- NASA’s New Horizons probe is approaching the Kuiper Belt.
- Freeman Dyson suggested Europa and the Kuiper Belt as habitats for life in the solar system.
- Europa’s ocean is under an ice pack, so life would be undetectable.
- If there is life in the Kuiper Belt, New Horizons may find it.
It won’t stop there. It will make its closest approach to Pluto on 14th July, by which time it will have added an enormous amount to the sum of knowledge on Pluto and its moons. It will then whizz out of Pluto’s system and continue its exploration of the Kuiper belt.
New Horizons will not be the first probe in the Kuiper belt, as the Voyager probes passed through it some years ago. Unlike the Voyagers, New Horizons was intended from the outset to explore Kuiper Belt objects. Nine years and three billion miles after it was launched, Its flyby of Pluto is the beginning of that mission.
Moving from the realms of fact to the realms of wild speculation, one thing that makes New Horizons particularly interesting is that in a 2003 TED talk, physicist Freeman Dyson named the Kuiper belt as one of the more likely places to find life in the solar system:
Is there life in Europa’s ocean?
Along with the Kuiper Belt, Dyson hypothesises Jupiter’s moon Europa as a likely candidate for harbouring life. Life on Europa has been speculated ever since the Voyager probes photographed its ice surface in 1979. The speculations were shared more widely when Arthur C Clarke made Europan life central to his novel, 2010: Odyssey Two.The speculation was given more credence by the conclusion that there is probably an ocean of liquid water beneath Europa’s ice crust. Europa warmed by friction from its ongoing tug-of-war with Jupiter and its other moons, which leads to tidal flexing. The water and whatever rocky material lies under it is pulled in different directions in a similar process to the way the gravity of the sun and the moon cause tides on earth. Depending on the geology of whatever rocky core lies beneath that ocean, Europa’s close proximity to the enormous mass of Jupiter may lead to volcanic activity, which would make the emergence of life even more likely.
In the deep oceans of earth, there are whole ecosystems that feed off the hydrogen sulphide released by submarine volcanoes. It has been hypothesised that the first life on earth originated in such an environment. If similar volcanoes exist on Europa, all the conditions for the origins of life would be there.
Life on Europa’s surface
Dyson states that his philosophy is to ‘look for what’s detectable, not for what’s probable’, and we have no way of detecting anything going on under Europa’s ice pack. Dyson speculates that Europan organisms may have grown through the crust of ice to emerge on to the surface. He goes further, suggesting that such life would make use of sunlight, in the same way that plants on earth use it to drive photosynthesis. Europa only receives around 4% as much sunlight as earth, so such a plant would have to use mirrors or lenses to concentrate sunlight and so create reflections that would be visible from earth, or at least from a probe.
Dyson was openly speculating and was restricted to the 18min of a TED talk, but there are several problems with his hypothesis. For one thing, it appears very unlikely that a photosynthetic plant could evolve on Europa’s surface at all. It would take a fairly complex organism to break through a solid ice crust to reach the surface, and complexity does not lend itself to adaptability. The hypothetical icebreaker would have lived its entire evolutionary history at high pressure, surrounded by water, and protected from cosmic radiation.
Europa’s atmosphere is negligible and composed mainly of oxygen, which is toxic to organisms that have not evolved to deal with it. Consequently the icebreaker would emerge from a high pressure water environment into a very low pressure environment of toxic gas that is scoured by radiation. Before an organism could evolve the complex chemistry needed to make use of that radiation, it would need to evolve a way of surviving it. Life on Europa’s surface may be as untenable as life beyond earth’s atmosphere.
Europa’s barren iceWhile it would be evolutionarily very difficult for an organism to live on Europa’s surface, it is impossible to rule it out completely so we may ask how such an organism might be detected if it exists. Dyson suggests that in Europa’s dim sunlight, a photosynthesising organism would need to capture light by reflecting it toward a central point. He suggests that the reflection could be detected as a bright point on Europa’s surface.
