Project Icarus it was called, the fourth space program of that name and the first for which it was appropriate. Long before Jacob’s parents were born—before the Overturn and the Covenant, before the Power Satellite League, before even the full flower of the old Bureaucracy—old grandfather NASA decided that it would be interesting to drop expendable probes into the Sun to see what happened.

They discovered that the probes did a quaint thing when they got close. They burned up.

In America’s “Indian Summer” nothing was thought impossible. Americans were building cities in space—a more durable probe couldn’t be much of a challenge!

Shells were made, with materials that could take unheard of stress and whose surfaces reflected almost anything. Magnetic fields guided the diffuse but tremendously hot plasmas of corona and chromosphere around and away from those hulls. Powerful communications lasers pierced the solar atmosphere with two-way streams of commands and data.

Still, the robot ships burned. However good the mirrors and insulation, however evenly the superconductors distributed heat, the laws of thermodynamics still held. heat will pass from a higher temperature to a zone where the temperature is lower, sooner or later.

The solar physicists might have gone on resignedly burning up probes in exchange for fleeting bursts of information had Tina Merchant not offered another way. “Why don’t you refrigerate?” she asked. “You have all the power you want. You can run refrigerators to push heat from one part of the probe to another.”

Her colleagues answered that, with superconductors, equalizing heat throughout was no problem.

“Who said anything about equalizing?” the Belle of Cambridge replied. “You should take all excess heat from the part of the ship were the instruments are and pump it into another part where the instruments aren’t.”

“And that part will burn up!” one colleague said. “Yes, but we can make a chain of these ‘heat dumps,’” said another engineer, slightly more bright. “And then we can drop them off, one by one …”

“No, no you don’t quite understand.” The triple Nobel Laureate strode to the chalkboard and drew a circle, then another circle within.

'Here!" She pointed to the inner circle. “You pump your heat into here until it is, for a short time, hotter than the ambient plasma outside of the ship. Then, before it can do harm there, you dump it out into the chromosphere.”

“And how,” asked a renowned physicist, “do you expect to do that?”

Tina Merchant had smiled as if she could almost see the Astronautics Prize held out to her. “Why I’m surprised at all of you!” she said. “You have onboard a communications laser with a brightness temperature of millions of degrees! Use it!”

Enter the age of the Solar Bathysphere. Floating in part by buoyancy and also by balancing atop the thrust of their refrigerator lasers, probes lingered for days, weeks, monitoring the subtle variations at the Sun, that wrought weather on the Earth.

— David Brin, Sundiver, 1980

Here’s an interesting discussion about the concept, with Brin himself explaining his reasoning.

None of the moons in our solar system have atmospheres.

Except for Titan. Titan has a lot of atmosphere.

Ah, doing your best to break the Therac-25’s record, I see.