Scratching Beneath the Surface

Posted on Wed, May 16, 2012
  • by: Michelle Selvans

What's inside a planet? What instruments do scientists use to figure it out? And what clues does a planet's surface give us? On Saturday, April 21, Lisa Walsh and I, scientists from the Museum's Center for Earth and Planetary Studies, invited visitors to the National Air and Space Museum's Explore the Universe Family Day to think about these questions, through two hands-on activities relating to our research into tectonics on Mercury. As the MESSENGER (Mercury Surface, Space ENvironment, Geochemistry, and Ranging) spacecraft starts its second Earth year in orbit around Mercury, we interacted with approximately 900 kids and kids-at-heart, asking them to figure out what was inside balloons by using tools analogous to those used in planetary science (scales, magnets, and, slightly less analogously, a good hard shake), and to piece together a puzzle made from images of Mercury's surface. Evidently you can't just do one piece of the puzzle, because often people stuck around until the whole thing was put together, talking with Lisa about MESSENGER results and her own research.

Explore the Universe Family Day

Lisa Walsh talks with young visitors about her research during the Explore the Universe Family Day at the National Air and Space Museum in Washington, DC on April 21, 2012.

Lisa studies wrinkle ridges, which form on the surface of a planet when rock layers are crunched in from the sides, like scuffing in the edge of a rug with your shoe. This causes the layers to fault and fold, leaving ‘wrinkles’ in the surface. Wrinkle ridges are found throughout the inner Solar System, and have been mapped in greater detail on Mercury during the last year than was possible before the arrival of MESSENGER. Lisa wants to understand why wrinkle ridges on Mercury are so much larger than those on the Earth’s Moon, and what they look like beneath the surface on both planetary bodies. The balloons were seemingly irresistible, since holding one out to any passing kid and asking them if they wanted to figure out "What's Inside?" usually resulted in them spending the time to figure out all six, whether with a cohort of siblings or fellow boy scouts, or with a parent as engaged as they were. The balloons separately contained sand, iron filings, yarn, a magnet, a marble, and beads, with the iron filings being the most popular for further investigation. As the afternoon progressed, I frequently interacted again with previous visitors to the table, when they brought back friends or family to check it out.

Explore the Universe Family Day

Dr. Michelle Selvans helps young investigators as they determine the interior materials of balloons, using scales, magnets, and a good shake.

Every participant left the table with something in hand (sticker, button, poster, or a model of MESSENGER to put together at home). But even more gratifying was seeing everyone leave with an appreciation for who studies the planets in our Solar System (we do!), how they’re studied (for example, through missions like MESSENGER, using instruments like the multi-spectral and multi-resolution camera we depend on for our research), and why they’re studied. Why do we as a species study our neighbors in space? Why do we look for Earth-like planets around neighboring stars (the ongoing Kepler mission)? Why even study our own planet, its life and climate and geology? If you ask ten people these same questions, you could very well get ten different answers. We all have our own reasons for being interested in the world around us. Maybe we’re concerned about how to protect people from natural hazards like hurricanes or earthquakes. Maybe we want to know if we are ‘alone’ in the universe, or whether life in any form exists elsewhere. Maybe we are awed by the beauty, intricacy, and divinity of the physical universe and just want to commune with it more intimately. Maybe, like for myself, practical, personal, and spiritual reasons all factor in.

Beethoven Basin

Mosaic of high-resolution MESSENGER images taken at dawn, showing several newly-identified tectonic features (arrows). Made by Dr. Michelle Selvans.

I study large faults on Mercury, which cast long shadows at dawn and dusk, so they’re easy to see when we take pictures at those times of (Mercury) day. They’ve been mapped previously all across the surface (using images from before MESSENGER went into orbit), and appear to be placed in a pattern that suggests global-scale stresses. As we collect pictures at dawn and dusk, I am mapping the greater number of scarps that are being revealed, to see if the pattern holds. I also use the elevation maps that other MESSENGER Science Team members are producing, in order to understand the shapes of the most intriguing faults (measured across the scarp). Those shapes will help me model the fault structure below the surface, in order to understand the shallow structure of Mercury’s crust. That’s a little bit of what I do here in the Center for Earth and Planetary Studies. What would you want to know about Mercury if you were in my place? Or about any other planet in our Solar System, or beyond? Why are you interested in those questions? And how could we go about figuring out the answers? We would like to thank everyone who participated in the April 21 Family Day fun, as well as the MESSENGER spacecraft Education Team for developing the puzzle, and the Lunar and Planetary Institute Education Team for the inspiration behind the balloon activity (the Investigating the Insides module, on their Explore! website).