Terrestrial Planet Optical Phase Curves. I. Direct Measurements of the Earth

Abstract NASA’s EPOXI mission used the Deep Impact spacecraft to observe the disk-integrated Earth as an analog to terrestial exoplanets’ appearance. The mission took five 24 hr observations in 2008–2009 at various phase angles (57.°7–86.°4) and ranges (0.11–0.34 au), of which three equatorial (E1, E4, E5) and two polar (P1, North and P2, South). The visible data taken by the HRIV instrument ranges from 0.3 to 1.0 μm, taken trough seven spectral filters that have spectral widths of about 100 nm, and which are centered about 100 nm apart, from 350 to 950 nm. The disk-integrated, 24 hr averaged signal is used in a phase angle analysis. A Lambertian-reflecting, spherical planet model is used to estimate geometric albedo for every observation and wavelength. The geometric albedos range from 0.143 (E1, 950 nm) to 0.353 (P2, 350 nm) and show wavelength dependence. The equatorial observations have similar values, while the polar observations have higher values due to the ice in view. Therefore, equatorial observations can be predicted for other phase angles, but (Earth-like) polar views (with ice) would be underestimated.

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Umov effect in asteroid (3200) Phaethon

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833408 ◽

2018 ◽

Vol 620 ◽

pp. A179 ◽

Cited By ~ 4

Author(s):

Maxim Zheltobryukhov ◽

Ekaterina Chornaya ◽

Anton Kochergin ◽

Gennady Kornienko ◽

Alexey Matkin ◽

...

Keyword(s):

Linear Polarization ◽

Lunar Regolith ◽

Wavelength Dependence ◽

Parent Body ◽

Meteor Shower ◽

Accurate Estimation ◽

Space Technology ◽

Large Phase ◽

Phase Angles ◽

Geometric Albedo

Context. The near-Earth asteroid (3200) Phaethon occasionally reveals a comet-like activity. It is a parent body to the Geminid meteor shower and considered as a target for the space mission called Demonstration and Experiment of Space Technology for Interplanetary Voyage Phaethon Flyby Dust Science, DESTINY+. Aims. We aim to characterize Phaethon through measurements of the degree of linear polarization P measured on Phaethon at large phase angles on its closest approach to Earth on December 17, 2017. These observations allow a more accurate estimation of the maximum value of the degree of linear polarization Pmax of Phaethon, and therefore, of studying the Umov effect. Methods. We performed polarimetric measurements of Phaethon at large phase angles α and thus constrained its Pmax. We also estimated the geometric albedo a based on the data available in the literature. The obtained Pmax and A were analysed with the Umov effect previously derived for the Moon that establishes an inverse linear correlation between log(Pmax) and log(A) in the lunar regolith. Results. Our polarimetric observations of Phaethon in the visible reveal the degree of linear polarization P ≈ (17.23 ± 2.00)% at α ≈ 57.9° and P ≈ (31.86 ± 2.00)% at α ≈ 73.2°, which demonstrates no significant wavelength dependence within the error bars of our measurements (± 2%). These data, when combined with what has previously been reported in the literature, suggests at least three types of polarimetric response on Phaethon. For two of them, we infer the maximum linear polarization to be Pmax ≈ 57.9%, occurring at αmax = 131° and Pmax ≈ 44.5% occurring at αmax = 127°. We estimate the geometric albedo (adjusted to α = 3°) to be AR = 0.075 ± 0.007 in the R filter, which appears to be consistent with dark F-type asteroids, as which Phaethon was first classified. We examine the Umov diagrams previously inferred for lunar regolith and find that they are hardly applicable to Phaethon and therefore not to other asteroids either.

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Ceres’ opposition effect observed by the Dawn framing camera

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833596 ◽

2018 ◽

Vol 620 ◽

pp. A201 ◽

Cited By ~ 6

Author(s):

Stefan E. Schröder ◽

Jian-Yang Li ◽

Marc D. Rayman ◽

Steven P. Joy ◽

Carol A. Polanskey ◽

...

Keyword(s):

