Earth and Pluto don’t have much in common. Earth is a vibrant, living world, whereas Pluto is cold, distant and lifeless. But one thing they do have in common is nitrogen. Earth’s atmosphere is about 78% nitrogen, and Pluto’s primary atmospheric constituent is also nitrogen, although the exact percentage is unclear.
On Pluto, where the surface temperature is about 42 Kelvin (-231 Celsius) most of that nitrogen is frozen. A new study says that Pluto’s frozen nitrogen drives the planet’s winds, and shapes its feature surfaces.
NASA’s New Horizons mission taught us a lot about Pluto, the ice dwarf planet. But the spacecraft sped past Pluto so quickly, we only got high-resolution images of one side of the planet, the so-called “encounter side.” New Horizons gave us a big leap in understanding, but in a way, it asked more questions than it answered.
The next step is clearly an orbiter, and now NASA is starting to seriously consider one.
Pluto is getting some new names. In the past, prior to the New Horizons mission, there wasn’t much to name. But now that that spacecraft has flew past Pluto and observed it up close, there’s some features that need naming.
Now the IAU (International Astronomical Union) has approved a new set of names for 14 of the dwarf planet’s surface features.
In July of 2015, NASA’s New Horizons mission made history by becoming the first spacecraft to ever conduct a flyby with Pluto. In addition to providing the world with the first up-close images of this distant world, New Horizons‘ suite of scientific instruments also provided scientists with a wealth of information about Pluto – including its surface features, composition, and atmosphere.
The images the spacecraft took of the surface also revealed unexpected features like the basin named Sputnik Planitia – which scientists saw as an indication of a subsurface ocean. In a new study led by researchers from the University of Hokkaido, the presence of a thin layer of clathrate hydrates at the base of Pluto’s ice shell would ensure that this world could support an ocean.
In 2015, the New Horizons mission became the first robotic spacecraft to conduct a flyby of Pluto. In so doing, the probe managed to capture stunning photos and valuable data on what was once considered to be the ninth planet of the Solar System (and to some, still is) and its moons. Years later, scientists are still poring over the data to see what else they can learn about the Pluto-Charon system.
For instance, the mission scienceteam at the Southwest Research Institute (SwRI) recently made an interesting discovery about Pluto and Charon. Based on images acquired by the New Horizons spacecraft of some small craters on their surfaces, the team indirectly confirmed something about the Kuiper Belt could have serious implications for our models of Solar System formation.
In 2006, during their 26th General Assembly, the International Astronomic Union (IAU) passed a resolution to adopt a formal definition for the term “planet”. According to this definition, bodies that orbit the Sun, are spherical, do not orbit other bodies, and have cleared their orbits were designated planets. Pluto, and other such bodies that did not meet all of these requirements, would thereafter be designated as “dwarf planets”.
However, according to a new study led by Philip T. Metzger – a planetary scientists from the Florida Space Institute (at the University of Central Florida) – the IAU’s standard for classifying planets is not supported by the research literature on Pluto, and is therefore invalid. For those people who have maintained that “Pluto is still planet” for the past twelve years, this is certainly good news!
Missed the planets in the dusk sky in early 2018? This summer’s astronomical blockbuster sees the return of all the classical naked eye planets in the dusk sky, in a big way.
The Sky Scene in July
This coming July 2018 features a rare look at the solar system in profile: you can see Mercury and Venus low in the dusk looking westward immediately after sunset, with Jupiter high to the south, Saturn rising in the east, and Mars rising just behind. This isn’t a true grouping or grand conjunction, as the planets span a 170 degree swath of the ecliptic from Mercury to Mars (too bad they’re not in orbital order!) but a product of our Earthly vantage point looking out over the swath of inner solar system in the evening sky.
