These last years, the search for extrasolar planets has been successful. To date, the astronomers have detected more than 300 extrasolar planets. Among these 300 planets, only ten have been discovered by their own light.
There is perhaps a phenomenon which could facilitate this search for extrasolar planets.
The astronomer Michael Mumma and his team have discovered in 1981 (*) a natural laser emission produced by the Martian upper atmosphere. This very fine emission ray centered on 10,33 µm is due to carbon dioxide, majority component of the Martian atmosphere. This natural laser emission has been not only confirmed by other teams but another natural laser has been discovered in the Venusian upper atmosphere.
In consequence of these discoveries, one can suppose that this phenomenon of stimulated emission generated by a planetary atmosphere is frequent.
This phenomenon of stimulated emission could be used for the search for extrasolar planets. The direct detection of an extrasolar planet conflicts, with current technology, with a considerable obstacle: the difference of brightness between planet and its star companion. If the studied planet has an atmosphere and if this one presents a stimulated emission, the brightness of planet in the emission ray could be amplified considerably. To benefit from this emission, it would be necessary to detect very thin rays. With this condition, the ratio of brightness between star and planet could become more favorable for a direct detection.
A first step in the use of this phenomenon could be the checking of its presence on the extrasolar planets already discovered.
Several ray masers would deserve a detailed attention: the ray at 23.7 GHz emitted by molecule NH3 and the rays at 22 GHz and 1.66 GHz emitted by molecule H2O and radical OH. As the stars emit little in this part of electromagnetic spectrum, one can hope for a ratio of brightness more favorable for the planet detection. The ray maser of ammonia could be a good marker for gas giant planets. The masers of water and radical hydroxyl would be good indices for planets similar to Earth.
(*): “Discovery of Natural Gain Amplification in the 10-Micrometer Carbon Dioxide Laser Bands one Mars: A Natural Laser”; MICHAEL J MUMMA, DAVID BUHL, GORDON CHIN, DRAKE DEMING, FRED ESPENAK, THEODOR KOSTIUK, and DAVID ZIPOY; Science, 3 April 1981, Vol. 212, No 4490, pp. 45 – 49.