What is the Color of Pluto?

Pluto was re-classified as a dwarf planet based on our growing understanding of its nature. Will Schlaufman's new study help us more accurately classify gas giants and brown dwarfs? NASA's New Horizons spacecraft captured this high-resolution enhanced color view of Pluto on July 14, 2015. Credit: NASA/JHUAPL/SwRI

When Pluto was first discovered by Clybe Tombaugh in 1930, astronomers believed that they had found the ninth and outermost planet of the Solar System. In the decades that followed, what little we were able to learn about this distant world was the product of surveys conducted using Earth-based telescopes. Throughout this period, astronomers believed that Pluto was a dirty brown color.

In recent years, thanks to improved observations and the New Horizons mission, we have finally managed to obtain a clear picture of what Pluto looks like. In addition to information about its surface features, composition and tenuous atmosphere, much has been learned about Pluto’s appearance. Because of this, we now know that the one-time “ninth planet” of the Solar System is rich and varied in color.

Composition:

With a mean density of 1.87 g/cm3, Pluto’s composition is differentiated between an icy mantle and a rocky core. The surface is composed of more than 98% nitrogen ice, with traces of methane and carbon monoxide. Scientists also suspect that Pluto’s internal structure is differentiated, with the rocky material having settled into a dense core surrounded by a mantle of water ice.

The Theoretical structure of Pluto, consisting of 1. Frozen nitrogen 2. Water ice 3. Rock. Credit: NASA/Pat Rawlings

The diameter of the core is believed to be approximately 1700 km, which accounts for 70% of Pluto’s total diameter. Thanks to the decay of radioactive elements, it is possible that Pluto contains a subsurface ocean layer that is 100 to 180 km thick at the core–mantle boundary.

Pluto has a thin atmosphere consisting of nitrogen (N2), methane (CH4), and carbon monoxide (CO), which are in equilibrium with their ices on Pluto’s surface. However, the planet is so cold that during part of its orbit, the atmosphere congeals and falls to the surface. The average surface temperature is 44 K (-229 °C), ranging from 33 K (-240 °C) at aphelion to 55 K (-218 °C) at perihelion.

Appearance:

Pluto’s surface is very varied, with large differences in both brightness and color. Pluto’s surface also shows signs of heavy cratering, with ones on the dayside measuring 260 km (162 mi) in diameter. Tectonic features including scarps and troughs has also been seen in some areas, some as long as 600 km (370 miles).

Mountains have also been seen that are between 2 to 3 kilometers (6500 – 9800 ft) in elevation above their surroundings. Like much of the surface, these features are believed to be composed primarily of frozen nitrogen, carbon monoxide, and methane, which are believed to sit atop a “bedrock” of frozen water ice.

Color mosaic map of Pluto’s surface, created from the New Horizons many photographs. Credit: NASA/JHUAPL/SwRI

The surface also has many dark, reddish patches due to the presence of tholins, which are created by charged particles from the Sun interacting with mixtures of methane and nitrogen. Pluto’s visual apparent magnitude averages 15.1, brightening to 13.65 at perihelion. In other words, the planet has a range of colors, including pale sections of off-white and light blue, to streaks of yellow and subtle orange, to large patches of deep red.

Overall, its appearance could be described as “ruddy”, given that the combination can lend it a somewhat brown and earthy appearance from a distance. In fact, prior to the New Horizon‘s mission, which provided the first high-resolution, close-up images of the planet, this is precisely what astronomers believed Pluto looked like.

Major Surface Features:

Several different regions (“regio”) have been characterized based on the notable features they possess. Perhaps the best known is the large, pale area nicknamed the “Heart” – aka. Tombaugh Regio (named after Pluto’s founder). This large bright area is located on the side of Pluto that lies opposite the side that faces Charon, and is named because of its distinctive shape.

Tombaugh Regio is about 1,590 km (990 mi) across and contains 3,400 m (11,000 ft) mountains made of water ice along its southwestern edge. The lack of craters suggests that its surface is relatively young (about 100 million years old) and hints at Pluto being geologically active. The Heart can be subdivided into two lobes, which are distinct geological features that are both bright in appearance.

