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Thread: Thought Experiment: A Mercury-like Earth

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    Question Thought Experiment: A Mercury-like Earth

    What if the Earth was smaller but denser, about the same as it is now with 1.0 Earth gravity and a Moon? Thought it might be fun to have a group thought experiment sot of like the "blueberry Earth" thing a couple weeks ago in the news.

    I call it the Mercury-Earth only because Mercury is a smaller world than ours but much denser, with a Mars-like gravity. Mercury has about 5.4 g/cm^3, and the highest density for a terrestrial exoplanet is about 7.5 g/cm^3, I think. Will look up source. Wonder how small an exoplanet could be and still have 1.0 Earth gravity, and what the results would be.

    People can contribute anything but should name at least one actual science paper to support their ideas. Anyone?
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    https://www.forbes.com/sites/davidbr.../#2dee18b7f495

    This is a link to the "blueberry Earth" thought experiment. I was actually thinking of something more like one of the scenarios from Neil Comins's "What If the Moon Didn't Exist?" or "What If the Earth Had Two Moons?"

    Here are two papers that got me to thinking about this issue.


    https://arxiv.org/abs/1805.08405

    An Earth-sized exoplanet with a Mercury-like composition

    A. Santerne, B. Brugger, D. J. Armstrong, V. Adibekyan, J. Lillo-Box, H. Gosselin, A. Aguichine, J.-M. Almenara, D. Barrado, S. C. C. Barros, D. Bayliss, I. Boisse, A. S. Bonomo, F. Bouchy, D. J. A. Brown, M. Deleuil, E. Delgado Mena, O. Demangeon, R. F. Díaz, A. Doyle, X. Dumusque, F. Faedi, J. P. Faria, P. Figueira, E. Foxell, H. Giles, G. Hébrard, S. Hojjatpanah, M. Hobson, J. Jackman, G. King, J. Kirk, K. W. F. Lam, R. Ligi, C. Lovis, T. Louden, J. McCormac, O. Mousis, J. J. Neal, H. P. Osborn, F. Pepe, D. Pollacco, N. C. Santos, S. G. Sousa, S. Udry, A. Vigan
    (Submitted on 22 May 2018)

    The Earth, Venus, Mars, and some extrasolar terrestrial planets have a mass and radius that is consistent with a mass fraction of about 30% metallic core and 70% silicate mantle. At the inner frontier of the solar system, Mercury has a completely different composition, with a mass fraction of about 70% metallic core and 30% silicate mantle. Several formation or evolution scenarios are proposed to explain this metal-rich composition, such as a giant impact, mantle evaporation, or the depletion of silicate at the inner-edge of the proto-planetary disk. These scenarios are still strongly debated. Here we report the discovery of a multiple transiting planetary system (K2-229), in which the inner planet has a radius of 1.165+/-0.066 R-earth and a mass of 2.59+/-0.43 M-earth. This Earth-sized planet thus has a core-mass fraction that is compatible with that of Mercury, while it was expected to be similar to that of the Earth based on host-star chemistry. This larger Mercury analogue either formed with a very peculiar composition or it has evolved since, e.g. by losing part of its mantle. Further characterisation of Mercury-like exoplanets like K2-229 b will help putting the detailed in-situ observations of Mercury (with Messenger and BepiColombo) into the global context of the formation and evolution of solar and extrasolar terrestrial planets.

    =================

    https://arxiv.org/abs/1805.04774

    Super-Earth of 8 M earth in a 2.2-day orbit around the K5V star K2-216

    C.M. Persson, M. Fridlund, O. Barragán, F. Dai, D. Gandolfi, A.P. Hatzes, T. Hirano, S. Grziwa, J. Korth, J. Prieto-Arranz, L. Fossati, V. Van Eylen, A. Bo Justesen, J. Livingston, D. Kubyshkina, H.J. Deeg, E.W. Guenther, G. Nowak, J. Cabrera Ph. Eigmüller, Sz Csizmadia, A.M.S. Smith, A. Erikson, S. Albrecht R. Alonso Sobrino, W.D. Cochran, M. Endl, M. Esposito, A. Fukui, P. Heeren, D. Hidalgo, M. Hjorth, M. Kuzuhara, N. Narita, D. Nespral, E. Palle, M. Pätzold, H. Rauer, F. Rodler, J.N. Winn
    (Submitted on 12 May 2018 (v1), last revised 9 Jul 2018 (this version, v5))

