These strange features showed people for the first time how radically different the surface of Pluto is from Earth and the other planets of the inner Solar System. But strangely, they also showcased how this distant world is also quite similar to Earth. For instance, in a new study, a team of researchers working on the images from the New Horizons mission noticed “dunes” on the surface of Pluto that resemble sand dunes here on Earth.
The study, titled “Dunes on Pluto“, was recently published in the journal Science. The study was led by Matthew Telfer, a Lecturer in Physical Geography from the University of Plymouth, with significant contributions provided by Eric J. R. Parteli and Jani Radebaugh – geoscientists from the University of Cologne, and Brigham Young University, respectively.
On Earth, dunes are formed by wind-blown sand that create repeated ridges in the desert or along beaches. Similar patterns have been observed along river beds and alluvial plains, where water deposits sediment over time. In all cases, dune-like formations are the result of solid particles being transported by a moving medium (i.e. air or water). Beyond Earth, such patterns have been observed on Mars, Titan, and even on Comet 67P/Churyumov-Gerasimenko.
However, when consulting images from New Horizons probe, Telfer and his colleagues noted similar formations in the Sputnik Planitia region on Pluto. This region, which constitutes the western lobe of the heart-shaped Tombaugh Regio, is essentially a massive ice-covered basin. Already, researchers have noted that the surface appears to consist of irregular polygons bordered by troughs, which appear to be indications of convection cells.
As Dr. Telfer told Universe Today via email:
“We first saw some features looked kind of dune-like within the first few days, but as time passed, and new images came in, most of these seemed less and less convincing. But one area became more and more convincing with every pass. This is what we’re reporting on.”
Another interesting feature is the dark streams that are a few kilometers long and are all aligned in the same direction. But equally interesting were the features that Telfer and his team noticed, which looked like dunes that ran perpendicular to the wind streaks. This indicated that they were transverse dunes, the kinds that pile up due to prolonged wind activity in the desert.
To determine if this was a plausible hypothesis, the researchers constructed models that took into account what kind of particles would make up these dunes. They concluded that either methane or nitrogen ice would be able to form sand-sized grains that could be transported by typical winds. They then modeled the physics of Pluto’s winds, which would be strongest coming down the slopes of the mountains that border Sputnik Planum.
However, they also determined that Pluto’s winds would not be strong enough to push the particles around on their own. This is where sublimation played a key role, where surface ice goes from a solid phase directly to a gas when warmed by sunlight. This sublimation would provide the upward force necessary to lift the particles, at which point they would be caught by Pluto’s winds and blown around.
As Dr. Telfer explained, this conclusion was made possible thanks to the immense amount of support his team got, much of which came from the New Horizons Geology, Geophysics and Imaging Science Theme Team:
“Once we’d done the spatial analysis that made us really sure that these features made sense as dunes, we had the great opportunity to hook up with Eric Parteli at Cologne; he showed us through his modelling that the dunes should form, as long as the grains become airborne in the first place. The NASA New Horizons team really helped here, as they pointed out that mixed nitrogen/methane ices would preferentially fling methane ice grains upwards as the ices sublimated.”
In addition to showing that Pluto, one of the most distant objects in the Solar System, has a few things in common with Earth, this study has also shown just how active Pluto’s surface is. “It shows us that not only is Pluto’s surface affecting its atmosphere, the converse is also true,” said Dr. Telfer. “We have a really dynamic world’s surface, so far out in the solar system.
On top of that, understanding how dunes can form under Pluto’s conditions will help scientists to interpret similar features found elsewhere in the Solar System. For example, NASA is planning on sending a mission to Titan in the coming decade to study its many interesting surface features, which include its dune formations. And many more missions are being sent to explore the Red Planet before a crewed mission takes place in the 2030s.
Knowing how such formations were created are key to understanding the dynamics of the planet, which will help answer some of the deeper questions about what is taking place on the surface.
Pluto has been the focus of a lot of attention for more than a decade now. This began shortly after the discovery of Eris in the Kuiper Belt, one of many Kuiper Belt Objects (KBOs) that led to the “Great Planetary Debate” and the 2006 IAU Resolution. Interest in Pluto also increased considerably thanks to the New Horizons mission, which conducted the first flyby of this “dwarf planet” in July of 2015.
The data this mission provided on Pluto is still proving to be a treasure trove for astronomers, allowing for new discoveries about Pluto’s surface, composition, atmosphere, and even formation. For instance, a new study produced by researchers from the Southwest Research Institute (and supported by NASA Rosetta funding) indicates that Pluto may have formed from a billion comets crashing together.
The origin of Pluto is something that astronomers have puzzled over for some time. An early hypothesis was that it was an escaped moon of Neptune that had been knocked out of orbit by Neptune’s current largest moon, Triton. However, this theory was disproven after dynamical studies showed that Pluto never approaches Neptune in its orbit. With the discovery of the Kuiper Belt in 1992, the true of origin of Pluto began to become clear.
Essentially, while Pluto is the largest object in the Kuiper Belt, it is similar in orbit and composition to the icy objects that surround it. On occasion, some of these objects are kicked out of the Kuiper Belt and become long-period comets in the Inner Solar System. To determine if Pluto formed from billions of KBOs, Dr. Glein and Dr. Waite Jr. examined data from the New Horizons mission on the nitrogen-rich ice in Sputnik Planitia.