This new global mosaic view of Pluto was created from the latest high-resolution images to be downlinked from NASA’s New Horizons spacecraft and released on Sept. 11, 2015. Credits: NASA/Johns Hopkins APL/SwRI/Marco Di Lorenzo/Ken Kremer

The western lobe, Sputnik Planitia, is vast plain of nitrogen and carbon monoxide ices measuring 1000 km in width. It is divided into polygonal sections that are believed to be convection cells, which carry blocks of water ice and sublimation pits along towards the edge of the plain. This region is especially young (less than 10 million years old), which is indicated by its lack of cratering.

Then there is the large, dark area on the trailing hemisphere known as Cthulhu Regio (aka.the “Whale”). Named for its distinctive shape, this elongated, dark region along the equator is the largest dark feature on Pluto – measuring 2,990 km (1,860 mi) in length. The dark color is believed to be the result methane and nitrogen in the atmosphere interacting with ultraviolet light and cosmic rays, creating the dark particles (“tholins”) common to Pluto.

And then there are the “Brass Knuckles”, a series of equatorial dark areas on the leading hemisphere. These features average around 480 km (300 mi) in diameter, and are located along the equator between the Heart and the tail of the Whale.

New Horizons Mission:

The NH mission launched from Cape Canaveral Air Force Station in Florida on January 19th, 2006. After swinging by Jupiter for a gravity boost and to conduct some scientific studies in February of 2007, it reached Pluto in the summer of 2015. Once there, it conducted a six month-long reconnaissance flyby of Pluto and its system of moons, culminating with a closest approach that occurred on July 14th, 2015.

A portrait from the final approach of the New Horizons spacecraft to the Pluto system on July 11th, 2015. Pluto and Charon display striking color and brightness contrast in this composite image. Credit: NASA-JHUAPL-SWRI.

The first images of Pluto acquired by NH were taken on September 21st to 24th, 2006, during a test of the Long Range Reconnaissance Imager (LORRI). At the time, the probe was still at a distance of approximately 4.2 billion km (2.6 billion mi) or 28 AU, and the photos were released on November 28th, 2006. Between July 1st and 3rd, the first images were taken that were able to resolved Pluto and its largest moon, Charon, as separate objects.

Between July 19th–24th, 2014, the probe snapped 12 images of Charon revolving around Pluto, covering almost one full rotation at distances ranging from 429 to 422 million kilometers (267,000,000 to 262,000,000 mi). After a brief hibernation during its final approach, New Horizons “woke up” on Dec. 7th, 2014. Distant-encounter operations began on January 4th, 2015, and NH began taking images of Pluto as it grew closer.

During its closest approach (July 14th, 2015, at at 11:50 UTC), the NH probe passed within 12,500 km (7,800 mi) of Pluto. About 3 days before making its closest approach, long-range imaging of Pluto and Charon took place that were 40 km (25 mi) in resolution, which allowed for all sides of both bodies to be mapped out.

Close-range imaging also took place twice a day during this time to search for any indication of surface changes. The NH probe also analyzed Pluto’s atmosphere using its suite of scientific instruments. This included it’s ultraviolet imaging spectrometer (aka. Alice) and the Radio Science EXperiment (REX), which analyzed the composition and structure of Pluto’s atmosphere.

Haze with multiple layers in the atmosphere of Pluto. Part of the plain Sputnik Planitia with nearby mountains is seen below. Photo by New Horizons, taken 15 min after the closest approach to Pluto. Credit: NASA/JHUAPL/SwRI

It’s Solar Wind Around Pluto (SWAP) and Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) examined the interaction of Pluto’s high atmosphere with solar wind. Pluto’s diameter was also resolved by measuring the disappearance and reappearance of the radio occultation signal as the probe flew by behind Pluto. And the gravitational tug on the probe were used to determine Pluto’s mass and mass distribution.

All of this information has helped astronomers to make the first detailed maps of Pluto, and led to numerous discoveries about Pluto’s structure, composition, and the kinds of forces that actively shape its surface. The mission also led to the first true images of what Pluto looks like up close, revealing its true colors, it’s famous “Heart” region, and the many other now-famous features.

We have written many interesting articles about the colors of astronomical bodies here at Universe Today. Here’s What Color is the Sun?, What are the Colors of the Planets?, What Color is Mercury?, What Color is Venus?, What Color is the Moon?, Why is Mars Red?, What Color is Jupiter?, What Color is Saturn?, What Color is Uranus?, and What Color is Neptune?

