The words in the image above form part of the conclusion to Arthur C. Clarke’s 2010: Odyssey Two, the sequel to Stanley Kubrick’s collaboration with Clarke, 2001: A Space Odyssey, and itself made into a film by Peter Hyams. They come as the alien force responsible for the strange monoliths that triggered the events of 2001: A Space Odyssey cause the gravitational collapse of Jupiter, generating sufficient compression to start nuclear fusion, turning it into a mini-sun.
The actions were taken due to primitive life being found in the waters under Europa’s crust of ice; life trapped in an evolutionary cul-de-sac unless Europa received greater sunlight to melt the ice, evaporate some of the sea to expose landmasses and allow its burgeoning life the opportunity to grow and evolve. The words were issued to prevent humanity interfering in this process.
While there is no sign of aliens, monoliths, or anything like it around Jupiter, we do know there is a vast salty ocean under Europa’s ice, potentially 100 km (62.5 mi) deep and kept liquid as a result of the gravitational forces of Jupiter and other Galilean moons causing Europa to “flex” and generate heat deep within itself – and that ocean could be the home of life.
It had generally been thought that the salt in Europa’s ocean was likely magnesium chloride. Now a new study indicates that the salt could well be sodium chloride – the same salt present in our own oceans. This has important implications for the potential existence of life in Europa’s hidden depths.
Scientists believe that hydrothermal circulation within the ocean, mostly likely driven by hydrothermal vents created on the ocean floor as a result of Europa’s “flexing”, might naturally enrich the ocean in sodium chloride. On Earth, hydrothermal vents have been shown to support life around them, which utilises the minerals and heat from the vent. Much the same could be occurring on Europa.
Identifying the presence of sodium chloride has been a long time coming. Europa is tidily-locked with Jupiter, meaning it always keeps the same side pointed toward the planet. As a result, studies of the moon have been focused on its far side relative to Jupiter, as this side of the moon reveals much of the complex and continuing interaction taking place between Jupiter, Europa, and Jupiter’s innermost moon, Io, which results in sulphur from Io to be deposited on Europa.
Mixed in with these sulphur deposits are traces of magnesium chloride, which led researchers to believe it had been ejected from the moon’s ocean through the cracks and breaks that occur in Europa’s icy shell as a result of the internal “flexing”. However, when reviewing recent data obtained from the Keck Observatory, the team responsible for the new study found something odd. The data – gathered in infra-red – included the “side” of Europa facing along the path of its orbit around Jupiter – a face largely free from sulphur deposits from Io, although it is still stained yellow.
It had been assumed that this discolouration was due to more magnesium chloride being ejected from within Europa. But magnesium chloride is visible in the infra-red – and the Keck data didn’t reveal any such infra-red signature associated with the discolouration. So what might be causing them?
One of the study’s authors, Kevin Hand of NASA’s Jet Propulsion Laboratory, realised that sodium chloride is “invisible” under infra-red – but it can change colour when irradiated. Carrying out tests on ocean salts, he found they did turn yellow under visible light when irradiated. He then analysed the yellow in the salt and the yellow on Europa imaged by Hubble – and found the two exhibited exactly the same absorption line in the visible spectrum.
We’ve had the capacity to do this analysis with the Hubble Space Telescope for the past 20 years. It’s just that nobody thought to look.
Mike Brown, Professor of Planetary Astronomy at Caltech, and study co-author
This is the clearest evidence yet as to the nature of Europa’s ocean and its similarity to our own, life-supporting ocean. However, it’s not absolute proof: the sodium chloride might be indicative of salt deposited in Europa’s icy crust from long ago, rather than evidence of it being contained with the moon’s oceans. However – and despite the fictional warning from Clarke’s novel – the study ups the need for us to send a mission to Europa that is capable of penetrating its icy surface and directly studying the ocean beneath ice, both for signs of possible life, and better understand the processes that might be occurring within its depths.
Starshade: The Quest to See Exoplanets
Over the last few decades, astronomers have discovered over 4,000 exoplanets orbiting other stars, leading to wide-ranging debates as to the suitability of such worlds supporting life. One of the ways we could better make such a determination would be through direct analysis of their atmospheres. The problem here is that given the distances involved, the atmospheres of exoplanets are effectively masked from observation from Earth by the glare of their parent star.
Plans are in hand to achieve this. When the WFIRST telescope is launched in the mid-2020s – assuming it continues to survive attempts by the White House to delay or cancel it – it will carry an instrument called the stellar coronagraph. This will effectively block the light of a star from reaching the telescope’s imaging systems, allowing it to see the atmospheres of planets roughly the size of Saturn or Jupiter or larger. But to see the atmospheres of smaller exoplanets – the size of the majority so far discovered – an alternative its required. Enter Starshade.
Also called the New World Project, Starshade has been in development since 2005 – although it has yet to gain formal mission status. In essence, it proposes the deployment of a purpose-built space telescope and an “occulter” – a massive deployable, adjustable shade, 26 metres (85 ft) in diameter.
The idea is that, placed between the telescope and a star with known exoplanets, the shade would block the star’s light – but allow the light from the planets be received by the telescope, allow it to be spectrographically analysed. This would allow scientists to understand the nature and composition of any atmospheres these planets might have, and thus determine their possible suitability for life.
One of the stumbling blocks for the proposal has been cost: developing and launching both a purpose-built telescope and occulter has been put at US $3 billion. However, were Starshade to be used with an already budgeted telescope – say WFIRST – that cost comes down to just US $750 million. Thus, the most recent studies related to the project have been focused on achieving this. In doing so, they’ve raised a significant technical issue: alignment.