This large glacier forms the left lobe of the bright Tombaugh Regio feature on Pluto’s surface (aka. Pluto’s “Heart”). They then compared this to data obtained by the NASA/ESA Rosetta mission, which studied the comet 67P/Churyumov–Gerasimenko (67P) between 2014 and 2016. As Dr. Glein explained:
“We’ve developed what we call ‘the giant comet’ cosmochemical model of Pluto formation. We found an intriguing consistency between the estimated amount of nitrogen inside the glacier and the amount that would be expected if Pluto was formed by the agglomeration of roughly a billion comets or other Kuiper Belt objects similar in chemical composition to 67P, the comet explored by Rosetta.”
This research also comes up against a competing theory, known as the “solar model”. In this scenario, Pluto formed from the very cold ices that were part of the protoplanetary disk, and would therefore have a chemical composition that more closely matches that of the Sun. In order to determine which was more likely, scientists needed to understand not only how much nitrogen is present at Pluto now (in its atmosphere and glaciers), but how much could have leaked out into space over the course of eons.
They then needed to come up with an explanation for the current proportion of carbon monoxide to nitrogen. Ultimately, the low abundance of carbon monoxide at Pluto could only be explained by burial in surface ices or destruction from liquid water. In the end, Dr. Glein and Dr. Waite Jr.’s research suggests that Pluto’s initial chemical makeup, which was created by comets, was modified by liquid water, possibly in the form of a subsurface ocean.
“This research builds upon the fantastic successes of the New Horizons and Rosetta missions to expand our understanding of the origin and evolution of Pluto,” said Dr. Glein. “Using chemistry as a detective’s tool, we are able to trace certain features we see on Pluto today to formation processes from long ago. This leads to a new appreciation of the richness of Pluto’s ‘life story,’ which we are only starting to grasp.”
While the research certainly offers an interesting explanation for how Pluto formed, the solar model still satisfies some criteria. In the end, more research will be needed before scientists can conclude how Pluto formed. And if data from the New Horizons or Rosetta missions should prove insufficient, perhaps another to New Frontiers mission to Pluto will solve the mystery!
In 2015, the New Horizons mission made history by being the first spacecraft to conduct a flyby of Pluto. In addition to revealing things about the planet’s atmosphere, its geology and system of moons, the probe also provided the first clear images of the surface of Pluto and its largest moon, Charon. Because of this, scientists are now able to study Pluto and Charon’s many curious surface features and learn more about their evolution.
Another interesting thing that has resulted from this surface imaging has been the ability to name these features. Recently, the IAU Working Group for Planetary System Nomenclatureofficially approved of a dozen names that had been proposed by NASA’s New Horizons team. These names honor legendary explorers and visionaries, both real and fictitious, and include science fiction authors Octavia Butler and Arthur C. Clarke.
Aside from being Pluto’s largest moon, Charon is also one of the larger bodies in the Kuiper Belt. Because of its immense size, Charon does not orbit Pluto in the strictest sense. In truth, the barycenter of the Pluto-Charon system is outside Pluto, meaning the two bodies almost orbit each other. The moon also has a wealth of features, which include valleys, crevices, and craters similar to what have been seen on other moons.
For some time, the New Horizons team has been using a series of informal names to describe Charon’s many features. The team gathered most of them during the online public naming campaign they hosted in 2015. Known as “Our Pluto“, this campaign consisted of people from all over the world contributed their suggestions for naming features on Pluto and Charon.
The New Horizons team also contributed their own suggestions and (according to the IAU) was instrumental in moving the new names through approval. As Dr. Alan Stern, the New Horizon team leader, told Universe Today via email: “We conduced a public feature name bank process in 2015 before flyby. Once flyby was complete our science team created a naming proposal for specific features and sent it to IAU.”
A similar process took place last year, where the IAU officially adopted 14 place names that were suggested by the New Horizons team – many of which were the result of the online naming campaign. Here too, the names were those that the team had been using informally to describe the many regions, mountain ranges, plains, valleys and craters that were discovered during the spacecraft’s flyby.
The names that were ultimately selected honored the spirit of epic exploration, which the New Horizons mission demonstrated by being the first probe to reach Pluto. As such, the names that were adopted honored travelers, explorers, scientists, pioneering journeys, and mysterious destinations. For example, Butler Mons honors Octavia E. Butler, a celebrated author and the first science fiction writer to win a MacArthur fellowship.
Similarly, Clarke Montes honors Sir Arthur C. Clarke, the prolific writer and futurist who co-wrote the screenplay for 2001: A Space Odyssey (which he later turned into a series of novels). Stanley Kubrik, who produced and directed 2001: A Space Odyssey, was also honored with the feature Kubrik Mons. Meanwhile, several craters were named in honor of fictional characters from famous stories and folklore.
The Revati Crater is named after the main character in the Hindu epic narrative Mahabharata while the Nasreddin Crater is named for the protagonist in thousands of folktales told throughout the Middle East, southern Europe and parts of Asia. Nemo Crater honors the captain of the Nautilus in Jule’s Verne’s novels Twenty Thousand Leagues Under the Sea (1870) and The Mysterious Island (1874).
The Pirx Crater is name after the main character in a series of short stories by Polish sci-fi author Stanislaw Lem, while the Dorothy Crater takes its name from the protagonist in The Wizard of Oz, one of several children’s stories by L. Frank Baum that was set in this magical land.
As Rita Schulz, chair of the IAU Working Group for Planetary System Nomenclature, commented, “I am pleased that the features on Charon have been named with international spirit.” Dr. Alan Stern expressed similar sentiments. When asked if he was happy with the new names that have been approved, he said simply, “Very.”
