3 ms·

Hey, I'm the first author on this paper. We don't expect solar wind to have a strong effect. I focus on dynamics and not electromagnetic effects, but we took ou

by zyrxvo 4y ago

Hey, I'm the first author on this paper. We don't expect solar wind to have a strong effect. I focus on dynamics and not electromagnetic effects, but we took our values for the effects contributing to the perihelion precession of Mercury from NASA by Park et al. (2017) Precession of Mercury's Perihelion from Ranging to the MESSENGER Spacecraft <https://iopscience.iop.org/article/10.3847/1538-3881/aa5be2 https://iopscience.iop.org/article/10.3847/1538-3881/aa5be2>. However, I don't have an order of magnitude estimate for the effect and like you said, the effect is certainly subject to variation, especially due to the Sun's solar cycle <https://en.wikipedia.org/wiki/Solar_cycle https://en.wikipedia.org/wiki/Solar_cycle>. My guess is that since the effect of solar wind isn't included in the calculations and measurements by Park et al. (2017), then it's likely around a thousandth of an arcsecond per century or less.

defrost 4y ago
Thanks for the reply, I was in the ground based geophysics game for a decade or two and I'm fine with the envelope guess work and principle focus on gravity + GR dynamics .. but I am now piqued by this, I'm grabbing Park (thanks for the link) and will poke about further.
- raattgift 4y ago
  There's an orbiting-body size and shape (and ultimately mass) dependence on solar radiation pressure's effects on the evolutions of orbits in the solar system that dominates other factors for bigger solar system bodies (planets, dwarf planets, round moons). For planetary orbits, perturbations from radiation pressure while the sun is on the main sequence will be so small as to be negligible. Small perturbations may matter over billions of years, but perhaps more billions than the sun has life. Small bodies which are not in hydrostatic equilibrium (i.e., not massive enough to be round through gravitational collapse) can experience many orders of magnitude larger perturbations. However, for lumpy asteroids, radiation pressure gives net accelerations orders of magnitude below 10^-10 m/s^2. A literature search on the Yarkovksy effect might take you to radiation-pressure work on larger, rounder bodies (or more likely their outermost layers' chemistry and density), possibly even planets. Effects like these are generally proportional to ellipticy of the body itself and its rotation, and inversely proportional the body's size, with insolation and albedo as surprisingly minor factors. The Yarkovsky effect might cause a small, lumpy, quickly-spinning asteroid-belt body to dive into the inner solar system. https://arxiv.org/abs/1708.05513 https://arxiv.org/abs/1708.05513 has an interesting overview. At a more pop-sci level, https://skyandtelescope.org/astronomy-news/the-asteroid-and-the-pea/ https://skyandtelescope.org/astronomy-news/the-asteroid-and-... The MESSENGER programme did some science on Mercury's exosphere <https://en.wikipedia.org/wiki/Atmosphere_of_Mercury https://en.wikipedia.org/wiki/Atmosphere_of_Mercury> (and effects like ion sputtering photon-stimulated desorption, each of which kicks mainly sodium atoms off Mercury's surface into its long cometary tail) that is likely to be interesting, but is likely to undermine the idea that electromagnetic forces are significant with respect to the planet's orbital evolution. There is a substantial body of literature on radiation pressure's effects on artificial Earth satellites, but such devices are certainly not in hydrostatic equilibrium and rarely anything close to spherical (extended solar panels, etc.) Putting "solar radiation pressure satellites" into your favourite Internet search engine will be fruitful. There is also a body of literature where the radial solar radiation force is important in calculating the trajectories of space probes sent to various parts of our solar system. Again, these are low-mass objects on many-year flights. The Mariner programme generated papers relevant to Mercury e.g. the 160 pages of <https://ntrs.nasa.gov/citations/19750009204 https://ntrs.nasa.gov/citations/19750009204>.
