More than 100 km of Liquid Water Beneath Pluto’s Surface

Pluto's famous "heart," half of which was created by an ancient impact, offers clues about a possible subsurface ocean.

What lies beneath Pluto’s icy heart? New research indicates there could be a salty “Dead Sea”-like ocean more than 100 kilometers thick.

“Thermal models of Pluto’s interior and tectonic evidence found on the surface suggest that an ocean may exist, but it’s not easy to infer its size or anything else about it,” said Brandon Johnson from Brown University. “We’ve been able to put some constraints on its thickness and get some clues about composition.”

Research by Johnson and his team focused Pluto’s “heart” – a region informally called Sputnik Planum, which was photographed by the New Horizons spacecraft during its flyby of Pluto in July of 2015.

New Horizons’ Principal Investigator Alan Stern called Sputnik Planum “one of the most amazing geological discoveries in 50-plus years of planetary exploration,” and previous research showed the region appears to be constantly renewed by current-day ice convection.

The heart is a 900 km wide basin — bigger than Texas and Oklahoma combined — and at least the western half of it appears to have been formed by an impact, likely by an object 200 kilometers across or larger.

Johnson and colleagues Timothy Bowling of the University of Chicago and Alexander Trowbridge and Andrew Freed from Purdue University modeled the impact dynamics that created a massive crater on Pluto’s surface and also looked at the dynamics between Pluto and its moon Charon.

The two are tidally locked with each other, meaning they always show each other the same face as they rotate. Sputnik Planum sits directly on the tidal axis linking the two worlds. That position suggests that the basin has what’s called a positive mass anomaly — it has more mass than average for Pluto’s icy crust. As Charon’s gravity pulls on Pluto, it would pull proportionally more on areas of higher mass, which would tilt the planet until Sputnik Planum became aligned with the tidal axis.

So instead of being a hole in the ground, the crater actually has been filled back in. Part of it has been filled in by the convecting nitrogen ice. While that ice layer adds some mass to the basin, it isn’t thick enough on its own to make Sputnik Planum have positive mass.

The rest of that mass, Johnson said, may be generated by a liquid lurking beneath the surface.

Johnson and his team explained it like this:

Like a bowling ball dropped on a trampoline, a large impact creates a dent on a planet’s surface, followed by a rebound. That rebound pulls material upward from deep in the planet’s interior. If that upwelled material is denser than what was blasted away by the impact, the crater ends up with the same mass as it had before the impact happened. This is a phenomenon geologists refer to as isostatic compensation.

Water is denser than ice. So if there were a layer of liquid water beneath Pluto’s ice shell, it may have welled up following the Sputnik Planum impact, evening out the crater’s mass. If the basin started out with neutral mass, then the nitrogen layer deposited later would be enough to create a positive mass anomaly.

“This scenario requires a liquid ocean,” Johnson said. “We wanted to run computer models of the impact to see if this is something that would actually happen. What we found is that the production of a positive mass anomaly is actually quite sensitive to how thick the ocean layer is. It’s also sensitive to how salty the ocean is, because the salt content affects the density of the water.”

The models simulated the impact of an object large enough to create a basin of Sputnik Planum’s size hitting Pluto at a speed expected for that part in the solar system. The simulation assumed various thicknesses of the water layer beneath the crust, from no water at all to a layer 200 kilometers thick.

The scenario that best reconstructed Sputnik Planum’s observed size depth, while also producing a crater with compensated mass, was one in which Pluto has an ocean layer more than 100 kilometers thick, with a salinity of around 30 percent.

“What this tells us is that if Sputnik Planum is indeed a positive mass anomaly —and it appears as though it is — this ocean layer of at least 100 kilometers has to be there,” Johnson said. “It’s pretty amazing to me that you have this body so far out in the solar system that still may have liquid water.”

Johnson he and other researchers will continue study the data sent back by New Horizons to get a clearer picture Pluto’s intriguing interior and possible ocean.

Further reading: Brown University, New Horions/APL

The post More than 100 km of Liquid Water Beneath Pluto’s Surface appeared first on Universe Today.