Even though the encounter with the Pluto system happened almost three years ago, scientists are still busy studying all the information gathered during the historic flyby. In addition, the New Horizons spacecraft will be making history again in the not-too-distant future. At present, the spacecraft is making its way farther into the outer Solar System with the intention of rendezvousing with two Kuiper Belt Objects.
On Jan. 1st, 2019, it will rendezvous with its first destination, the KBO known as 2014 MU69 (aka. “Ultima Thule“). This object will be the most primitive object ever observed by a spacecraft, and the encounter will the farthest ever achieved in space exploration. Before this intrepid exploration mission is complete, we can expect that a lot more of the outer Solar System will be mapped and named.
When it made its historic flyby of Pluto in July of 2015, the New Horizons spacecraft gave scientists and the general public the first clear picture of what this distant dwarf planet looks like. In addition to providing breathtaking images of Pluto’s “heart”, its frozen plains, and mountain chains, one of the more interesting features it detected was Pluto’s mysterious “bladed terrain”.
According to data obtained by New Horizons, these features are made almost entirely out of methane ice and resemble giant blades. At the time of their discovery, what caused these features remained unknown. But according to new research by members of the New Horizons team, it is possible that these features are the result of a specific kind of erosion that is related to Pluto’s complex climate and geological history.
Ever since the New Horizons probe provided a detailed look at Pluto’s geological features, the existence of these jagged ridges has been a source of mystery. They are located at the highest altitudes on Pluto’s surface near it’s equator, and can reach several hundred feet in altitude. In that respect, they are similar to penitentes, a type of structure found in high-altitude snowfields along Earth’s equator.
These structures are formed through sublimation, where atmospheric water vapor freezes to form standing, blade-like ice structures. The process is based on sublimation, where rapid changes in temperature cause water to transition from a vapor to a solid (and back again) without changing into a liquid state in between. With this in mind, the research team considered various mechanisms for the formation of these ridges on Pluto.
What they determined was that Pluto’s bladed terrain was the result of atmospheric methane freezing at extreme altitudes on Pluto, which then led to ice structures similar to the ones found on Earth.The team was led by Jeffrey Moore, a research scientist at NASA’s Ames Research Center who was also a New Horizons’ team member. As he explained in a NASA press statement:
“When we realized that bladed terrain consists of tall deposits of methane ice, we asked ourselves why it forms all of these ridges, as opposed to just being big blobs of ice on the ground. It turns out that Pluto undergoes climate variation and sometimes, when Pluto is a little warmer, the methane ice begins to basically ‘evaporate’ away.”
But unlike on Earth, the erosion of these features are related to changes that take place over the course of eons. This should come as no surprise seeing as how Pluto’s orbital period is 248 years (or 90,560 Earth days), meaning it takes this long to complete a single orbit around the Sun. In addition, the eccentric nature of it orbit means that its distance from the Sun ranges considerably, from 29.658 AU at perihelion to 49.305 AU at aphelion.
When the planet is farthest from the Sun, methane freezes out of the atmosphere at high altitudes. And as it gets closer to the Sun, these ice features melt and turn directly into atmospheric vapor again. As a result of this discovery, we now know that the surface and air of Pluto are apparently far more dynamic than previously thought. Much in the same way that Earth has a water cycle, Pluto may have a methane cycle.
This discovery could also allow scientists to map out locations of Pluto which were not photographed in high-detail. When the New Horizons mission conducted its flyby, it took high-resolution pictures of only one side of Pluto – designated as the “encounter hemisphere”. However, it was only able to observe the other side at lower resolution, which prevented it from being mapped in detail.
But based on this new study, NASA researchers and their collaborators have been able to conclude that these sharp ridges may be a widespread feature on Pluto’s “far side”. The study is also significant in that it advances our understanding of Pluto’s global geography and topography, both past and present. This is due to the fact that it demonstrated a link between atmospheric methane and high-altitude features. As such, researchers can now infer elevations on Pluto by looking for concentrations of methane in its atmosphere.
Not long ago, Pluto was considered one of the least-understood bodies in our Solar System, thanks to its immense distance from the Sun. However, thanks to ongoing studies made possible by the data collected by the New Horizons mission, scientists are becoming increasingly familiar with what its surface looks like, not to mention the types of geological and climatological forces that have shaped it over time.
And be sure to enjoy this video that details the discovery of Pluto’s bladed terrain, courtesy of NASA’s Ames Research Center:
On July 14th, 2015, the New Horizons mission made history when it became the first spacecraft to conduct a flyby of Pluto and its moons. In the course of making its way through this system, the probe gathered volumes of data on Pluto and its many satellites using a sophisticated suite of instruments. These included the first detailed images of what Pluto and its largest moon (Charon) look like up close.
And while scientists are still analyzing the volumes of data that the probe has sent home (and probably will be for years to come), the New Horizons mission team has given us plenty of discoveries to mull over in the meantime. For instance, using the many images taken by the mission, they recently created a series of high-quality, highly-detailed global maps of Pluto and Charon.
The maps were created thanks to the plethora of images that were taken by New Horizons’ Long-Range Reconnaissance Imager (LORRI) and its Multispectral Visible Imaging Camera (MVIC). Whereas LORRI is a telescopic camera that was responsible for obtaining encounter and high-resolution geologic data of Pluto at long distances, the MVIC is an optical and infrared instrument that is part of the Ralph instrument – the main imaging device of the probe.