Wavelength Dependence ◽

Phase Curve ◽

Angular Width ◽

Opposition Effect ◽

Physically Based ◽

Phase Angles ◽

Coherent Backscatter ◽

Zero Phase ◽

Geometric Albedo ◽

Framing Camera

Context. The surface reflectance of planetary regoliths may increase dramatically towards zero phase angle, a phenomenon known as the opposition effect (OE). Two physical processes that are thought to be the dominant contributors to the brightness surge are shadow hiding (SH) and coherent backscatter (CB). The occurrence of shadow hiding in planetary regoliths is self-evident, but it has proved difficult to unambiguously demonstrate CB from remote sensing observations. One prediction of CB theory is the wavelength dependence of the OE angular width. Aims. The Dawn spacecraft observed the OE on the surface of dwarf planet Ceres. We aim to characterize the OE over the resolved surface, including the bright Cerealia Facula, and to find evidence for SH and/or CB. It is presently not clear if the latter can contribute substantially to the OE for surfaces as dark as that of Ceres. Methods. We analyze images of the Dawn framing camera by means of photometric modeling of the phase curve. Results. We find that the OE of most of the investigated surface has very similar characteristics, with an enhancement factor of 1.4 and a full width at half maximum of 3° (“broad OE”). A notable exception are the fresh ejecta of the Azacca crater, which display a very narrow brightness enhancement that is restricted to phase angles <0.5° (“narrow OE”); suggestively, this is in the range in which CB is thought to dominate. We do not find a wavelength dependence for the width of the broad OE, and lack the data to investigate the dependence for the narrow OE. The prediction of a wavelength-dependent CB width is rather ambiguous, and we suggest that dedicated modeling of the Dawn observations with a physically based theory is necessary to better understand the Ceres OE. The zero-phase observations allow us to determine Ceres’ visible geometric albedo as pV = 0.094 ± 0.005. A comparison with other asteroids suggests that Ceres’ broad OE is typical for an asteroid of its spectral type, with characteristics that are primarily linked to surface albedo. Conclusions. Our analysis suggests that CB may occur on the dark surface of Ceres in a highly localized fashion. While the results are inconclusive, they provide a piece to the puzzle that is the OE of planetary surfaces.

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Forming terrestrial planets and delivering water

Proceedings of the International Astronomical Union ◽

10.1017/s174392131600572x ◽

2015 ◽

Vol 11 (A29B) ◽

pp. 427-430

Author(s):

Kevin J. Walsh

Keyword(s):

Planet Formation ◽

Semimajor Axis ◽

Giant Planet ◽

Terrestrial Planet ◽

Giant Planets ◽

Asteroid Belt ◽

Terrestrial Planets ◽

The Earth ◽

Building Models ◽

Rich Material

AbstractBuilding models capable of successfully matching the Terrestrial Planet's basic orbital and physical properties has proven difficult. Meanwhile, improved estimates of the nature of water-rich material accreted by the Earth, along with the timing of its delivery, have added even more constraints for models to match. While the outer Asteroid Belt seemingly provides a source for water-rich planetesimals, models that delivered enough of them to the still-forming Terrestrial Planets typically failed on other basic constraints - such as the mass of Mars.Recent models of Terrestrial Planet Formation have explored how the gas-driven migration of the Giant Planets can solve long-standing issues with the Earth/Mars size ratio. This model is forced to reproduce the orbital and taxonomic distribution of bodies in the Asteroid Belt from a much wider range of semimajor axis than previously considered. In doing so, it also provides a mechanism to feed planetesimals from between and beyond the Giant Planet formation region to the still-forming Terrestrial Planets.

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BepiColombo – Mercury Swing-Bys

10.5194/epsc2021-353 ◽

2021 ◽

Author(s):

Joe Zender ◽

Johannes Benkhoff ◽

Go Murakami ◽

Elsa Montagnon

Keyword(s):

Remote Sensing ◽

Space Exploration ◽

Terrestrial Planet ◽

Field Of View ◽

Space Craft ◽

Joint Project ◽

The Earth ◽

Space Agency ◽

Euro Pean ◽

French Guyana

Abstract The BepiColombo spacecraft was launched on 20 October 2018 from the European spaceport in French Guyana and is currently on its way to Mercury. On its way, the spacecraft will swing-by Mercury six times in its stacked configuration, before releasing the Mercury Magnetospheric Orbiter (MMO) and the Mercury Planetary Orbiter (MPO) in their corresponding orbits around the target planet. Introduction Mercury is in many ways a very different planet from what we were expecting. On 20 October 2018 the BepiColombo spacecraft [1] started its 7 year journey to the innermost terrestrial planet to investigate on the fundamental questions about its evolution, composition, interior, magnetosphere, and exosphere. BepiColombo is a joint project between the Euro- pean Space Agency (ESA) and the Japanese Aero- space Exploration Agency (JAXA). The Mission con- sists of two orbiters, the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO). From their dedicated orbits the two space- craft will be studying the planet and its environment. The mission has been named in honor of Giuseppe (Bepi) Colombo (1920&#8211;1984), who was a brilliant Italian mathematician, who made many significant contributions to planetary research and celestial mechanics. During the cruise phase, the spacecraft flies in a stacked configuration: the MMO and MPO are mounted ontop of the Mercury Transfer Module (MTM). As a consequence, most remote sensing instruments onboard the MPO are mounted towards the MTM and have a fully obstructed field-of-view. The MMO instrumentation is shielded by a protection shield (MOSIF) and several instruments still await the deployment on measurement booms. Despite the reduced instrument availability, scientific and engineering operations will be scheduled during the cruise phase, especially during the swing-bys. Mercury Swing-bys Following the Earth and two Venus swing-bys, six Mercury swing-bys are foreseen from October 2021 until 9 January 2025. The poster will discuss the flyby geometries and potential operation opportunities, in comparison with the three MESSENGER Mercury swing-bys from 2008 and 2009 [2][3]. References: [1] Benkhoff, J., et al. (2010) Planet. Space Sci. 58, 2-20. [2] Baker, D.N. et al. (2011) Planet. Space Sci 59, 2066-2074. [3] McNutt, R.L. et al. (2010), Acta Astronautica V67, Iss 7-8, p 681-687

