On December 14, 1962, after a three-and-a-half-month journey of 293 million kilometres from Earth, NASA’s Mariner 2 spacecraft, approached Venus. Forty-four minutes before closest approach – at a distance of 34,773 kilometers from Venus, Mariner’s 2 radiometers began to scan the planet’s dayside.

On January 3, 1963, twenty days after passing Venus, Mariner 2 transmitted half an hour of telemetry and then went silent. Radio contact was lost for ever. Mariner 2 became a mute piece of metal, endlessly circling the Sun in a heliocentric orbit.

Mariner 2 was the first spacecraft to successfully flyby another planet. The mission was an outstanding success and it created a great deal of publicity. William Pickering, the director of the Jet Propulsion Laboratory, which was responsible for designing Mariner 2,  found himself featured on the cover of Time Magazine and rode as Grand Marshall of the Tournament of Roses Parade in Pasadena.

William Pickering, on the cover of Time magazine. Cover Credit Boris Artzybasheff

In the meantime, the scientific debate over what Mariner 2 might find at Venus had been intensified.  Radio observations in the 1950s gave rise to two interpretations – an extremely hot planet, with surface temperature at least at 342°C or a planet with a relatively benign surface temperature. But all the evidence from Mariner 2 seemed to confirm the high surface temperature interpretation. Venus was a hellish world. Ground temperatures were as high as 428oC (800oF). There was no evidence of a magnetic field around the planet and they couldn’t detect any water vapour in its atmosphere. Five years later, Mariner 5 revealed a thick cloud-covered planet with even higher temperatures and a crushing atmosphere.

Space exploration brought the development of the comparative planetology, a field of studies which compares the properties and the corresponding characteristics of planets in the solar system and understand better, the conditions under which planets develop.

A couple years before Mariner’s 2 successful flyby, a young astronomer called Carl Sagan, suggested that Venus was an inferno.  The reason, he said, seems to be a greenhouse effect that roasted the surface of the planet. Sagan had estimated that Venus had started out with roughly the same amount of CO2 as earth and that made him wonder what would happen if our own moderate greenhouse effect here on Earth were to intensify as it had on Venus. Carl Sagan was one of the first scientists to sound the alarm on global warming.

“The greenhouse effect can make an earth-like world into a planetary inferno…the hell of Venus is in stark contrast to the comparative heaven of its neighbouring world, our little planetary home, the earth….Carbon dioxide and water vapour make a modest greenhouse effect without which, our oceans would be frozen solid. A little greenhouse effect is a good thing. But Venus is an ominous reminder that in a world rather like the earth, things can go wrong. There is no guarantee that our planet will always be so hospitable.  To maintain this clement world we must understand it and appreciate it. The runaway greenhouse effect on Venus is a valuable reminder that we should take the increasing greenhouse effect on earth seriously.”

The growth of Comparative planetology also energised James Lovelock’s Gaia Hypothesis.  With its first explorations of the solar system, NASA was keen to examine the soil of other planets for sighs of life or conditions that could support life but it couldn’t be done without instruments designed especially for detecting life in space. NASA turned to James E. Lovelock an English chemist who, in the 1957s, had invented an ingenious device, the electron capture detector that could detect tiny amounts of chemicals. “That work provided the hard data that allowed Rachel Carson to write her book Silent Spring,” said Lovelock to Fred Pearce, during a talk in 1997.

In 1961, Lovelock moved to California, to help the JPL scientists to develop sensitive instruments able to detect life in Mars. The assumption at that time was that life on Mars would be much the same as life on Earth.  But Lovelock was sceptical. What if life on Mars didn’t look like terrestrial life? How would they be able to recognise and detect it?  And what is life, anyway, he wondered. Lovelock started thinking about the real character of life and finally he decided that he would look for an entropy reduction, “since this must be a general characteristic of life.”

Entropy is a measure of disorder in systems. For an isolated system, entropy always increases or remains the same.  But life is highly ordered, so living organisms decrease entropy. By absorbing energy from the sun, the plants convert carbon dioxide and water into leaves, stems and flowers.  In contrast, they eject infrared light which is a much less concentrated form of energy. The decrease in energy is only local; the overall entropy of the universe increases.

Lovelock decided that it would be a good idea to use our own planet as a model. He thought about Earth’s atmosphere, it’s chemical composition. The atmosphere contains both methane and oxygen, which react with one another to form carbon dioxide and water.

CH4 + 2 O2 -> CO2 + 2 H20

The reaction destroys methane. If no living organisms were present, methane would disappear from Earth’s atmosphere. But methane is also continuously produced from bacteria in natural wetlands, in rice paddles, in the ocean, and in cows’ stomachs, replenishing that destroyed in the atmosphere. With this thought, Lovelock realised that the Earth’s atmosphere could be seen as an extension of the planet’s biosphere. He envisioned Earth as a living system, an organism, in which physical and biological components worked together to enable life. He named this system, this super – organism, Gaia, after the Greek goddess of the Earth.

During the 1960s, James Lovelock and Lynn Margulis, a microbiologist at Boston University, developed the Gaia hypothesis.  The Gaia Hypothesis never developed to be a significant science theory, but it made both scientists and environmentalists to consider Earth as a global and integrated system that needed to be investigated and understood.

Sources and further reading:

William H. Pickering, Former Director of JPL, Dies, https://www.jpl.nasa.gov/news/news.php?feature=351

Sagan, Carl (1960). “The Radiation Balance of Venus”. Pasadena, CA, California Institute of Technology, Jet Propulsion Laboratory: 34 pp.

One Man and his Widget,  Sunday, 29 March 1997, The Independent,  http://www.independent.co.uk/arts-entertainment/one-man-and-his-widget-1274674.html

Lovelock, James (1979). GAIA – A New Look at Life on Earth. Oxford University Press