Dr. Stern, who is also the PI of the New Horizons mission, commented on the release of the maps in a recent NASA press statement. As he stated, they are just the latest example of what the New Horizons mission accomplished during its historic mission:
“The complexity of the Pluto system — from its geology to its satellite system to its atmosphere— has been beyond our wildest imagination. Everywhere we turn are new mysteries. These new maps from the landmark exploration of Pluto by NASA’s New Horizons mission in 2015 will help unravel these mysteries and are for everyone to enjoy.”
And these were not the only treats to come from the New Horizons team in recent days. In addition, the mission scientists used actual New Horizons data and digital elevation models to create flyover movies that show what it would be like to pass over Pluto and Charon. These videos offer a new perspective on the system and showcase the many unusual features that were discovered on both bodies.
The video of the Pluto flyover (shown above) begins over the highlands that are located to the southwest of Sputnik Planitia – the nitrogen ice basin that measures some 1,050 by 800 km (650 by 500 mi) in size. These plains constitute the western lobe of the feature known as Tombaugh Regio, the heart-shaped region that is named after the man who discovered Pluto in 1930 – Clyde Tombaugh.
The flyover also passes by cratered terrain of Cthulhu Macula before moving north past the highlands of Voyager Terra. It then turns south towards the pitted region known as Pioneer Terra before concluding over Tartarus Dorsa, a mountainous region that also contains bowl-shaped ice and snow features called penitentes (which are found on Earth and are formed by erosion).
The flyover video of Charon begins over the hemisphere that the New Horizons mission saw during its closest approach to the moon. The view then descends over Serenity Chasma, the wide and deep canyon that is named after the ship from the sci-fi series Firefly. This feature is part of the vast equatorial belt of chasms on Charon, which is one of the longest in the Solar System – 1,800 km (1,100 mi) long 7.5 km (4.5 mi) deep.
The view then moves north, passing over the Dorothy Gale crater and the dark polar region known as Mordor Macula (appropriately named after the domain of the Dark Lord Sauron in The Lord of the Rings). The video then turn south to fly over the northern terrain known as Oz Terra before finishing over the equatorial plans of Vulcan Planum and the mountain of Clarke Montes.
These videos were color-enhanced in order to bring out the surface details, and the topographic relief was exaggerated by a factor or two to three to emphasize the topography of Pluto and its largest moon. Digital mapping and rendering of these videos was performed by Paul Schenk and John Blackwell of the Lunar and Planetary Institute (LPI) in Houston.
It may be many years before another mission is able to travel to the Trans-Neptunian region and Kuiper Belt. As a result, the maps and videos and images that were taken by the New Horizons mission may the last glimpse some us get of the Pluto system. Luckily, the New Horizons mission has provided scientists and the general public with enough information to keep them busy and fascinated for years!
It was two years ago this morning that we awoke to see the now iconic image of Pluto that the New Horizons spacecraft had sent to Earth during the night. You, of course, know the picture I’m talking about – the one with a clear view of the giant heart-shaped region on the distant, little world (see above).
This image was taken just 16 hours before the spacecraft would make its closest approach to Pluto. Then, during that seemingly brief flyby (after traveling nine-and-a-half years and 3 billion miles to get there), the spacecraft gathered as much data as possible and we’ve been swooning over the images and pondering the findings from New Horizons ever since.
“This is what we came for – these images, spectra and other data types that are helping us understand the origin and the evolution of the Pluto system for the first time,” New Horizons principal investigator Alan Stern told me last year. “We’re seeing that Pluto is a scientific wonderland. The images have been just magical. It’s breathtaking.”
See a stunning new video created from flbyby footage in honor of the two-year anniversary of the flyby:
All the images have shown us that Pluto is a complex world with incredible diversity, in its geology and also in its atmosphere.
While the iconic “heart” image shows a clear and cloudless view of Pluto, a later image showed incredible detail of Pluto’s hazy atmosphere, with over two dozen concentric layers that stretches more than 200 km high in Pluto’s sky.
With all those layers and all that haze, could there be clouds on Pluto too?
This is a question Stern and his fellow scientists have been asking for a long time, actually, as they have been studying Pluto for decades from afar. Now with data from New Horizons, they’ve been able to look closer. While Stern and his colleagues have been discussing how they found possible clouds on Pluto for a few months, they have now detailed their findings in a paper published last month.
“Numerous planets in our solar system, including Venus, Earth, Mars, Titan, and all four of the giant planets possess atmospheres that contain clouds, i.e., discrete atmospheric condensation structures,” the team wrote in their paper. “This said, it has long been known that Pluto’s current atmosphere is not extensively cloudy at optical or infrared wavelengths.”
They explained that evidence for this came primarily from the “high amplitude and temporal stability of Pluto’s lightcurve,” however, because no high spatial resolution imagery of Pluto was possible before New Horizons, it remained to be seen if clouds occur over a small fraction of Pluto’s surface area.
But now with flyby images in hand, the team set out to do searches for clouds on Pluto, looking at all available imagery from the Long Range Reconnaissance Imager and the Multispectral Visible Imaging Camera, looking at both the disk of Pluto and near and on the limb. Since an automated cloud search was nearly impossible, it was all done by visual inspection of the images by the scientists.
They looked for features in the atmosphere that including brightness, fuzzy or fluffy-looking edges and isolated borders.
In all, they found seven bright, discrete possible cloud candidates. The seven candidates share several different attributes including small size, low altitude, they all were visible either early or late in the day local time, and were only visible at oblique geometry – which is basically a sideways look from the spacecraft.
Also, several cloud candidates also coincided with brighter surface features below, so the team is still pondering the correlation.