    The KESPRINT consortium identified K2-216 as a planetary candidate host star in the K2 space mission Campaign 8 field with a transiting super-Earth. The planet has recently been validated as well. Our aim was to confirm the detection and derive the main physical characteristics of K2-216b, including the mass. We performed a series of follow-up observations: high resolution imaging with the FastCam camera at the TCS, the Infrared Camera and Spectrograph at Subaru, and high resolution spectroscopy with HARPS (ESO, La Silla), HARPS-N (TNG), and FIES (NOT). The stellar spectra were analyzed with the SpecMatch-Emp and SME codes to derive the stellar fundamental properties. We analyzed the K2 light curve with the Pyaneti software. The radial-velocity measurements were modelled with both a Gaussian process (GP) regression and the floating chunk offset (FCO) technique to simultaneously model the planetary signal and correlated noise associated with stellar activity. Imaging confirms that K2-216 is a single star. Our analysis discloses that the star is a moderately active K5V star of mass 0.70+/-0.03 M-sun and radius 0.72+/-0.03 R-sun. Planet b is found to have a radius of 1.75+0.17-0.10 R-earth and a 2.17-day orbit in agreement with previous results. We find consistent results for the planet mass from both models: 7.4+/-2.2 M-earth from the GP regression, and 8.0+/-1.6 M-earth from the FCO technique, which implies that this planet is a super-Earth. The planet parameters put planet b in the middle of, or just below, the gap of the radius distribution of small planets. The density is consistent with a rocky composition of primarily iron and magnesium silicate. In agreement with theoretical predictions, we find that the planet is a remnant core, stripped of its atmosphere, and is one of the largest planets found that has lost its atmosphere.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
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    Set up an Excel spreadsheet and input some dimensions. It is obvious you can only get so small with 1.0 g, because the planetary density rises very fast. I'm mentally bookmarking a radius of .75 to .80 Earth as about the minimum it can get. Check the attached table for details.

    You can get a Mercury-type density from repeated planetary impacts that blast off some of the rock but leave the iron in its place, per the paper below.

    https://arxiv.org/abs/1808.02448

    Forming Mercury by Giant Impacts

    Alice Chau, Christian Reinhardt, Ravit Helled, Joachim Gerhard Stadel
    (Submitted on 7 Aug 2018)

    The origin of Mercury's high iron-to-rock ratio is still unknown. In this work we investigate Mercury's formation via giant impacts and consider the possibilities of a single giant impact, a hit-and-run, and multiple collisions in one theoretical framework. We study the standard collision parameters (impact velocity, mass ratio, impact parameter), along with the impactor's composition and the cooling of the target. It is found that the impactor's composition affects the iron distribution within the planet and the final mass of the target by up to 15\%, although the resulting mean iron fraction is similar. We suggest that an efficient giant impact requires to be head-on with high velocities, while in the hit-and-run case the impact can occur closer to the most probable collision angle (45 ∘ ). It is also shown that Mercury's current iron-to-rock ratio can be a result of multiple-collisions, with their exact number depending on the collision parameters. Mass loss is found to be more significant when the collisions are tight in time.

    ==================================

    It seems that a smaller, denser Earth might have something in common with Mercury on a chemical/geological level, so the next two papers are attached in the event they add something to the discussion.

    https://arxiv.org/abs/1712.02187

    The Chemical Composition of Mercury

    Larry R. Nittler, Nancy L. Chabot, Timothy L. Grove, Patrick N. Peplowski
    (Submitted on 6 Dec 2017)

    The chemical composition of a planetary body reflects its starting conditions modified by numerous processes during its formation and geological evolution. Measurements by X-ray, gamma-ray, and neutron spectrometers on the MESSENGER spacecraft revealed Mercury's surface to have surprisingly high abundances of the moderately volatile elements sodium, sulfur, potassium, chlorine, and thorium, and a low abundance of iron. This composition rules out some formation models for which high temperatures are expected to have strongly depleted volatiles and indicates that Mercury formed under conditions much more reducing than the other rocky planets of our Solar System. Through geochemical modeling and petrologic experiments, the planet's mantle and core compositions can be estimated from the surface composition and geophysical constraints. The bulk silicate composition of Mercury is likely similar to that of enstatite or metal-rich chondrite meteorites, and the planet's unusually large core is most likely Si rich, implying that in bulk Mercury is enriched in Fe and Si (and possibly S) relative to the other inner planets. The compositional data for Mercury acquired by MESSENGER will be crucial for quantitatively testing future models of the formation of Mercury and the Solar System as a whole, as well as for constraining the geological evolution of the innermost planet.

