Martyn Fogg - Academia.edu (original) (raw)

Book by Martyn Fogg

TERRAFORMING: Engineering Planetary Environments, 1995

Papers by Martyn Fogg

Arxiv preprint arXiv:0902.0052

Context. Extrasolar giant planets are found to orbit their host stars with a broad range of semi-... more Context. Extrasolar giant planets are found to orbit their host stars with a broad range of semi-major axes 0.02 ≤ a ≤ 6 AU. Current theories suggest that giant planets orbiting at distances between ≃ 0.02 – 2 AU probably ...

Astronomy Now, Jul 1, 1990

The origin of the group of stars known as blue stragglers is not known, but several suggestions h... more The origin of the group of stars known as blue stragglers is not known, but several suggestions have been made. The author presents a review of these suggestions.

JBIS, 2010

During the 1970s members of the British Interplanetary Society embarked on a landmark theoretical... more During the 1970s members of the British Interplanetary Society embarked on a landmark theoretical engineering design study to send a probe to Barnard's star. Project Daedalus was a two-stage vehicle employing electron beam driven inertial confinement fusion engines to reach its target destination. This paper sets out the proposal for a successor interstellar design study called Project Icarus. This is an attempt to redesign the Daedalus vehicle with similar terms of reference. The aim of this study is to evolve an improved engineering design and move us closer to achieving interstellar exploration. Although this paper does not discuss prematurely what design modification are likely to occur some indications are given from the nature of the discussions. This paper is a submission of the Project Icarus Study Group.

Astronomy & Astrophysics, 2009

""Context. Extrasolar giant planets are found to orbit their host stars with a broad range of sem... more ""Context. Extrasolar giant planets are found to orbit their host stars with a broad range of semi-major axes 0.02 ≤ a ≤ 6 AU. Current theories suggest that giant planets orbiting at distances between 0.02−2 AU probably formed at larger distances and migrated to their current locations via type II migration, disturbing any inner system of forming terrestrial planets along the way. Migration probably halts because of fortuitously-timed gas disk dispersal.
Aims. The aim of this paper is to examine the effect of giant planet migration on the formation of inner terrestrial planet systems. We consider situations in which the giant planet halts migration at semi-major axes in the range 0.13−1.7 AU due to gas disk dispersal, and examine the effect of including or neglecting type I migration forces on the forming terrestrial system.
Methods. We employ an N-body code that is linked to a viscous gas disk algorithm capable of simulating gas loss via accretion onto the central star and photoevaporation, gap formation by the giant planet, type II migration of the giant, optional type I migration of protoplanets, and gas drag on planetesimals.
Results. Most of the inner system planetary building blocks survive the passage of the giant planet, either by being shepherded inward or scattered into exterior orbits. Systems of one or more hot-Earths are predicted to form and remain interior to the giant planet, especially if type II migration has been limited, or where type I migration has affected protoplanetary dynamics. Habitable planets in low-eccentricity warm-Jupiter systems appear possible if the giant planet makes a limited incursion into the outer regions of the habitable zone (HZ), or traverses its entire width and ceases migrating at a radial distance of less than half that of the HZ’s inner edge.
Conclusions. Type II migration does not prevent terrestrial planet formation. A wide variety of planetary system architectures exists that can potentially host habitable planets.""