Scientists Assemble Fresh Global Map of Pluto Comprising Sharpest Flyby Images

NASA’s New Horizons mission science team has produced this updated panchromatic (black-and-white) global map of Pluto. Credits: NASA/JHUAPL/SWRI

The science team leading NASA’s New Horizons mission that unveiled the true nature of Pluto’s long hidden looks during the history making maiden close encounter last July, have published a fresh global map that is the sharpest glimpse yet of the mysterious, icy world.

The newly updated global Pluto map is comprised of all the highest resolution images transmitted back to Earth thus far and provides the best perspective yet.

Click on the lead image above to enjoy Pluto revealed at its finest thus far. Click on this link to view the highest resolution version.

Prior to the our first ever flyby of Pluto barely 8 months ago, the planet was nothing more than a fuzzy blob with very little in the way of identifiable surface features – even in the most powerful telescopic views lovingly obtained from the Hubble Space Telescope (HST).

Dead center in the new map is the mesmerizing heart shaped region informally known as Tombaugh Regio, unveiled in all its glory and dominating the diminutive world.

The panchromatic (black-and-white) global map of Pluto published by the team includes the latest images received as of less than one week ago on April 25.

The images were captured by New Horizons’ high resolution Long Range Reconnaissance Imager (LORRI).

The science team is working on assembling an updated color map.

During its closest approach at approximately 7:49 a.m. EDT (11:49 UTC) on July 14, 2015, the New Horizons spacecraft swoop to within about 12,500 kilometers (nearly 7,750 miles) of Pluto’s surface and about 17,900 miles (28,800 kilometers) from Charon, the largest moon.

The map includes all resolved images of Pluto’s surface acquired in the final week of the approach period ahead of the flyby starting on July 7, and continuing through to the day of closest approach on July 14, 2015 – and transmitted back so far.

The pixel resolutions are easily seen to vary widely across the map as you scan the global map from left to right – depending on which Plutonian hemisphere was closest to the spacecraft during the period of close flyby.
They range from the highest resolution of 770 feet (235 meters), at center, to 18 miles (30 kilometers) at the far left and right edges.

The Charon-facing hemisphere (left and right edges of the map) had a pixel resolution of 18 miles (30 kilometers).

“This non-encounter hemisphere was seen from much greater range and is, therefore, in far less detail,” noted the team.

However the hemisphere facing New Horizons during the spacecraft’s closest approach on July 14, 2015 (map center) had a far higher pixel resolution reaching to 770 feet (235 meters).

Coincidentally and fortuitously the spectacularly diverse terrain of Tombaugh Regio and the Sputnik Planum area of the hearts left ventricle with ice flows, mountains and river channels was in the region facing the camera and sports the highest resolution imagery.

See below a newly released shaded relief map of Sputnik Planum.

“Sputnik Planum – shows that the vast expanse of the icy surface is on average 2 miles (3 kilometers) lower than the surrounding terrain. Angular blocks of water ice along the western edge of Sputnik Planum can be seen “floating” in the bright deposits of softer, denser solid nitrogen,” according to the team.

Pluto is the last planet in our solar system to be visited in the initial reconnaissance of planets by spacecraft from Earth since the dawn of the Space Age.

New Horizons remains on target to fly by a second Kuiper Belt Object (KBO) on Jan. 1, 2019 – tentatively named PT1, for Potential Target 1. It is much smaller than Pluto and was recently selected based on images taken by NASA’s Hubble Space Telescope.

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

Ken Kremer

The post Scientists Assemble Fresh Global Map of Pluto Comprising Sharpest Flyby Images appeared first on Universe Today.

“X” Marks the Spot of Convective Churning on Hot Pluto

“X” marks the spot in this image transmitted to Earth on Dec. 24, 2015 from the Long Range Reconnaissance Imager (LORRI) from NASA’s New Horizons’ showing the highest-resolution swath of Pluto at the center of Sputnik Planum, the informally named plain that forms the left side of Pluto’s “heart.”  The pattern of polygonal cells stems from the slow thermal convection of the nitrogen-dominated ices.  Also visible is a a dirty block of water ice “floating” in denser solid nitrogen.  Credits: NASA/JHUAPL/SwRI

“X” marks the spot that’s illustrative of “convective churning” resulting from subsurface planetary heating, as seen in a fascinating new super high resolution image received from NASA’s New Horizons spacecraft on Christmas Eve, Dec. 24, 2015. Its situated at the very center of the left ventricle of Pluto’s huge “heart” – an icy flow plain that’s informally named “Sputnik Planum.”