Sources:

Possible Ice Volcanoes Discovered on Pluto

Ice Volcanoes on Pluto?
The informally named feature Wright Mons, located south of Sputnik Planum on Pluto, is an unusual feature that’s about 100 miles (160 kilometers) wide and 13,000 feet (4 kilometers) high. It displays a summit depression (visible in the center of the image) that’s approximately 35 miles (56 kilometers) across, with a distinctive hummocky texture on its sides. The rim of the summit depression also shows concentric fracturing. New Horizons scientists believe that this mountain and another, Piccard Mons, could have been formed by the ‘cryovolcanic’ eruption of ices from beneath Pluto’s surface. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute[/caption]

The possible discovery of a pair of recently erupting ice volcanoes on Pluto are among the unexpected “astounding” findings just unveiled by perplexed scientists with NASA’s New Horizons spacecraft, barely four months after the historic first flyby of the last unexplored planet in our solar system.

“Nothing like this has been seen in the deep outer solar system,” said Jeffrey Moore, New Horizons Geology, Geophysics and Imaging team leader from NASA Ames Research Center, Moffett Field, California, as the results so far were announced at the 47th Annual Meeting of the Division for Planetary Sciences (DPS) of the American Astronomical Society (AAS) this week in National Harbor, Maryland.

“The Pluto system is baffling us,” said mission Principal Investigator Alan Stern of the Southwest Research Institute, Boulder, Colorado, at a news media briefing on Nov. 9.

Two large mountainous features tens of miles across and several miles high, have been potentially identified by the team as volcanoes.

Scientists using New Horizons images of Pluto’s surface to make 3-D topographic maps have discovered that two of Pluto’s mountains, informally named Wright Mons and Piccard Mons, could possibly be ice volcanoes. The color is shown to depict changes in elevation, with blue indicating lower terrain and brown showing higher elevation; green terrains are at intermediate heights.  Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Scientists using New Horizons images of Pluto’s surface to make 3-D topographic maps have discovered that two of Pluto’s mountains, informally named Wright Mons and Piccard Mons, could possibly be ice volcanoes. The color is shown to depict changes in elevation, with blue indicating lower terrain and brown showing higher elevation; green terrains are at intermediate heights. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

They were found in terrain located south of Sputnik Planum – a vast area of smooth icy plains located within Pluto’s huge heart shaped region informally known as Tombaugh Regio. It may have formed very recently resulting from geologic activity within the past 10 million years.

The possible ice volcanoes, or cryovolcanoes, were found at two of Pluto’s most distinctive mountains and identified from images taken by New Horizons as it became Earth’s first emissary to hurtle past the small planet on July 14, 2015.

“All of our flyby plans succeeded,” Stern stated at the briefing.

“All of the data sets are spectacular.

Scientists created 3-D topographic maps from the probes images and discovered the possible ice volcanoes – informally named Wright Mons and Piccard Mons.

Wright Mons, pictured above, is about 100 miles (160 kilometers) wide and 13,000 feet (4 kilometers) high.

Both mountains appear to show summit depressions “with a large hole” visible in the center, similar to volcanoes on Earth. Scientists speculate “they may have formed by the ‘cryovolcanic’ eruption of ices from beneath Pluto’s surface.”

The erupting Plutonian ices might be composed of a melted slurry of water ice, nitrogen, ammonia and methane.

The depression inside Wright Mons is approximately 35 miles (56 kilometers) across and exhibits a “distinctive hummocky texture on its sides. The rim of the summit depression also shows concentric fracturing.”

“These are big mountains with a large hole in their summit, and on Earth that generally means one thing—a volcano,” said Oliver White, New Horizons postdoctoral researcher with NASA Ames, in a statement.

The team is quick to caution that the “interpretation of these features as volcanoes is tentative” and requires much more analysis.

“If they are volcanic, then the summit depression would likely have formed via collapse as material is erupted from underneath. The strange hummocky texture of the mountain flanks may represent volcanic flows of some sort that have travelled down from the summit region and onto the plains beyond, but why they are hummocky, and what they are made of, we don’t yet know.”