    =============================================

    https://arxiv.org/abs/1712.08234

    The Elusive Origin of Mercury

    Denton S. Ebel, Sarah T. Stewart
    (Submitted on 21 Dec 2017)

    The MESSENGER mission sought to discover what physical processes determined Mercury's high metal to silicate ratio. Instead, the mission has discovered multiple anomalous characteristics about our innermost planet. The lack of FeO and the reduced oxidation state of Mercury's crust and mantle are more extreme than nearly all other known materials in the solar system. In contrast, moderately volatile elements are present in abundances comparable to the other terrestrial planets. No single process during Mercury's formation is able to explain all of these observations. Here, we review the current ideas for the origin of Mercury's unique features. Gaps in understanding the innermost regions of the solar nebula limit testing different hypotheses. Even so, all proposed models are incomplete and need further development in order to unravel Mercury's remaining secrets.
    Attached Images Attached Images
    Last edited by Roger E. Moore; 2018-Aug-12 at 06:48 PM.
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    You could calculate a planet with a much larger iron core could be maybe Mars-size and still have 1g surface gravity (I've not done the calculation but a much smaller Earth is surely feasible).

    Maybe it would spin faster on its axis and the day length would be shorter. Tidal effects would be smaller so it could retain its rotation for longer. This could enable Earth-like conditions closer in to smaller stars than the sun, i.e by avoiding tidal locking.

    Maybe also it would have a stronger magnetic field, which again would help shield its atmosphere from being stripped by being close-in to its star.

    This possibility of high-density Earths extends the potential for habitable planets to smaller stars than the sun.

    An interesting question is what happens to the escape velocity? Escape velocity = SQRT(2GM/r), I have not got my head round whether escape velocity would decrease or increase. But that has ramifications as to how easy or difficult it is for the inhabitants to do space travel.

    That's all I can think of for now, all my own thoughts so sorry no links.
    Last edited by kzb; 2018-Aug-13 at 11:37 AM.

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    https://en.wikipedia.org/wiki/Iron_planet

    Starting from the above, the following relevant articles appear. However, some are not available, so I cannot make use of them.

    https://www.nasa.gov/centers/goddard...d_planets.html

    https://arxiv.org/abs/0707.2895
    Mass-Radius Relationships for Solid Exoplanets
    S. Seager (MIT), M. Kuchner (GSFC), C. Hier-Majumder (DTM/Ciw), B. Militzer (GL/Ciw)
    (Submitted on 19 Jul 2007)
    We use new interior models of cold planets to investigate the mass-radius relationships of solid exoplanets, considering planets made primarily of iron, silicates, water, and carbon compounds. We find that the mass-radius relationships for cold terrestrial-mass planets of all compositions we considered follow a generic functional form that is not a simple power law ... This functional form arises because the common building blocks of solid planets all have equations of state that are well approximated by a modified polytrope of the form ρ=ρ0+cPn. We find that highly detailed planet interior models, including temperature structure and phase changes, are not necessary to derive solid exoplanet bulk composition from mass and radius measurements. For solid exoplanets with no substantial atmosphere we have also found that: with 5% fractional uncertainty in planet mass and radius it is possible to distinguish among planets composed predominantly of iron or silicates or water ice but not more detailed compositions; with ~5% uncertainty water ice planets with ≳25 water by mass may be identified; the minimum plausible planet size for a given mass is that of a pure iron planet; and carbon planet mass-radius relationships overlap with those of silicate and water planets due to similar zero-pressure densities and equations of state. We propose a definition of "super Earths'' based on the clear distinction in radii between planets with significant gas envelopes and those without.

