No. 73: Jan-Feb 1991
"Japanese physicists claim to have found evidence of 'strange matter' in cosmic rays. Their detectors have recorded two separate events, each of which can be explained by the arrival of a particle with a charge 14 times as great as the charge on a proton, and a mass 170 times the proton's mass. No atomic nucleus -- made of protons and neutrons -- exists that matches this description, but these properties are precisely in the range predicted for so-called quark nuggets, which physicists believe may be made of a type of material dubbed strange matter."
(Gribbin, John; "New Kind of Matter Turns Up in Cosmic Rays," New Scientist, p. 22, November 10, 1990.)
The original report appeared in Physical Review Letters, 65:2094, 1990. In it, the Japanese scientists describe their balloon-borne equipment, proving that one does not need fancy spacecraft to make important discoveries.
The key feature of the quark nugget is its very high mass-to-charge ratio. Where do quark nuggets come from? The theoreticians surmise that they may be created when neutron stars collide or, perhaps, they are left over from the hypothetical Big Bang.