A guest blog by Benjamin Palmer.
Graphite is a common mineral on Earth. // Henk Caspers/Naturalis
Take a thoughtful glance around you. What do you see? Perhaps you’re ensconced in an office, fingers poised on a laptop’s trackpad, screen illuminating the paint on the walls. Maybe you’re gazing out the kitchen window, observing passing cars cast in the wash of street lamps below. You might even be out under the stars, eyes drawn from your Smartphone to the cosmic depths above. Three random scenarios, Venn-diagramed by unique grains of commonality. Hexagonal, crystalline grains to be precise. In every object just sighted, say “hello” to graphite, the transformative mineral that permeates modern astronomy.
What’s in a name?
Graphite derives its linguistic origins from the Greek word graphein, defined as “to write.” In 1789, geologist Abraham Gottlob Werner applied the “ite” suffix, earning the rebranded “graphite” a smooth new translation: “writing stone.” It’s a fitting title for an element written in astronomy’s past, present, and future.
From a mineral standpoint, graphite travels first class, literally. This form of crystalline carbon maintains both semimetal and native element components. Appearance wise, envision a silky iron-black or steel gray specimen, steeped in hexagonal, dihexagonal, and dipyramidal symmetry and shining with metallic luster.
Primarily forming in metamorphic and igneous rocks (meteorites contain quantities as well), graphite exhibits striking atomic structure. Nature’s layered, planar engineering weaves carbon atoms into honeycomb lattices, spaced 0.142 nanometers (nm) apart, stacked like Belgian waffles in planes with 0.335nm of distance separation. Within those planes, covalently bonded atoms (those that share electron pairs) connect with just three out of four bonding points, leaving an open field for the fourth electron. Sauntering between planes, this fourth electron unlocks graphite’s electrical conductivity.
But that matrix holds far more tricks up its scientific sleeve. Graphite’s crystalline atomic web promotes high thermal tolerance, low friction levels, light weight, and composite-blend potential, all beneficial to astronomy.
Humans have been obsessed with those potent properties for millennia. Long before contemporary astronomers, Neolithic (4th Millennium BC) graphite pigments from Grecian Sitagroi and the Giuleşti-Mariţa culture (present day Romania) adorned pottery pieces. Britain’s Royal Navy once utilized graphite-lined molds to improve the ballistics of cannonballs, heavily influencing her oceanic empire.
In today’s society, graphite is simply everywhere. In golf clubs and tennis rackets, brake linings and electrodes, DNA sequencers and nuclear reactors, graphite’s influence reigns supreme. At least a dozen scientific disciplines and a myriad of industries lay claim to this carbon-based gold. And astronomy doesn’t hesitate to join the mix.
From the Ground … Up
Almost overnight, the secret was out. As natural philosophy morphed into astrophysics, observational astronomers demanded new tools to decipher a growing chain of cosmic enigmas. Graphite provided a unique answer. Swiftly converting, enhancing, and fusing aspects of this “wonder mineral,” astrophysical engineers turned graphite from rock in the ground to eye in the sky. And its cosmological stock continues to rise.
The story begins with aeronautics. In seven decades, the aerospace revolution took us from looking there to being there, an omnipresent race for space increasingly ambitious in scope. But there’s a catch: space isn’t cheap. At $2,000 to $13,000 per orbital pound, tossing satellites, scopes, and supply ships beyond Earth’s atmosphere necessitates light, efficient vehicles. It almost makes gas pump prices appealing!
But here’s where the symbiotic graphite/astronomy relationship gets interesting. Remember those honeycomb lattices? And that composite blend potential? Enter graphite-epoxy composites, the star material of applied aeronautics.
Introducing high specific strength and stiffness with low coefficients of thermal expansion, graphite-epoxy composites are the go-to choice for spacecraft construction. Molded to a plethora of substructures, they can be found in antennas, booms, mirror cells, support frames, and spectrometers, and that’s merely scratching the instrument surface.
Early satellites like Intelsat IV and Anik readily demonstrated graphite-epoxy’s power in geosynchronous orbital communication. But NASA’s Viking program really put graphite on the (martian) map, utilizing a five-foot graphite-epoxy skin antenna for communications. Contemporary probes including NASA’s Dawn and MAVEN continue the graphite quest. Everyday, countless new navigational, astrophysical, and cosmological satellites clamor for such crucial material.