    http://www.jbis.org.uk/paper.php?p=2014.67.105
    http://www.jbis.org.uk/preview/2014.67.105.jpg
    Big Planets: Super-Earths in Science Fiction
    S. Baxter (2014), JBIS, 67, pp.105-109
    This paper is a survey of the portrayal of super-Earths in science fiction. The discovery of super-Earths is so recent that the theoretical study of such worlds is in its infancy. However super-Earths were anticipated to some extent in science fiction. While in retrospect not all these fictional worlds are physically plausible, they do offer a glimpse of the wide array of super-Earths, and perhaps life forms, to be anticipated in reality.

    http://iopscience.iop.org/article/10...773/1/L15/meta
    THE ROCHE LIMIT FOR CLOSE-ORBITING PLANETS: MINIMUM DENSITY, COMPOSITION CONSTRAINTS, AND APPLICATION TO THE 4.2 hr PLANET KOI 1843.03
    Saul Rappaport, Roberto Sanchis-Ojeda, Leslie A. Rogers, Alan Levine, and Joshua N. Winn
    Published 2013 July 29
    The requirement that a planet must orbit outside of its Roche limit gives a lower limit on the planet's mean density. The minimum density depends almost entirely on the orbital period and is immune to systematic errors in the stellar properties. We consider the implications of this density constraint for the newly identified class of small planets with periods shorter than half a day. When the planet's radius is accurately known, this lower limit to the density can be used to restrict the possible combinations of iron and rock within the planet. Applied to KOI 1843.03, a 0.6 R ⊕ planet with the shortest known orbital period of 4.245 hr, the planet's mean density must be 7 g cm–3. By modeling the planetary interior subject to this constraint, we find that the composition of the planet must be mostly iron, with at most a modest fraction of silicates ( 30% by mass).
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
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    If it is true that the maximum density of a terrestrial planet is 7.5 g/cm^3, then the smallest planet with Earth like (1 gee) gravity would have a diameter of 9300km. Note that uncompressed iron has a density of 7.8 g/cm^3.

    But we haven't allowed for compression yet. According to this calculator, a planet made of pure iron with 1 gee surface gravity would have a diameter of 6520km and a density of 10.8 g/cm^3, much smaller and denser. However I don't know what assumptions were made when that calculator was made up.

    According to some of my references, a planet made of pure iron would be unlikely to occur in nature, but it is an interesting prospect. The magnetic field could be ferocious.
    Last edited by eburacum45; 2018-Aug-21 at 02:55 PM.

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    Quote Originally Posted by eburacum45 View Post
    According to some of my references, a planet made of pure iron would be unlikely to occur in nature, but it is an interesting prospect. The magnetic field could be ferocious.
    That last sentence is what puzzles me most. Some sources I have read seem to indicate that with increasing amounts of planetary iron, there is a cutoff point where the planet is more likely to "freeze" all the way through as it evolves, so that there would not be a rotating iron core, and thus no magnetic field. If this is true, I am interested in learning at what limit can iron make up a planet before there is a risk of the world turning geologically dead. I will continue researching this.

    My original goal with this thread was to figure out how a smaller planet with a stronger magnetic field would affect native life. I thought the smaller globe would increase competitive pressure on species to find living space, meaning there would be fewer species than on Earth, with a faster turnover in evolutionary time. However, with smaller living space there would also be increased risk of mass die-offs from disease or other disaster.

    A stronger magnetic field might greatly boost magnetic-based senses of direction and position, so that, for example, flying species would have a far more acute sense of where they were and where homes (or secondary migratory homes) were.

    Partial source list:

    https://en.wikipedia.org/wiki/Magnetoreception

    https://link.springer.com/article/10...359-005-0627-7
    Magnetic orientation and magnetoreception in birds and other animals

    https://arxiv.org/ftp/arxiv/papers/1511/1511.09302.pdf
    Evidence for Magnetoreception in Red Drum (Sciaenops ocellatus), Black Drum (Pogonias cromis), and Sea Catfish (Ariopsis felis)

    Another result of having a smaller world would be smaller tidal effects acting upon it. The tidal effects of the planet's sun and any moons it has (and any other worlds around it) depend greatly on that planet's radius/diameter. The smaller the world, the less that tides from other sources can affect it.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
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    Other stuff I found helpful...


