Space Sunday: moon water and space telescopes

A visualisation of subsurface water ice deposits within PSR – permanently shadowed regions – of the Moon’s south pole, including the craters Cabeus, Shoemaker and Faustini. Credit: NASA Goddard Space Centre

The Moon is a fascinating place; there is no two ways about it. Like many bodies within the solar system, it is proving to be a lot more surprising than we’d previously thought. Up until 2009, for example, it was accepted that the Moon was a dry, arid place with little or no subsurface bodies of water ice. This idea was turned on its head in 2009 after India’s first lunar mission, Chandrayaan I, and NASA’sLunar Reconnaissance Orbiter (LRO) confirmed the presence of water ice within the so-called permanently shadowed regions (PSRs) – deep craters around the lunar poles which never see direct sunlight in their basins.

However, one of the questions surrounding these discoveries is just how much water might actually exist as ice within these shadowed craters? A new study,  published in August 2018, has sought to address this question; it is the work of Shuai Li – a post-doctoral researcher at the University of Hawaii, and  produced with the assistance of researchers from Brown University, the University of Colorado Boulder, the University of California Los Angeles, John Hopkins University, and NASA’s Ames Research Centre.

Li’s study focuses on data returned by NASA’s Moon Minerology Mapper (M³), flown aboard the Chandrayaan I mission. M³ was designed to measure light being reflected from the illuminated regions on the Moon, making its use over the PSRs had been considered of minimal value. Nevertheless, Li believed that what data M³ had gathered on the south polar craters might hep in determining the potential volume of water ice within those craters, as indicated by the Lunar Orbiter Laser Altimeter (LOLA), Lyman-Alpha Mapping Project and Diviner Lunar Radiometer Experiment on the LRO mission. However, what he found came as a complete surprise.

While I was interested to see what I could find in the M3 data from PSRs, I did not have any hope to see ice features when I started this project. I was astounded when I looked closer and found such meaningful spectral features in the measurements … We found that the distribution of ice on the lunar surface is very patchy, which is very different from other planetary bodies such as Mercury and Ceres where the ice is relatively pure and abundant. The spectral features of our detected ice suggest that they were formed by slow condensation from a vapour phase either due to impact or water migration from space.

– Shuai Li, leader of the study team

 

Exposed water ice (green or blue dots) in lunar polar regions and temperature. Credit: Shuai Li

While likely the results of vapour capture following asteroid impacts, Li’s study again opens the door as to how much sub-surface water ice might also exist deeper within the polar regions of the Moon. As I recently noted, a separate study, evidence has been put forward for periods in the Moon’s early history when liquid water existed on the lunar surface at a time when the Moon had a volcanically-induced atmosphere. Much of this water was likely lost to space as that atmosphere dissipated at the end of the Moon’s active volcanic period; however, some of it may have gone underground again, notably in these polar regions.

Either way, the existence of water ice deposits strengthen the case for a return to the Moon and – as NASA Administrator Jim Bridenstine recently indicated – see the establishment of a permanent human presence on the Moon.  An available and plentiful supply of water would go a long way to easing many of the logistical requirements for such a human presence. Once melted, a local supply of water can be filtered and purified to provide drinking water; it can also be used in construction work and as “grey” water for use in growing local foodstuffs through hydroponic or other means; it can be electrolysed to produce oxygen in support of the atmosphere within a base and hydrogen than could be used to power fuel cells, and so on.

The European Space Agency (ESA) in particular is researching ways and means to build a lunar settlement using what is called “in-situ resource utilisation” (ISRU), or the use of locally available materials. In particular ESA has been using locally available “lunar simulants” available here on Earth – notably certain types of volcanic dusts that have been shown to have very similar properties to the dry dust of the surface-covering lunar regolith on the Moon – to test potential options for base construction.

One of these I’ve again previously written about, is the idea of using regolith to effectively “3D print” a protective “shield” of regolith over the facilities of a lunar base to protect it against solar radiation. Referred to as “additive manufacture”, such a technique might be aided with a readily available source of water which can help mix the regolith into a cement-like form that can be “printed” over the structure of a base in layers. In addition, ESA is using a regolith simulant to make “bricks” which can be used to physically construct the walls, floors and ceilings of a base – a process that might again  be easier with a supply of water for use in the process.

A “lunar brick” produced by ESA using “3D printing” techniques and lunar regolith simulants. Credit: ESA

But it is in production of oxygen and hydrogen, as well as offering a source for liquid water, that the ice deposits offer the greatest potential benefit. Up until now, ideas for oxygen production on the Moon have focused on “cracking” the regolith to release the oxygen within it (thought to be around 40% by volume). This requires a lot of energy to achieve –  more than is needed to melt and electrolyse ice to produce both oxygen and hydrogen.

However, it’s not all plain sailing for humans on the Moon. The dust comprising lunar regolith is extremely electro-statically charged, making it stick to just about anything – so keeping it out of a lunar habitat could prove difficult. Worse, it also presents a range of potential health hazards – up to and including major respiratory problems such as lung cancer. These risks have yet to be fully assessed, and countering them as far as possible must be a priority before there can be real talk of a long-term human presence on the Moon.

