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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Age verification rules won't just affect porn sites – they'll harm our ability to discuss sex

Relying on censorship to avoid talking about sex lets children down.

The British have a long history of censoring sex. In 1580, politician William Lambarde drafted the first bill to ban "licentious" and "hurtful... books, pamphlets, ditties, songs, and other works that promote the art of lascivious ungodly love". Last week, the UK government decided to have another crack at censorship, formally announcing that age verification for all online pornographic content will be mandatory from April 2018.

It is unclear at this point what this mandatory check will entail, but it's expected that you will need to submit your credit card details to a site before being allowed to access adult content (credit cards can’t be issued to under-18s).

The appointed regulator will almost certainly be the British Board of Film Classification who will have the authority to levy fines of up to £250,000 or shut down sites that do not comply. These measures are being directly linked to research conducted by the NSPCC, the Children’s Commissioner and the University of Middlesex in 2016, which surveyed more than 1,000 11 to 16-year-olds about viewing online pornography and found over half had accessed it. 

Digital minister Matt Hancock said age verification "means that while we can enjoy the freedom of the web, the UK will have the most robust internet child protection measures of any country in the world". And who can argue with that? No sane adult would think that it’s a good idea for children to watch hardcore pornography. And because we all agree kids should be watching Peppa Pig rather than The Poonies, the act has been waved through virtually unchallenged.

So, let’s put the issue of hardcore pornography to one side, because surely we are all in agreement. I’m asking you to look at the bigger picture. It’s not just children who will be censored and it’s not just Pornhub and Redtube which will be forced to age check UK viewers. This act will potentially censor any UK site that carries adult content, which is broadly defined by the BBFC as "that it was produced solely or principally for the purposes of sexual arousal".

I am a UK academic and research the history of sexuality. I curate the online research project www.thewhoresofyore.com, where academics, activists, artists and sex workers contribute articles on all aspects of sexuality in the hope of joining up conversations around sex that affect everyone. The site also archives many historical images; from the erotic brothel frescoes of Pompeii to early Victorian daguerreotypes of couples having sex. And yet, I do not consider myself to be a porn baron. These are fascinating and important historical documents that can teach us a great deal about our own attitudes to sex and beauty.

The site clearly signposts the content and asks viewers to click to confirm they are over 18, but under the Digital Economy Act this will not be enough. Although the site is not for profit and educational in purpose, some of the historical artefacts fit the definition of  "pornographic’" and are thereby liable to fall foul of the new laws.

And I’m not the only one; erotic artists, photographers, nude models, writers, sex shops, sex education sites, burlesque sites, BDSM sites, archivists of vintage erotica, and (of course) anyone in the adult industry who markets their business with a website, can all be termed pornographic and forced to buy expensive software to screen their users or risk being shut down or fined. I have contacted the BBFC to ask if my research will be criminalised and blocked, but was told "work in this area has not yet begun and so we are not in a position to advice [sic] you on your website". No one is able to tell me what software will need to be purchased if I am to collect viewers' credit card details, how I would keep them safe, or how much this would all cost. The BBFC suggested I contact my MP for further details. But, she doesn’t know either.

Before we even get into the ethical issues around adults having to enter their credit card details into a government database in order to look at legal content, we need to ask: will this work? Will blocking research projects like mine make children any safer? Well, no. The laws will have no power over social media sites such as Twitter, Snapchat and Periscope which allow users to share pornographic images. Messenger apps will still allow users to sext, as well as stream, send and receiving pornographic images and videos. Any tech savvy teenager knows that Virtual Private Network (VPN) software will circumvent UK age verification restrictions, and the less tech savvy can always steal their parents' credit card details.

The proposed censorship is unworkable and many sites containing nudity will be caught in the crossfire. If we want to keep our children "safe" from online pornography, we need to do something we British aren’t very good at doing; we need to talk openly and honestly about sex and porn. This is a conversation I hope projects like mine can help facilitate. Last year, Pornhub (the biggest porn site in the world) revealed ten years of user data. In 2016, Brits visited Pornhub over 111 million times and 20 per cent of those UK viewers are women. We are watching porn and we need to be open about this. We need to talk to each other and we need to talk to our kids. If you’re relying on government censorship to get you out of that tricky conversation, you are letting your children down.

The NSPCC report into children watching online pornography directly asked the participants about the effectiveness of age verification, and said the children "pointed out its limitations". When asked what intervention would most benefit them, this was the overwhelming response: "Whether provided in the classroom, or digitally, young people wanted to be able to find out about sex and relationships and about pornography in ways that were safe, private and credible." I suggest we listen to the very people we are trying to protect and educate, rather than eliminate. 

Dr Kate Lister researches the history of sexuality at Leeds Trinity University