    https://www.hou.usra.edu/meetings/me...8/pdf/6036.pdf

    A Large Solid Inner Core at Mercury

    Genova, A.; Goossens, S.; Mazarico, E.; Lemoine, F. G.; Neumann, G. A.; Kuang, W.; Sabaka, T. J.; Smith, D. E.; Zuber, M. T.
    05/2018

    New measurements of the polar moments of inertia of the whole planet and of the outer layers (crust+mantle), and simulations of Mercury's magnetic field dynamo suggest the presence of a solid inner core with a Ric 0.3-0.5 Roc. [[Outer core, however, is liquid.--REM]]

    ======================

    https://arxiv.org/pdf/1806.02024.pdf

    Mercury's Internal Structure

    Jean-Luc Margot, Steven A. Hauck II, Erwan Mazarico, Sebastiano Padovan, Stanton J. Peale
    (Submitted on 6 Jun 2018)

    We describe the current state of knowledge about Mercury's interior structure. We review the available observational constraints, including mass, size, density, gravity field, spin state, composition, and tidal response. These data enable the construction of models that represent the distribution of mass inside Mercury. In particular, we infer radial profiles of the pressure, density, and gravity in the core, mantle, and crust. We also examine Mercury's rotational dynamics and the influence of an inner core on the spin state and the determination of the moment of inertia. Finally, we discuss the wide-ranging implications of Mercury's internal structure on its thermal evolution, surface geology, capture in a unique spin-orbit resonance, and magnetic field generation.
    "These results provided direct observational evidence that Mercury has a molten outer core (Margot et al. 2007)."
    "...an alloy of Fe with both S and Si is likely in the core."
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    Wondering if volcanism would be increased on Mercury-Earth, given that molten Outer Core would be so close, relatively speaking, to the Mantle and Crust.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
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    Relevant article. Still wondering how life would evolve differently on a Mercury-type Earth.


    https://arxiv.org/abs/1808.10246

    Selective Aggregation Experiments on Planetesimal Formation and Mercury-Like Planets

    Gerhard Wurm
    (Submitted on 30 Aug 2018)

    Much of a planet's composition could be determined right at the onset of formation. Laboratory experiments can constrain these early steps. This includes static tensile strength measurements or collisions carried out under Earth's gravity and on various microgravity platforms. Among the variety of extrasolar planets which eventually form are (Exo)-Mercury, terrestrial planets with high density. If they form in inner protoplanetary disks, high temperature experiments are mandatory but they are still rare. Beyond the initial process of hit-and-stick collisions, some additional selective processing might be needed to explain Mercury. In analogy to icy worlds, such planets might, e.g., form in environments which are enriched in iron. This requires methods to separate iron and silicate at early stages. Photophoresis might be one viable way. Mercury and Mercury-like planets might also form due to the ferromagnetic properties of iron and mechanisms like magnetic aggregation in disk magnetic fields might become important. This review highlights some of the mechanisms with the potential to trigger Mercury formation.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
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    Why are we limiting ourselves to conventional compositions?

    What's the heaviest stable element we could spin off of a couple neutron star mergers? Lump a few of such debris together if we have to.

    Then what can we see?

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    https://www.universetoday.com/139774...-the-universe/

    Thanks to Frazier, a Universe Today article discussing a previously posted paper.
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    Quote Originally Posted by JCoyote View Post
    Why are we limiting ourselves to conventional compositions? What's the heaviest stable element we could spin off of a couple neutron star mergers? Lump a few of such debris together if we have to. Then what can we see?
    Not sure the planet would be habitable (chemical interactions), but it would be funny to see a Mario Universe-style planet around, tiny but you can walk on it.
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    Quote Originally Posted by Roger E. Moore View Post
    Not sure the planet would be habitable (chemical interactions)
    Habitability is relative to biochemistry. I could see very complex and varied chemicals being part of such a debris planet, so it could have its own forms of life.

