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A Thermal Map of Europa (& an Intriguing Anomaly)

Europa stays in this news this morning as we continue to correlate recent observations with the invaluable results of the Galileo mission. Hubble data have played a role in this, with researchers identifying plume activity in 2013 that recalled the geysers of Enceladus, a possible indication of venting from the subsurface ocean. But analysis of Cassini data from its 2001 Jupiter flyby enroute to Saturn showed no evidence of plume activity through its ultraviolet imaging spectrograph (UVIS).

So what exactly did Hubble see? Yesterday’s post highlighted Julie Rathbun’s contention that if they are there, Europan plumes show no thermal signature in Galileo data, while Xianzhe Jia (University of Michigan) and the SETI Institute’s Melissa McGrath have used Galileo magnetometer data to support possible plume activity. We may need Europa Clipper to resolve the matter.

Now the 66 dish antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) have been turned on Europa in an attempt to study the entire moon — not just the areas of possible plume activity — to develop a thermal model. The data allow us to find what the authors of the paper on this work describe as “significant thermal structure.” What we get out of this is the ability to construct a global map showing the varying heat signatures across this remote world, in the process revealing an unusual cold spot on Europa’s northern hemisphere.

“These ALMA images are really interesting because they provide the first global map of Europa’s thermal emission,” said Samantha Trumbo, a planetary scientist at the California Institute of Technology and lead author on a paper published in the Astronomical Journal. “Since Europa is an ocean world with potential geologic activity, its surface temperatures are of great interest because they may constrain the locations and extents of any such activity.”

Image: ALMA image of Jupiter’s moon Europa. ALMA was able to map out thermal variations on its surface. Hubble image of Jupiter in the background. Credit: ALMA (ESO/NAOJ/NRAO), S. Trumbo et al.; NRAO/AUI NSF, S. Dagnello; NASA/Hubble.

ALMA’s ability to detect Europa’s thermal ‘glow’ is remarkable given that its surface temperature is never warmer than about minus 160 degrees Celsius, but this is an instrument that can provide insights into not just Jovian moons but asteroids and comets as well. On Europa, ALMA’s images have a resolution of 200 kilometers. Learning more about Europa’s surface can give us insights into its geological processes, especially interesting given that this surface is comparatively young, an indication of thermal or geological activity that has yet to be identified.

Image: Series of 4 images of the surface of Europa taken with ALMA, enabling astronomers to create the first global thermal map of Jupiter’s icy moon. Credit: ALMA (ESO/NAOJ/NRAO), S. Trumbo et al.

Trumbo and colleagues developed their global thermal model of Europa based on the ALMA observations, folding in an albedo map constructed from Voyager measurements and factoring in Galileo data. As for that odd cold spot on Europa’s northern hemisphere, it stands out on the ALMA maps near 90 degrees West and 23 degrees North. It also appears in two different images at two different times of day, an indication that it is genuinely distinct in its thermal properties. Moreover, Galileo may not be able to help us here, as the paper explains:

This region coincides with the location of highest water ice abundance mapped by Brown & Hand (2013) and the location suggested to have the most crystalline water ice by Ligier et al. (2016). However, it does not correspond to any particular geologic unit (Leonard et al. 2017) or any unusual visible morphological or albedo features (USGS 2002). The anomaly is located within a region of relatively low-resolution imaging and was not covered by the published Galileo PPR [Photopolarimeter-Radiometer] data, so it is possible that a corresponding morphological, geologic, or thermal feature was simply not seen by Galileo.

What to make of it? Except for discrepancies like this one, the model the authors work with reproduces the thermal structure seen by ALMA, an indication that we are seeing the results of albedo variation across the surface and the absorption and re-emission of sunlight. However, they find little correlation between the heat signatures and surface geology except for the area around Pwyll crater (this is similar to crater ejecta data elsewhere in the Solar System, which also show a distinctive signature). The cold spot referenced above remains enigmatic and will await future ALMA observations.

An afterword on Pwyll crater, which has been associated with possible plume activity: The ALMA map shows that Pwyll has a “locally elevated thermal inertia.” What this means is that this area takes longer to reach equilibrium with local temperature change than areas around it. Various factors are at play here, including density and thermal conductivity. Of particular interest is that the ‘cold spot’ anomaly is almost directly on the other side of Europa from Pwyll.

