Astronomy Picture of the Day

Explanation: What is that changing object in a cold hydrocarbon sea of Titan? Radar images from the robotic Cassini spacecraft orbiting Saturn have been recording the surface of the cloud-engulfed moon Titan for years. When imaging the flat -- and hence radar dark -- surface of the methane and ethane lake called Ligeia Mare, an object appeared in 2013 just was not there in 2007. Subsequent observations in 2014 found the object remained -- but had changed! The featured image shows how the 20-km long object has appeared and evolved. Current origin speculative explanations include bubbling foam and floating solids, but no one is sure. Future observations may either resolve the enigma or open up more speculation.