Whatever I read I find Hayavusa brought some microscopic particles.
But what was the mass of the sample?
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The JAXA website for Hayabusa samples has a list of all samples, but this does not contain the mass per sample or the total mass of all samples.
The sample catalog PDF (warning, 175 Mb file) is a copy of the above list, plus details on each sample. This does not contain the mass per sample or the total mass of all samples either.
My guess: the total sample mass is so low there was no easy way to measure it. A crate with macroscopic samples can be set on a scale, subtract the weight of the empty crate and you're done. When the sample mass is much smaller than the mass of the container, any scale large enough to weigh the container may be too imprecise to weigh the sample.
Fellow member Jack extracted the data from the available pdfs and collated it to get a very rough value - 60 mg. It's based on what he hopes is a representative sample from categories 1 and 2 which account for ~75% of the particles, then just multiplied by 1500. Data on Dropbox.
Here's what I've found so far:
The Wikipedia article Sample-return mission#New missions after a 20-year hiatus says:
In June 2010 the Japan Aerospace Exploration Agency (JAXA) Hayabusa probe returned asteroid samples to Earth after a rendezvous with (and a landing on) S-type asteroid 25143 Itokawa. In November 2010, scientists at the agency confirmed that, despite failure of the sampling device, the probe retrieved micrograms of dust from the asteroid, the first ever brought back to Earth in pristine condition.
But I don't know where "micrograms" comes from exactly.
In several places I see about 1,500 grains which I think means the number of particles, not the unit of mass called "grain".
for more information, and copies of these images, the first of which shows some of the individual grains that are perhaps 10's of microns in size each. I guess the answer is that the exact mass may not be known as they haven't separated all particles and classified each as asteroid or non-asteroid with certainty. They think the aluminum particles for example (the ones labeled "artifact" in the first image) are from terrestrial origin, the spacecraft sample collector or holder for example. This is why you can't find an exact mass reported anywhere.
Here are some (unfortunately paywalled) articles all published in Science together in 2011 as well, from Hot Topic: Hayabusa—Dust from Itokawa. At some point I'll try to look them up and if I find more I'll make note of it here:
below: "The Hayabusa capsule, a spacecraft launched by the Japan Aerospace Exploration Agency in 2003, landed in South Australia." From NYTimes. Credit: JAXA/ISIS