Lunar optical interferometry and hypertelescope for direct imaging at high resolution
Professor Antoine Labeyrie, Collège de France, France
Moon-based optical interferometers, proposed since 1990, are expected to greatly benefit from the absence of atmosphere, and also from the many dark craters usable for nesting a fixed concave array of mirrors. Hypertelescopes are extended versions utilising many sub-apertures and a 'densified' beam combination scheme. Providing direct high-resolution images of compact resolved sources, or clusters of such sources, the scheme also improves the limiting magnitude, identical to that of a monolithic telescope having the same collecting area. Since ESA’s comparative study of Moon-based and space-based hypertelescope concepts, which concluded in favour of the latter unless a manned lunar station becomes established, both options are further studied, including a space flotilla of many small mirrors, potentially spanning up to 100,000 km and controlled by laser beams. On the Moon, two versions are proposed: a) a short-term version similar to the terrestrial 'Ubaye hypertelescope' prototype currently tested in a high south-Alpine valley. The lunar version can be nested in a dark crater, with a focal camera suspended from a traversing cable above an active paraboloidal array of nearly fixed small mirrors. Its the meta-aperture diameter may reach a few kilometers. b) A larger meta-aperture, spanning 100km, may be feasible with a laser-levitated focal camera 200km above. This latter version is expected to provide direct spectro-images of Earth-like exoplanets with 30x30 resel resolution, usable for searching seasonal variations indicative of photosynthetic life. Both versions are also suitable for observing stellar, galactic and extra-galactic sources such as AGNs, and neutron stars, the angular size of which is resolvable with a 100,000km flotilla.
Is the Moon the future of infrared astronomy?
Dr Jean-Pierre Maillard, Institut d'Astrophysique de Paris, France
With the perspective of future permanent basis on the Moon, the development of astronomical sites on our natural satellite becomes a subject to consider. The history of the progress of infrared astronomy over the last 50 years, a spectral domain essential for the study of the origins of stars, then galaxies and of planets, can help to understand the unique capabilities that a future lunar implementation could offer. A very large multi-mirror telescope, up to 100m could become feasible, thanks to the low gravity on the Moon. Installed in the bottom of a crater at the northern or the southern pole, it would be permanently, passively cooled at a temperature as low as 26K. Such a big telescope, combined to the advantages of transparency of space, would be reaching a sensitivity and a resolution on a continuous spectral domain up to 400 microns, making possible the detection of the most distant galaxies and the detailed analysis of terrestrial exoplanets. No competitor on ground and in space can be possible, except in the sub-millimetric domain. However, due to the enormous cost of such a project, its pertinence must be examined.
Observing the Earth as an exoplanet from the moon, to prepare for detecting life on Earth-like exoplanets
Dr Daphne M Stam, Delft University of Technology, The Netherlands
LOUPE, the Lunar Observatory for Unresolved Polarimetry of Earth, is a small, robust spectropolarimeter for monitoring the Earth from the moon, as if it were an exoplanet. More than 4000 exoplanets are currently known, including numerous small, presumably rocky, Earth-like planets in the habitable zones of their stars. While upcoming space telescopes like JWST and ESA's ARIEL will be able to characterise atmospheres of giant exoplanets through transit spectroscopy, the characterisation of Earth-like exoplanets requires the direct detection of a planetary signal. In particular polarimetry promises to be a strong tool for such characterisation as the state of polarisation of light that is reflected by a planet is very sensitive to the properties of the atmosphere and surface, and for signatures of life.
From the moon, LOUPE's continuous view of the Earth will allow it to record spectral changes in total flux and polarisation during the planet's daily rotation, over all phase angles, and across seasons. LOUPE's unique data will be used to test numerical codes that predict signals of Earth-like exoplanets, to test algorithms that retrieve planet properties, and thus to fine-tune the technological design and observational strategies of future space observatories. Dr Stam will present both the science case and the technology behind LOUPE's design.
OWL-Moon, a giant lunar telescope, and beyond
Dr Jean Schneider, Paris Observatory, France
Dr Schneider will first describe some configurations of OWL-Moon such as a single 50-100 m telescope and/or several 20-30 metre class telescopes. 20-30 metre telescopes will become routine in 2050 and the ESA Moon Village initiative will provide the desirable infrastructure. Dr Schneider will discuss the advantages of a telescope on the Moon: no wind, low gravity and dark sky. OWL-Moon will be located at one of the lunar poles (or both of them) to allow for uninterrupted observations of targets. In addition, Dr Schneider will describe a novel idea: an Earth-Moon Intensity Interferometer, allowing for a 100 metre resolution at the distance of the Alfa Cen planetary system. Dr Schneider will then review the most interesting science cases, from Cosmology (such as high resolution imaging of lensed quasars) to Exoplanets (such as biosignatures, volcanoes, glint of exo-oceans and transits of exoplanet moutains) and more prospective ones such as communications with future interstellar probes. Dr Schneider will end with a few other aspects of a Moon base, including a test of Quantum Mechanics.
The lunar surface as recorder of astrophysical processes
Professor Ian Crawford, Birkbeck College, University of London, UK
The lunar surface has been exposed to the space environment for billions of years and during this time will have accumulated records of a wide range of astrophysical phenomena. These include solar wind particles implanted in the lunar regolith, and thus a record of the past evolution of the Sun, and cosmogenic products of galactic cosmic rays interacting with the surface, and thus a record of the galactic environment of the Solar System including past proximity to supernova explosions. In addition, the lunar surface may have directly accreted material from the local interstellar medium, including supernova ejecta and material from interstellar clouds encountered by the Solar System on its journey around the Galaxy. The lunar surface is likely to be ideal, and perhaps unique, in its ability to collect and preserve these records owing to the Moon’s relatively low level of geological activity, absence of atmosphere, and, for most of its history, lack of magnetic field. Crucially, and unlike equally old and exposed asteroid surfaces, the Moon has been sufficiently geologically active throughout its history to bury, and thus both preserve and ‘time stamp’, ancient astrophysical records in the near sub-surface. In a sense, therefore, the lunar surface can be viewed as a giant ‘telescope’ which has been observing and recording astrophysical processes for 4.5 billion years. However, fully accessing these astronomical records may require significant scientific infrastructure on the lunar surface, perhaps comparable to that provided by scientific outposts in Antarctica. Such a lunar surface infrastructure would also support other aspects of lunar-based astronomy, including the deployment and maintenance of a wide range of astronomical instruments.
The lunar dust environment and the Next Generation Lunar Retroreflector
Professor Douglas G Currie, University of Maryland, College Park, USA
The top layer of the lunar regolith is composed of a very fine 'dust', which is unlike any material we find on Earth. The physical description, physical properties, and method and rate of formation of this unique material will be discussed. This dust is composed of extremely fine particles with shapes that have made drilling into the regolith extremely difficult. In addition, various observations addressing the dynamics of the motion and elevation of the dust will be considered. Various practical aspects and problems of this lunar dust will be addressed. These will include the impact on manned missions, on various scientific experiments and on optical telescopes. The impact of the deposition of dust on our Apollo retroreflectors that continue in operation and yield new science after 50 years will be described. Our new Next Generation Lunar Retroreflectors (NGLRs) will support an improvement in the ranging accuracy by a factor of 100 and will be deployed on the lunar surface in 2021. The background and science of the Lunar Laser Ranging (LLR) to both the Apollo retroreflectors and the NGLRs will be described. Finally, the science that we expect to be generated by the LLR program will be briefly described and the role and impact of dust deposition over the next 50 years considered.