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Scientists, like other people, are always pleased to have their own ideas confirmed. So, I was gratified by a report which appeared in the August 1963 issue of the Journal of the British Astronomical Association. This report was written by the famous Soviet astronomer Dr Nikolai Kozyrev, who several years ago discovered evidence in telescopic photographs to support the belief that some of the craters on the moon are sites of presently active volcanoes. When Or Kozyrev first published what he thought he had seen on the moon, his interpretation was doubted by many astronomers in other lands, including the United States. Subsequently. however, astronomers here have seen colour changes which they, too, believe are signs of continuing volcanic activity on the previously supposed dead body of the moon. Hence, we can be confident that Dr Kozyrev is not only a diligent but a reliable observer.
In the Journal of the British Astronomical Association just referred to, Dr Kozyrev explained that during the months of April and May 1963 he had been studying the planet Mercury through the big telescope at Pulkovo Observatory in Crimea. His purpose was to compare the sunlight reflected by Mercury with light corning directly from the sun. Since each element in the chemical table gives off a characteristic colour of light, the differences detectable in the spectra of the sun and of Mercury would help to determine what gases make up the atmosphere of Mercury. Historically, astronomers had not been too interested in the atmosphere of Mercury because one of the theories on which prevailing concepts &the universe are built says Mercury couldn't possess much of an atmosphere. Atmospheres are complexes of gases, which cling to planets in response to the pull of gravity. Gravitational attraction diminishes with, the mass of the planet, and Mercury is quite small—only about one-twentieth the mass of the earth.
But Soviet scientists, like scientists in this country, have become engaged in the growing possibility of actually going out in person to explore the solar system and see on the spot the wonders which up to now have been visible only at a distance through powerful magnifying lenses. Planetary atmospheres are being analysed with unprecedented zeal.
During the solar eclipse of February 1961, Dr Kozyrev observed Mercury with the hope of confirming, my presence of an atmosphere. His results were negative. This was something of a surprise since A. Dolhus of France had earlier measured a tenuous atmosphere which he estimated to be about 1/300th to 1/1,000th as dense as our own atmosphere. Dolfus assumed that this very thin 'air' would be composed of heavy gases such as xenon, krypton, argon, and carbon dioxide because the gravitational pull of such a small planet as Mercury would not hold the lighter, faster atoms.
What Dr Kozyrev discovered while looking at Mercury through the Polkovo telescope in the spring of 1963 was an even greater surprise. Indeed, it was a theoretical impossibility. For in the spectrum of Mercury he saw the characteristic spectral lines of hydrogen, lightest of all the elements!
According to a mathematical equation worked out by the late Sir James Jeans and applied successfully to the solution of many astronomical problems, the hydrogen originally associated with the formation of the planet Mercury should have floated away from the planet in several hundreds of thousands of years. In other words, the Jeans equation says the hydrogen supply with which Mercury began its life as a planet should have disappeared long, long ago; for the solar system is believed to be eight to ten billion years old.
How, then, could there be hydrogen in the atmosphere of Mercury today?
In thinking about the question, Dr Kozyrev made some intricate calculations. Mercury is closest of the planets to the sun. Obviously, it gets more radiation from the sun than do the more distant planets. Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Included in this radiation are protons the nuclei of hydrogen atoms. Dr Kozyrev figured how big a yearly share of these protons would go to Mercury because of its proximity to the sun. The answer was just about enough to replace the hydrogen that would have escaped from mercury’s weak gravitational attraction yearly. If Dr Kozyrev is right, Mercury now has an atmosphere containing about as much hydrogen as it contained billions of years ago.