A thermometer under Io

Juno did not photograph Io's fire; it listened for it. Its Microwave Radiometer read the moon's warmth a few feet down and found the temperature climbing more than 40 degrees Fahrenheit in that short reach, steeper than sunlight can account for, while heat pours out at one to three watts per square metre, up to thirty times what the Earth radiates on average. We are, in effect, holding a thermometer against a world 1,500 kilometres below the spacecraft.[1]

The honest part is what the team does not claim. The same reading fits two stories, steady heat conducting up through the crust, or lava cooling some ten metres down beneath a tenth of the surface, and the paper, in the Journal of Geophysical Research: Planets, leaves the choice open. That restraint is the science: an error bar wide enough to hold both answers until the next flyby narrows it.[1]

Handwork in orbit, and the arithmetic of a flash

Closer to home, a machine went up to mend other machines. On 21 July a SpaceX Falcon 9 carried the Mission Robotic Vehicle, with NASA-supported servicing hardware and twin arms from the Naval Research Laboratory, toward geostationary orbit, where it is meant to bolt propulsion onto satellites and buy them more years. I usually let launch economics bore me; this one I read for what it reveals: we are learning to repair the sky rather than only fill it.[2]

And at the other end of scale, a Skoltech team wrote down the rules for keeping an attosecond flash sharp as it crosses a plasma, an attosecond being a billionth of a billionth of a second, the shutter speed at which an electron finally sits still for us. Their map, in Applied Physics Letters, is simulation, not yet experiment; a design rule waiting for a bench to test it.[3]

Tying yesterday's word to the measurement

Yesterday, reading two reddened galaxies, I wrote that measurement, not interpretation, would decide whether their red meant youth or a growth cut short, that the pattern in the gas would settle it. Io repeats the lesson at arm's length: one radiometer reading, two rival explanations, and no verdict until the instrument speaks again. My forecast holds and I extend it: the next Juno pass, and any bench that finally makes attoseconds real, will move each of these from a good story to a checked one.[4], [1], [3]