Signs of water plumes on Jupiter’s moon Europa suggest it might harbour life

Jupiter. Image: Getty.

Along with Mars, Jupiter’s moon Europa has long captured the imagination of science fiction writers as a potential place for life in the solar system beyond Earth. In science fact, missions have found hints of a subsurface water ocean below the icy crust of the moon. And where there’s warm, liquid water, and the right chemistry, there could indeed be life.

Finding out whether this is the case is not going to be easy though. One complicated and expensive solution would be landing on the moon and drilling a hole through the ice to sample the water beneath. But now research has thrown up a better option. The exciting results, published in Nature Astronomy, suggest there may be plumes emanating from Europa’s ocean – meaning a spacecraft could simply fly though them to test the water. The findings are important for the upcoming Europa Clipper missions and JUICE missions.

It’s not the first time it’s been suggested that there are geyser-like features on the moon. The Hubble Space Telescope saw transient signs of plumes from Europa’s subsurface ocean in 2012 and 2016. However, the result was controversial – the data was after all captured from far away (Hubble orbits the Earth). The new evidence instead comes from an actual flyby of Europa by the Galileo mission in 1997 – significantly strengthening the evidence that there are plumes on the moon.

We don’t know exactly how thick Europa’s ice shell is or how deep its subsurface ocean is. A 2011 study showed that there are locations where water may be relatively close to the surface in great lakes, near chopped up icy “chaos regions”, which are similar to some Antarctic structures on Earth.

Lessons from Enceladus

The Cassini mission to Saturn discovered huge plumes of water coming from the small moon Enceladus. The first hints were from magnetic field deflections and an abundance of charged particles in a certain region of the moon. We know that the dense gas of newly emerged molecules and atoms in a watery plume becomes charged (ionised) as electrons are knocked off. This makes it electrically conducting, causing changes to surrounding magnetic fields.

Enceladus’s south polar plumes, as seen by Cassini, 30 November 2010. Image: NASA/JPL-Caltech/Space Science Institute.

Next, the plumes were actually spotted in spectacular images, emanating from what looks like tiger stripes near the south pole. There is evidence from gravity measurements that the source is a subsurface ocean.

Cassini flew past Enceladus 22 times, enabling exploration of the plumes ejected directly from the ocean below. As well as simple water, ions and charged grains in the plumes, Cassini found sodium – a sign that the ocean is salty. It also found silicates, which indicate a sandy ocean floor and potentially the existence of hydrothermal vents.

This is important as chemical reactions between sand and water can provide enough energy in the water to feed microbial life (and tends to happen near hydrothermal vents on Earth). Finally, in 2107, Cassini also discovered hydrogen in the plumes, which should be a byproduct of such water-sand reactions. This is as close as you can get to a proof that it is a suitable candidate to host life.

Following these exciting discoveries, the hunt was on for plumes at Europa. Based on the Hubble measurements, estimates in 2012 showed that the amount of water released in the Europa plumes could be a factor 30 times that of Enceladus. The plumes appeared to have a height of some 200km. Like Enceladus, the floor of Europa’s ocean is likely in contact with sand and rock. This is in contrast to some other moons with subsurface oceans – including Ganymede and Callisto – where the ocean floor is ice.

In the new study, magnetometer data from a Galileo flyby less than 400km above Europa’s icy surface was reexamined and compared with a modern computer model of how charged gas on Europa should behave. The results – based on an observed deflection and decrease in the observed magnetic field over a distance of 1,000km – imply that there’s a dense region of charged particles. This is very likely to be the result of a plume, making it the best direct evidence for such an occurence yet.

Upcoming missions

As with Enceladus, the Europa plumes offer the tantalising prospect of directly sampling material from the subsurface ocean. Two future missions will be able to explore this. The European Space Agency’s JUICE mission, which I am involved in developing, is due to launch in 2022 and will arrive in the Jupiter system on 2030. Two close flybys of Europa are planned as part of a sequence, before going into orbit around the moon Ganymede in 2032.

NASA’s Europa Clipper will perform 45 flybys of Europa. Both these missions can explore the plumes in the same way the Cassini orbiter did at Enceladus. Following these, landers or penetrators at Europa have been proposed (but yet to secure funding). In the meantime, sampling the plumes could provide many exciting insights into what’s going on in the ocean. If we are really lucky we may even be able to detect signatures of biological activity. Unfortunately, Cassini was not equipped to look for such signatures at Enceladus.

Image: NASA/JPL-Caltech/SETI Institute.

This means there are now four likely locations for life beyond Earth in our solar systems. First Mars, where conditions were right for life to form 3.8bn years ago. We will explore this further with the ExoMars 2020 rover, which I am also involved in developing. This will be able to drill up to two metres underneath the surface to search for biomarkers, as well as the NASA Mars 2020 rover and the related helicopter recently announced.

But on Europa and Enceladus there could actually be life now, and sampling the plumes will help reveal whether this is the case. At Saturn’s moon Titan, we have also found signs of complex prebiotic chemistry that once gave rise to life on Earth. This means it is a location for future or perhaps current life.

As well as the planned missions to Mars and Europa, it is therefore also important that we also return to the Saturn system to track down where there may be life elsewhere. NASA’s Dragonfly quadcopter proposed for Titan is one possibility.

The ConversationWith so many promising candidates for life in our own solar system, it is exciting to think that it could be just a few years until we discover some form of microbial alien life.

Andrew Coates, Professor of Physics, Deputy Director (Solar System) at the Mullard Space Science Laboratory, UCL.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

The risk of ‘cascading’ natural disasters is rising

A man watches wildfires in California, 2013. Image: Getty.