This new global mosaic view of Pluto was created from the latest high-resolution images to be downlinked from NASA’s New Horizons spacecraft and released on Sept. 11, 2015.   The images were taken as New Horizons flew past Pluto on July 14, 2015, from a distance of 50,000 miles (80,000 kilometers).  This new mosaic was stitched from over two dozen raw images captured by the LORRI imager and colorized.  Right side inset from New Horizons team focuses on Tombaugh Regio heart shaped feature.  Annotated with informal place names.  Credits: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Marco Di Lorenzo/Ken Kremer/kenkremer.com
This new global mosaic view of Pluto was created from the latest high-resolution images to be downlinked from NASA’s New Horizons spacecraft and released on Sept. 11, 2015. The images were taken as New Horizons flew past Pluto on July 14, 2015, from a distance of 50,000 miles (80,000 kilometers). This new mosaic was stitched from over two dozen raw images captured by the LORRI imager and colorized. Right side inset from New Horizons team focuses on Tombaugh Regio heart shaped feature. Annotated with informal place names. Credits: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Marco Di Lorenzo/Ken Kremer/kenkremer.com

More than 50 papers about the Pluto system are being presented at the AAS meeting this week.

So far New Horizon has transmitted back only about 20 percent of the data gathered, according to mission Principal Investigator Alan Stern.

“It’s hard to imagine how rapidly our view of Pluto and its moons are evolving as new data stream in each week. As the discoveries pour in from those data, Pluto is becoming a star of the solar system,” said Stern.

“Moreover, I’d wager that for most planetary scientists, any one or two of our latest major findings on one world would be considered astounding. To have them all is simply incredible.”

Locations of more than 1,000 craters mapped on Pluto by NASA’s New Horizons mission indicate a wide range of surface ages, which likely means that Pluto has been geologically active throughout its history.  Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Locations of more than 1,000 craters mapped on Pluto by NASA’s New Horizons mission indicate a wide range of surface ages, which likely means that Pluto has been geologically active throughout its history. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

The piano shaped probe gathered about 50 gigabits of data as it hurtled past Pluto, its largest moon Charon and four smaller moons.

Stern says it will take about a year for all the data to get back. Thus bountiful new discoveries are on tap for a long time to come.

With 20 percent of the data now returned and more streaming back every day, the team is excited to debate what is all means.

“This is when the debates begin,” said Curt Niebur, New Horizons program scientist at NASA Headquarters, at the missions Nov 9 media briefing. “This is when the heated discussions begin. This is when the entire science community starts staying up throughout the night.”

Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.

Ken Kremer

Just 15 minutes after its closest approach to Pluto on July 14, 2015, NASA's New Horizons spacecraft looked back toward the sun and captured this near-sunset view of the rugged, icy mountains and flat ice plains extending to Pluto's horizon - shown in this colorized rendition. The smooth expanse of the informally named icy plain Sputnik Planum (right) is flanked to the west (left) by rugged mountains up to 11,000 feet (3,500 meters) high, including the informally named Norgay Montes in the foreground and Hillary Montes on the skyline. To the right, east of Sputnik, rougher terrain is cut by apparent glaciers. The backlighting highlights more than a dozen layers of haze in Pluto’s tenuous but distended atmosphere. The image was taken from a distance of 11,000 miles (18,000 kilometers) to Pluto; the scene is 780 miles (1,250 kilometers) wide. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute. Colorized/Annotated: Marco Di Lorenzo/Ken Kremer/kenkremer.com
Just 15 minutes after its closest approach to Pluto on July 14, 2015, NASA’s New Horizons spacecraft looked back toward the sun and captured this near-sunset view of the rugged, icy mountains and flat ice plains extending to Pluto’s horizon – shown in this colorized rendition. The smooth expanse of the informally named icy plain Sputnik Planum (right) is flanked to the west (left) by rugged mountains up to 11,000 feet (3,500 meters) high, including the informally named Norgay Montes in the foreground and Hillary Montes on the skyline. To the right, east of Sputnik, rougher terrain is cut by apparent glaciers. The backlighting highlights more than a dozen layers of haze in Pluto’s tenuous but distended atmosphere. The image was taken from a distance of 11,000 miles (18,000 kilometers) to Pluto; the scene is 780 miles (1,250 kilometers) wide. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute. Colorized/Annotated: Marco Di Lorenzo/Ken Kremer/kenkremer.com

Celestial Body

[/caption]The term celestial body is as expansive as the entire universe, both known and unknown. By definition a celestial body is any natural body outside of the Earth’s atmosphere. Easy examples are the Moon, Sun, and the other planets of our solar system. But those are very limited examples. The Kuiper belt contains many celestial bodies. Any asteroid in space is a celestial body. So, what do you write about with such a broad topic? How about a sampling of five of my favorites and leave it at that for now? Which five, though. Well, let’s cover Ceres, the Kuiper belt, the asteroid Cruithne, Achernar, and Apophis.

