#year of pluto

Walking to Pluto with Kids.

This is the Year of Pluto and Lowell Observatory in Flagstaff, Arizona where Pluto was discovered is celebrating the 85th anniversary in cosmic style and walking to Pluto is only part of the fun.

An artful cosmic cat guards the Pluto Telescope at Lowell Observatory on Mars Hill above Flagstaff, AZ.

I have always had a soft spot in my heart for Pluto because when I was in the fifth grade I played…

So near liv’d LOWELL to the shining skies, In crystal air with upward soaring sight, That he must needs a little farther rise, And dwell among his cherish’ orbs of light.

His soul to Heav’n enduring kinship own’d, Pure with the grace of high ethereal thought; Celestial spheres a graceful love inton’d, And friendly stars his closer presence sought.

Upon the earth our strains threnetic mourn With poignant sorrow his untimely loss; But he, through realms of glad refulgence borne, Adds a new brilliant to the Southern Cross!

Published initially in Excelsior, March 1917 (v1:n1) p 3. Editor Verna McGeoch, Greenwich NY. [This reproduction is found in the 1977 first ed. of A Winter’s Wish p 103 by Whispers Press]. Lowell was the most famous astronomer of the age. Writing about this poem in the United Amateur, May 1917 (v16:n8), HPL said, “ ‘Percival Lowell’ by Howard Phillip Lovecraft, is an abominably dull elegiac piece of heavy verse.”

Happy New Year!  Welcome to 2015, the year of Pluto!  It’s hard to believe that we’re so close to encounter time!  Things are going to be picking up quite a bit around here.

  So, today I just got back from holiday break with my family back east and found a nice holiday present from my boss, New Horizons Principal Investigator Alan Stern sitting on my desk.

  The note says that it’s a Pluto stress ball, sold at Lowell Observatory in Flagstaff, Arizona (where Pluto was discovered in 1930 and well worth a visit).  Now, I know complaining about Christmas gifts is pretty rude, but this is not a very accurate depiction of Pluto.  Let’s talk about why.

  Firstly, the stress ball is the wrong color.  While we can’t yet see Pluto clearly, indirect mapping and spectroscopy tell us that it’s reddish in color and has bright and dark patches.  This stress ball is gray and the same color and brightness all around, like, well, Charon.

  The stress ball is also covered in craters.  We don’t know if Pluto has craters or not. It might have some, or there might be frequent resurfacing, and Pluto might be full of mountains, canyons and plumes.

  There are three major types of craters: simplex, complex and multi-ring basins.  Which one you see depends on how big the thing that crashed was.  Small impactors make simple, bowl shaped craters.  If the impactor is big enough, the crater will be more pie-pan shaped and there will be a peak in the middle, and that’s a complex crater.  A humongous collision will make a multi-ring basin, like Orientale on the Moon.  All of the craters on the stress ball are simple, and some of them are, well, a bit big to be simple craters. 

  In general, the simple craters are about 5 times wider across than they are deep, and complex craters and basins are even shallower. Based on what we've seen on moons of Saturn and Uranus, we predict that Pluto's craters would be 10 times wider than they are across before they get shallower too.  Based on highly scientific measurements from sticking my pencil eraser in some crater and measuring them with the ruler on my protractor, I’ve determined that these craters are only 3-4 times wider than they are deep, in other words, too deep!  Making craters deeper requires different surface properties, and so perhaps Pluto and Charon are actually made of squishy foam?

  The craters are also very well preserved.  Alan, fellow postdoc Simon Porter and I have written a paper predicting what types of craters on Pluto and Charon we’ll see and what different scenarios will tell us about the makeup of Pluto’s surface and the population of objects available to hit them. 

We find that escape erosion (the idea that Pluto is losing its surface gradually to space) and relaxation (due to meltier nitrogen at Pluto temperatures) might cause Pluto’s craters to either shrink, flatten or disappear altogether in just a short amount of time.  This won’t happen on Charon because it’s covered in rock-hard water ice (I explain why the two surfaces are so different here).  If something hits Charon and takes a big chunk out of it, unless there’s tectonic activity on Charon or something, that big hole in the ground will be there forever.

  Actually, the idea that there’s a big chunk missing out of Charon isn’t unheard of.  In 2005, Charon passed in front of a bright star (aka a stellar occultation), and folks from the MIT-Williams occultation group caught it from several sites (I used to work for this collaboration, but this was before my time). There were some anomalies that were consistent with either a timing discrepancy between measurements from the SOAR and Gemini Telescopes (check out Figure 2), or there’s a large, disfiguring crater on Charon that makes it not otherwise round.

Personally, I think it’s a timing discrepancy, but we’ll be able to track where that spot was on Charon and learn the answer soon.