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Register a new userWas the Sun a Slow Rotator? -- Sodium and Potassium Constraints from the Lunar Regolith
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While the Earth and Moon are generally similar in composition, a notable difference between the two is the apparent depletion in moderately volatile elements in lunar samples. This is often attributed to the formation process of the Moon and demonstrates the importance of these elements as evolutionary tracers. Here we show that paleo space weather may have driven the loss of a significant portion of moderate volatiles, such as sodium and potassium from the surface of the Moon. The remaining sodium and potassium in the regolith is dependent on the primordial rotation state of the Sun. Notably, given the joint constraints shown in the observed degree of depletion of sodium and potassium in lunar samples and the evolution of activity of solar analogues over time, the Sun is highly likely to have been a slow rotator. Since the young Suns activity was important in affecting the evolution of planetary surfaces, atmospheres, and habitability in the early Solar System, this is an important constraint on the solar activity environment at that time. Finally, since solar activity was strongest in the first billion years of the Solar System, when the Moon was most heavily bombarded by impactors, evolution of the Suns activity may also be recorded in lunar crust and would be an important well-preserved and relatively accessible record of past Solar System processes.
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Extrasolar satellites are generally too small to be detected by nominal searches. By analogy to the most active body in the Solar System, Io, we describe how sodium (Na I) and potassium (K I) $textit{gas}$ could be a signature of the geological activity venting from an otherwise hidden exo-Io. Analyzing $sim$ a dozen close-in gas giants hosting robust alkaline detections, we show that an Io-sized satellite can be stable against orbital decay below a planetary tidal $mathcal{Q}_p lesssim 10^{11}$. This tidal energy is focused into the satellite driving a $sim 10^{5 pm 2}$ higher mass loss rate than Ios supply to Jupiters Na exosphere, based on simple atmospheric loss estimates. The remarkable consequence is that several exo-Io column densities are on average $textit{more than sufficient}$ to provide the $sim$ 10$^{10 pm 1}$ Na cm$^{-2}$ required by the equivalent width of exoplanet transmission spectra. Furthermore, the benchmark observations of both Jupiters extended ($sim 1000$ R$_J$) Na exosphere and Jupiters atmosphere in transmission spectroscopy yield similar Na column densities that are purely exogenic in nature. As a proof of concept, we fit the high-altitude Na at WASP 49-b with an ionization-limited cloud similar to the observed Na profile about Io. Moving forward, we strongly encourage time-dependent ingress and egress monitoring along with spectroscopic searches for other volcanic volatiles.
Since the Apollo program or earlier it has been widely believed that the lunar regolith was compacted through vibrations including nearby impact events, thermal stress release in the regolith, deep moon quakes, and shallow moon quakes. Experiments have shown that vibrations both compact and re-loosen regolith as a function of depth in the lunar soil column and amplitude of the vibrational acceleration. Experiments have also identified another process that is extremely effective at compacting regolith: the expansion and contraction of individual regolith grains due to thermal cycling in the upper part of the regolith where the diurnal thermal wave exists. Remote sensing data sets from the Moon suggest that the soil is less compacted in regions where there is less thermal cycling, including infrared emissions measured by the Diviner radiometer on the Lunar Reconnaissance Orbiter (LRO). Here, we performed additional experiments in thermal cycling simulated lunar regolith and confirm that it is an effective compaction mechanism and may explain the remote sensing data. This creates a consistent picture that the soil really is looser in the upper layers in polar regions, which may be a challenge for rovers that must drive in the looser soil.
The small atmosphereless objects of our solar system, such as asteroids, the moon are covered by layer of dust particles known as regolith, formed by meteoritic impact. The light scattering studies of such dust layer by laboratory experiment and numerical simulation are two important tools to investigate their physical properties. In the present work, the light scattered from a layer of dust particles, containing 0.3{mu}m Al2O3 at wavelength 632.8 nm is analysed. This work has been performed by using a light scattering instrument ellipsometer, at the Department of Physics, Assam Universiy, Silchar, India. Through this experiment, we generated in laboratory the photometric and polarimetric phase curves of light scattered from such a layer. In order to numerically simulate this data, we used Hapkes model combined with Mies single particle scattering properties. The perpendicular and parallel components of single particle albedo and the phase function were derived from Mie theory. By using the Hapkes model combined with Mie theory, the physical properties of the dust grain such as grain size, optical constant (n,k) and wavelength can be studied through this scheme. In literature, till today no theoretical model to represent polarisation caused due to scattering from rough surface is available, which can successfully explain the scattering process. So the main objective of this work is to develop a model which can theoretically estimate polarisation as caused due to scattering from rough surface and also to validate our model with the laboratory data generated in the present work.
Meteorites, which are remnants of solar system formation, provide a direct glimpse into the dynamics and evolution of a young stellar object (YSO), namely our Sun. Much of our knowledge about the astrophysical context of the birth of the Sun, the chronology of planetary growth from micrometer-sized dust to terrestrial planets, and the activity of the young Sun comes from the study of extinct radionuclides such as 26Al (t1/2 = 0.717 Myr). Here we review how the signatures of extinct radionuclides (short-lived isotopes that were present when the solar system formed and that have now decayed below detection level) in planetary materials influence the current paradigm of solar system formation. Particular attention is given to tying meteorite measurements to remote astronomical observations of YSOs and modeling efforts. Some extinct radionuclides were inherited from the long-term chemical evolution of the Galaxy, others were injected into the solar system by a nearby supernova, and some were produced by particle irradiation from the T-Tauri Sun. The chronology inferred from extinct radionuclides reveals that dust agglomeration to form centimeter-sized particles in the inner part of the disk was very rapid (<50 kyr), planetesimal formation started early and spanned several million years, planetary embryos (possibly like Mars) were formed in a few million years, and terrestrial planets (like Earth) completed their growths several tens of million years after the birth of the Sun.
NASA has developed a Figure of Merit method to grade the fidelity of lunar simulants for scientific and engineering purposes. Here we extend the method to grade asteroid simulants, both regolith and cobble variety, and we apply the method to the newly developed asteroid regolith and cobble simulant UCF/DSI-CI-2. The reference material that is used to evaluate this simulant for most asteroid properties is the Orgueil meteorite. Those properties are the mineralogical and elemental composition, grain density, bulk density of cobbles, magnetic susceptibility, mechanical strength of cobbles, and volatile release patterns. To evaluate the regolith simulants particle sizing we use a reference model that was based upon the sample returned from Itokawa by Hayabusa, the boulder count on Hayabusa, and four cases of disrupted asteroids that indicate particle sizing of the subsurface material. Compared to these references, the simulant has high figures of merit, indicating it is a good choice for a wide range of scientific and engineering applications. We recommend this methodology to the wider asteroid community and in the near future will apply it to additional asteroid simulants currently under development.
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