Many giant exoplanets are thought to have formed in the outer regions of a protoplanetary disk, ... more Many giant exoplanets are thought to have formed in the outer regions of a protoplanetary
disk, and to have then migrated close to the central star. Hence, it is uncertain
whether terrestrial planets can grow and be retained in these `hot-Jupiter' systems.
Previous speculations, based on the assumption that migrating giant planets will clear
planet-forming material from their swept zone, have concluded that such systems
should lack terrestrial planets.
This thesis presents a succession of four planet formation models, of increasing
sophistication, aimed at examining how an inner system of solid bodies, undergoing
terrestrial planet formation, evolves under the inuence of a giant planet undergoing
inward type II migration. Protoplanetary growth is handled by an N+N'-body code,
capable of simulating the accretion of a two-phase protoplanetplanetesimal population,
and tracking their volatiles content. Gas dynamics and related dissipative processes
are calculated with a linked viscous gas disk algorithm capable of simulating:
gas accretion onto the central star and photoevaporation; type II migration of the giant
planet; type I migration of protoplanets; and the effect of gas drag on planetesimals.
In all simulations, a large fraction of the inner system material survives the passage
of the giant, either by accreting into massive planets shepherded inward of the
giant (reminiscent of the short-period `hot-Earths' discovered recently), or by being
scattered into external orbits. Typically, sufcient mass is scattered outward to provide
for the eventual accretion of a set of terrestrial planets in external orbits.
The results of this thesis lead to the prediction that hot-Jupiter systems are likely
to harbor water-rich terrestrial planets in their habitable zones and hot-Earths may
also be present. These planets may be detected by future planet search missions.

Astronomy & Astrophysics, 2007

"Context. Our previous models of a giant planet migrating through an inner protoplanet/planetesim... more "Context. Our previous models of a giant planet migrating through an inner protoplanet/planetesimal disk find that the giant shepherds a portion of the material it encounters into interior orbits, whilst scattering the rest into external orbits. Scattering tends to dominate, leaving behind abundant material that can accrete into terrestrial planets.
Aims. We add to the possible realism of our model by simulating type I migration forces which cause an inward drift, and strong eccentricity and inclination damping of protoplanetary bodies. This extra dissipation might be expected to enhance shepherding at the expense of scattering, possibly modifying our previous conclusions.
Methods. We employ an N-body code that is linked to a viscous gas disk algorithm capable of simulating: gas accretion onto the
central star; gap formation in the vicinity of the giant planet; type II migration of the giant planet; type I migration of protoplanets; and the effect of gas drag on planetesimals. We use the code to re-run three scenarios from a previous work where type I migration
was not included.
Results. The additional dissipation introduced by type I migration enhances the inward shepherding of material but does not severely reduce scattering. We find that >50% of the solids disk material still survives the migration in scattered exterior orbits: most of it well placed to complete terrestrial planet formation at <3 AU. The shepherded portion of the disk accretes into hot-Earths, which survive in interior orbits for the duration of our simulations.
Conclusions. Water-rich terrestrial planets can form in the habitable zones of hot-Jupiter systems and hot-Earths and hot-Neptunes may also be present. These systems should be targets of future planet search missions."

Extreme Solar Systems, ASPCS, 398, 2007

Models of terrestrial planet formation in the presence of a migrating giant planet have challenge... more Models of terrestrial planet formation in the presence of a migrating giant planet have challenged the notion that hot-Jupiter systems lack terrestrial planets. We briefly review this issue and suggest that hot-Jupiter systems should be prime targets for future observational missions designed to detect Earth-sized and potentially habitable worlds.

Astronomy & Astrophysics, 2007

"Context. There are numerous extrasolar giant planets which orbit close to their central stars. T... more "Context. There are numerous extrasolar giant planets which orbit close to their central stars. These “hot-Jupiters” probably formed in the outer, cooler regions of their protoplanetary disks, and migrated inward to ∼0.1 AU. Since these giant planets must have migrated through their inner systems at an early time, it is uncertain whether they could have formed or retained terrestrial planets.
Aims. We present a series of calculations aimed at examining how an inner system of planetesimals/protoplanets, undergoing terrestrial planet formation, evolves under the influence of a giant planet undergoing inward type II migration through the region bounded between 5–0.1 AU.
Methods. We have previously simulated the effect of gas giant planet migration on an inner system protoplanet/planetesimal disk using a N-body code which included gas drag and a prescribed migration rate. We update our calculations here with an improved model that incorporates a viscously evolving gas disk, annular gap and inner-cavity formation due to the gravitational field of the giant planet, and self-consistent evolution of the giant’s orbit.
Results. We find that 60% of the solids disk survives by being scattered by the giant planet into external orbits. Planetesimals are scattered outward almost as efficiently as protoplanets, resulting in the regeneration of a solids disk where dynamical friction is strong and terrestrial planet formation is able to resume. A simulation that was extended for a few Myr after the migration of the giant planet halted at 0.1 AU, resulted in an apparently stable planet of ∼2 m⊕ forming in the habitable zone. Migration–induced mixing of volatile-rich material from beyond the “snowline” into the inner disk regions means that terrestrial planets that form there are likely to be water-rich.
Conclusions. We predict that hot-Jupiter systems are likely to harbor water-abundant terrestrial planets in their habitable zones. These planets may be detected by future planet search missions."

