Space Sunday: Europa, a Starshade and ambitions

Arthur C. Clarke’s fictional warning from 2010: Odyssey Two, given with regards to Europa. Now we may have a further reason to send a mission to probe the ocean beneath the moon’s icy crust. Credit: NASA / I. Pey

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.

Europa’s internal structure, showing the subsurface ocean which could be up to 100 km (62.5 mi) deep. Credit: NASA

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.

NASA has had many plans for missions to explore Europa’s ocean. Thus far, none have got beyond the the planning phase. Credit: NASA

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.

A pair of composite images of Europa. On the left, as seen in natural light; on the right the same image that has been colour enhanced. They show, on the right, the “far side” of Europa relative to Jupiter, the rust colour the result of sulphur ejected from Jupiter’s inner moon Io being deposited on Europa by Jupiter’s radiation belts, and which show evidence of magnesium chloride. On the left, the yellow staining, originally thought to be the result of further magnesium chloride deposits from within the moon – but which now have been shown to be sodium chloride – the same salt as found in our own oceans. Credit: NASA/JPL / University of Arizona

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.

Starshade proposes using a large “occulter” (left) to block the light of distant stars so that a telescope (right) to study the atmospheres of planets orbiting the star. Note this image shows the shade unfurling following its deployment from its carrier vehicle, which also includes the originally-proposed telescope (seen at the right-hand end of the vehicle). once separated, the telescope vehicle would move away from the starshade before turning to align the telescope with it. Credit: NASA, 2014

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.

An artist’s concept – not to scale – showing how Starshade would allow a space telescope to observe planets orbiting another star without the star’s light obscuring them. Credit: NASA

If used with WFIRST, with a 2.4 metre primary mirror, Starshade will have to be deployed 40,000 km (25,000 mi) away – and it would have remain aligned with the telescope to an accuracy of just one metre in order to prevent starlight “leaking” around it and obscuring any potential planetary atmospheres.

The distances we’re talking about for the Starshade technology are kind of hard to imagine. If the Starshade were scaled down to the size of a drink coaster, the telescope would be the size of a pencil eraser and they’d be separated by about 100 km [62.5 mi]. Now imagine those two objects are free-floating in space. They’re both experiencing these little tugs and nudges from gravity and other forces, and over that distance we’re trying to keep them both precisely aligned to within about 2mm.

– Michael Bottom, NASA JPL

A half-scale Starshade demonstrator in its deployed mode and with four of the light-blocking outer petals attached, at NASA’s Jet Propulsion Laboratory, 2014. Credit: NASA/JPL

Maintaining this level of alignment is far from easy. Both telescope and Starshade will be under different gravitational influences, and so are bound to drift out of alignment. Now a team from NASA’s Jet Propulsion Laboratory and led by Michael Bottom believe they have a solution: place a specific light-and-dark pattern on Starshade designed to be centred in WFIRST’s view. Then equip both WFIRST and Starshade with a couple of computer programmes. The first, on WFIRST, notes when the pattern on Starshade starts to drift and calculates the amount of drift. This is sent to Starshade, where it is used to calculate how its thrusters need to be used to re-centre the pattern at the centre of WFIRST’s view.

While this doesn’t move Starshade close to being adopted as a mission, it does overcome a major technology blocker preventing it from proceeding. If funding were to be provided, it is estimated the mission could be launched a few years after WFIRST.

India’s Ambitions

India is determined to become a major force in space. On July 15th, the country will launch Chandrayaan-2, an ambitious lunar mission comprising an orbiter, a lander and a rover vehicle.

The Vikram lunar lander under construction at India’s Space Research Organisation (ISRO). Credit: ISRO

Once it reaches the Moon, Chandrayaan-2 will remain in orbit for 27 days prior to releasing the Vikram lander – named for Vikram Sarabhai, regarded as the father of the Indian space programme. This will attempt a soft-landing in the lunar south polar region on September 6th. If successful, the lander should deploy the Pragyan (Sanskrit for wisdom) rover. Overall, the mission will carry 13 science missions: eight on the orbiter, which is expected to operate for a year, with three on the lander and two on the rover, both of which are expected to operate for 14 days.

I’ll have more on this mission in a future Space Sunday. Beyond it, India’s plans become even more ambitious. In 2020, the India Space Research Organisation plans to launch a solar mission, while in 2022, then plan to launch their first human mission to orbit.

This should comprise 2 or 3 astronauts on a 7-day flight called Gaganyaan, and start India on the road to establishing their own “mini space station” by the end of the 2020s. , but the mission marks part of India’s ramping-up on its space activities. While much smaller in scale than either the ISS or China’s planned station, it will be designed to support rotating crews “for years”, and support resupply from Earth. Then, in 2023, ISRO plan to launch a mission to Venus.

China and the UN Announce International Science for the Chinese Space Station

On June 13th, the China Manned Space Agency (CMSA) and the United Nations Office for Outer Space Affairs (UNOOSA) announced that up to nine international experiments have been selected to fly aboard the upcoming Chinese Space Station (CSS), the first element of which is targeted for a launch in late 2020. Six packages will definitely fly, with a further three dependent on meeting further conditions of acceptance.

An element of China’s new space station under construction. Credit: China Academy of Space Technology

The packages represent various international partnerships that encompass Belgium, France, Germany, India, Italy, Japan, Kenya, the Netherlands, Norway, Mexico, Poland, Peru, Russia, Saudi Arabia, Spain and Switzerland. They cover astronomy, space medicine, space life science, biotechnology, microgravity fluid physics, microgravity combustion and space technologies.

Despite the incredible advances made in the space sector in recent decades, many millions of people worldwide still do not have access to the benefits of space. This opportunity with CMSA helps bridge this gap by opening the unique research environment on board the CSS to all Member States.

– Simonetta Di Pippo, UNOOSA Director

China has been isolated from international cooperation in space efforts due to the United States imposing various technology embargoes. Opening up the CSS to international participation is thus seen as both a charm offensive by China to gain wider international recognition, and to demonstrate that there are routes for other countries on Earth to stimulate their space technology and science sectors without a dependence on the United States.


One thought on “Space Sunday: Europa, a Starshade and ambitions

  1. “China has been isolated from international cooperation in space efforts due to the United States imposing various technology embargoes.”

    Couldn’t have said it better. Shorter, yes, but not as charming. 😉


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