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The surface of Mars has been well mapped and characterized, yet the subsurface — the most likely place to find signs of extant or extinct life and a repository of useful resources for human exploration — remains unexplored. In the near future this is set to change.

NASA’s two spacecraft ARTEMIS mission will address both heliospheric and planetary research questions, first while in orbit about the Earth with the Moon and subsequently while in orbit about the Moon. Heliospheric topics include the structure of the Earth’s magnetotail; reconnection, particle acceleration, and turbulence in the Earth’s magnetosphere, at the bow shock, and in the solar wind; and the formation and structure of the lunar wake. Planetary topics include the lunar exosphere and its relationship to the composition of the lunar surface, the effects of electric fields on dust in the exosphere, internal structure of the Moon, and the lunar crustal magnetic field. This paper describes the expected contributions of ARTEMIS to these baseline scientific objectives.

Meteorites with a history Most iron meteorites come from the main asteroid belt, but the available evidence does not tell us whether their parent bodies actually formed there. A combination of thermal, collisional and dynamical models has been used to show that the iron-meteorite parent bodies probably formed closer to the Sun, in the terrestrial planet region. These precursors then melted and fragments were scattered into the main belt early in Solar System history. Some asteroids today, such as the geologically diverse Vesta, are likely to be main-belt interlopers. And this scenario suggests that the main belt may also contain long-lost precursors of Solar System planets. Iron meteorites are core fragments from differentiated and subsequently disrupted planetesimals 1 . The parent bodies are usually assumed to have formed in the main asteroid belt, which is the source of most meteorites. Observational evidence, however, does not indicate that differentiated bodies or their fragments were ever common there. This view is also difficult to reconcile with the fact that the parent bodies of iron meteorites were as small as 20 km in diameter 2 , 3 and that they formed 1–2 Myr earlier than the parent bodies of the ordinary chondrites 4 , 5 , 6 . Here we show that the iron-meteorite parent bodies most probably formed in the terrestrial planet region. Fast accretion times there allowed small planetesimals to melt early in Solar System history by the decay of short-lived radionuclides (such as 26 Al, 60 Fe) 7 , 8 , 9 . The protoplanets emerging from this population not only induced collisional evolution among the remaining planetesimals but also scattered some of the survivors into the main belt, where they stayed for billions of years before escaping via a combination of collisions, Yarkovsky thermal forces, and resonances 10 . We predict that some asteroids are main-belt interlopers (such as (4) Vesta). A select few may even be remnants of the long-lost precursor material that formed the Earth.

The global tectonics of Venus may be dominated by plumes rising from the mantle and impinging on the lithosphere, giving rise to hot spots. Global sea-floor spreading does not take place, but direct convective coupling of mantle flow fields to the lithosphere leads to regional-scale deformation and may allow lithospheric transport on a limited scale. A hot-spot evolutionary sequence comprises (i) a broad domal uplift resulting from a rising mantle plume, (ii) massive partial melting in the plume head and generation of a thickened crust or crustal plateau, (iii) collapse of dynamic topography, and (iv) creep spreading of the crustal plateau. Crust on Venus is produced by gradual vertical differentiation with little recycling rather than by the rapid horizontal creation and consumption characteristic of terrestrial sea-floor spreading.

Research has concluded that Venus is the most similar to Earth in terms of distance from the Sun, mass and bulk density. Other recent discoveries in understanding the global tectonics of Venus are presented.

Amyloid beta peptide (Aβ) has a key role in the pathological process of Alzheimer's disease (AD), but the physiological function of Aβ and of the amyloid precursor protein (APP) is unknown 1 , 2 . Recently, it was shown that APP processing is sensitive to cholesterol and other lipids 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 . Hydroxymethylglutaryl-CoA reductase (HMGR) and sphingomyelinases (SMases) are the main enzymes that regulate cholesterol biosynthesis and sphingomyelin (SM) levels, respectively. We show that control of cholesterol and SM metabolism involves APP processing. Aβ42 directly activates neutral SMase and downregulates SM levels, whereas Aβ40 reduces cholesterol de novo synthesis by inhibition of HMGR activity. This process strictly depends on γ-secretase activity. In line with altered Aβ40/42 generation, pathological presenilin mutations result in increased cholesterol and decreased SM levels. Our results demonstrate a biological function for APP processing and also a functional basis for the link that has been observed between lipids and Alzheimer's disease (AD).