International Journal of Astrobiology, 2006

About a fifth of the exoplanetary systems that have been discovered contain a so-called hot-Jupit... more About a fifth of the exoplanetary systems that have been discovered contain a so-called hot-Jupiter – a giant planet orbiting within 0.1 AU of the central star. Since these stars are typically of the F/G spectral type, the orbits of any terrestrial planets in their habitable zones at y1 AU should be dynamically stable. However, because hot-Jupiters are thought to have formed in the outer regions of a protoplanetary disc, and to have then migrated through the terrestrial planet zone to their final location, it is uncertain whether terrestrial planets can actually grow and be retained in these systems. In this paper we review attempts to answer this question. Initial speculations, based on the assumption that migrating giant planets will clear planet-forming material from their swept zone, all concluded that hot-Jupiter systems should lack terrestrial planets. We show that this assumption may be incorrect, for when terrestrial planet formation and giant planet migration are simulated simultaneously, abundant solid material is predicted to remain from which terrestrial planet growth can resume.

Astronomy & Astrophysics, 2005

Giant planets found orbiting close to their central stars, the so called “hot Jupiters”, are thou... more Giant planets found orbiting close to their central stars, the so called “hot Jupiters”, are thought to have originally formed in the cooler outer regions of a protoplanetary disk and then to have migrated inward via tidal interactions with the nebula gas. We present the results of N-body simulations which examine the effect such gas giant planet migration has on the formation of terrestrial planets. The models incorporate a 0.5 Jupiter mass planet undergoing type II migration through an inner protoplanet-planetesimal disk, with gas drag included. Each model is initiated with the inner disk being at successively increased levels of maturity, so that it is undergoing either oligarchic or giant impact style growth as the gas giant migrates. In all cases, a large fraction of the disk mass survives the passage of the giant, either by accreting into massive terrestrial planets shepherded inward of the giant, or by being scattered into external orbits. Shepherding is favored in younger disks where there is strong dynamical friction from planetesimals and gas drag is more influential, whereas scattering dominates in more mature disks where dissipation is weaker. In each scenario, sufficient mass is scattered outward to provide for the eventual accretion of a set of terrestrial planets in external orbits, including within the system’s habitable zone. This scattering, however, significantly reduces the density of solid material, indicating that further accretion will occur over very long time scales. A particularly interesting result is the generation of massive, short period, terrestrial planets from compacted material pushed ahead of the giant. These planets are reminiscent of the short period Neptune-mass planets discovered recently, suggesting that such “hot Neptunes” could form locally as a by product of giant planet migration.

