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Do Planets Grow when they Accrete High Energy Particles?

-- | October 13, 2012

Question: The planets are receiving high energy bits of matter from the sun in the form of photons or in ionized atoms. Do planets grow in size from the material or matter output from the sun? — Glenn

Answer: Only a very small amount, but probably not directly from the Sun. Let’s look at an example, but expand our view to include all particles, not just those from the Sun. Cosmic rays are energetic charged particles, usually protons and some larger atomic nuclei, which continually bombard the Earth and whose origin is not well understood. When a cosmic ray strikes the Earth’s atmosphere it creates a shower of lower energy secondary particles, and these are observed to reach the ground. The number of cosmic rays that reaches the Earth’s surface varies as a function of the cosmic ray’s energy from 10,000 per square meter per second for 1 GeV cosmic rays with energy about a billion electron volts to 1 per square kilometer per year for 10 billion-billion (10 with 19 zeros) eV cosmic rays. Since the mass of the Earth is about 6×10^(27) grams while the mass of the proton, which is what most cosmic rays are, is about 1.7×10^(-24) grams, Each year this results in about 10 grams of mass added to the Earth. So, there is some growth of the Earth due to this accretion but it is very small. Compare this to the mass of material like cosmic dust and meteorites that falls on the Earth each year, which ranges from 37,000-78,000 tons.

Jeff Mangum

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