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Opportunity rover lands on surface of Mars

It landed three weeks after its twin Spirit. The landing site was in Meridiani Planum. It is a plain which hosts a crystalline hematite. On Earth, hematite is often formed in hot springs or in standing pools of water. Some people therefore believe that there was liquid water on Meridiani Planum in the past.

German-American seismologist Beno Gutenberg dies

He was interested in earthquakes. He was a collaborator Charles Richter in developing the Richter magnitude scale. Gutenberg invented the relationship between seismic magnitude and energy. He also co-discovered the Gutenberg–Richter law, which provides probability distribution of earthquakes for a given energy.

1st US city to fluoridate its water

It was Grand Rapids in Michigan. Main purpose of controlled addition of fluoride to a public water supply is to reduce tooth decay. The efficacy in children is proved, while in adults is less clear. Water fluoridation In the United states were proposed by a group of scientist led by H. Trendley Dean. They claimed that fluoride concentration of about 1 mg/L was associated with substantially fewer tooth cavities.

1st nuclear fission experiment in US

The experiment took place at the Columbia University, New York. Some of the investigators were Enrico Fermi, John Dunning or Francis G. Slack. Their work later led to the construction of Chicago Pile-1, the world's first artificial nuclear reactor. In 1942 it achieved self-sustaining nuclear chain reaction.

Anniversaries of the (in)famous