Studying Pluto from 3 Billion Miles Away

Today’s blog post is from Amanda Zangari, a member of the New Horizons’ Geology, Geophysics and Imaging Team. She works at Southwest Research Institute in Boulder, Colorado.

My name is Amanda Zangari, and I’ve been a postdoc on the New Horizons mission for 2 ½ years. It’s been a wild ride, and it’s amazing how the time has flown by.

In the 85 years between Pluto’s discovery and the New Horizons flyby, we’ve learned enough about the Pluto system to fill a textbook and several scientific journals. Telescopes, cleverness, and lots and lots of math enabled us to figure out many of the basics of the Pluto-Charon system before New Horizons arrived, even if Pluto was just 11 pixels across in the best images taken from Earth. We knew that Pluto was brownish-red with dark and light patches, and that the surface was covered with nitrogen, methane and tholins—brown gunk made when UV light hits nitrogen and methane.

We also saw a patch of carbon monoxide at Pluto’s brightest spot, which turned out to be the area that forms the left side of Pluto’s ‘heart,’ which we informally call Sputnik Planum. We determined that Pluto’s moon Charon has a surface that is instead made of water ice and is gray in color. (Charon’s red “hair” at the north pole was a surprise!)  We confirmed that we’d found all of Pluto’s small satellites. We also knew that Charon did not have an atmosphere and Pluto did, and we’ve been studying it for over 25 years.

New Horizons finally brought Pluto and Charon into focus, and we got to see just how much of that patchy map — the result of measuring reflected light from Pluto at different angles — turned into mountains, ice flows and the bladed terrain that hasn’t been seen anywhere else in the solar system.

I like to think of the whole experience as getting to look at the answer in the back of the book. To extend the back-of -the-book analogy, like many textbooks, we are only getting half the answer. With Pluto, that missing element isn’t the even problems, but time. Our greatest images are from the July 14 closest encounter, and thus we only have one glimpse of one side of Pluto on one day. Yet these images show Pluto as an active world, undergoing volatile-ice transport and change.

One of my big interests is tying past ground-based observations together and comparing them to what has been seen by New Horizons. I’ve been working on several different projects to this effect.

The first project took place during New Horizons’ journey to Pluto. I compiled all the available research journal articles to gather what measurements had been taken, and catalogued what longitude and latitude scale had been used to make measurements. In 2009, the IAU reversed the direction of Pluto’s pole, reversing both the direction of longitude and latitude on Pluto. Without that change, Pluto’s ‘heart’ would be upside down! Even before the change, latitude and longitude had been expressed in multiple different formats, official or not.

Pre-flyby maps of Pluto
Before: This is an example of the best pre-flyby maps of Pluto, made from images from the Hubble Space Telescope in 2002 and 2003, published in 2010. Credits: NASA/JHUAPL/SwRI/Marc Buie
Map of Pluto
After: Map of Pluto from New Horizons. Credits: NASA/JHUAPL/SwRI

The next project I’m working on involves comparing measurements of Pluto’s brightness taken by the New Horizons spacecraft between 2013 and 2015 against Hubble Space Telescope observations from 2002 and 2003. We’d like to see how Pluto’s surface has changed in that time, as there is already possible evidence of change on Pluto between the 90s and the early 2000s.

Finally, as you can see in the figure below, I’m looking at stellar occultations of Charon, using the Charon topography New Horizons imaged, to check if known features influenced these past results.

Charon occultation from 2005
Charon occultation from 2005. The map New Horizons made of Charon is overlaid with new data. I’m looking to see if any of the measurements of Charon’s size were affected by the topography seen by New Horizons. Credits: NASA/JHUAPL/SwRI/Michael Person/Amanda Zangari

Making ground-based comparisons to New Horizons is extremely important. Until we go back to Pluto (I’d love to see an orbiter), the only way we’ll be able to watch Pluto evolve is from Earth-based telescopes.

If we’ve learned anything from the flyby, we’ve learned that Pluto is worth continuing to watch.

Dr. Amanda Zangari
Amanda Zangari
Credit: Kyle Cassidy