• U.S.

Science: Pressure Metals

2 minute read
TIME

The structure of the planets, including the earth, can be understood best by studying the behavior of matter under very high pressure. Such is the theory of Astrophysicist William Henderson Ramsey of Britain’s University of Manchester. The simplest example is Jupiter, which Ramsey thinks is made largely of hydrogen. Near the surface where pressure is low, the hydrogen is in gaseous form. Deeper down it turns into a nonmetallic solid. It is still too light to account for the density of Jupiter’s interior.

When the pressure reaches about 800,000 atmospheres, a strange thing happens to hydrogen. Its molecular structure collapses, and it turns into a metal much heavier than nonmetallic solid hydrogen. No such pressure can be reached in the earth’s laboratories, but theoretical studies have proved that metallic hydrogen is a reality. Since the pressure at the center of Jupiter is something like 30 million atmospheres, there is plenty of room for a sphere of metallic hydrogen.

Professor Ramsey believes that Saturn has a similar structure. Uranus and Neptune are mostly ammonia and methane. Recent studies by M.J.M. Bernal and H.S.W. Massey at University College in London have shown that ammonia joins with hydrogen at 250,000 atmospheres to form metallic “ammonium”: NH4. So the interiors of Neptune and Uranus probably contain another metal made out of a gas by pressure.

On the earth, Professor Ramsey believes the same pressure effect comes into play. Since the deep interior of the earth is extremely dense, geologists generally assume that it is made of heavy nickel-iron. Ramsey’s theory is that the core is chemically much the same as the crust. Toward the center, the pressure is great enough to crush familiar rocky materials into heavy metals.

More Must-Reads from TIME

Contact us at letters@time.com