A cutaway view of Saturn's moon Enceladus, showing possible hydrothermal activity that may be taking place on and under the seafloor of its subsurface ocean. Image: NASA/JPL
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The unexpectedly watery moons of our Solar System may be friendlier to life than we thought

Secret oceans on the moons Enceladus and Ganymede were discovered within days of each other, reshaping our belief that the Earth is the Solar System's most watery, life-friendly habitat.

Jupiter’s moon Ganymede is named after the cup-bearer of the Greek gods; Saturn's sixth-largest moon, Enceladus, is named after a giant. Both names seem extra fitting in the light of recent, and surprisingly big, news about water.

In the (best-ever) anime series Cowboy Bebop, Ganymede is depicted as an aquatic, terraformed world entirely covered in water - and this may well be more accurate than we first thought, as Nasa’s Hubble Space Telescope has confirmed the existence of subsurface water on the huge moon by watching how its aurora lights slither around its edges. Astronomers believe this ocean, hidden underneath around 153km of crusty ice, is ten times deeper than those of Earth.

This new discovery has hoisted Ganymede up the list of the top contenders for places in our Solar System which could potentially harbour life. It also has relatively good timing - the European Space Agency (ESA) is currently working on mission plans ahead of the launch of the Jupiter Icy Moon Explorer (or Juice for short) in 2022, with the aim of getting a closer inspection of Jupiter’s moons Ganymede, Callisto and Europa through the 2030s.

Speculation about Ganymede’s secret ocean is not a new one, as scientists have suspected its existence since the 1970s, despite inconclusive evidence. What sets Ganymede apart from any other moon (aside from its size - it's larger than Mercury) is its self-generating magnetic field, which, just like Earth, is caused by its liquid, iron-rich core. This makes the detection of a copious amount of subsurface liquid water easier - more so than any other icy moon in our Solar System - because a magnetic field causes auroras, brightly-coloured ribbons of hot, electrified gas in the atmospheric regions circulating north and south poles. Ganymede is also close enough to Jupiter that their magnetic fields are interlaced, enhancing the aurora even more than usual. When Jupiter’s magnetic field changes, so does Ganymede’s, "rocking" back and forth over about a five hour period.

The auroras of Ganymede give away the existence of a subsurface saltwater ocean because saltwater can generate its own magnetic field when sloshing around, and can also therefore weaken the effects of Jupiter's. Joachim Saur and his colleagues of the University of Cologne in Germany came up with the idea of applying the motions of the two auroras to determine the amount (if any) of saltwater underneath Ganymede’s crust using the Hubble Space Telescope. He told the NS that the data showed that Ganymede had low auroral oscillations compared to models without an ocean - or, in other words, that Ganymede does have a saltwater ocean underneath its crust.

Nasa’s Galileo mission measured Ganymede’s magnetic field in 2002 but couldn’t see the full extent of its magnetic variation as its fly-bys of Ganymede lasted just 20 minutes - far too brief to measure the magnetic field of this subsurface saltwater ocean. Saur’s team instead watched Ganymede using the Hubble Space Telescope for seven hours. The data suggests that the global ocean is between 150 and 250km deep, and this broad range of approximation is likely caused by the presence of what may be two layers of ice sandwiched between the oceans.

So, could there be life on Ganymede? Hubble found evidence of a tenuous oxygen atmosphere in 1996, but it would be far too thin to support life (or, at least as we know it). We’ll have to wait and see if Juice can freshly squeeze anything more concrete when it arrives there, more than 15 years from now. In addition, Saur said that the aruoral technique used for Ganymede can help identify life-friendly water on other planets (or moons) with subsurface oceans outside the Solar System. Hubble isn’t powerful enough to capture these auroras yet, however it's only a matter of time, as more powerful instruments - like the James Webb Space Telescope, due in orbit in 2018 - are on their way.

Enceladus, meanwhile, is slightly different. We know it has water of some kind on it, as it has a crust of fresh, white ice, of thicknesses stretching from 30 to 40km. This gives it a high albedo, meaning it shines light brightly back into space; and it, too, is believed to be hiding a secret, warm, liquid ocean beneath its surface. Ever since Nasa’s Cassini spacecraft first discovered water vapour and ice spewing from vents near the moon’s south pole in 2005, researchers have theorised about the possible presence of liquid water there. 