But in the meantime, Li’s study potentially adds important food for thought for those thinking about establishing research facilities on the Moon.

Kepler: The End is Nigh?

Responsible for locating 70% of the almost 4,000 exoplanets discovered to date, NASA’s Kepler space observatory has re-entered a fuel-conserving “sleep” mode.  As I’ve previously reported in May and July, diminishing fuel supplies on the observatory mean that it is now coming to the end of a long and distinguished career.

An artist’s rendering of Kepler in its heliocentric orbit. Credit: NASA

In 2012 and 2013, the observatory issues with two of its four reaction wheels, which are used to hold it steady while observing distant stars. As a result, since 2014, the observatory has had to use small amounts of its finite reserves of  propellant to help hold it steady during operations. By May 2018, these reserves had reached a point of concern for engineers on Earth, who were unable to judge just how much fuel remained in Kepler’s tanks. In early July, the observatory entered a “sleep” mode as a result of a low fuel report. At the time, it had just completed its 18th observation campaign, but was not due to transmit its finding to Earth until the start of August, so the “sleep mode” was seen as an opportunity to conserve whatever fuel may be left.

It had always been hoped there would be sufficient fuel for Kepler to both make the data transfer to Earth – which it did – and go almost directly into its next 80-day observation campaign, which was due to start on August 6th. However, on August 24th, NASA confirmed that campaign had not started, as Kepler had once again entered its sleep mode on or around August 9th, 2018. No decision has as yet been taken on whether to send a wake up call the observatory, which is in an orbit around the Sun trailing the Earth, but it has been indicated the mission could be resumed and continued right up until Kepler can no longer make use of any dregs of fuel left in it tanks.

We can leave it in whatever state we want so we hadn’t given it a lot of thought. Now that we are here most of our thought is going in to, ‘How do we get the most final science off the spacecraft and down into the hands of scientists before it goes in to that final resting spot?’

– Charlie Sobeck, Kepler system engineer

Spitzer Hits 15

The Spitzer Space Telescope (SST) is perhaps the least-known of NASA’s space-based telescopes. Launched into a solar orbit on August 25th, 2003, it was the last of NASA’s “great observatory” programme, encompassing the Hubble Space Telescope (HST), the Compton Gamma Ray Observatory (CGRO), the Chandra X-ray Observatory (CXO) and Spitzer itself. However, as “unknown” as it might be to the public at large, Spitzer has an impressive history of observations.

Named for astronomer Lyman Spitzer, who had promoted the concept of space telescopes in the 1940s, Spitzer’s primary mission was planned for 2.5 years, with a possible extension of another 2.5 years, in what was referred to as the “cold mission”. As an infra-red telescope, Spitzer’s main instruments could only operate at extremely low temperatures, requiring super-cold liquid helium to cool them – hence the “cold” element of the mission title.  That liquid helium was exhausted by 2009, effectively ending the primary mission.

An artist’s rendering of the Spitzer Space Telescope. Credit: NASA

However, one of the telescope’s three instruments, the Infrared Array Camera (IRAC), can operate on two short wavelengths that do not require the instrument to be cooled by liquid helium. So from 2009 onwards, Spitzer has been operating in its “warm mission” phase, using IRAC on these two short wavelengths.

In its primary mission Spitzer looked deep into space, observing stars and other stellar and galactic objects in the infra-red wavelength. In its “warm mission” with only the shorter wavelengths available to IRAC, the telescope has been examining objects closer to our own solar system – including trying to directly capture light of some of the “hot Jupiter” class of exoplanets, work it actually started in 2005, when it captured light from HD 209458 b and TrES-1b, although not to a sufficient degree that the light could be resolved into images.

Spitzer’s “first light” images were of IC 1396, the Elephant’s Trunk nebula, roughly 4,200 light years from Earth and a concentration of interstellar gas and dust thought to be the stellar nursery for new stars. The image is a composite of the nebula captures using the IRAC and MIPS instruments on Spitzer. Credit: NASA/JPL / W. Reach (SSC/Caltech)

Spitzer also had a role in the discovery of the TRAPPIST-1 seven-planet system in 2016, and overall has been one of the most wide-ranging astronomical space mission undertaken, easily rivalling that of Hubble, and which currently includes preparing the way for the James Webb Space Telescope (JWST), which will also have an infra-red capability.

In its 15 years of operations, Spitzer has opened our eyes to new ways of viewing the universe. Spitzer’s discoveries extend from our own planetary backyard, to planets around other stars, to the far reaches of the universe, by working in collaboration with NASA’s other Great Observatories, Spitzer has helped scientists gain a more complete picture of many cosmic phenomena.

– Paul Hertz, director of NASA’s Astrophysics Division

Currently, Spitzer is in good shape and is scheduled to keep operating through at least November 2019 in the “Beyond” phase of its mission, preparing for the JWST missions (the launch of which will now not take place until 2021). So – happy anniversary, Spitzer!

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