“The seven candidates are all similar in that they are very low altitude,” Stern said last fall at the Division of Planetary Sciences meeting, “and they are all low-lying, isolated small features, so no broad cloud decks or fields. When we map them over the surface, they all lie near the terminator, so they occur near dawn or dusk. This is all suggestive they are clouds because low-lying regions and dawn or dusk provide cooler conditions where clouds may occur.”
While haze was detected as high as 220 km, the possible clouds were found at very low altitudes. Stern told Universe Today that these possible, rare condensation clouds could be made of ethane, acetylene, hydrogen cyanide or methane under the right conditions. Stern added these clouds are probably short-lived phenomena – again, likely occurring only at dawn or dusk. A day on Pluto is 6.4 days on Earth.
But all in all, they concluded that at the current time Pluto’s atmosphere is almost entirely free of clouds – in fact the dwarf planet’s sky was 99% cloud free the day that New Horizons whizzed by.
“But if there are clouds, it would mean the weather on Pluto is even more complex than we imagined,” Stern said last year.
The seven cloud candidates cannot be confirmed as clouds because none are in the region where there was stereo imaging or other available ways to cross-check it. They concluded that further modeling would be needed, but specifically a Pluto orbiter mission would be the only way to “search for clouds more thoroughly than time and space and was possible during the brief reconnaissance flyby by New Horizons.”
Once held to be the outermost planet of the Solar System, Pluto‘s designation was changed by the International Astronomical Union in 2006, owing to the discovery of many new Kuiper Belt Objects that were comparable in size. In spite of this, Pluto remains a source of fascination and a focal point of much scientific interest. And even after the historic flyby conducted by the New Horizons probe in July of 2015, many mysteries remain.
What’s more, ongoing analysis of the NH data has revealed new mysteries. For instance, a recent study by a team of astronomers indicated that a survey by the Chandra X-ray Observatory revealed the presence of some rather strong x-rays emissions coming from Pluto. This was unexpected, and is causing scientists to rethink what they thought they knew about Pluto’s atmosphere and its interaction with solar wind.
In the past, many Solar bodies have been observed emitting x-rays, which were the result of interaction between solar wind and neutral gases (like argon and nitrogen). Such emissions have been detected from planets like Venus and Mars (due to the presence of argon and/or nitrogen in their atmospheres), but also with smaller bodies like comets – which acquire halos due to outgassing.
Ever since the NH probe conducted its flyby of Pluto in 2015, astronomers have been aware that Pluto has an atmosphere which changes size and density with the seasons. Basically, as the planet reaches perihelion during its 248 year orbital period – a distance of 4,436,820,000 km, 2,756,912,133 mi from the Sun – the atmosphere thickens due to the sublimation of frozen nitrogen and methane on the surface.
The last time Pluto was at perihelion was on September 5th, 1989, which means that it was still experiencing summer when NH made its flyby. While studying Pluto, the probe detected an atmosphere that was primarily composed of nitrogen gas (N²) along with methane (CH4) and carbon dioxide (CO²). Astronomers therefore decided to look for signs of x-ray emissions coming from Pluto’s atmosphere using the Chandra X-ray Observatory.
Prior to the NH mission’s flyby, most models of Pluto’s atmosphere expected it to be quite extended. However, the probe found that the atmosphere was less extended and that its rate of loss was hundreds of times lower than what these models predicted. Therefore, as the team indicated in their study, they expected to find x-ray emissions that were consistent with what the NH flyby observed:
“Given that most pre-encounter models of Pluto’s atmosphere had predicted it to be much more extended, with an estimated loss rate to space of ~1027 to 1028 mol/sec of N² and CH4… we attempted to detect X-ray emission created by [solar wind] neutral gas charge exchange interactions in the low density neutral gas surrounding Pluto,” they wrote.
However, after consulting data from the Advanced CCD Imaging Spectrometer (ACIS) aboard Chandra, they found that x-ray emissions coming from Pluto were greater than what this would allow for. In some cases, strong x-ray emissions have been noted coming from other smaller objects in the Solar System, which is due to the scattering of solar x-rays by small dust grains composed of carbon, nitrogen and oxygen.
But the energy distribution they noted with Pluto’s x-rays were not consistent with this explanation. Another possibility that the team offered is that they could be due to some process (or processes) that focus the solar wind near Pluto, which would enhance the effect of its modest atmosphere. As they indicate in their conclusions:
“The observed emission from Pluto is not aurorally driven. If due to scattering, it would have to be sourced by a unique population of nanoscale haze grains composed of C, N, and O atoms in Pluto’s atmosphere resonantly fluorescing under the Sun’s insolation. If driven by charge exchange between [solar wind] minor ions and neutral gas species (mainly CH4) escaping from Pluto, then density enhancement and adjustment of the [solar wind] minor ion relative abundance in the interaction region near Pluto is required versus naïve models.”
For the time being, the true cause of these x-ray emissions is likely to remain a mystery. They also highlight the need for more research when it comes to this distant and most massive of Kuiper Belt Objects. Luckily, the data provided by the NH mission is likely to be poured over for decades, revealing new and interesting things about Pluto, the outer Solar System, and how the most distant worlds from our Sun behave.
It isn’t every day we get a new moon added to the list of solar system satellites. The combined observational power of three observatories — Kepler, Herschel and Hubble — led an astronomical detective tale to its climatic conclusion: distant Kuiper Belt Object 2007 OR10has a tiny moon.