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Evolution of the Earth’s atmosphere during Late Veneer accretion

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3210 ◽

2020 ◽

Vol 499 (4) ◽

pp. 5334-5362

Author(s):

Catriona A Sinclair ◽

Mark C Wyatt ◽

Alessandro Morbidelli ◽

David Nesvorný

Keyword(s):

Terrestrial Planet ◽

Hydrodynamic Simulations ◽

Substantial Growth ◽

Early Atmosphere ◽

The Earth ◽

Wide Range ◽

History Of ◽

Current Mass ◽

Low Mass ◽

Late Veneer

ABSTRACT Recent advances in our understanding of the dynamical history of the Solar system have altered the inferred bombardment history of the Earth during accretion of the Late Veneer, after the Moon-forming impact. We investigate how the bombardment by planetesimals left-over from the terrestrial planet region after terrestrial planet formation, as well as asteroids and comets, affects the evolution of Earth’s early atmosphere. We develop a new statistical code of stochastic bombardment for atmosphere evolution, combining prescriptions for atmosphere loss and volatile delivery derived from hydrodynamic simulations and theory with results from dynamical modelling of realistic populations of impactors. We find that for an initially Earth-like atmosphere, impacts cause moderate atmospheric erosion with stochastic delivery of large asteroids, giving substantial growth (× 10) in a few ${{\ \rm per\ cent}}$ of cases. The exact change in atmosphere mass is inherently stochastic and dependent on the dynamics of the left-over planetesimals. We also consider the dependence on unknowns including the impactor volatile content, finding that the atmosphere is typically completely stripped by especially dry left-over planetesimals ($\lt 0.02 ~ {{\ \rm per\ cent}}$ volatiles). Remarkably, for a wide range of initial atmosphere masses and compositions, the atmosphere converges towards similar final masses and compositions, i.e. initially low-mass atmospheres grow, whereas massive atmospheres deplete. While the final properties are sensitive to the assumed impactor properties, the resulting atmosphere mass is close to that of current Earth. The exception to this is that a large initial atmosphere cannot be eroded to the current mass unless the atmosphere was initially primordial in composition.

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Four-billion year stability of the Earth–Mars belt

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3076 ◽

2020 ◽

Vol 500 (1) ◽

pp. 1151-1157

Author(s):

Yukun Huang (黄宇坤) ◽

Brett Gladman

Keyword(s):

Semimajor Axis ◽

Orbital Stability ◽

Terrestrial Planet ◽

Small Bodies ◽

Mean Motion Resonances ◽

Mean Motion ◽

The Earth ◽

Steady State Model ◽

Near Earth Objects

ABSTRACT Previous work has demonstrated orbital stability for 100 Myr of initially near-circular and coplanar small bodies in a region termed the ‘Earth–Mars belt’ from 1.08 < a < 1.28 au. Via numerical integration of 3000 particles, we studied orbits from 1.04–1.30 au for the age of the Solar system. We show that on this time-scale, except for a few locations where mean-motion resonances with Earth affect stability, only a narrower ‘Earth–Mars belt’ covering a ∼ (1.09, 1.17) au, e < 0.04, and I < 1° has over half of the initial orbits survive for 4.5 Gyr. In addition to mean-motion resonances, we are able to see how the ν3, ν4, and ν6 secular resonances contribute to long-term instability in the outer (1.17–1.30 au) region on Gyr time-scales. We show that all of the (rather small) near-Earth objects (NEOs) in or close to the Earth–Mars belt appear to be consistent with recently arrived transient objects by comparing to a NEO steady-state model. Given the <200 m scale of these NEOs, we estimated the Yarkovsky drift rates in semimajor axis and use these to estimate that a diameter of ∼100 km or larger would allow primordial asteroids in the Earth–Mars belt to likely survive. We conclude that only a few 100-km sized asteroids could have been present in the belt’s region at the end of the terrestrial planet formation.