There is an analogy here with our own Moon, and the association with geological features on it that are directly opposite, or antipodal, to Tycho crater. But that is about as far as we can go with existing data. “Unfortunately,” the authors write, “without new, high-resolution imaging, the potential association of this feature with unique geology will likely remain an open question.”

The paper is Trumbo et al., “ALMA Thermal Observations of Europa,” Astronomical Journal Vol. 156, No. 4 (18 September 2018). Abstract / Preprint.


{ 12 comments… add one }
  • ljk October 24, 2018, 13:37

    I remember those Earth-based observations (infrared and radar) of the surface of Titan before Cassini-Huygens showed up in 2004/2005. While they certain had their uses and were obviously better than nothing, that they barely began to explain the real face of that distant alien moon was evident when Cassini and Huygens went to work. Even then when Cassini sent back its early images of the face of Titan, scientists were initially baffled as to what they were looking at.

    We need to go to Europa in person via our machines, as many times as necessary. A world the size of Earth’s moon with a global ocean sixty miles deep – that should be a top exploration priority, no contest.

  • ljk October 24, 2018, 13:39

    Conor Nixon • October 24, 2018

    In search of ice and fire: Europa analog fieldwork in Iceland, 2018

    This summer, I found myself standing on a glacier in Iceland, catching my breath, and staring upwards into a gray void. It was late in the day, and fog was descending over the icy volcano Kverkfjöll, obscuring the summit still more than an hour away above us. Ahead and behind were other members of our seven-strong climbing team, dimly visible in orange safety vests, strung out along 200 feet of climbing rope like holiday lights.

    I was there with a NASA-led team of astrobiologists sent to Iceland to study Jupiter’s moon Europa. Why go to Iceland to study Europa?

    First, a little background…


  • Harry R Ray October 25, 2018, 10:48

    Speaking of moons: The first follow-up work on exomoon candidate Kepler 1625b I presented at yesterday’s PLATOMissionCon by Kipping’s main exomoon compeditor, Rene Heller: bit.ly/2yWDPSV. “Detection of Extrasolar Moons in the Presence of Stellar Variability.” “Teaser” at the end. following slides with work from Heller, Rodenbeck, et al. (in prep.) embargoed. My take: For them to be embargoed means that they are very signifigant! So they must either, ONE: Refute the exomoon interpretation, or: TWO: CONFIRM the exomoon! However, a refutation usually takes place on ArXiv in the form of “Comment on…”, so very optimistically, I predict a possible confirmation.

    • Harry R Ray October 25, 2018, 12:44

      One way that Kepler 1625b i could be confirmed with existing data is if OTHER TTV’s were detected in the “cleaned up” version of the original 3 Kepler transits, and, if and only if the new TTV’s, should they exist, lead to an unimpeachable orbit with a precise(i.e. not the 22-24 day estimate)orbital period, which would then lead to precise masses for BOTH Kepler 1625b AND Kepler 1625b I.

  • Michael October 26, 2018, 17:38

    Just wondering if these spikes on the surface, if they exist, could alter the heat radiation signature. Having said that they would make great places for life to be protected from radiation around Jupiter.


  • Jesus Olmo October 27, 2018, 15:41

    Excerpt from Carolyn Ives Gilman’s sci-fi novel “Dark Orbit”:

    Is discovery impossible, or only implausible? That is what I wonder.
    We wait here, circling above our heart’s desire, caught in a paradox: to discover something new, we must understand it, yet the very act of understanding changes the thing we observe.
    To perceive, describe, explain: these are the essence of discovery. “I do not know” does not constitute learning. And yet, what happens when we encounter something so genuinely outside our previous experience that we have no mental categories for it, and the only truthful statement is “I do not know”? Why, we liken it to something we do know, however bad the analogy. We apply to it rules that lie within our experience. We resist incomprehension as reflexively as we recoil from pain.
    Only gradually, if all goes right, does the new information start to soften our mental walls, so that we can begin to perceive what we have encountered. But often by that time it is too late: we have so misconstrued the unknown that our learning is flawed forever. What was truly new is now just a subcategory of the old. Perhaps it is the only way we can learn, an anatomical limitation. We are organisms evolved to destroy unfamiliarity by the act of understanding it.
    I think of my companions, the argonauts of Iris, and wonder how their expectations will affect the planet. Our first impressions will shape our second ones, and those will shape the expectations of whoever comes after, till the planet is remade in our image forever. Are we the proper people to remake Iris? Do we carry with us desires like viruses that will infect the planet, and kill off the fragile truth?
    None of us has the qualifications to be first to witness a new world. But who does? It is not a skill you can learn, for who could teach it? All I know is, we are embarked on a mission of invention, and what we find will say as much about us as it does about Iris.

