Plutonium at Its Worst and Best

Hiroshima, after August 6, 1945
Hiroshima, before August 6, 1945


This week marks the anniversary of the bombings of Hiroshima and Nagasaki on August 6 and 9, respectively, in 1945. Tens of thousands died on those dates, and more people died, as a result of radiation sickness, in the weeks and years following. War reveals human beings at their worst. Nuclear weapons represent our largest, surest capability for self-destruction.

In commemoration for that time, we encourage you to read the poem “Hiroshima’s Secrets” at Lofty Ambitions and to seek out other ways to remember. We’ve written a lot more about nuclear weapons and the nuclear history of the United States—read some of it HERE.

The night before this anniversary—last night—our thoughts were elsewhere. We were following the story of Curiosity, the Mars rover that landed at 10:31pm Pacific Time. Or rather, the rover landed at 10:17pm, and the confirmation signal reached Earth fourteen minutes later. A few minutes after that, two thumbnail photos arrived from Curiosity’s Hazcams, cameras positioned on the front and rear of the rover, cameras with a fisheye lens and amazing focus from four inches to the horizon. Curiosity’s wheels were firmly planted on relatively smooth, even ground. We could see Curiosity’s shadow cast on the surface of Mars.

Curiosity Caught in the Act of Landing (NASA)

The two most recent rovers—Spirit and Opportunity—were powered by solar panels. Curiosity, though, is much larger and more complex than those predecessors, so it needed more oomph and a longer life. Besides, solar panels can be compromised by the dust whipping about the Martian landscape. Curiosity is powered, therefore, by what NASA calls “a multi-mission radioisotope thermoelectric generator (MMRTG) supplied by the Department of Energy.” In other words, Curiosity runs on a nuclear battery containing more than ten pounds of plutonium-238.

In 1941, chemist Glenn Seaborg developed Pu-238 from uranium-238. As it decays and generates the heat that makes it useful as fuel in a robot’s battery, Pu-238 decays back into that uranium isotope. The half-life for Pu-238 is more than eighty-seven years. In comparison, the isotope plutonium-239 used in nuclear weapons and in nuclear power plants has a half-life of more than 24,000 years. Pu-238 does not explode like a bomb and is made in a ceramic form in an attempt to reduce health hazards. Neither the United States nor Russia produce Pu-238 anymore, though Russia has a small stockpile from which NASA purchases the isotope. Because its primary use is as battery power for NASA’s robotic space missions, there is some discussion of restarting production in the United States to ensure that the sort of Mars and outer planet exploration NASA has in mind can continue beyond 2020, but funding has not been approved by Congress.

Curiosity Sees Its Own Shadow on Mars (NASA)

This week, we remember the destruction that nuclear weapons can unleash in a single instant. May we also look to the skies this week and know that Curiosity, powered by its nuclear battery, is readying itself to explore the geochemistry of another world. May we glimpse, in Bill Nye’s words last night, “Humans at their very best.”

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