The “X” feature – see image above – is located in an area of intersecting cells, shaped like polygons, on the plains of “Sputnik Planum” which are mostly comprised of frozen nitrogen ices.

So what’s really piqued the interest of scientists leading the New Horizons mission, is that the “X” feature is a residue of “convective churning” or internal heating and it has changed over time.

Indeed the “X” is found at what appears to be the melted remnants of a quadruple junction of the polygonal or cellular patterns, that dominate Sputnik Planum. And it’s not tiny!

“This part of Pluto is acting like a lava lamp,” said William McKinnon, deputy lead of the New Horizons Geology, Geophysics and Imaging team, from Washington University in St. Louis, “if you can imagine a lava lamp as wide as, and even deeper than, the Hudson Bay.”

The polygonal cell features are believed to have arisen over time from the slow thermal convection of the icy plains that are composed of a slushy mixture of mostly nitrogen ices along with some water ice mixed in.

The image was taken by the probes telescopic Long Range Reconnaissance Imager (LORRI) at a distance of approximately 10,000 miles (17,000 kilometers), about 15 minutes before New Horizons’ closest approach to Pluto.

Scientists currently interpret the dark patch near the top of the image to be a dirty water “iceberg” that’s “floating in denser solid nitrogen, and which has been dragged to the edge of a convection cell.” Also visible are thousands of surface pits arising from sublimation.

New Horizons made history when it became Earth’s first emissary to hurtle past the small planet on July 14, 2015.

Pluto – also now known as the ‘Other Red Planet’ – was the last unexplored planet in our solar system.

The LORRI image nearly completes a mosaic of New Horizons’ highest-resolution images taken of Pluto along a swath at the center of Sputnik Planum. They have a resolution of about 250-280 feet (77-85 meters) per pixel – “revealing features smaller than half a city block on Pluto’s surface,” according to the team in a NASA statement.

The newly released images, from NASA and the New Horizons team, illustrate the polygonal or cellular pattern of the plains, which “are thought to result from the convective churning of a deep layer of solid, but mobile, nitrogen ice.”
The LORRI images also reveal numerous, active triple junctions spread across the terrain.

Based on the data returned thus far, researcher say “the pattern of the cells stems from the slow thermal convection of the nitrogen-dominated ices that fill Sputnik Planum.”

“Computer models by the New Horizons team show that these blobs of overturning solid nitrogen can slowly evolve and merge over millions of years.”

The nitrogen ices rise and sink over time forming ridges along the edges of the polygonal cells that change with time due to the subsurface heating.

The polygons range in width from to 25 miles (16 to 40 kilometers). They are somewhat dome-like and rise slightly about 100 yards (100 meters) in the center.

Researchers say Sputnik Planum itself is likely several miles or kilometers deep in some places and the icy plains are a few miles lower that the surrounding areas on Pluto.

“The solid nitrogen is warmed at depth by Pluto’s modest internal heat, becomes buoyant and rises up in great blobs, and then cools off and sinks again to renew the cycle.”

The “Sputnik Planum” region dominates the left side of Pluto’s “heart-shape” feature informally dubbed “Tombaugh Regio.”

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

“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,” says 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.”

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.

During New Horizons flyby on July 14, 2015, it discovered that Pluto is the biggest object in the outer solar system and thus the ‘King of the Kuiper Belt.”

The Kuiper Belt comprises the third and outermost region of worlds in our solar system.

New Horizons remains on target to fly by a second Kuiper Belt Object (KBO) on Jan. 1, 2019 – tentatively named PT1, for Potential Target 1. It is much smaller than Pluto and was recently selected based on images taken by NASA’s Hubble Space Telescope.

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

Ken Kremer

The post “X” Marks the Spot of Convective Churning on Hot Pluto appeared first on Universe Today.

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