There is a further problem with Dyson’s hypothesis, which is that a plant using reflectors to capture light would not be reflecting it back outward, but rather capturing it. Rather than appearing as a bright spot, a plant capturing sunlight would appear as a dark spot on Europa’s highly reflective icy surface. As there is unlikely to be much variation in the nature of the ice, an organism that could grow on the surface at all could probably grow anywhere on the surface. Even if it was restricted by minimum or maximum radiation exposures, it could still cover substantial areas. Whether or not Dyson’s suggestion about reflectors is right, it is unlikely that the organisms would have exactly the same reflectivity as ice, so they would be visible from space, just as plant growth stains large areas of the earth’s surface green.Neither Dyson’s reflections nor any dark areas have been identified, which suggests that there is no life on Europa’s surface. Europa’s ocean may be teeming with life, but the only way we will ever find out is to burrow through the ice surface and go looking for it. NASA’s Europa Clipper mission, incorporating a lander operated by the European Space Agency, though it will not be designed for the considerable task of tunnelling through Europa’s ice pack. If the mission survives the vicissitudes of funding committees, it will begin exploring Europa in about 2030.
More definite but less thorough is the ESA’s Jupiter Icy Moon Explorer, rather fetchingly abbreviated to JUICE, which will make a flyby with radar that will penetrate the ice to a depth of 30km en route to its main objective of Ganymede. JUICE will tell us a lot more about how likely it is that Europa can support life, but it will not look for life itself.
Life in the Kuiper Belt
If Europa is harbouring life, it will keep it a secret for decades to come. That makes it all the more exciting that New Horizons will be able to explore Dyson’s speculations about the Kuiper Belt. Most of Kuiper Belt Objects are made of water, ammonia or methane, all of which are solid in the diffuse sunlight beyond Neptune’s orbit. Some, like Pluto, are large enough to be classified as dwarf planets, meaning that their gravity is strong enough to pull their surface into a stable spherical shape but not strong enough to have cleared their vicinity of other objects.Dyson points out that the volatiles that make up much of the mass of the Kuiper belt are the basics from which life probably emerged on earth, although they are in gas or liquid form this close to the sun. However, the distribution of the Kuiper Belt’s mass into small objects means that there is a considerable surface area that has been exposed to radiation for several billion years. The starting conditions for life may have emerged at least once, and once is all it would take.
Unlike on Europa, life that emerged on the surface of a Kuiper Belt object would originate and evolve in high radiation, so would not be constrained by it.
It would also evolve in very low gravity. The most massive object in the Kuiper Belt is Pluto, which has a surface gravity of less than 7% of earth’s. Most are considerably smaller, so it’s quite possible that something that evolved on the surface of a Kuiper Belt object may be able to spread to others. If so, life would have been spreading through the Kuiper Belt for billions of years and if it is on the surface of the Kuiper Belt Objects, New Horizons stands a good chance of spotting it.
Panspermia from the Kuiper Belt
Seeding through space has been suggested by the Panspermia hypothesis, which suggests that simple life forms which can survive conditions in space may be able to move from one solid object to another. It has been suggested that life on earth may have originated elsewhere and arrived here, either in the form of spores floating freely or on a meteorite. For an organism that evolved in the Kuiper Belt, the conditions it would encounter in space would be far more similar to the conditions it evolved in than they would be for something that evolved on a planet like earth.
Combining Dyson’s suggestion of life in the Kuiper Belt with the Panspermia hypothesis, we may – wildly – speculate that the Kuiper Belt may be the origin of all life in the solar system including that on earth, Europa and several other places where we have yet to find it.
Part of the reason we are free to speculate so wildly about the Kuiper Belt is that we know so little about it. Speculation about life in the solar system is always one step beyond exploration. Every time we have tested a new rock for the presence of life, we have confirmed its absence. Realistically, New Horizons will probably give us beautiful and fascinating pictures of barren ice.
That will not stop me speculating about the many places we still know nothing about. I hope you will join me.