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Winter on Pluto

Great job everyone on braving our record cold temperatures this week! In some places it got as cold as -16 degrees Fahrenheit! As we work to stay warm, and in some places dig ourselves out of our driveways, lets be thankful that none of us have to endure a winter on Pluto. Current Plutonian temperatures (it’s not even Winter there right now, Summer is just ending) average around -350 degrees Fahrenheit!


Chicago got lots of snow this year! Temperatures dropped to -16 degrees F.

Pluto is an extremely difficult object to study, it is tiny and its far away. It is roughly 7.5 billion miles from Earth, and takes 248.1 Earth years to orbit the Sun. Pluto was officially discovered in 1930 by Clyde Tombaugh. Interestingly enough Tombaugh was only 23 years old at the time, an intern of sorts. He was tasked with comparing images of the night sky taken at two week intervals using a device called a blink comparator. It would flip the images quickly back and forth, stars (which don’t change position relative to each other in that short of a time) would appear stationary. However a moving object like an asteroid or planet would appear to move past the stars as the images were flipped.  Tombaugh discovered Pluto using this method. Since Pluto’s year is 248 Earth years, and it was discovered in 1930, astronomers have yet to observe Pluto through its entire orbital cycle (which won’t happen until  the year 2178).


Tombaugh compared these two plates with the blink comparator and saw Pluto moving relative to the background stars. Source: Lowell Observatory Archives.

We still know very little about Pluto today, our best images are fuzzy, but they can tell us how Pluto changes appearance over time. We know what Pluto’s atmosphere is made out of, which by default can tell us what types of chemicals can most likely be found on the surface. Every chemical has its own unique spectrum (pattern of visible light emitted by the electrons in the atoms as they gain then release energy). By studying the spectra of Pluto, astronomers can pin point the chemicals found there.


Highest resolution images of Pluto taken by Hubble Space Telescope. Source:

Most recent studies of Pluto have monitored the thickness of its atmosphere. How do they do this, you ask? They monitor the light from a star that Pluto passes in front of. This is called a stellar occultation. Studying a stellar occultation of a tiny object that is 7 billion miles away is a very complex and delicate process. Basically astronomers observe changes in the star’s light as it is filtered through Pluto’s atmosphere, these changes can tell us about the atmosphere’s composition and thickness.

What is Plutonian winter like? We don’t entirely know. Recent theories suggest that as Pluto continues to get farther from the Sun in its orbit (as it is doing) and enters into winter time, the surface temperature will drop. This would then cause the atmosphere to freeze out and fall to the ground as a fine snow of nitrogen, carbon monoxide, methane, and other chemicals.


In “The Gravity Factor” it’s the next century, people live on Pluto in a large base station. For leisure, they snowmobile and ski around the snow covered surface. Source: LASM.

In fact, LASM is partnering with Houston Museum of Natural Science to produce a planetarium show called “The Gravity Factor”. It takes place in the next century, and explores the possibility of colonizing the planets and moons, and the type of work and life people would have in the different places. LASM is contributing to the show by producing a segment about astronauts living on Pluto during winter time after the annual snow fall. In the show astronauts living at the Pluto base occupy their free time with snowmobiling and rocket-powered skiing over the snow drifts on the surface. A fun prospect!

Most recent research has suggested an alternative to this theory. Astronomers have been observing Pluto’s atmosphere expecting to see evidence of it thinning as the “snow storm” begins, however they have observed the opposite. Pluto’s atmosphere is staying the same, in fact it appears to be getting thicker. Some scientists believe that this indicates that the snow storm isn’t going to happen (as it should have started by now). They conclude that this is an indication of thermal inertia, the ability for Pluto to retain energy absorbed from the Sun during the Summer. Pluto has higher thermal inertia than previously thought, so its atmosphere is not cooling as quickly as scientists would have expected, despite the planet approaching its Winter season.


Artist’s conception of the New Horizons Spacecraft.

So what does all of this mean? Our knowledge of Pluto is constantly changing as we learn more about this distant world. The New Horizons spacecraft is hurtling towards Pluto at a whopping 31,000 miles per hour, making it one of the fastest spacecraft ever. It will reach Pluto in 2015 and get an up close view of the dwarf planet. Astronomers eagerly anticipating data and imagery from New Horizons will help them gain a better understanding of Pluto. The general public is excited too, for the first time we’ll be able to see what Pluto looks like up close!

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