Safe on Mars National Research Council; Division on Engineering and Physical Sciences; Space Studies Board ...
2002, 2002-05-29, 2004-12-15
eBook
Odprti dostop
This study, commissioned by the National Aeronautics and Space Administration (NASA), examines the role of robotic exploration missions in assessing the risks to the first human missions to Mars. ...Only those hazards arising from exposure to environmental, chemical, and biological agents on the planet are assessed. To ensure that it was including all previously identified hazards in its study, the Committee on Precursor Measurements Necessary to Support Human Operations on the Surface of Mars referred to the most recent report from NASA's Mars Exploration Program/ Payload Analysis Group (MEPAG) (Greeley, 2001). The committee concluded that the requirements identified in the present NRC report are indeed the only ones essential for NASA to pursue in order to mitigate potential hazards to the first human missions to Mars.
Why did Mars lose so much of its surface water, whereas Earth retained its? Models of the evolution of minerals on the two planets suggest one explanation: the Martian water was drawn into the ...planetary interior.
We address the important question of whether the newly discovered exoplanet, Proxima Centauri b (PCb), is capable of retaining an atmosphere over long periods of time. This is done by adapting a ...sophisticated multi-species MHD model originally developed for Venus and Mars and computing the ion escape losses from PCb. The results suggest that the ion escape rates are about two orders of magnitude higher than the terrestrial planets of our Solar system if PCb is unmagnetized. In contrast, if the planet does have an intrinsic dipole magnetic field, the rates are lowered for certain values of the stellar wind dynamic pressure, but they are still higher than the observed values for our solar system's terrestrial planets. These results must be interpreted with due caution since most of the relevant parameters for PCb remain partly or wholly unknown.
Abstract
The terrestrial planets are believed to have formed by violent collisions of tens of lunar- to Mars-size protoplanets at time
t
< 200 Myr after the protoplanetary gas disk dispersal (
t
0
...). The solar system giant planets rapidly formed during the protoplanetary disk stage and, after
t
0
, radially migrated by interacting with outer disk planetesimals. An early (
t
< 100 Myr) dynamical instability is thought to have occurred with Jupiter having gravitational encounters with a planetary-size body, jumping inward by ∼0.2–0.5 au, and landing on its current, mildly eccentric orbit. Here we investigate how the giant-planet instability affected the formation of the terrestrial planets. We study several instability cases that were previously shown to match many solar system constraints. We find that resonances with giant planets help to remove solids available for accretion near ∼1.5 au, thus stalling the growth of Mars. It does not matter, however, whether the giant planets are placed on their current orbits at
t
0
or whether they realistically evolve in one of our instability models; the results are practically the same. The tight orbital spacing of Venus and Earth is difficult to reproduce in our simulations, including cases where bodies grow from a narrow annulus at 0.7–1 au, because protoplanets tend to spread radially during accretion. The best results are obtained in the narrow-annulus model when protoplanets emerging from the dispersing gas nebula are assumed to have (at least) the mass of Mars. This suggests efficient accretion of the terrestrial protoplanets during the first ∼10 Myr of the solar system.
Wind blowing over sand on Earth produces decimeter-wavelength ripples and hundred-meter— to kilometer-wavelength dunes: bedforms of two distinct size modes. Observations from the Mars Science ...Laboratory Curiosity rover and the Mars Reconnaissance Orbiter reveal that Mars hosts a third stable wind-driven bedform, with meter-scale wavelengths. These bedforms are spatially uniform in size and typically have asymmetric profiles with angle-of-repose lee slopes and sinuous crest lines, making them unlike terrestrial wind ripples. Rather, these structures resemble fluid-drag ripples, which on Earth include water-worked current ripples, but on Mars instead form by wind because of the higher kinematic viscosity of the low-density atmosphere. A reevaluation of the wind-deposited strata in the Burns formation (about 3.7 billion years old or younger) identifies potential wind-drag ripple stratification formed under a thin atmosphere.
Sovereign Mars Haqq-Misra, Jacob
2023, 2022, 2023-01-25
eBook
The goal of sending humans to Mars is becoming increasingly technologically feasible, but the prospect of space colonization raises important questions about civilizational ethics and collective ...morality. History shows how destructive colonialism has been, resulting in centuries-long struggles to achieve liberation from the violent competition for land and resources by colonial powers. Space settlement poses the same temptation on a cosmic scale, with commercial actors and government space agencies doing the work previously carried out by European empires. The question is whether humans will take a different approach in this new frontier.
In Sovereign Mars , astrobiologist Jacob Haqq-Misra argues that settling Mars offers humankind a transformative opportunity to avoid the mistakes of the past by “liberating Mars” as a sovereign planet from the start. Rather than see space as a way to escape human problems on Earth, Mars presents humanity with a challenge to address these problems by thinking carefully about the theory and practice of civilization. Drawing on past examples of cooperative sovereignty, such as the Outer Space Treaty of 1967, the United Nations Law of the Sea Conventions, and the Antarctic Treaty System, Haqq-Misra begins a conversation about governance in space well in advance of the first arrival of humans on Mars and makes the case for an analogous approach to space that will preserve the space environment and benefit future generations.
Haqq-Misra examines the emergence of sovereignty in space through the lens of historical precedent on Earth and develops models of shared governance that could maximize the transformative potential of Mars settlement. Sovereign Mars proposes the planet would serve humankind best as an independent planetary state, a juridical peer to Earth, to enable new experiments in human civilization and develop a pragmatic model for shared governance on Mars.
Clay minerals, recently discovered to be widespread in Mars's Noachian terrains, indicate long-duration interaction between water and rock over 3.7 billion years ago. Analysis of how they formed ...should indicate what environmental conditions prevailed on early Mars. If clays formed near the surface by weathering, as is common on Earth, their presence would indicate past surface conditions warmer and wetter than at present. However, available data instead indicate substantial Martian clay formation by hydrothermal groundwater circulation and a Noachian rock record dominated by evidence of subsurface waters. Cold, arid conditions with only transient surface water may have characterized Mars's surface for over 4 billion years, since the early-Noachian period, and the longest-duration aqueous, potentially habitable environments may have been in the subsurface.
Widespread evidence points to the existence of an ancient Martian ocean. Most compelling are the putative ancient shorelines in the northern plains. However, these shorelines fail to follow an ...equipotential surface, and this has been used to challenge the notion that they formed via an early ocean and hence to question the existence of such an ocean. The shorelines' deviation from a constant elevation can be explained by true polar wander occurring after the formation of Tharsis, a volcanic province that dominates the gravity and topography of Mars. However, surface loading from the oceans can drive polar wander only if Tharsis formed far from the equator, and most evidence indicates that Tharsis formed near the equator, meaning that there is no current explanation for the shorelines' deviation from an equipotential that is consistent with our geophysical understanding of Mars. Here we show that variations in shoreline topography can be explained by deformation caused by the emplacement of Tharsis. We find that the shorelines must have formed before and during the emplacement of Tharsis, instead of afterwards, as previously assumed. Our results imply that oceans on Mars formed early, concurrent with the valley networks, and point to a close relationship between the evolution of oceans on Mars and the initiation and decline of Tharsis volcanism, with broad implications for the geology, hydrological cycle and climate of early Mars.
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