'City of Fresno'

[jemhouston]

Good geology lesson

[Nik_SpeakerToCats]

Context is important.
Also, per 'Chekov's Gun', plot building...

[Nik_SpeakerToCats]

City of Fresno #142

Sweeping the vicinity for both prograde and retrograde moonlets, 'City of Fresno' sidled into the lee of the largest prograde 'Outer', soon to win the name 'Lumpy'. About twenty kilometres on the longest axis, with a ninety-two day orbit, this was a generic mixed-ice and silicate rock aggregation. It would have made a pretty comet. Spectra showed there were no minerals or volatiles to be gleaned beyond the usual materials, of which we had enough. Still, it would be big and safe enough to extend 'surface' training. Already, there was a waiting list. I was 'borrowed' to over-see the brisk suit 'Refresher' courses, making sure the 'Trainers' had stayed sharp. Which, yes, they had. Then the two work-pods with extended air-lock / mini-habs again played 'Dive Boat', ferrying small groups the dozen 'stand-off' kilometres to and from the surface.

This delay also provided time for 'Fresno' scans to better identify, document sundry moonlets, both large and small. With our orbital locale sufficiently mapped, Tug 'Cooberra' loaded a 'Front End' Gas Diving Pod plus both 'Main' and 'Auxiliary' tanks. Again, they led due to their more powerful Radar. Beyond 'Situational Awareness', combining their wary 'On the Fly' data with those preliminary findings from 'Fresno' sensors would significantly narrow many minor moonlets' orbital parameters' 'error bars'.

The Tug was only a day out when Lt. Richards contacted me with uncommon urgency. "Mr. Kinson, 'Cooberra' are reporting 'Anomalous Radar Returns' from some of the moonlets. Optical spectra seem routine, but RF bounces are, quote, 'Weird'. What do you make of it ?"

I'd been researching the competing geological processes of a 'Snowball Earth'. In fact, I'd made some preliminary estimates of how to flip it. Upside, provided the underlying ocean was sterile, we could do the 'Terraform': After scattering some dozen Tug-loads of grey asteroidal gravel to raise that critical mid-latitude albedo, we'd drop two ten kilo-tonne bolides into sea-ice over deep, near-Equatorial water to trigger persistent 'Super-Nyos' mega-plumes. Atmosphere CO₂ would soar, empowering the 'Greenhouse' effect. Thaw being much, much faster than freeze, the planet would then stay warm.

Down-side, vast areas of the revealed land would be planed smooth, bare, utterly sterile. Even the toughest lichen would need centuries to gain a significant foot-hold. Worse, with land surfaces still depressed by a third of former ice-cap's thickness, the rapid sea-level rise would surely submerge most lowland. By the time isostatic rebound over-took this tectonic tide, many, many years must pass. So, no...

Well, 'no', for prompt settlement rather than a few upland outposts: Yet, if this was but a system or two over from where we *did* settle, we would so make a start. After a partial thaw, with a basic hydrological cycle restored, we'd seed the anoxic uplands' new maze of pools, streams and braided rivers with blue-green photo-synthetic algae, AKA 'Pond Scum'. Seed toxic seas' and oceans' shores with tougher photo-synthetic cyano-bacteria. When our distant descendants wanted the elbow room, the planet, now partly oxygenated, would be ready and waiting...

Setting such aside, I studied Lt. Richards' data for long, long minutes. Yes, 'Weird' was a fair description. 'Cooberra', like most Rock Tugs, used Radar of two significantly different frequency bands. The longer wavelength had better range, the shorter gave better detail. At these distances, allowing for 'typical' moonlet mineralogy, return strengths should sorta-correlate. Yet these moonlets' response varied rapidly, almost wildly, as 'Cooberra' crossed their path. It was not by distance. Or, I realised, not just by distance. In fact, it was some-what like the way 'Odd Bod' looked from a-far, its rotation alternately showing brighter and 'bleme' phases. Except, here, it was not the moonlets' rotation, but the passing Tug seeing different aspects.

So, why would optical spectra appear generic, yet Radar returns fluctuate so much ? Almost twinkle ? It was not moonlets' rapid rotation, such would give a clear Doppler 'smear'. Which left only that their hypothetical reflectors must 'look' very different from even mildly differing angles at those different frequencies. And, yet, must be too small for 'Fresno' scans to 'acquire'.

Systematically considering, discarding multiple generic possibilities, I cautiously admitted, "I can't see how ordinary Nickel-Iron inclusions as small bolides could give such wide variation...

"But, yes, while 'Rock Hopping', I heard of something...

"To help track their 'local' and 'crossing' asteroids, most communities tag them with retro-reflectors. Usually four in a tetrahedron for 4π coverage, each with at least three half-metre foil panels arranged as half corner-cubes, plus an optical prism tucked into the apex. These give Broadband RF response for reliable location, the laser bounce for precision. Even if angles are slightly off, they're sufficiently isotropic.

"This, though... " I hesitated, continued, "About a decade earlier, a tagged 'Rubble Pile' asteroid was whanged by 'Crossing Traffic'. Impactor lacked the energy to significantly disperse the asteroid, just shook it apart. But, as the components slowly re-gathered, they variously scrunched the flimsy retro-reflectors. Combined RF response went from isotropic to 'spiky'..."

"Like this ?"

"Yes." I took a careful breath, stated, "We may have crumpled, metallic debris. Possibly wreckage."