TERRAFORMING: Engineering Planetary Environments, 1995

Arxiv preprint arXiv:0902.0052

Astronomy Now, Jul 1, 1990

JBIS, 2010

Astronomy & Astrophysics, 2009

Astronomy & Astrophysics, 2007

Extreme Solar Systems, ASPCS, 398, 2007

Astronomy & Astrophysics, 2007

International Journal of Astrobiology, 2006

Astronomy & Astrophysics, 2005

Evidence for the existence of planetary mass objects, unattached to any star and free-floating in... more Evidence for the existence of planetary mass objects, unattached to any star and free-floating in interstellar space, has recently emerged. In this paper, this evidence and the history of the concept of free-floating planets is reviewed and a classification is proposed, based on mode of origin. It is suggested that free floating planets can originate in two settings: 1) interstellar space, where the object forms in the manner of a star; 2) circumstellar space, where the object forms in the manner of a conventional planet and is subsequently lost to interstellar space. We designate the former type of object a planetar and the latter an unbound planet. Three possible scenarios of planetar formation and four scenarios of unbound planet origin are explored and discussed. Estimates of the abundance of these objects suggest that planetars in the mass range of 1 – 13 M♃ may be about as common as stars and brown dwarfs. The number of unbound planets however may exceed the number of stars by two orders of magnitude, although most of them should be low-mass rock/ice planetary embryos ejected from planetary systems in formation. It seems likely therefore that advances in observational techniques, such as infrared astronomy and microlensing, will lead to the discovery of many more free-floating planets in the future, securing their recognition as genuine astrophysical objects.

Space Policy, 2000

While proposals for settling in the space frontier have appeared in the technical literature for ... more While proposals for settling in the space frontier have appeared in the technical literature for over 20 years, it is in the case of Mars that the ethical dimensions of space settlement have been most studied. Mars raises the questions of the rights and wrongs of the enterprise more forcefully because: (a) Mars may possess a primitive biota; and (b) it may be possible to terraform Mars and transform the entire planet into a living world. The moral questions implicit in space settlement are examined below from the standpoints of four theories of environmental ethics: anthropocentrism, zoocentrism, ecocentrism and preservationism. In the absence of extraterrestrial life, only preservationism concludes that space settlement would be immoral if it was seen to be to the benefit of terrestrial life. Even if Mars is not sterile, protection for Martian life can be argued for either on intrinsic or instrumental grounds from the standpoints of all of these theories. It is argued further that a strict preservationist ethic is untenable as it assumes that human consciousness, creativity, culture and technology stand outside nature, rather than having been a product of natural selection. If Homo sapiens is the first spacefaring species to have evolved on Earth, space settlement would not involve acting outside nature, but legitimately within our
nature.

Advances in Space Research, 1998

It is possible in the future that Mars might be transformed into a habitable planet by a process ... more It is possible in the future that Mars might be transformed into a habitable planet by a process of global environmental engineering known as terraforming. This paper provides a thumb-nail sketch of the terraforming concepts that have appeared in the technical literature, focussing on the steps required in order to render Mars fir for anaerobic life. Its intention is the provide a referenced guide of progress to date for any future researchers of the subject.

JBIS, 1996

The exploitation of geothermal energy has been absent from previous considerations for providing ... more The exploitation of geothermal energy has been absent from previous considerations for providing power for settlements on Mars. The reason for this is the prevailing paradigm that places all of Mars' volcanic activity in the remoter past and hence postulates a crust that is frozen to great depths. It is argued in this paper that this view may be true in general, but false in particular. Geological evidence is reviewed that suggests that magmatism may have been active on Mars until recent times and hence may still be ongoing. Thus the presence of significant, localized, hyperthermal areas cannot be ruled out on the basis of the low mean heat flows predicted by global heat flow models. The possibility of the presence of useful geothermal fields is further strengthened by observations of fluvial outflows that seem to have been associated with certain magmatic extrusions and which therefore hint at favourable groundwater conditions. Such a geothermal energy source would be of great potential economic value, being of use for the generation of electricity and direct heating for industry and habitation. The addition of this energy option to those of solar, wind and nuclear, cannot but enhance the prospects of a Martian civilization that must start afresh, without an equivalent to Earth's stock of fossil fuels.

JBIS, 1995

Aspects of currently understood planetology relevant to the possibility of terraforming Mars are ... more Aspects of currently understood planetology relevant to the possibility of terraforming Mars are reviewed. Evidence that Mars may have been naturally habitable in the past, for at least anaerobic life, is supportive of the feasibility of rendering the planet habitable in the future. The physical and the chemical state of the intrinsic resources needed for such a task and their whereabouts are less certain. However, what constraints can be placed provide a context in which superficially realistic terraforming models can be proposed. It is argued that the detailed knowledge needed in order to assess the ultimate realism of terraforming requires the presence of a permanently established population, exploring Mars as part of living there.