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    Quote Originally Posted by JCoyote View Post
    Habitability is relative to biochemistry. I could see very complex and varied chemicals being part of such a debris planet, so it could have its own forms of life.
    Cannot argue with that. I have had trouble finding the info on this, as it was a quote from Wikipedia but I cannot read the original paper. I believe it was written by an SF writer, so who knows.
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    Mercury's interior turns out to be just like Earth's, thus relevant to this topic. A tiny Earth possible?

    https://phys.org/news/2019-04-closer...ls-planet.html

    A closer look at Mercury's spin and gravity reveals the planet's inner solid core

    by Michelle Thaller, NASA's Goddard Space Flight Center (4/17/2019)

    It has long been known that Mercury and the Earth have metallic cores. Like Earth, Mercury's outer core is composed of liquid metal, but there have only been hints that Mercury's innermost core is solid. Now, in a new study, scientists from NASA's Goddard Space Flight Center in Greenbelt, Maryland have found evidence that Mercury's inner core is indeed solid and that it is very nearly the same size as Earth's inner core. Some scientists compare Mercury to a cannonball because its metal core fills nearly 85 percent of the volume of the planet. This large core—huge compared to the other rocky planets in our solar system—has long been one of the most intriguing mysteries about Mercury.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
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    Quote Originally Posted by Roger E. Moore
    What if the Earth was smaller but denser, about the same as it is now with 1.0 Earth gravity and a Moon? Thought it might be fun to have a group thought experiment sot of like the "blueberry Earth" thing a couple weeks ago in the news.

    I call it the Mercury-Earth only because Mercury is a smaller world than ours but much denser, with a Mars-like gravity. Mercury has about 5.4 g/cm^3, and the highest density for a terrestrial exoplanet is about 7.5 g/cm^3, I think. Will look up source. Wonder how small an exoplanet could be and still have 1.0 Earth gravity, and what the results would be.
    on a planet mercury-like earth ("blueberry earth"?), the horizon would be quite closer - say 2 km instead of 5-6 km... a short walk could take you out of sight in an eyeblink

    it would be sort of living in a hedge maze, where you can disappear and reappear in a couple steps
    Last edited by Barabino; 2019-May-18 at 10:35 AM.

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    Quote Originally Posted by eburacum45 View Post
    If it is true that the maximum density of a terrestrial planet is 7.5 g/cm^3, then the smallest planet with Earth like (1 gee) gravity would have a diameter of 9300km. Note that uncompressed iron has a density of 7.8 g/cm^3.

    But we haven't allowed for compression yet. According to this calculator, a planet made of pure iron with 1 gee surface gravity would have a diameter of 6520km and a density of 10.8 g/cm^3, much smaller and denser.

    According to some of my references, a planet made of pure iron would be unlikely to occur in nature, but it is an interesting prospect. The magnetic field could be ferocious.
    Call it Braavos, after their Iron Bank


    How about gold?

    A neutron star collision can yield quite a lot after all. Maybe something for the Ferengi or the Muunilinst Banking Clan.

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    Quote Originally Posted by euburacum
    a planet made of pure iron would be unlikely to occur in nature, but it is an interesting prospect. The magnetic field could be ferocious.
    Now I have a realistic (not sci-fi) question: is a powerful magnetic field harmful?

    old cars are manipulated for demolition using big magnets and the workers seem careless about it... but is there an upper limit where it gets harmful?

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    google's short answer is: no, a strong magnetic field can't kill me instantly, but a long term exposure MAY (maybe can, maybe not)

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    I've worked with electromagnets lifting heavy ferrous objects; you can't feel the magnetic field at all, but it is not a good place to wear steel-toecapped boots.

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    I've read that a magnetic field from a magnetar can kill at something like a few thousand kilometers (of course, other things would kill you first). I don't know about that.
    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

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    that's sci-fi but it's interesting: is the magnetic field is so STRONG that it affects the organic iron atoms in our hemoglobine? :flash:

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    Quote Originally Posted by Barabino View Post
    that's sci-fi but it's interesting: is the magnetic field is so STRONG that it affects the organic iron atoms in our hemoglobine? :flash:
    At that strength all matter is magnetic. They can levitate glass and small animals in labs. https://en.wikipedia.org/wiki/Diamagnetism#Levitation
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    South Carolina
    Posts
    2,988
    I would look at a small, powerful magnetic field around a small Earthlike world as a huge benefit. One does wonder how small a world could go and still retain its biosphere and magnetosphere.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

  26. #26
    Join Date
    Feb 2005
    Posts
    11,354
    A solid Osmium planet might be the smallest diameter object to give Earth gravity--right there with gold.

    call it OZMA?

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