  • ljk November 5, 2018, 13:54

    NASA’s Astrobiology Programs Ignore One Another

    By Keith Cowing on November 4, 2018 7:21 PM


    To quote:

    I’m really shaking my head at this one since this entire effort is 200% about Astrobiology – and it resonates with what the recent NAS report and Congress want NASA to be doing with regard to Astrobiology – specifically with regard to Europa. If NASA is going to be re-organizing its Astrobiology research, a good place to start would be on super simple things like this. One hand does not seem to know – or care – what the other is doing in Astrobiology with NASA funding.

  • ljk November 8, 2018, 13:20

    Elections Can Have Consequences Billions Of Miles Away…


    This next article is from The Planetary Society blog:


    To quote:

    “If pressed, I would say the odds of Europa Clipper launching on an SLS have now dropped considerably, and its launch date also now likely to be in the mid-2020s as opposed to 2022. I have a hard time seeing how the Europa lander project continues without Culberson, because NASA has not formally requested the mission, and it lacks consensus support from the scientific community. Culberson had been planning — and still may be able to — allocate hundreds of millions of dollars to this effort in fiscal year 2019, but no other member of Congress is likely to pick up that effort in 2020 or beyond.”

  • ljk November 13, 2018, 10:37

    The end of an era in the exploration of Europa

    Last week’s midterm elections saw the defeat of Rep. John Culberson, a major advocate for missions to Jupiter’s moon Europa. Jason Callahan explains what that means for NASA missions under development, and why some scientists might not be that surprised.

    Monday, November 12, 2018


  • ljk November 13, 2018, 10:42

    A different trajectory for funding space science missions

    The budget increases that NASA’s planetary science program has enjoyed for the last several years may soon come to an end, even while there’s no shortage of compelling mission concepts. Jeff Foust reports on two alternative approaches under study for doing planetary exploration, involving philanthropy and coalitions.

    Monday, November 12, 2018


  • ljk November 19, 2018, 12:18

    This is what happens when you have a population that is undereducated regarding their place in the real Universe:


    The public was generally more dedicated to space exploration back in the 1950s and early 1960s in comparison. There is a rise happening again, but obviously not soon or fast enough.

    Let us not have a repeat of the 2012 US Presidential elections, where the subject of a manned lunar base was met with ridicule and in the case of Mitt Romney, declaring he would fire any of his staff who dared to bring up such a subject to him.

    • ljk November 19, 2018, 12:21

      Quoting from the above blog piece – and note this is something we all need to be involved with, if Centauri Dream readers ever really want to see humanity explore the stars:

      Make no mistake, this ad is anti-science. This dismissal of a scientifically valid area of study—one that could potentially reshape entire fields of science—should be roundly rejected by any citizen committed to a modern scientific society, regardless of political affiliation.

      The point here is not to draw conclusions about Republicans versus Democrats, or whether Culberson deserved to be reelected by his district. Nor is it to say that this ad was the primary factor as to why Culberson lost his seat. The point is that supporting space science was seen as a liability—something to be exploited instead of commended—and it was used to diminish and embarrass the candidate for having the nerve to embrace far-reaching scientific goals. No doubt this lesson will be internalized by other politicians: space science and exploration should be pursued quietly and apologetically, an extravagance to be indulged only after “real” issues are addressed.

      It is likely that the individuals who made this ad did not think about these implications, nor do they consider themselves anti-science. But the message they sent was clear: to anyone who dares to dream about exploration and discovery, to anyone who finds their soul stirred by the thought of discovering life beyond Earth, to anyone who finds the courage to take the cosmic perspective—you do not belong here, and you do not deserve to have access to power. And in that sense, we as a nation, as a polity, and as a species, are diminished.

      A new congress convenes next year. There will be many new faces, including Lizzie Fletcher, that have yet to understand the awesome scientific potential of planetary exploration. The political implications from this election are a setback, but they are not permanent. It’s up to us as Planetary Society members and supporters to ensure the new Congress learns that an ancient ocean on a distant moon has value—and is worth their support—in addition to issues here on Earth.

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