In a warming world, the dangers from natural disasters are changing. In a recent commentary, we identified a number of costly and deadly catastrophes that point to an increase in the risk of “cascading” events – ones that intensify the impacts of natural hazards and turn them into disasters.

Multiple hazardous events are considered cascading when they act as a series of toppling dominoes, such as flooding and landslides that occur after rain over wildfires. Cascading events may begin in small areas but can intensify and spread to influence larger areas.

This rising risk means decision-makers, urban planners and risk analysts, civil engineers like us and other stakeholders need to invest more time and effort in tracking connections between natural hazards, including hurricanes, wildfires, extreme rainfall, snowmelt, debris flow, and drought, under a changing climate.

Cascading disasters

Since 1980 to January 2018, natural disasters caused an inflation-adjusted $1,537.4bn in damages in the United States.

The loss of life in that period – nearly 10,000 deaths – has been mounting as well. The United States has seen more billion-dollar natural disaster events recently than ever before, with climate models projecting an increase in intensity and frequency of these events in the future. In 2017 alone, natural disasters resulted in $306bn losses, setting the costliest disaster year on record.

We decided it was important to better understand cascading and compound disasters because the impacts of climate change can often lead to coupled events instead of isolated ones. The United Nations Office for Disaster Risk Reduction, or UNISDR, claims: “Any disaster entails a potentially compounding process, whereby one event precipitates another.”

For example, deforestation and flooding often occur together. When vegetation is removed, top soil washes away and the earth is incapable of absorbing rainfall. The 2004 Haiti flood that killed more than 800 people and left many missing is an example of this type of cascading event. The citizens of the poverty-stricken country destroyed more than 98 per cent of its forests to provide charcoal for cooking. When Tropical Storm Jeanne hit, there was no way for the soil to absorb the rainfall. To further complicate existing issues, trees excrete water vapor into the air, and so a sparser tree cover often yields less rain. As a result, the water table may drop, making farming, which is the backbone of Haiti’s economy, more challenging.


Rising risk from climate change

Coupled weather events are becoming more common and severe as the earth warms. Droughts and heatwaves are a coupled result of global warming. As droughts lead to dry soils, the surface warms since the sun’s heat cannot be released as evaporation. In the United States, week-long heatwaves that occur simultaneously with periods of drought are twice as likely to happen now as in the 1970s.

Also, the severity of these cascading weather events worsens in a warming world. Drought-stricken areas become more vulnerable to wildfires. And snow and ice are melting earlier, which is altering the timing of runoff. This has a direct relationship with the fact that the fire season across the globe has extended by 20 per cent since the 1980s. Earlier snowmelt increases the chance of low flows in the dry season and can make forests and vegetation more vulnerable to fires.

These links spread further as wildfires occur at elevations never imagined before. As fires destroy the forest canopy on high mountain ranges, the way snow accumulates is altered. Snow melts faster since soot deposited on the snow absorbs heat. Similarly, as drought dust is released, snow melts at a higher rate as has been seen in the Upper Colorado River Basin.

Fluctuations in temperature and other climatic patterns can harm or challenge the already crumbling infrastructure in the United States: the average age of the nation’s dams and levees is over 50 years. The deisgn of these aging systems did not account for the effects of cascading events and changes in the patterns of extreme events due to climate change. What might normally be a minor event can become a major cause for concern such as when an unexpected amount of melt water triggers debris flows over burned land.

There are several other examples of cascading disasters. In July, a deadly wildfire raged through Athens killing 99 people. During the same month on the other side of the world in Mendocino, California, more than 1,800 square kilometers were scorched. For scale, this area is larger than the entire city of Los Angeles.

When landscapes are charred during wildfires, they become more vulnerable to landslides and flooding. In January of this year, a debris flow event in Montecito, California killed 21 people and injured more than 160. Just one month before the landslide, the soil on the town’s steep slopes were destabilised in a wildfire. After a storm brought torrential downpours, a 5-meter high wave of mud, tree branches and boulders swept down the slopes and into people’s homes.

Hurricanes also can trigger cascading hazards over large areas. For example, significant damages to trees and loss of vegetation due to a hurricane increase the chance of landslides and flooding, as reported in Japan in 2004.

Future steps

Most research and practical risk studies focus on estimating the likelihood of different individual extreme events such as hurricanes, floods and droughts. It is often difficult to describe the risk of interconnected events especially when the events are not physically dependent. For example, two physically independent events, such as wildfire and next season’s rainfall, are related only by how fire later raises the chances of landslide and flooding.

As civil engineers, we see a need to be able to better understand the overall severity of these cascading disasters and their impacts on communities and the built environment. The need is more pronounced considering the fact that much of the nation’s critical infrastructure is aged and currently operate under rather marginal conditions.

A first step in solving the problem is gaining a better understanding of how severe these cascading events can be and the relationship each occurrence has with one another. We also need reliable methods for risk assessment. And a universal framework for addressing cascading disasters still needs to be developed.

A global system that can predict the interactions between natural and built environments could save millions of lives and billions of dollars. Most importantly, community outreach and public education must be prioritised, to raise awareness of the potential risks cascading hazards can cause.

The Conversation

Farshid Vahedifard, CEE Advisory Board Endowed Professor and Associate Professor of Civil and Environmental Engineering, Mississippi State University and Amir AghaKouchak, Associate Professor of Civil & Environmental Engineering, University of California, Irvine.

This article is republished from The Conversation under a Creative Commons license. Read the original article.