The dwarf planet itself is an enigma wrapped in a mystery: with a long orbit taking it out to a distant aphelion 101 astronomical units (AU) from the Sun, back into the environs of Neptune and Pluto for a perihelion 33 AU from the Sun once every 549 years, 2007 OR10 was discovered by Caltech astronomers Megan Schwamb and Mike Brown in 2007. Nicknamed “Snow White” by Mike Brown for its presumed high albedo, 2007 OR10 was 85 AU distant in the constellation Aquarius at the time of discovery and outbound towards aphelion in 2135. 2007 OR10 is about 1,500 kilometers in diameter, the third largest body known beyond Neptune in our solar system next to Pluto and Eris (nee Xena).
Enter the Kepler Space Telescope, which imaged 2007 OR10 crossing the constellation Aquarius as part of its extended K2 exoplanet survey along the ecliptic plane. Though Kepler looks for transiting exoplanets — worlds around other stars that betray their presence by tiny dips in the brightness of their host as they pass along our line of sight — it also picks up lots of other things that flicker, including variable stars and distant Kuiper Belt Objects. But the slow 45 hour rotational period of 2007 OR10 noted by Kepler immediately grabbed astronomers interest: could an unseen moon be lurking nearby, dragging on the KBO like a car brake?
“Typical rotation periods for Kuiper Belt Objects are under 24 hours,” says Csaba Kiss (Konkoly Observatory) in a recent press release. “We looked in the Hubble archive because the slower rotation period could have been caused by the gravitational tug of a moon.”
And sure enough, digging back through archival data from the Hubble Space Telescope taken during a survey of KBOs, astronomers turned up two images of the faint moon from 2009 and 2010. Infrared observations of 2007 OR10 and its moon by the European Space Agency’s Herschel Space Telescope cinched the discovery, and noted an albedo of 19% (similar to wet sand) for 2007 OR10, much darker than expected. The moon is about 200 miles (320 kilometers) in diameter, in a roughly 9,300 mile (15,000 kilometer) orbit.
The discovery was announced at an AAS meeting just last year, and even now, we’re still puzzling out what little we know about these distant worlds. Just what 2007 OR10 and its moon looks like is any guess. New Horizons gave us our first look at Pluto and Charon two short summers ago in 2015, and will give us a fleeting glimpse of 2014 MU69 on New Year’s Day 2019. All of these objects beg for proper names, especially pre-2019 New Horizons flyby.
What would the skies from the tiny moon look like? Well, ancient 2007 OR10 must loom large in its sky, though Sol would only shine as a bright -15th magnitude star, (a little brighter than a Full Moon) its illumination dimmed down to 1/7,000th the brightness enjoyed here on sunny Earth, which would be lost in its glare.
And looking at the strange elliptical orbits of these outer worldlets, we can only surmise that something else must be out there. Will the discovery of Planet 9 be made before the close of the decade?
One thing’s for sure: this isn’t your parent’s tidy solar system with “Excellent Mothers” serving “Nine Pizzas.”
For decades, we could only imagine what the view of Pluto’s surface might be. Now, we have the real thing.
The images and data from the New Horizons’ mission flyby of Pluto in July 2015 showed us an unexpectedly stunning and geologically active world. Scientists have used words like ‘magical,’ ‘breathtaking’ and ‘scientific wonderland’ to describe the long-awaited close-up views of distant Pluto.
Even though scientists are still analyzing the data from New Horizons, ideas are starting to formulate about sending another spacecraft to Pluto, but with a long-term orbiter mission instead of a quick flyby.
“The next appropriate mission to Pluto is an orbiter, maybe equipped with a lander if we had enough funding to do both,” New Horizons’ principal investigator Alan Stern told Universe Today in March.
This week, Stern has shared on social media that the New Horizons’ science team is meeting. But, separately, another group is starting to talk about a possible next mission to Pluto.
Getting a spacecraft to the outer regions of our solar system as fast as possible provides challenges, particularly in being able to slow down enough to enable going into orbit around Pluto. For the speedy and lightweight New Horizons, an orbital mission was impossible.
What propulsion system might make a Pluto orbiter and/or lander mission possible?
A few ideas are being tossed around.
Space Launch System
One concept takes advantage of NASA’s big, new Space Launch System (SLS), currently under development to enable human missions to Mars. NASA describes the SLS as “designed to be flexible and evolvable and will open new possibilities for payloads, included robotic scientific missions.” Even the first Block 1 version can launch 70 metric tons (later versions might be able to lift up to 130 metric tons.) Block 1 will be powered by twin five-segment solid rocket boosters and four liquid propellant engines, with a proposed 15% more thrust at launch than the Saturn V rockets that sent astronauts to the Moon.
But an orbiter mission to Pluto might not be the best use of the SLS alone.
It takes a lot of fuel to accelerate a vehicle to fast enough speed to get to Pluto in a reasonable amount of time. For example, New Horizons was the fastest spacecraft ever launched, using a souped-up Atlas V rocket with extra boosters, it performed a big burn when New Horizons departed Earth orbit. The lightweight spacecraft sped away from the Earth at 36,000 miles per hour (about 58,000 km/ hour), then used a gravity assist from Jupiter to boost New Horizons’ speed to 52,000 mph (83,600 km/h), traveling nearly a million miles (1.5 million km) a day in its 3 billion mile (4.8 billion km) journey to Pluto. The flight took nine and a half years.
