A new look at old data suggests that something is missing on suspected feathers on Europe: a source of heat
Usually we publish articles about things that astronomers find in the universe ̵
There is a lot of evidence that Jupiter's moon Europe has water flags. Observations with the Hubble Space Telescope revealed an emission of hydrogen and oxygen over part of the surface – and over this same region two years later. Reanalyzed data from the Galileo spacecraft that the system visited in the 1990s shows that the ship also felt the taste of a feather. It's all on the verge of what these instruments can do, but given the ocean's subterranean ocean and its fractured surface, not to mention the small pockmarks lenticulae ("freckles") that could be cryovolcanoes, Researchers expect springs . And the water emanating from Saturn's much smaller moon Enceladus gives reason for hope.
The European studies traced the alleged plumes back to two places near the equator of the moon. If the features were really thrown from water vapor into space, then if they look similar to geysers in the entire solar system (even on Earth), they need some kind of energy source. Such energy sources normally heat up the surface: we see these hotspots from anywhere in Yellowstone to the Tiger Strip Cracks at Enceladus & # 39; South Pole.
But Europe does not seem to have hotspots.
We might think so. The surface on which Hubble discovered vapors coincided with a small increase in surface temperature seen by Galileo, a region north of a crater named Pwyll, which was covered with a blanket of expelled debris. But the difference was only a few Kelvin, and there was only good data for the local night. When the data was first published in 1999, the authors had doubts about an underground heat source.
Earlier this year, Samantha Trumbo (Caltech) and others threw another look at the surface of Europe, this time during the day of 2015 with ALMA. They found that the same place looked colder than its surroundings during the day – a very unlikely behavior for a hotspot, especially when it spat out the Hubble data discovered in 2016.
Julie Rathbun of the Planetary Science Institute and John Spencer of the Southwest Research Institute have now cast their own global view of Europe with the data of Galileo and ALMA. They calculated how different parts of Europe's surface could absorb and reheat the heat of sunlight, and in particular looked at the two surface areas over which the feathers appeared. The calculations confirm the conclusion of the Trumbo team: Hotspots do not look like the right solution. We are more concerned with surfaces with different thermal inertias – surfaces that offer different resistance to cooling or heating.
"When you're on the beach, the sand reacts differently to sunlight than a stone [does]," Rathbun told a press conference on October 22 at the annual meeting of the American Astronomical Society's Department of Planetary Sciences. "The sand warms up very quickly and cools down very quickly, the rock takes a while: nice and cool in the morning, and then it stays warm at night." The same thing seems to happen to Europe.
So if the feathers exist – they could not – then they are in power? The answer could still be hotspots if they are small enough: heat sources about the same size as the average lenticula and the same temperature of Enceladus & # 39; tiger stripes would penetrate the detection in the current data. Lenticulae are certainly a good suspect if they are really ice volcanoes. Or the feathers are sporadic. Or maybe there is an outrageous way to create geysers without heat.
For an answer to this question, Rathbun refers to NASA's upcoming Europa Clipper mission (of which she is a member), which will launch Moon in the 2020s. The spacecraft's thermal imager will produce images at a resolution 100 times better than the one we have now, she said, and would undoubtedly find hotspots if they exist.
A video of the press conference will be available shortly.