cahron, the big image is from New Horizons flyby. Credit: U.S. Naval Observatory; NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

By astronomical tradition, the discoverer of an object gets the first chance to suggest a name for the object. The name does not have to be recognised by the International Astronomers Union. Christy wanted to name the moon after his wife, Charlene. To make it sound more scientific he took his nickname for her “Char” and added an “on”. The “on” was from his interest in atoms, and words like proton and neutron. He suggested the name on the June 24th, 1978. Colleagues at the observatory prefered the name Persephone, but Christy noticed that Charon was actually a real Greek mythological figure. Charon is the ferryman of the dead, associated with the god Hades. Creepily the Romans identified Hades with their god Pluto. The name was eventually adopted on January the 3rd 1986.

The greek Charon
The name Charon was partially adopted because it is the name of the ferrymen of the dead in greek mythology. this is a nineteenth century painting by Alexander Litovchenko

Charon is the largest moon of Pluto, and is about the size of Texas. It also makes Charon the largest moon relative to its parent planet at about 12% of the size. So big in fact that Charon and Pluto are seen as a double planet or binary planets. They have a common centre of gravity that is outside of either of them. It is believed that it was formed by some sort of giant impact, much like the Earth and the Moon. The sheer size and proximity to Pluto meant it was a good choice for a scientific mission to take a closer look at the system. The mission, New Horizons was launched in 2006, with a  primary mission to performa flyby study of the Pluto system.

New Horizons Artist
An artistic impression of what New Horizons looked like when it passed Pluto and Charon. Credit: NASA Goddard Media Studios.

Passing about 18,000 miles (29,000 km) away from Charon on the 24th of July 2015, New Horizons gave the world a brand new stunning view of the moon from up close. At its closest point it was 7,800 miles (12,500 km) from Pluto, mapping both the planet and the moon using its long range imaging cameras. It mapped them to a resolution of 25 mi (40 km). The way they entered the system and the speed they were going allowed them to map all sides of both bodies. They took multiple images with the close range camera to find any surface changes. They also characterised the atmosphere, using the on board ALICE experiment.

Best Charon Images
A mosaic of the best images taken by New Horizons of Charon, from a few different angles. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

The science gained by New Horizons has given astronomers a new look into the outer reaches of the solar system, and it is still planning to take more images of comets and asteroids it comes into contact with in 2019. The first close up images of Charon were revealed  to the world at the John Hopkins Applied Physics Lab in Maryland to a packet auditorium. Jim Christy, the discoverer of Charon and his wife who it was named after were there at the unveiling, were recognized by the crowd. He said “When you go from this little blur in which you don’t actually see anything, to the enormous detail New Horizons sent back,” Christy said, “it’s incredible.” That amount of change in just 40 years.