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An instrument designed by a Southwest Research Institute scientist has made the first direct temperature measurements beneath the surface of Io, a moon of Jupiter.
The mission launched in 2011 and reached Jupiter in 2016. More recently the scientists behind the probe became excited about these first-ever measurements on Io.
TPR’s Jerry Clayton recently spoke with Dr. Scott Bolton, Juno’s principal investigator at Southwest Research Institute in San Antonio.
This interview has been edited for length and clarity.
Clayton: The initial mission of Juno was not necessarily to study Io, is that correct?
Bolton: It was intended to study Jupiter, but fortuitously our spacecraft remained healthy, and Jupiter's gravity field kept pulling our orbit around until we had the opportunity to pass close by Io.
Clayton: Tell us a little bit about Io.
Bolton: Io is a fascinating object. It's the most volcanic body in the entire solar system. There are volcanoes all over the place going off all the time and we can see all these volcanoes all over both poles, the North and South Pole, across the middle. It's basically getting squeezed.
We call it tidal forces, but it's going around Jupiter and Jupiter's gravity field and its orbit are a little bit asymmetric. And so as it goes around Jupiter, it's getting squeezed constantly.
Clayton: Juno took these measurements during a couple of flybys when you were able to get fairly close. How does all that work?
Bolton: We did it with a radio microwave instrument that actually we didn't know this at the time but could penetrate through the surface into the regolith by probably several meters, and that enabled us to see that the temperature beneath the surface was warmer than the surface itself.
Clayton: What was the most surprising thing that your team found during these measurements?
Bolton: That we actually saw inside. Many of the scientists on the team thought because we expected it to be rock that it would not be transparent to the microwave radiation, and so you would only see the top part of the surface even though you had something that normally would see through, say, Jupiter's atmosphere.
That trick would not work at Io because it was a more rock-like surface. And so the surprise was when we saw that our lowest frequencies, which penetrate the deepest, actually saw and measured warmer temperatures, and so that told us right away that we must be seeing where there's magma underneath the surface.
Clayton: What does this tell us about IO and potentially other bodies in space?
Bolton: It tells us right away that moons are made of ice or rock and actually we can measure the heat underneath and that and the fundamental measurement of how much heat is coming out of a body, because a lot of the bodies in the solar system are cooling either because of radiogenic heating that's in the middle or tidal forces that are squeezing the insides.
That's what makes these oceans or volcanoes. And so, when we measure that we're really seeing how the body or moon or an asteroid or a comet is formed and whether it's still warm underneath, is it still cooling off, and so it's a real basic property. So, this may help us throughout the solar system as we go to explore. We can use an instrument like this to look at many kinds of bodies.
Clayton: And this could help us understand a little more about volcanic activity on Earth, right?
Bolton: It's interesting that you would go so many hundreds of millions of miles away, make a discovery, and then turn around and potentially find a way to actually learn about a process here on the Earth that is very dangerous to people.
If we can learn how volcanoes work and monitor them and even maybe learn how to do better predictions, that would be a great goal, and I'm hoping that maybe some of these discoveries will lead to something like that.
