I don't have a SO account, so I'll post here. I'm having trouble finding the reference, but there's an IKEA in Sweden or Norway that is really far away from industrial pollution, and so gets basically no soot deposited on its perfectly white painted roof. Some intrepid amateur astronomer put 2 + 2 together and realized it's a perfect collection mechanism for space dust. They thoroughly cleaned the roof, then came back a week later and carefully collected the accumulated dust. Looking at it under a microscope confirmed minerals that only form in microgravity environments.
> Jon Larsen, a Norwegian jazz musician and creator of Project Stardust, was able to show that it is possible to find micrometeorites in more populated areas. In a study published in January 2017 in the journal Geology, he and his colleagues catalogued more than 500 lustrous micrometeorites (and counting), all recovered from rooftops in urban areas.
Dust is composed of things like pollen, dirt, tiny particles of sand, dried plant material, and so forth. There is plenty of outdoor dust that is natural.
I have an incredibly hard time seeing how an outdoor IKEA roof, with tons of shoppers in their cars and delivery trucks and whatnot, is going to be some kind of pristine collection area.
I'm guessing the bottleneck lies in surface area to effectively collect samples rather than the effort to inspect samples and processing them to determine origin. The roof is going to have contaminants, sure, but so is any other collection area. Using a magnet to get iron based particulate then picking out rocks with unique elements is likely a lot cheaper than a purpose built facility to collect micrometeoroid samples with reduced contamination
Yeah it was the fact that they could power wash the roof clean and then use it as a collection mechanism, and it was high enough to be isolated from other sources of dust.
>> confirmed minerals that only form in microgravity environments.
So? That doesn't mean they landed on the roof from space. The really tiny stuff can be blown around. It may land on the ground at point A and then be blown onto a roof miles away at point B. This is why we should not use the simple math of a roof's size to determine the rate of material falling from space.
Hmmm, so you say if a particle reaches a spot not in straight and shortest line from space then it does not count as a particle originated in space fallen on that spot? Could we have a wiggle room still? Like allowing trade winds carry it some limited km laterally, or such?
They originate in space but do not necessarily come directly from space. Stuff is landing on earth all the time. Much of it then becomes dust/sand and gets moved around. What appears on a roof can be new falls from space, but also space stuff blown from elsewhere. Take a an amount of topsoil or sand. Run a magnet over it and you will find tiny flecks of space rock.
I think finding such stuff is regarded by the author as cool. I don't remember the author saying so, but personally I would think finding it is cool whether it first landed on my neighbor's tree, or went straight to my roof.
A significant amount of carbon-14 was added to the atmosphere from nuclear weapons testing. Since it has a half-life of about 5,000 years, most of it is still around. (The rest of it comes from cosmic rays smashing into atmospheric nitrogen.)
Granted, that's an isotope of a well-known element, not one of the "extra elements tacked to the end of the periodic table". I can point out that [tiny traces of plutonium-244 have been found in the ocean seafloor](https://www.npr.org/2021/05/13/996499035/freshly-made-pluton...). That has a half-life of about 80 million years; it's probably the result of ejecta from a supernova washing over the Earth several million years ago.
