Europa is a moon of Jupiter, the smallest of the four Jovian moons discovered by Galileo in 1610. Juipter has 63 objects circling it that are called moons, though only eight of them are “regular” in their orbit and other characteristics. The rest are bits and pieces of clumped up matter that were probably captured by Jupiter’s big-ass gravitational field, and have irregular orbits, i.e., they go the wrong-way around the planet, or are not in the solar plane, etc.
Europa is almost as big as the Earth’s moon, probably has an iron core, and is otherwise made of silica. There is an atmosphere made mostly of oxygen, and the surface is covered with ice made of water. Beneath the ice might be liquid water. Although Europa is not sufficiently warmed by the sun to have enough warmth for nice M-class conditions, there is heat provided by the giant planet’s gravitational interactions with its moon. Any largish object in a strong gravitational field will experience differential pull across its mass. Depending on what the object is made of and other factors, it can simply heat up due to the forces of gravity being converted to kinetic energy at a molecular level.
Europa’s surface is nearly devoid of impact scars and is covered with cracks and other features that together indicate a liquid water layer beneath the ice surface, as well as melting and refreezing of the surface. Unless catastrophic life-unfriendly events are common on Europa, if it does indeed have constant liquid water owing to tidally induced warmth, then there IS life on this moon!
Maybe. If live is the kind of thing that evolves wherever certain conditions are present, then there is a pretty good chance that there is life there. Or at least, the chances of life on Europa in the past or present are good enough that if one is serious about one’s astrobiology, one would want to go there, a feat best accomplished vicariously through the use of probes and robots.
There is a controversy among planetary scientists as to how think the ice on Europa is. Some say that it is very thick, others say that it is either thin or has the capacity to become very thinned out over large period and for considerable periods of time. The thickness vs. thinness of ice on Europa, and the frequency with which water is exposed directly to the atmosphere will impact both the likelihood of life being there and what that life may be up to, as well as any strategy to examine it directly. For instance, a thin layer of ice would allow some interaction between the atmosphere and the liquid below, and certainly, any regular breaks would enhance this. This brings up several issues not only related to methods and approaches to the exploration of Europa, but also, ethics.
What if there is life there? What if, for instance, life is present in the sub-ice sea like so many walleye in a Minnesota lake in January, but exposure of the sea via holes punched in the surface (by meteors, for example) is deadly and causes local extinctions? An Earthling probe would arrive on the surface of the ice, drill a hole through it like a fisherman on a Minnesota lake in January, and as soon as the hole is punched through, mayhem ensues. Or, if the estimate of thickness of the ice is way off, maybe the machine we send will go crashing through the ice. Like a fisherman on a Minnesota lake in late February. If the life is complex and intelligent, perhaps the Earthling probe’s blunder will kill Europa’s leader. Or a school full of beloved Europan children. Or, if we are lucky, the Europan equivalent of Adolph Hitler.
Of course, most likely, life on Europa would not have intelligence. For that matter, it might not even have multicellularity. Or any cellularity. Which is why we want to look … if there is life there, we want to see what the heck it looks like, and learn how it works, and try to figure out how it came to be and how it may have changed over time, and so on and so forth, because a) that would be so freakin’ cool and b) we would learn so much about what life is, simply by adding to our sample of instances of life in our solar system.
If Europan life includes children and philosophers and workers and criminals, it would be highly unethical to do something that did damage to it … them … whatever. But even if Europan life is essentially bacterial, it would be wrong to mess up the ecology of another planet by simply arriving there and mucking around. And there are plans to go there. Therefore perhaps there should be plans to go there in a way to minimize harm, and that take into account the full range of models of how the ice is distributed, how thick it is, and how it changes over time. This is the subject of a recent paper by Richard Greenberg, who is the author of Unmasking Europa: The Search for Life on Jupiter’s Ocean Moon. Greenberg is one of the scientists who thinks the ice surface of Europa is thin and dynamic and that there is significant ocean-atmosphere interaction. That and the nasty big-science politics linked to this debate are covered in his book. I’m sure the paper, which he sent me last week, will spark some controversy.
Here’s the abstract from Greenberg’s paper, published in Astrobiology:
Europa has become a high-priority objective for exploration because it may harbor life. Strategic planning for its exploration has been predicated on an extreme model in which the expected oceanic biosphere lies under a thick ice crust, buried too deep to be reached in the foreseeable future, which would beg the question of whether other active satellites might be more realistic objectives. However, Europa’s ice may in fact be permeable, with very different implications for the possibilities for life and for mission planning. A biosphere may extend up to near the surface, making life far more readily accessible to exploration while at the same time making it vulnerable to contamination. The chances of ?nding life on Europa are substantially improved while the need for planetary protection becomes essential. The new National Research Council planetary protection study will need to go beyond its current mandate if meaningful standards are to be put in place. Key Words: Europa–Planetary protection–Mission planning–Spacecraft–Geology. Astrobiology 11, 183-191.
The long term plan for exploration of Europa involves three phases: First, an orbiter around the moon, then a lander to explore the surface of the ice, and later a rig to drill through what is assumed (by the dominant thick-ice school of thought) to be a few thousand meters of ice and into the ocean below. This model is predicated on the idea that the Europa’s ocean is fully separate from its atmosphere, and that life on that moon would have evolved along some Europan equivalent of Earth’s hydrothermal vents.
One of Greenberg’s complaints about this stems from the mission’s obvious near-impossibility, especially with respect to the deep drilling part. The assumption of thick ice leads to an assumption of great technical difficulty in the mission which in turn leads to the schedule for the mission being extended significantly. At this point, the orbiter, originally scheduled to have been sent there already, will not be in place until nearly 2030. Greenberg claims that since that plan was originally developed in the 1990s our conception of Europa has changed enough that the mission itself needs to change as well. From the paper:
If Europa’s ice is in fact permeable, it would have major implications for mission planning, because organisms or their markers would be readily accessible near the surface. The prospects for discovering extraterrestrial life in the foreseeable future would improve immensely. At the same time, a europan ecosystem would be highly vulnerable to contamination, so planetary protection becomes a critical issue.
Greenberg goes on to describe his updated model of Europa’s surface conditions and the dynamics of the ice surface, and to suggest alternative views of Europa’s possible biosphere. And, of course, he makes the point that if the ice is permeable, the prospects for life there are enhanced significantly.
There is a lot more to the discussion of ethics (and the evolution over time of ethical guidelines in space exploration) that I will not go into here, but it’s all in the paper. Unfortunately, you may have to subscribe to Astrobiology to get it. If you have questions, put them in the comments and perhaps I can persuade Dr. Greenberg to have a look.
Greenberg, R. (2011). Exploration and Protection of Europa’s Biosphere: Implications of Permeable Ice Astrobiology, 11 (2), 183-191 DOI: 10.1089/ast.2011.0608