R. Ramachandran, former Associate Editor of Frontline, has won the Mumbai Press Club’s RedInk Awards 2018 in the “Science & Innovation (Print)” category. His award-winning article, “An oxygen mystery”, was published in the Frontline issue dated July 21, 2017. The award carries a trophy, a citation and Rs.75,000. The citation read: “...for outstanding piece of journalism and the effort to put together a story of high calibre under Science & Innovation—Print”.
The National RedInk Awards were instituted in 2010.
“An oxygen mystery” is an outstanding example of cross-disciplinary research. It describes how research techniques to improve the performance of semiconductor microchips provided insight into the satellite observation, three years ago, of the outgassing of molecular oxygen from a comet surface—unexpected given the current understanding about the formation of the solar system and its constituent planets, comets, asteroids, and so on.
The European Space Agency’s orbiter-cum-lander spacecraft Rosetta, launched in March 2004 to study the comet 67P/Churyumov-Gerasimenko, had its close encounters with the comet between September 2014 and March 2015. During this period, it detected abundant molecular oxygen in the comet’s coma, the central part of comet’s atmosphere immediately surrounding the nucleus.
This surprised astronomers because the present understanding about the solar system’s formation 4.6 billion years ago is that there are no free oxygen molecules at all. Being highly reactive, oxygen readily combines with other elements to form water, carbon dioxide, carbon monoxide, silicates and metal oxides.The earth is an exception because of constant oxygen production by photosynthesis. Wherever traces of free oxygen have been found (through spectroscopy), such as in the Orion Nebula and the Ophiuchi A Cloud Complex, they can be attributed to the splitting of water and CO2 by UV light or high-energy radiation.
Therefore, any trace of primordial oxygen (formed during the evolution of the solar system 4.6 billion years ago) should have disappeared by now. Since there is no trace of life on comets, and because the abundance of oxygen detected by Rosetta is an order of magnitude higher than what chemistry of interstellar molecular clouds would suggest, the discovery of abundant free oxygen molecules from 67P/C-G is a mystery. The Rosetta team had proposed certain primordial scenarios that could have trapped free oxygen in the proto-solar nebula before planets and other projects froze out. But these explanations were not satisfactory and the mystery remained.
Two scientists from the California Institute of Technology, Konstantios Giapis and Yunxi Yao, developed techniques that used chemical processes called Eley-Rideal (ER) reactions, in which ions with “hyperthermal” energies (10-200 electronvolt) are bombarded on material surfaces,to improve the performance of semiconductor chips. In ER reactions, when energetic atomic or molecular projectiles collide with adsorbed surface atoms, new molecules are formed which are then ejected from the surface. This is distinct from the physical sputtering of the surfaces, the traditionally used method to bring about changes on semiconductor surfaces. But nine years ago, the two Caltech scientists found that ER reactions also contributed to the changes in the semiconductor surfaces and offered a better control parameter for changes desired. They reasoned that since ions produced in a comet’s coma by solar flares had energies of about the same order as the ions they used in their laboratory apparatus, the ER reactions may be responsible for kicking out free oxygen radicals from oxides of different elements from the comet’s surface. Giapis and Yao proposed that energetic water ions formed by the action of solar flares result in the release of certain oxygen complexes, which ultimately break up to yield free oxygen in situ, and this happens continually. They also demonstrated through laboratory experiments with substrates containing compounds (such as silicates and iron oxides) characteristic of comet surfaces, that when energetic water ions bombard the surface oxygen is indeed released on a continual basis through the formation of short-lived transient states. The puzzle is not, however, fully resolved because of lack of data about ion flux in the coma. But the finding of the two Caltech scientists gives an important insight into the chemical processes in cometary atmospheres.