“To enter Pluto orbit, a vehicle [like SLS] would have to boost up to that same speed, then turn around and decelerate for half the trip to arrive at Pluto with a net velocity of zero relative to the planet,” explained Stephen Fleming, an investor in several alt-space startups including XCOR Aerospace, Planetary Resources and NanoRacks. “Unfortunately, due to the tyranny of the rocket equation, you would have to carry all the fuel/propellant to decelerate with you at launch … which means accelerating the orbiter AND all that fuel in the initial phase. That requires logarithmically more fuel for the initial burn, and it turns out to be a LOT of fuel.”
Fleming told Universe Today that using the multi-billion dollar SLS to launch a Pluto orbiter, you would wind up launching an entire payload full of propellant just to accelerate and decelerate a tiny Pluto orbiter.
“That’s an extraordinarily expensive mission,” he said.
A better option might be to use a propulsion system of combined technologies. Stern mentioned a NASA study that looked at using the SLS as the launch vehicle and to boost the spacecraft towards Pluto, but then using an RTG (Radioisotope Thermoelectric Generator) powered ion engine to later brake for an orbital arrival.
An RTG produces heat from the natural decay of non-weapons-grade plutonium-238, and the heat is converted into electricity. An RTG ion engine would be a more powerful ion propulsion system than the current solar electric ion engine on the Dawn spacecraft, now orbiting Ceres, in the asteroid belt, plus it would enable operation in the outer solar system, far from the Sun. This nuclear powered ion engine would enable a speeding spacecraft to slow down and go into orbit.
“The SLS would boost you to fly out to Pluto,” Stern said, “and it would actually take two years to do the braking with ion propulsion.”
Stern said the flight time for such a mission to Pluto would be seven and a half years, two years faster than New Horizons.
The proposal uses a Direct Fusion Drive (DFD) engine that has propulsion and power in one integrated device. DFD provides high thrust to allow for a flight time of about 4 years to Pluto, plus being able to send substantial mass to orbit, perhaps between 1000 to 8000 kg.
If this propulsion system works as planned, it could launch a Pluto orbiter and a lander (or possibly a rover), and provide enough power to maintain an orbiter and all its instruments, as well as beam a lot of power to a lander. That would enable the surface vehicle to beam back video to the orbiter because it would have so much power, according to Stephanie Thomas from Princeton Satellite Systems, Inc., who is leading the NIAC study.
“Our concept is generally received as, ‘wow, that sounds really cool! When can I get one?’” Thomas told Universe Today. She said her and her team chose a prototype Pluto orbiter and lander mission in their proposal because it’s a great example of what can be done with a fusion rocket.
Their fusion system uses a small linear array of solenoid coils, and their fuel of choice is deuterium helium 3, which has very low neutron production.
“It fits on a spacecraft, it fits on a launch vehicle,” Thomas explained in a NIAC symposium talk (her talk starts about 17:30 in the linked video). “There’s no lithium, or other dangerous materials, it produces very few damaging particles. It’s about the size of a minivan or small truck. Our system is cheaper and faster to develop than other fusion proposals.”
The Princeton team has been able to produce 300 millisecond pulses with their plasma heating experiment, orders of magnitude better than any other system.
“The biggest hurdle is the fusion itself,” she said. “We need to build a bigger experiment to finish proving the new heating method, which will require an order of magnitude more resources than the project has been receiving from the Department of Energy so far,” Thomas said via email. “However, it’s still small in the grand scheme of advanced technology projects, about $50 million.”
Thomas said that DARPA has spent much more on many technology initiatives that ended up canceled. And it’s also much less than other fusion technologies require for the same stage of research, since our machine is so small and has a simple coil configuration.” (Thomas said have a look at the budget for ITER, the international nuclear fusion research and engineering megaproject, currently running over $20 billion).
“To put it simply, we know our method heats electrons really well and can extrapolate to heating ions, but we need to build it and prove it,” she said.
Thomas and her team are currently working on the “balance of plant” technology – the subsystems that will be required to operate the engine in space, assuming the heating method works as currently predicted.
In terms of the Pluto mission itself, Thomas said there aren’t any particular hurdles on the orbiter itself, but it would involve scaling up a few technologies to take advantage of the very large amount of power available, such as the optical communications.
“We could dedicate tens or more kW of power to the communication laser, not 10 watts, [like current missions]” she said. “Another unique feature of our concept is being able to beam a lot of power to a lander. This would enable new classes of planetary science instruments like powerful drills. The technology to do this exists but the specific instruments need to be designed and built. Additional technology that will be needed that is under development in various industries are lightweight space radiators, next-generation superconducting wires, and long-term cryogenic storage for the deuterium fuel.”
Thomas said their NIAC research is going well.
“We were selected for the NIAC Phase II study, and are in contract negotiations now,” she said. “We are busy working on higher fidelity models of the engine’s thrust, designing components of the trajectory, and sizing the various subsystems, including the superconducting coils,” she said. “Our current estimates are that a single 1 to 10 MW engine will produce between 5 and 50 N thrust, at about 10,000 sec specific impulse.”
Laser Zapping to Pluto
Another futuristic propulsion possibility is the laser-based systems proposed by Yuri Milner for his Breakthrough Starshot proposal, where small cubesats could be zapped by lasers on Earth, basically “bug zapping” spacecraft to reach incredible speeds (possibly millions of miles/km per hour) to visit the outer solar system or beyond.
“It’s not really in the cards for us to use this kind of technology, because we’d have to wait decades just for this to be developed,” Stern said. “But if you could send lightweight, inexpensive spacecraft at speeds like one-10th the speed of light based on lasers from Earth. We could send these small spacecraft to hundreds or thousands of objects in the Kuiper Belts, and you’d be out there in a matter of two-and-a-half days. You could send a spacecraft past Pluto every day. That would be really game changing.”
