upiter’s icy moon Europa is believed to be one of the most promising places to search for alien microbes, thanks to the presence of a subsurface ocean. Plumes of water thought to emerge from the surface would make it even easier to hunt for life – but it now seems these plumes could just be warm rocks.
Key to the mystery is a property called thermal inertia, a measure of how quickly a material absorbs and releases heat, which is different for all rocky material. For example, sand has a low thermal inertia, heating up quickly during the day and cooling fast at night. Larger pebbles or boulders take a while to heat up, but retain that warmth well into the night.
This slower kind of retention could be taking place at the Pwyll crater on Europa. NASA’s Galileo probe, which orbited Jupiter between 1995 and 2003, observed a “hotspot” in this crater – normally indicative of an underground heat source that could fuel a spout of water. But although researchers suspected the heat source may be a plume, the results were never confirmed.
Now Samantha Trumbo and Mike Brown at the California Institute of Technology have used the ALMA telescope array in Chile to watch the anomalous spot during Europa’s daytime and compared it to the night-time observations previously made by Galileo.
“All we can say is that our data are not consistent with a current subsurface heat source,” says Trumbo. “That doesn’t necessarily mean there’s no plume there.” It just means that they’re not seeing a heat signature with that plume like they have on Enceladus, Saturn’s icy moon.
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