  - defrost 4y ago
    Cheers. On a related note, are there any examples of magnetic field coupling having a significant effect (for some time scale) on orbiting masses? Mercury, again, might be good case for such a thing. In a similar vein as > (searching) "solar radiation pressure satellites" is "Magnetorquer satellites" - small effects for attitude adjustment with a complicated "surfing" twist as the field fluxes so much on a daily basis. I'm under no illusions that these (solar particle pressure, magnetic coupling) would be significant - but theis is a thread about a paper on the evolution of small perturbations :-)
    - raattgift 4y ago
      We are straying far from my area of expertise. :-) (except at the end). > Mercury, again, might be a good case In our solar system I'd look to Jupiter, whose magnetic strength is tens of thousands of times stronger than Earth's, and which has lots of bodies of various sizes orbiting it. There are magnetic interactions with several of the moons explored by recent space probes, but they are very small. Ganymede is probably the most interesting case. I would be surprised if there were significant orbital perturbations from magnetics on the Galilean moons, or even the mid-size ones. Smaller, especially grain-sized bodies, I don't know. I know next to nothing about Jupiter's rings, but on general chemistry grounds there will be electromagnetic interactions with the planet's magnetosphere. (I suspect these are dwarfed by radiation pressures though; the biggest forcing radiation will be tangential to the ring-components' orbits around Jupiter, and as those objects are small the effect will be relatively large, causing illuminated grains to tend to spiral inwards to Jupiter, but how long does a ring particle stay illuminated rather than in shadow? And there are likely forces that push grains outward, too). None of this likely needs corrections to classical Newtonian gravitation. (The authors of the paper linked at the top do not consider any of the solar system's moons or smaller objects). I'd start here <https://en.wikipedia.org/wiki/Magnetosphere_of_Jupiter#Interaction_with_rings_and_moons https://en.wikipedia.org/wiki/Magnetosphere_of_Jupiter#Inter...>, notably the paragraph starting, "The icy Galilean moons, Europa, Ganymede and Callisto, all generate induced magnetic moments in response to changes in Jupiter's magnetic field", and visit the various citations in that paragraph and the following two. > evolution of small parameters You've hit on the right word, "evolution", which is much more important than "small". Can we apply perturbation theory? Do we get a nice Taylor-series-like expansion where higher order terms can be treated as marginal or negligible, in the style of Wilsonian effective field theory? See Clifford Will's article, <https://www.pnas.org/doi/pdf/10.1073/pnas.1103127108 https://www.pnas.org/doi/pdf/10.1073/pnas.1103127108>, which is probably close to accessible. It is mainly interested in "quite relativistic" systems, however, and we do not have those in our solar system. Almost nothing in the solar system needs even 1PN (see what that means in the article, or in e.g. the wikipedia article on the post-Newtonian expansion) correction. The work linked at the top is neat because PN effects may actually matter for the ultimate fate of Mercury. Finally, this beautiful paper by Soffel (Past President of IAU Commission 52 Relativity in Fundamental Astronomy) discusses the (ir)relevance of higher-order post-Newtonian corrections to the Earth's gravitational field. <https://link.springer.com/article/10.1007/s00190-016-0927-4 https://link.springer.com/article/10.1007/s00190-016-0927-4> (find it on sci-hub.ru). ("Above, we have demonstrated that the first post-Newtonian approximation is completely sufficient for a description of the Earth's gravitational field and also for a description of satellite orbits."). Table 3 lists the various accelerations on the LAGEOS satellite. Solar radiation pressure, thermal re-radiation, and even albedo pressure (at 3.5e-19 m/s^2) are in the table; nothing like like "magnetotorquer" effects even appears.