The Realistic Future
But even if everyone agrees a Pluto orbiter should be done, the earliest possible date for such a mission is sometime between the early 2020s and the early 2030s. But it all depends on the recommendations put forth by the scientific community’s next decadal survey, which will suggest the most top-priority missions for NASA’s Planetary Science Division.
These Decadal Surveys are 10-year “roadmaps” that set science priorities and provide guidance on where NASA should send spacecraft and what types of missions they should be. The last Decadal Survey was published in 2011, and that set planetary science priorities through 2022. The next one, for 2023-2034, will likely be published in 2022.
The New Horizons mission was the result of the suggestions from the 2003 planetary science Decadal Survey, where scientists said visiting the Pluto system and worlds beyond was a top-priority destination.
So, if you’re dreaming of a Pluto orbiter, keep talking about it.
Discovered in 1930 by Clyde Tombaugh, Pluto was once thought to be the ninth and outermost planet of the Solar System. However, due to the formal definition adopted in 2006 at the 26th General Assembly of the International Astronomical Union (IAU), Pluto ceased being the ninth planet of the Solar System and has become alternately known as a “Dwarf Planet”, “Plutiod”, Trans-Neptunian Object (TNO) and Kuiper Belt Object (KBO).
Despite this change of designation, Pluto remains one of the most fascinating celestial bodies known to astronomers. In addition to having a very distant orbit around the Sun (and hence a very long orbital period) it also has the most eccentric orbit of any planet or minor planet in the Solar System. This makes for a rather long year on Pluto, which lasts the equivalent of 248 Earth years!
With an extreme eccentricity of 0.2488, Pluto’s distance from the Sun ranges from 4,436,820,000 km (2,756,912,133 mi) at perihelion to 7,375,930,000 km (4,583,190,418 mi) at aphelion. Meanwhile, it’s average distance (semi-major axis) from the Sun is 5,906,380,000 km (3,670,054,382 mi). Another way to look at it would be to say that it orbits the Sun at an average distance of 39.48 AU, ranging from 29.658 to 49.305 AU.
At its closest, Pluto actually crosses Neptune’s orbit and gets closer to the Sun. This orbital pattern takes place once every 500 years, after which the two objects then return to their initial positions and the cycle repeats. Their orbits also place them in a 2:3 mean-motion resonance, which means that for every two orbits Pluto makes around the Sun, Neptune makes three.
The 2:3 resonance between the two bodies is highly stable, and is preserved over millions of years. The last time this cycle took place was between 1979 to 1999, when Neptune was farther from the Sun than Pluto. Pluto reached perihelion in this cycle – i.e. its closest point to the Sun – on September 5th, 1989. Since 1999, Pluto returned to a position beyond that of Neptune, where it will remain for the following 228 years – i.e. until the year 2227.
Sidereal and Solar Day:
Much like the other bodies in our Solar System, Pluto also rotates on its axis. The time it takes for it to complete a single rotation on its axis is known as a “Sidereal Day”, while the amount of time it takes for the Sun to reach the same point in the sky is known as a “Solar Day”. But due to Pluto’s very long orbital period, a sidereal day and a solar day on Pluto are about the same – 6.4 Earth days (or 6 days, 9 hours, and 36 minutes).
It is also worth noting that Pluto and Charon (its largest moon) are actually more akin to a binary system rather than a planet-moon system. This means that the two worlds orbit each other, and that Charon is tidally locked around Pluto. In other words, Charon takes 6 days and 9 hours to orbit around Pluto – the same amount of time it takes for a day on Pluto. This also means that Charon is always in the same place in the sky when seen from Pluto.
In short, a single day on Pluto lasts the equivalent of about six and a half Earth days. A year on Pluto, meanwhile, lasts the equivalent of 248 Earth years, or 90,560 Earth days! And for the entire year, the moon is hanging overhead and looming large in the sky. But factor in Pluto’s axial tilt, and you will come to see just how odd an average year on Pluto is.
It has been estimated that for someone standing on the surface of Pluto, the Sun would appear about 1,000 times dimmer than it appears from Earth. So while the Sun would still be the brightest object in the sky, it would look more like a very bright star that a big yellow disk. But despite being very far from the Sun at any given time, Pluto’s eccentric orbit still results in some considerable seasonal variations.
On the whole, the surface temperature of Pluto does not change much. It’s surface temperatures are estimated to range from a low of 33 K (-240 °C; -400 °F ) to a high of 55 K (-218 °C; -360°F) – averaging at around 44 K (-229 °C; -380 °F). However, the amount of sunlight each side receives during the course of a year is vastly different.
Compared to most of the planets and their moons, the Pluto-Charon system is oriented perpendicular to its orbit. Much like Uranus, Pluto’s very high axial tilt (122 degrees) essentially means that it is orbiting on its side relative to its orbital plane. This means that at a solstice, one-quarter of Pluto’s surface experiences continuous daylight while the other experiences continuous darkness.
This is similar to what happens in the Arctic Circle, where the summer solstice is characterized by perpetual sunlight (i.e. the “Midnight Sun”) and the winter solstice by perpetual night (“Arctic Darkness”). But on Pluto, these phenomena affect nearly the entire planet, and the seasons last for close to a century.
Even if it is no longer considered a planet (though this could still change) Pluto still has some very fascinating quarks, all of which are just as worthy of study as those of the other eight planets. And the time it takes to complete a full year on Pluto, and all the seasonal changes it goes through, certainly rank among the top ten!