On Earth, the kind of hydrothermal activity that would cause the ejection of water from vents tends to happen when seawater interacts with gaps in the planetary crust, so the Cassini data seemed to suggest this was what was happening on Enceladus as well. This deduction was strengthened further by the detection of methane in the plumes, and microscopic granules of silica - exactly the kinds of materials that should be generated around underwater vents.

In a Nasa statement, Sean Hsu, a postdoctoral researcher at the University of Colorado and the lead author of the paper published in Nature, said: "It's very exciting that we can use these tiny grains of rock, spewed into space by geysers, to tell us about conditions on - and beneath - the ocean floor of an icy moon." Cassini hit the jackpot with the detection of silicates, which are believed to have come from inside the vents and then became wedged in icy structures called clathrates before being fired upwards into space. It indicates that these volcanic vents are still active, and generating new silicates - and that they're therefore also likely to still be warm enough to support microbial life, if it exists there.

This evidence all strongly suggests that Enceladus contains within it a 10km-deep ocean, with temperatures as high as 90oC in some parts - any little critters down there just have to swim to the hot bit to get to someplace comfy (though the chances of anything bigger than single-cell organisms existing there are extraordinarily slim). Enceladus and Ganymede are now part of a growing list of strong candidates for hosting alien microbial life, as well as Neptune’s moon Triton and Jupiter’s other moon Europa, as well as the dwarf planet Ceres.

Tosin Thompson writes about science and was the New Statesman's 2015 Wellcome Trust Scholar. 

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Why have men become so lonely – and how does it affect their health?

New findings show the consequences of having a lonely heart.

Go out and get some friends. No, seriously. Hop on the Tube and act faux-interested in the crap-looking book your fellow commuter is reading, even if it's on their Kindle. Chances are it's better than the one in your bag, and they're probably a decent human being and just as lonely, like you and me.

A new slate of facts and figures are showing just how widespread loneliness, is while simultaneously being amazingly terrible for your health.

Research led by Steven Cole from the medicine department at University of California, Los Angeles is showing the cellular mechanisms behind the long known pitfalls of loneliness. Perceived social isolation (PSI) – the scientific term for loneliness –increases the exposure to chronic diseases and even mortality for individuals across the world.

The authors examined the effects of loneliness on leukocytes, also known as white blood cells, which are produced from stem cells in the bone marrow and are critical to the immune system and defending the body against bacteria and viruses. The results showed loneliness increases signalling in the sympathetic nervous system, which is responsible for controlling our fight-or-flight responses, and also affects the production of white blood cells.

Recently, the Movember Foundation, which focuses on men's health and wellbeing, carried out a survey with the help of YouGov investigating friendship and loneliness amongst men. The results are alarming, with only 11 per cent of single men across the spectrum in their early 20s to late-middle age saying they had a friend to turn to in a time of crisis, the number rising to 15 per cent for married men.

Friendship has shown not only to be important to a person's overall wellbeing, but can even add to a person's earnings. A previous study involving 10,000 US citizens over 35 years showed people earned 2 per cent more for each friend they had.

The Movember Foundation survey comes soon after the Office for National Statistics (ONS) showed that men in Britain make up 58 per cent of the 2.47m people living alone between the ages of 45 and 64. The reasons behind this figure include marrying later in life and failed marriages, which usually result in children living with the mother. Women still make up the majority of the 7.7m single-occupant households across all ages in the country, at approximately 54 per cent.

Chronic loneliness seems to have slowly become a persistent problem for the country despite our hyper-connected world. It's an issue that has made even Jeremy Hunt say sensible things, such as "the busy, atomised lives we increasingly lead mean that too often we have become so distant from blood relatives" about this hidden crisis. He's previously called for British families to adopt the approach of many Asian families of having grandparents live under the same roof as children and grandchildren, and view care homes as a last, not first, option.

The number of single-person households has continued to increase over the years. While studies such as this add to the list of reasons why being alone is terrible for you, researchers are stumped as to how we can tackle this major social issue. Here's my suggestion: turn off whatever screen you're reading this from and strike up a conversation with someone who looks approachable. They could end up becoming your new best friend.