Bone has been around for 500 million years, and a small fraction of it has been preserved as fossils—stone bones. Bone in another form, charcoal, has a shorter but extremely dark history, which extends into popular culture and space exploration. Variously known as bone charcoal, bone black, and bone char; it is produced by burning bones, byproducts of the meatpacking industry, in an oxygen-starved environment.

Almost 40,000 years ago, cave artists drew with charcoal made from either wood or bone, and Egyptian tomb painters used it about 5000 years ago. Why the ancients chose one type of charcoal over the other is unclear, but their properties do differ. Wood charcoal is blacker and is now known to be carcinogenic when ingested. Without realizing that the alternative was toxic, Hippocrates recommended bone char for treating epilepsy, anthrax, gangrene, and bad breath. (Black tongue, anyone?)

About 1800, someone discovered that pouring vinegar or wine through a bed of bone char clarified the liquid. It was soon revealed that bone char would do the same for sugar syrup, refining brownish raw sugar and making it white. The sugar industry could not get enough of it, and pioneers prospered by picking up and selling bleached bison bones that littered the American prairies to sugar refineries. (These bones were also a much-in-demand raw material for the fertilizer industry. See https://aboutbone.com/when-bone-piles-became-cash-cows )

Presently various industries use bone char to color linoleum, paint, printing ink, wallpaper, plastic, and concrete. Also, Hollywood has casted bone char as a nontoxic stand-in for oil slicks and spills in movies including On Deadly Ground, Beverly Hillbillies, Die Hard III, Waterworld, Down Periscope, and Men in Black. In other productions it has also mimicked mud and lava.

On Deadly Ground

The truly out-of-this-world applications for bone char, however, relate to satellites. Launched in 1977, Voyager I and II have some of their optical components coated with bone char. These satellites are two of only several Earth objects that have left the Solar System, and both are expected to maintain some functions until at least 2025. They will continue to drift intergalactically at minus 455 degrees Fahrenheit until eventually some distant star vaporizes them or a black hole engulfs them—extraordinary trips for some cow and pig bones.

At the opposite end of the thermal spectrum, the Solar Orbiter, a European Space Agency/NASA joint venture,  took off on its seven-year mission in February 2020. During the next two years, the satellite will position itself into a solar orbit closer than Mercury’s to explore the previously poorly observed solar poles. In doing so, it will experience light intensity 13 times that present on Earth and temperatures as high as 1000 degrees Fahrenheit. (Image putting your cell phone in an extremely hot oven and doubling the temperature.)

An eight-by-ten foot heat shield on the face of Solar Orbiter will protect the delicate scientific instruments from the Sun’s withering heat and light and allow them to function at a constant temperature. During planning, requirements for the shield included a surface that, over the course of the mission, would not flake off or fade from intense ultraviolet light. It could not emit vapors or build up static electric charges because either would distort the instruments’ measurements. The shield also had to be light weight in order for the satellite to escape Earth’s gravity at the journey’s onset.

The shield is made of titanium foil which is permanently bonded to a thin layer of, you guessed it, bone char. It proved best in meeting all the requirements; and yes, black does absorb heat, but bone char quickly radiates it away. Furthermore, the shield is positioned four inches in front of the satellite’s main body, allowing for adequate ventilation. Small openings in the shield allow cameras and other sensing devices to momentarily stare directly at the Sun before their overlying “eyelids” blink closed.  

Between now and 2027, the ten onboard instruments (one from the US and the others from individual European countries) will have a lot to tell us about solar winds and geomagnetic storms. They reach Earth in their mildest forms as aurora phenomena (northern and southern lights). In their harshest forms they could create havoc in our electrical systems, which could knock out satellites, GPS, electrical grids, and computer networks. So we should take a personal interest in the success of the high-tech Solar Orbiter, whose fate relies on humble bone.   

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