Saturn's moon Titan glowing at dusk and dawn: NASA

In a potentially "groundbreaking discovery", scientists led by NASA have found large patches of trace gases shining brightly near the north and south poles of Saturn's moon Titan during the moon's dusk and dawn.

The pair of patches was spotted by a NASA-led international team of researchers investigating the chemical make-up of Titan's atmosphere. The large patches of trace gases were spotted shining brightly near the north and south poles.

These regions are curiously shifted off the poles, to the east or west, so that dawn is breaking over the southern region while dusk is falling over the northern one, researchers said. "This is an unexpected and potentially groundbreaking discovery," said Martin Cordiner, an astrochemist working at NASA's Goddard Space Flight Center in Greenbelt, Maryland and lead author of the study. "These kinds of east-to-west variations have never been seen before in Titan's atmospheric gases. Explaining their origin presents us with a fascinating new problem," Cordiner said.

The mapping comes from observations made by the Atacama Large Millimeter/submillimeter Array (ALMA), a network of high-precision antennas in Chile. At the wavelengths used by these antennas, the gas-rich areas in Titan's atmosphere glowed brightly. Because of ALMA's sensitivity, the researchers were able to obtain spatial maps of chemicals in Titan's atmosphere from a "snapshot" observation that lasted less than three minutes.

Titan's atmosphere has long been of interest because it acts as a chemical factory, using energy from the Sun and Saturn's magnetic field to produce a wide range of organic, or carbon-based, molecules. Studying this complex chemistry may provide insights into properties of Earth's very early atmosphere, which may have shared many chemical characteristics with present-day Titan.

In this study, the researchers focused on two organic molecules, hydrogen isocyanide (HNC) and cyanoacetylene (HC3N), that are formed in Titan's atmosphere. At lower altitudes, the HC3N appears concentrated above Titan's north and south poles. The surprise came when the researchers compared the gas concentrations at different levels in the atmosphere. At the highest altitudes, the gas pockets appeared to be shifted away from the poles. These off-pole locations are unexpected because the fast-moving winds in Titan's middle atmosphere move in an east-west direction, forming zones similar to Jupiter's bands, though much less pronounced.

Within each zone, the atmospheric gases should, for the most part, be thoroughly mixed, researchers said. "It seems incredible that chemical mechanisms could be operating on rapid enough timescales to cause enhanced 'pockets' in the observed molecules," said Conor Nixon, a planetary scientist at Goddard and a coauthor of the paper published in the Astrophysical Journal Letters.