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Hillary Shaw
Newport, Shropshire, UK
I am not sure how a lump of antimatter as big as a meteor would form or survive in interstellar space, but suppose one did. Say it is 10 × 10 × 10 metres, and let’s give it similar properties to rock, specifically a heat capacity of 2000 joules per kilogram, and a density of 2.5 grams per cubic centimetre. The solar system has about 106 hydrogen atoms per cubic metre at its outer edges, rising to 107 in the vicinity of Earth.
The distance from a little beyond Pluto’s orbit to the sun is about 1013 metres, so along this path this antimatter “meteor” would encounter, and annihilate to energy, some 1022 hydrogen atoms, total mass 10-2 kg. That produces about 1015 J of energy. Based on these figures, it would take around 1010 J to heat this antimeteor by 1°C, so, neglecting energy losses by radiation, it should heat up to a toasty 105°C. Even at 104°C, it would glow white, and at 105°C it would be blue-white, emitting mainly UV and X-rays. We would probably spot that.
If it hit the sun, the resulting explosion as it all annihilated would probably destroy all life on Earth. Any planet it hit, including Jupiter, would be instantly destroyed. If it hit Neptune, we might survive for a while, with spectacular night shows, but the gravitational disturbances might change our orbit and kill us all later via heat, cold or meteorite strikes.
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