Pluto and Earth

The first thought I had watching the press conference on the initial images from the New Horizons flyby of Pluto was how much accessible these events are to the public than in the days of Voyager.  During the 1980’s, unless you had a NASA press pass, you did not get to watch mission updates live.  No twitter feeds to tell you right away when telemetry is being received, no websites to go back and review the images at your leisure.  And you had to wait at least a year, maybe more, for astronomy textbooks to be updated.  What you got was short segments on the nightly news such as this:

One of my favorite teaching techniques is to compare the surface features of planets to things we are familiar with here on Earth to give it proper perspective.  And that seems to me to be a good place to start with the first images released today.

Lets begin with the mountains located near the now famous heart-shaped region of Pluto.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

This image was taken while New Horizons was 77,000 km away from Pluto.  That’s 10 times farther away than the closest approach and gives a good idea what to look forward to as more images are released.

The tallest of these mountains are about 11,000 feet (3,500 m).  How does this compare to Earth?  These are less than half as tall as Mt. Everest which clocks in at 29,029 feet.  Still, pretty impressive mountains considering how small Pluto is.  The height of these mountains are similar to Mt. Hood in Oregon.

Image: Wiki Commons

The first age estimate of these mountains are about 100 million years.  That sounds pretty old.  In fact, dinosaurs were roaming around on Earth when these mountains formed.  In geological terms, this is pretty young, only 2% the age of the Solar System (4.5 billion years).  How do we know these mountains are young?  By the lack of craters in the region.  The less craters there are, the younger a surface is.  These mountains are younger than the Alps which are 300 million years old.  They are older than the Himalayan Mountains which formed as the Indian Sub-Continent plowed into Asia 25 million years ago.

Mountains on Earth are the result of plate tectonics.  At this very early juncture, planetary scientist have their work cut out for them as none of the current models can account for such mountain formation on an icy outer Solar System body in the absence of tidal flexing.  It is thought that the mountains are regions of water-ice bedrock poking through the methane ice surface.  Methane ice is too weak to build mountainous structures.

Below is Pluto’s largest moon Charon:

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

The outstanding feature here is the large canyon in the upper right corner.  This canyon is 4 to 6 miles (7 to 9 km) deep.  The Grand Canyon’s greatest depth is a little over a mile.  This channel is comparable to the deepest reaches of the Pacific Ocean, the Mariana Trench, that lies about 6.8 miles below sea level.  It’s interesting to consider than more humans have walked the surface of the Moon (12) than have reached the bottom of the Mariana Trench (3).  To be fair, no nation has ever decided to spend $150 billion (2015 dollars) and employ 400,000 people to reach the Mariana Trench, such as the United States did during the Apollo program.

This image maps methane on the surface of Pluto.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

The New Horizons press release describes the greenish area of Pluto’s North Pole as methane ice diluted in nitrogen ice.  Does that sound odd?  Typically, we see neither of these substances in a solid state on Earth.  Methane and nitrogen are known as volatiles, which means they take gaseous form at room temperature.  As you may have surmised, Pluto is not at room temperature.  The freezing point of methane is -295.60 F (-1820 C) on Earth.  The freezing point of nitrogen is even lower at -3460 F (-2100 C).  These figures are lower on Pluto as the atmospheric pressure does not match that of Earth.  The temperature of Pluto ranges from -3870 to -3690 F (-2330 to -2230 C).  Yeah, the outer reaches of the Solar System are pretty chilly.

In our day to day lives, you may be familiar with methane as the main component of natural gas.  You may have learned about it first as a source of middle school humor.  While methane is a gas on Earth, the Saturn moon Titan is cold enough for it to be a liquid.  Below is an image of methane lakes on Titan.  Instead of raining water, you could dance in the methane rain on Titan.  Earth and Titan are the only bodies in the Solar System to have stable liquid lakes on the surface.

Credit: NASA/JPL-Caltech/ASI/USGS

Neptune has trace amounts of methane in its atmosphere.  Methane has the property of absorbing red light and scattering blue light.  The result is the rich blue hue of Neptune as first seen in the 1989 Voyager flyby:

Credit: NASA

Methane also absorbs infrared light at certain wavelengths.  The methane profile image of Pluto was produced by measuring infrared absorption from surface methane.   When methane absorbs infrared light at these wavelengths, the infrared energy is converted in vibrational motion in the molecular bonds.  Once the molecule settles down, the energy is released back out as infrared light.  We cannot see infrared light, but we feel it as heat.  In the atmosphere, some of this heat is directed back towards the Earth, warming the surface.  In other words, methane is a greenhouse gas like carbon dioxide and water vapor.

And for that, we should be grateful.  Without greenhouse gasses, the Earth would be 600 F colder (like the Moon), and human life would not be possible.  However, you can have too much of a good thing.  As temperatures rise in the Arctic warming up the permafrost, methane that has been locked up for thousands of years as frozen, undecomposed plant life, could be released into the atmosphere.  When you consider the Arctic region has been most affected by rising global temperatures, then you can understand why climate scientists are concerned about this scenario.

On Friday, New Horizons should be releasing the first color images from the flyby.  Should be quite an interesting week.

*Image on top shows part of Pluto’s heart region the mountain closeup was taken.  Credit:  NASA

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