by zyrxvo 4y ago

defrost 4y ago

Thanks for the reply, I was in the ground based geophysics game for a decade or two and I'm fine with the envelope guess work and principle focus on gravity + GR dynamics .. but I am now piqued by this, I'm grabbing Park (thanks for the link) and will poke about further.

raattgift 4y ago
There's an orbiting-body size and shape (and ultimately mass) dependence on solar radiation pressure's effects on the evolutions of orbits in the solar system that dominates other factors for bigger solar system bodies (planets, dwarf planets, round moons). For planetary orbits, perturbations from radiation pressure while the sun is on the main sequence will be so small as to be negligible. Small perturbations may matter over billions of years, but perhaps more billions than the sun has life. Small bodies which are not in hydrostatic equilibrium (i.e., not massive enough to be round through gravitational collapse) can experience many orders of magnitude larger perturbations. However, for lumpy asteroids, radiation pressure gives net accelerations orders of magnitude below 10^-10 m/s^2. A literature search on the Yarkovksy effect might take you to radiation-pressure work on larger, rounder bodies (or more likely their outermost layers' chemistry and density), possibly even planets. Effects like these are generally proportional to ellipticy of the body itself and its rotation, and inversely proportional the body's size, with insolation and albedo as surprisingly minor factors. The Yarkovsky effect might cause a small, lumpy, quickly-spinning asteroid-belt body to dive into the inner solar system. https://arxiv.org/abs/1708.05513 https://arxiv.org/abs/1708.05513 has an interesting overview. At a more pop-sci level, https://skyandtelescope.org/astronomy-news/the-asteroid-and-the-pea/ https://skyandtelescope.org/astronomy-news/the-asteroid-and-... The MESSENGER programme did some science on Mercury's exosphere <https://en.wikipedia.org/wiki/Atmosphere_of_Mercury https://en.wikipedia.org/wiki/Atmosphere_of_Mercury> (and effects like ion sputtering photon-stimulated desorption, each of which kicks mainly sodium atoms off Mercury's surface into its long cometary tail) that is likely to be interesting, but is likely to undermine the idea that electromagnetic forces are significant with respect to the planet's orbital evolution. There is a substantial body of literature on radiation pressure's effects on artificial Earth satellites, but such devices are certainly not in hydrostatic equilibrium and rarely anything close to spherical (extended solar panels, etc.) Putting "solar radiation pressure satellites" into your favourite Internet search engine will be fruitful. There is also a body of literature where the radial solar radiation force is important in calculating the trajectories of space probes sent to various parts of our solar system. Again, these are low-mass objects on many-year flights. The Mariner programme generated papers relevant to Mercury e.g. the 160 pages of <https://ntrs.nasa.gov/citations/19750009204 https://ntrs.nasa.gov/citations/19750009204>.
- defrost 4y ago
  Cheers. On a related note, are there any examples of magnetic field coupling having a significant effect (for some time scale) on orbiting masses? Mercury, again, might be good case for such a thing. In a similar vein as > (searching) "solar radiation pressure satellites" is "Magnetorquer satellites" - small effects for attitude adjustment with a complicated "surfing" twist as the field fluxes so much on a daily basis. I'm under no illusions that these (solar particle pressure, magnetic coupling) would be significant - but theis is a thread about a paper on the evolution of small perturbations :-)
  - raattgift 4y ago
    We are straying far from my area of expertise. :-) (except at the end). > Mercury, again, might be a good case In our solar system I'd look to Jupiter, whose magnetic strength is tens of thousands of times stronger than Earth's, and which has lots of bodies of various sizes orbiting it. There are magnetic interactions with several of the moons explored by recent space probes, but they are very small. Ganymede is probably the most interesting case. I would be surprised if there were significant orbital perturbations from magnetics on the Galilean moons, or even the mid-size ones. Smaller, especially grain-sized bodies, I don't know. I know next to nothing about Jupiter's rings, but on general chemistry grounds there will be electromagnetic interactions with the planet's magnetosphere. (I suspect these are dwarfed by radiation pressures though; the biggest forcing radiation will be tangential to the ring-components' orbits around Jupiter, and as those objects are small the effect will be relatively large, causing illuminated grains to tend to spiral inwards to Jupiter, but how long does a ring particle stay illuminated rather than in shadow? And there are likely forces that push grains outward, too). None of this likely needs corrections to classical Newtonian gravitation. (The authors of the paper linked at the top do not consider any of the solar system's moons or smaller objects). I'd start here <https://en.wikipedia.org/wiki/Magnetosphere_of_Jupiter#Interaction_with_rings_and_moons https://en.wikipedia.org/wiki/Magnetosphere_of_Jupiter#Inter...>, notably the paragraph starting, "The icy Galilean moons, Europa, Ganymede and Callisto, all generate induced magnetic moments in response to changes in Jupiter's magnetic field", and visit the various citations in that paragraph and the following two. > evolution of small parameters You've hit on the right word, "evolution", which is much more important than "small". Can we apply perturbation theory? Do we get a nice Taylor-series-like expansion where higher order terms can be treated as marginal or negligible, in the style of Wilsonian effective field theory? See Clifford Will's article, <https://www.pnas.org/doi/pdf/10.1073/pnas.1103127108 https://www.pnas.org/doi/pdf/10.1073/pnas.1103127108>, which is probably close to accessible. It is mainly interested in "quite relativistic" systems, however, and we do not have those in our solar system. Almost nothing in the solar system needs even 1PN (see what that means in the article, or in e.g. the wikipedia article on the post-Newtonian expansion) correction. The work linked at the top is neat because PN effects may actually matter for the ultimate fate of Mercury. Finally, this beautiful paper by Soffel (Past President of IAU Commission 52 Relativity in Fundamental Astronomy) discusses the (ir)relevance of higher-order post-Newtonian corrections to the Earth's gravitational field. <https://link.springer.com/article/10.1007/s00190-016-0927-4 https://link.springer.com/article/10.1007/s00190-016-0927-4> (find it on sci-hub.ru). ("Above, we have demonstrated that the first post-Newtonian approximation is completely sufficient for a description of the Earth's gravitational field and also for a description of satellite orbits."). Table 3 lists the various accelerations on the LAGEOS satellite. Solar radiation pressure, thermal re-radiation, and even albedo pressure (at 3.5e-19 m/s^2) are in the table; nothing like like "magnetotorquer" effects even appears.