Strong, yet supple, graphite composites, alongside neighboring silicon carbides (SiC) reflect perfection. We speak of mirror cells and support structures, the vivid life force of large space-based reflectors. The iconic Hubble Space Telescope (HST) leads the charge, incorporating graphite-epoxy in a 252-pound skeletal truss, grounding all optical systems. HST sports twin Defense Advanced Research Projects Agency antenna booms, exploiting graphite’s radio conduction properties to better collect signals.
Hubble is far from alone. Graphite-epoxy or SiCs traverse the skies, in ESA’s Herschel Space Observatory and the audacious Gaia Telescope. And in a visage of things to come, NASA’s handsome James Webb Space Telescope deploys a graphite composite backplane, responsible for holding the 6.5-meter primary mirror plus 2.5 tons of hardware.
The visible spectrum doesn’t monopolize graphite applications. X-ray telescopes liberate graphite’s functionality as well. NASA’s pioneering Orbiting Solar Observatory (OSO) was an early proving ground, culminating in OSO 8, featuring a Graphite Crystal X-ray Spectrometer that analyzed various X-ray energy ranges.
NASA’s Swift X-ray telescope utilizes an X-ray imager composed of a 508mm tube forged in graphite fiber and cyanate ester. In the near future, Russia’s Spectrum-X-Gamma will use mosaic graphite crystals to study X-ray sources
Graphite’s aforementioned thermal tolerance found a home in its most famous patron, NASA’s Space Shuttle. Laminated graphite-rayon sheeting adorned the Shuttle’s nose cone and leading wing edges, part of the Thermal Protection System that brought our astronauts home.
Mineral it may be, but in aerospace, graphite’s a GEM — a graphite-epoxy motor — a solid-fuel rocket commonly used for space payload transportation. Graphite-epoxy casings lined Oribital ATK’s Delta II-IV rockets, and a similar set-up will drive United Launch Alliance’s Atlas V and Vulcan boosters to new heights.
Let’s shift gears for a second. If minerals are made of star stuff, shouldn’t graphite actively interact with our universe? With all these sophisticated gadgets, might mankind witness such activity? If you answered yes, great call. Observer and observee, graphite connotes a mighty cosmic presence.
In 2010, geophysicists revealed graphite whiskers in a lunar sample returned by Apollo 17 astronauts. Via light microscopy, specimen 722255 divulged wispy trails from the Late Heavy Bombardment, a graphite time machine 3.8 to 4.1 billion years in the making.
That same year, the Spitzer Telescope unveiled WASP-12b, the first carbon-rich exoplanet possibly harboring foreign graphite. Equally shocking, Spitzer exposed solid buckyball formations in the interstellar medium, opening new realms for carbon compound existence. In June 2016, Dawn discovered graphitized carbon on dwarf planet Ceres.
But perhaps graphite’s most captivating habitat lies within stardust, the primordial breath of bygone supernovae. These moving presolar grains shed fresh light on nucleosynthesis, imparting profound glimpses into stars, stellar winds, and supernovae decompressions.
Rock On: Big Bang to Backyard
One of the most common uses for graphite, and one that serves astronomy well, is the common 'lead' pencil. // Wikimedia Commons
While professional astronomers bask in the aura of graphite’s power, what about us, the backyard, star-driven skywatchers? How does graphite affect
our nightly sojourns? What personal benefits do amateur astronomers gain?
For many observers, no session is complete without ample astro-tech. Everyday, an electronic parade of CCDs, laptops, and computerized telescopes pervade observational endeavors with increasing regularity. They share a common hunger: power. Power equals batteries, and batteries equal graphite. Nourished by negative graphite electrodes, a growing syndicate of lithium-ion batteries is taking both the market and astronomy by storm. Manifested in electronic mounts, field batteries, smartphones and laptops, tech-savvy observers are inadvertently accompanied by graphite every night.
But the humble sketch pencil may be graphite’s greatest astronomical achievement. Graphite’s soft, flaky exterior, long-prized in artistic renderings, recasts the way astro-sketchers record the heavens.
Like this author, you probably maintain a weathered astronomy sketch kit, wood or plastic shell guarding erasers, blending stumps, and HB graphite pencils or sticks. Since the 16th century, graphite has dotted stars and shaded galaxies in the journals of stargazers worldwide. Each sketch recorded honors the cherished legacy of Galileo and Lord Rosse, etching our universe through personal perspective.
We often hear, “Nothing is written in stone.” In mineralogy, the reverse is true. Every element tells a scientific story, puzzle pieces that form the grand picture of the universe. But graphite’s chapter remains unique. From “writing stone” to Rosetta stone, graphite’s complex simplicity has altered the script of history, cosmology, and our very lives.