JBIS

The widespread growth of plants on Mars following ecopoiesis has often been invoked as a method o... more The widespread growth of plants on Mars following ecopoiesis has often been invoked as a method of generating atmospheric oxygen. However, one issue that has been overlooked in this regard is the fact that terrestrial plants do no thrive under conditions of low oxygen tension. A review of the relevant botanical literature reveals that the high oxygen demands of root respiration could limit the introduction of most plants on Mars until after terraforming has raised the atmospheric pO2 to 20 - 100 mbar. A variety of physiological strategies are discussed which, if it is possible to implement them in a genetically engineered plant specifically designed for life on Mars, might allow this problem to be overcome.

JBIS, 1993

The outcome of terraforming on Mars is examined by considering the function of its biosphere. By ... more The outcome of terraforming on Mars is examined by considering the function of its biosphere. By borrowing a life-support model of the Earth's biosphere, scenarios of ecopoiesis and full terraforming are contrasted in terms of their energy flow and matter cycling. It is argued that Martian colonists are unlikely to be satisfied with the services provided by the anaerobic biosphere produced by ecopoiesis and that full terraforming will be the specific goal of planetary engineering. The distance of Mars from the sun and its probable lack of a closed rock cycle will require small scale, conscious intervention in biogeochemical cycles to maintain the habitability of the planet. Vernadsky's concept of the noosphere (an envelope of mind) will thus have more relevance to Mars as an abode of life than Lovelock's Gaia hypothesis.

The Environmentalist, 1993

The concept of modifying the environment of another planet, so that it can support terrestrial li... more The concept of modifying the environment of another planet, so that it can support terrestrial life, is known as terraforming. As a speculative scientific subject, it has been slowly gaining in respectability and, over the past 30 years, has amassed a considerable body of published work. In this paper, the present day capabilities of civilisation to bring about global environmental change are breifly discussed, followed by a review of the progress of research into the terraforming of the planet Mars. Whilst such an undertaking does not appear technologically impossible, whether it will actually happen is an unanswerable question. However, the control space for thought experimentation that terraforming provides is of use for both planetological research and education. The subject is therefore relevant to the present day, as well as to a possible future.

JBIS, 1992

A two-stage terraforming scenario is outlined for Mars. The approach adopted differs from past me... more A two-stage terraforming scenario is outlined for Mars. The approach adopted differs from past methodology in two ways. It adopts a more conservative and plausible Martian volatile inventory. Possible planetary engineering solutions, including possible synergic use of terraforming techniques, are examined in detail. In the first stage, the Martian environment is modified to a state where it can support microbial and hardy plant life in approximately 200 years. While this step is conceptually similar to past scenarios, it differs greatly in detail. The second stage deals with the creation of conditions tolerable for human beings over a period of approximately 21,000 years. It is concluded that terraforming Mars is possible but not by the passive, or near-spontaneous, methods favored by some workers. A powerful industrial effort is required both on the planet's surface and in space as will be continuing technological intervention to stabilize the postterraformed regime.

Spaceflight, 2001

One of the stated goals of NASAs Astrobiology Institute is to investigate the possibility of whe... more One of the stated goals of NASAs Astrobiology Institute is to investigate the possibility of whether life can spread beyond its home planet: What is the potential for survival and biological evolution beyond the planet of origin? This boils down to where we are going as a species, and the really big question is, could Mars have a biosphere once again? In October 2000 a two-day conference entitled The Physics and Biology of making Mars Habitable was organised by Chris McKay at the NASA Ames Laboratory to discuss the possibility of one day changing the climate of Mars to a more Earth-like environment, suitable for terrestrial species to flourish. Twenty six papers, by an international cast of authors, were listed on the programme and the attendance was so good that the venue had to be transferred to a larger auditorium.