Is that simply because they are rare so unlikely to be found without a wave scanner, or do they not actually spawn in the first place?
Certainly not a definitive answer but my guess would be that they don't spawn.
I've spent quite a bit of time flying over planet surfaces and, even so, I only have 3 real experiences which to base that opinion on.
When I'm surface-prospecting, I always de-orbit heading for the rim of a crater, in the hope of landing in a spot with lots of meteorites.
On one occasion I was heading for the rim of a crater when I thought I saw
something to the South of the crater rim.
I adjusted my glide, came out a couple of km South of the crater and realised that the "thing" I'd spotted was simply 3 large, flat, rocks in a sort of "C shape".
I carried on North to the crater rim and landed.
Deployed my SRV and got a fairly big signal to the South.
Drove toward it and found myself back at the 3 large, flat, rocks but now there was an outcrop right in front of them.
I couldn't
swear it wasn't there when I saw the 3 rocks from my ship but I didn't notice it.
On another occasion I did something similar; de-orbited aiming for the ground right between 2 craters.
At ground level I realised there was actually about 10km between the craters so I picked the Northern crater and flew toward it.
Landed, deployed the SRV and, again, noticed a big "high frequency" signal to the South.
Drove toward it and almost straight away an exclusion zone appeared on my scanner.
Arrived, blasted a couple of skimmers and there were half a dozen containers lying on the surface, inside the exclusion zone.
Again, I couldn't swear it wasn't there when I was in my ship but, having just flown about 5km over that area, neither the exclusion zone
or the containers were visible from my ship.
The closest to a "conclusive" thing happened one time while I was doing the "Ancient Ruins" mission.
I landed at one Guardian Ruins site, about 100m away from a group of obelisks.
After landing I spent a bit of time faffing around, figuring out how many scans I had to make and where they were etc.
Deployed my SRV, there was immediately a "rumbling noise", a white blob appeared on my SRV scanner and then a monolith appeared
right underneath my ship and skewered it. [where is it]
Now, the fact that the monolith didn't appear (and skewer my ship) when I
landed and only popped-up when I deployed my SRV would definitely seem to suggest that they only "activate" in response to the presence of an SRV - and
not a ship.
Again, I couldn't swear to it but if
all surface POIs adhere to the same "rules" as the monolith did, I'd guess that they don't spawn in response to a ship being nearby, only an SRV.