Ceres is a celestial body that is by far the largest and most massive asteroid in the belt between Mars and Jupiter. It is approximately the size of Texas or 975km x 909 km with a mass of 9.5×1020. It actually represents 1/3 of all of the mass of the asteroid belt. It has enough mass for self gravity which is a major requirement to be considered a dwarf planet. It revolves around the sun every 1679.819 days with a very small axial tilt. The surface is relatively warm. The high temperature is thought to be in the neighborhood of -38°C(235 K). Ceres has a visual brightness magnitude of +6.9 to +9. When it is at the brightest point possible, Ceres is nearly bright enough to be seen with the naked eye. It can be seen with binoculars whenever it is above the horizon on a completely dark night.

The Kuiper belt contains many a celestial body. It is actually a disk-shaped region in the outer solar system lying beyond the orbit of Neptune and extending to a distance of about 50 astronomical units, containing thousands of small icy bodies, some of which are on highly elliptical orbits, periodically visiting the inner solar system as comets. It is thought to be a collection of the remnants of the formation of the solar system. Who knows what may be found when we are able to send spacecraft to its edges?

As a celestial body, the asteroid Cruithne is sort of small and indistinct until you consider that it is locked in a 1:1 orbit with the Earth. The asteroid is sometimes referred to as the Earth’s second moon. It is not a true moon because the Earth’s gravity does not effect it nor does its effect the Earth. Cruithne’s nearest pass to Earth is .1 AU (40 moon lengths), although right now it never comes closer than .3 AU. The asteroid sort of runs like a corkscrew around the Earth while both are revolving around the Sun. The asteroid Cruithne is in a normal elliptic orbit around the Sun. Its revolution around the Sun, approximately 364 days at present, is almost equal to that of the Earth. Because of this, Cruithne and Earth appear to follow each other in their paths around the Sun.

The celestial body Achernar is a bright, blue, B3-type star of six to eight solar masses lying approximately 144 light years away. It is classified as a dwarf, but it is 3,000 times more luminous than our Sun. It is in the deep southern sky and never rises above 33°N. Achernar is best seen from the southern hemisphere in November; it is circumpolar below 33°S. Achernar spins so quickly that is spherical in shape. The distance along its equator is 50% greater than its polar diameter. It is the brightest star in the Eridanus constellation. It is also the 9th brightest star in the night sky. Of the 10 brightest stars, other than our Sun, it is the hottest and bluest.

The celestial body Apophis is one of the most intriguing, to me. It is the stuff that many sci-fi legends have been based on. Apophis is most famous for the stir it caused in 2004. The asteroid was discovered on its way towards the Earth and was predicted to have a 2.7% chance of impacting the Earth. That in and of itself is not significant. Objects impact the Earth on a yearly basis. The size of Apophis was the major concern. Even a small chance that an asteroid the size of a small town hitting the Earth rightly caused a large commotion. It achieved the highest score ever on the Torino scale and it stayed on an elevated level for longer than any other asteroid ever has. It was eventually studied enough to know that it would not hit the Earth in 2004. The asteroid will pass again in 2029. Scientists predict that it will not hit the Earth, but it may pass through a gravitational keyhole that could alter its orbit enough that it could impact in 2036. The chances are slight, but real. Even if it doesn’t hit a keyhole in 2029 it will return every seven years and may pose a serious threat in the future. Scientists have proposed that Apophis be nudged out of its present orbit into an orbit that takes it further from the keyhole. NASA scientist David Morrison says, “After 2029, the deflection would have to be vigorous enough to miss not just a tiny keyhole but the much larger target of the Earth itself. And such a deflection is far beyond present technology for an asteroid this large.”.

Many things can make a celestial body interesting. Everyone has their favorites. Mine happen to be the five I have listed. Each can be further researched here on Universe Today. Follow these links to find what you need: Ceres, the Kuiper belt, the asteroid Cruithne, Achernar, and Apophis. Astronomy Cast offers a good episode about the mind-boggling possibility of multiple universes. Here’s a list of the 10 brightest stars.

Sources:
http://planetary.org/explore/topics/asteroids_and_comets/ceres.html
http://userpages.umbc.edu/~gwilson/kuiper.html
http://www.astro.uwo.ca/~wiegert/3753/3753.html
http://en.wikipedia.org/wiki/Achernar
http://neo.jpl.nasa.gov/apophis/