NASA has released images of the two unexplained bright spots in Titan's largest sea known as “magic islands.”
In June, astronomers drew attention to a bright spot in Ligeia Mare, the second largest liquid body on Titan. The spot was visible in images taken in July 2013, but had disappeared thereafter.
NASA/JPL-Caltech/ASI/Cornell.The changing face of Ligeia Mare
Titan's seasons seemed to be the likely explanation for the images since they were taken in spring in the northern hemisphere, where all three hydrocarbon seas are situated. Four main theories provided a more direct explanation: waves driven by increasing winds, frozen subsurface material, solids floating on the surface and bubbles of gas released from a warming sea floor.
Last week, a Planetary Sciences Division of the American Astronomical Society workshop was told that two more appearing/disappearing acts had been spotted, this time in Kraken Mare, Titan's largest sea.
These images have now been released, showing Kraken's objects to be larger and clearer than the original
Cassini's radar struck the surface at different angles on the two days: 56° in May and 5° in August. However, astronomers at the Jet Propulsion Laboratory are confident the differences in the images represent something physical, rather than being an artifact of the Cassini's location at the time.
"They could be waves, or they could be something more solid," MIT's Jason Soderblom, told National Geographic. "We definitely know now they are something reflecting from the surface." The fact that the Kraken Mare “islands” were photographed at visible and infrared wavelengths, as well as using radar, has raised hopes that more will be learned about their nature than could be gleaned from the radar images of the original island alone.
Already the shorter wavelength images have ruled out one of the original theories. Since frozen hydrocarbons are denser than their liquid forms, Titan's equivalents of icebergs would be submerged, and it was suggested the Ligeia Mare specter might have been a frozen body just below the surface. However, Soderblom says this, along with the possibility of some sort of fog, can now now dismissed.