Can you manage a “planetary marathon” and collect all five this coming Fourth of July weekend? Here’s a quick rundown of all the planetary action from west to east:
Mercury’s July apparition – fleeting Mercury is always the toughest of the planets to catch, low to the west. -0.3 magnitude Mercury actually forms a straight line with the bright +1st/2nd magnitude stars Castor and Pollux in Gemini the Twins later this week on the evening of June 27th. Mercury reaches greatest elongation 26 degrees east of the Sun on July 12th, presenting a half illuminated, 8” disk. The angle of the evening ecliptic is canted southward in July, meaning that the position of the planets in the evening sky also favors southern viewers. July also presents another interesting mercurial challenge, as Mercury passes in front of the Beehive Open cluster (Messier 44) in the heart of the constellation Cancer on the night of July 3rd/4th.
Venus this summer – higher up at dusk, brilliant Venus rules the evening sky, shining at magnitude -4. Venus is so bright that you can easily pick it up this month before sunset… if you know exactly where to look for it. Venus reaches greatest elongation 46 degrees east of the Sun on August 17th, presenting a featureless half-illuminated disk 25” in diameter near a point known as dichotomy. Venus also flirts with the bright star Regulus (Alpha Leonis) in July, passing a degrees from the star on July 10th. Fun fact: Venus can actually occult (pass in front of) Regulus and last did so on July 7th, 1959 and will do so next on October 1st, 2044.
Jupiter Rules – The King of the Planets, Jupiter rules the sky after darkness falls, crossing the astronomical constellation Libra the Scales. Fresh off of its May 9th opposition, Jupiter still shines at a respectable magnitude -2 in July, with a disk 36” across. Jupiter heads towards quadrature 90 degrees east of the Sun on August 6th, meaning the planet and its retinue of four Galilean moons cast their respective shadows off to one side. In fact, we also see a series of fine double shadow transits across the Jovian cloud tops involving Io and Europa starting on July 29th.
…and Saturn makes five: Stately Saturn never fails to impress. Also just past its June 27th opposition, the rings are still tipped open narrowing down only slightly from last year’s widest angle of 27 degrees, assuring an amazing view. Shining at magnitude 0 and subtending 42” (including rings) in July, Saturn traverses the star-rich fields of the astronomical constellation Sagittarius the Archer this summer. Look at Saturn, and you’re glimpsing the edge of the known solar system right up until William Herschel discovered Uranus on the night of March 13th, 1781.
Enter Mars: We saved the best for last. The Red Planet races towards a fine opposition on July 27th. This is the best approach of Mars since the historic 2003 opposition, and very nearly as favorable: Mars shines at magnitude -2.8 at the end of July, and presents a 24.3” disk. More to come as Mars approaches!
And as with many an opposition, dust storm season has engulfed Mars. Be vigilant, as the ‘Red’ Planet often takes on a sickly yellowish tint during a large dust storm, and this cast will often be apparent even to the naked eye. NASA’s aging Opportunity rover has fallen silent due to the lack of sunlight and solar power, and it’s to be seen if the rover can ride out the storm.
The path of the Moon – The Moon makes a good guidepost as it visits the planets in July. The first eclipse season of 2018 also begins in July, with a partial solar eclipse for Tasmania, SE Australia and the extreme southernmost tip of New Zealand on July 13th and wrapping up with a fine total lunar eclipse favoring Africa, Europe, Asia and Australia on July 27th. Note that this eclipse is only 14 hours after Mars passes opposition… we expect to see plenty of pictures of a ruddy Mars near a Blood Moon eclipse.
The Moon also makes a handy guide to catch each of the planets in the daytime sky… though you’ll need binoculars or a telescope to nab Mercury or Saturn (also, be sure the Sun is physically blocked out of view while hunting for Mercury in the daytime sky!) Here are the respective passes of the Moon near each planet in July:
Unfortunately, the telescopic planets Uranus and Neptune are left out of the July evening view; Uranus is currently crossing the constellation Aries and Neptune resides in Aquarius, respectively. Pluto is, however, currently in the direction of Sagittarius, and you can also wave to NASA’s New Horizons spacecraft en route to its New Year’s Day 2019 KBO destination Ultima Thule (nee 2014 MU69) near the waxing gibbous Moon on the night of July 26th.
And finally, another solar system destination in Ophiuchus the Serpent Bearer beckons telescope owners in July: asteroid 4 Vesta.
All of this is more than enough planetary action to keep planetary observers and imagers up late on forthcoming July evenings.
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!