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Polarimetric Properties of Halley’s Dust

International Astronomical Union Colloquium ◽

10.1017/s0252921100066975 ◽

1991 ◽

Vol 126 ◽

pp. 285-288

Author(s):

A.K. Sen ◽

M.R. Deshpande ◽

U.C. Joshi

Keyword(s):

Phase Angle ◽

Wavelength Dependence ◽

Complete Picture ◽

Refractive Indices ◽

Polarization Data

Abstract:Comet P/Halley was observed polarimetrically for seven nights in IHW and other continuum filters, during the pre and post perihelion passages. The polarimetric observations have been combined with the observations taken by other investigators, to get a complete picture of phase angle and wavelength dependence of polarization of comet P/Halley. Assuming Mie type scattering by cometary grains, the observed polarization data were fitted for a set of complex refractive indices which are (1.387, .032), (1.375, .040) and (1.374, .052) at .365, .484 and .684μm respectively.

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The Earth as an extrasolar planet: the vegetation spectral signature today and during the last Quaternary climatic extrema

International Journal of Astrobiology ◽

10.1017/s1473550409004406 ◽

2009 ◽

Vol 8 (2) ◽

pp. 81-94 ◽

Cited By ~ 20

Author(s):

Luc Arnold ◽

François-Marie Bréon ◽

Simon Brewer

Keyword(s):

Reflectance Spectrum ◽

Terrestrial Planet ◽

Spectral Signature ◽

The Holocene ◽

Ice Cap ◽

The Earth ◽

The Mean ◽

Earth’S Climate ◽

The Last Glacial Maximum ◽

The Last Glacial

AbstractThe so-called vegetation red-edge (VRE), a sharp increase in the reflectance around 700 nm, is a characteristic of vegetation spectra, and can therefore be used as a biomarker if it can be detected in an unresolved extrasolar Earth-like planet integrated reflectance spectrum. Here, we investigate the potential for the detection of vegetation spectra during the last Quaternary climatic extrema, the Last Glacial Maximum (LGM) and the Holocene optimum, for which past climatic simulations have been made. By testing the VRE detectability during these extrema, when Earth's climate and biomes maps were different from today, we are able to test the vegetation detectability on a terrestrial planet different from our modern Earth. Data from the Biome3.5 model have been associated to visible Global Ozone Monitoring Experiment (GOME) spectra for each biome and cloud cover to derive Earth's integrated spectra for given Earth phases and observer positions. The VRE is then measured. Results show that the vegetation remains detectable during the last climatic extrema. Compared to the current Earth, the Holocene optimum, with a greener Sahara, slightly increases the mean VRE on one hand, while on the other hand, the large ice cap over the northern hemisphere during the LGM decreases vegetation detectability. We finally discuss the detectability of the VRE in the context of recently proposed space missions.

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Attention and Temporal Expectations Modulate Power, Not Phase, of Ongoing Alpha Oscillations

Journal of Cognitive Neuroscience ◽

10.1162/jocn_a_00803 ◽

2015 ◽

Vol 27 (8) ◽

pp. 1573-1586 ◽

Cited By ~ 53

Author(s):

Rosanne M. van Diepen ◽

Michael X Cohen ◽

Damiaan Denys ◽

Ali Mazaheri

Keyword(s):

Phase Angle ◽

Phase Locking ◽

Auditory Target ◽

Alpha Power ◽

Visual Condition ◽

Top Down ◽

Alpha Oscillations ◽

Alpha Oscillation ◽

Sensory Cortices ◽

Phase Angles

The perception of near-threshold visual stimuli has been shown to depend in part on the phase (i.e., time in the cycle) of ongoing alpha (8–13 Hz) oscillations in the visual cortex relative to the onset of that stimulus. However, it is currently unknown whether the phase of the ongoing alpha activity can be manipulated by top–down factors such as attention or expectancy. Using three variants of a cross-modal attention paradigm with constant predictable stimulus onsets, we examined if cues signaling to attend to either the visual or the auditory domain influenced the phase of alpha oscillations in the associated sensory cortices. Importantly, intermixed in all three experiments, we included trials without a target to estimate the phase at target presentation without contamination from the early evoked responses. For these blank trials, at the time of expected target and distractor onset, we examined (1) the degree of the uniformity in phase angles across trials, (2) differences in phase angle uniformity compared with a pretarget baseline, and (3) phase angle differences between visual and auditory target conditions. Across all three experiments, we found that, although the cues induced a modulation in alpha power in occipital electrodes, neither the visual condition nor the auditory cue condition induced any significant phase-locking across trials during expected target or distractor presentation. These results suggest that, although alpha power can be modulated by top–down factors such as attention and expectation, the phase of the ongoing alpha oscillation is not under such control.

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Significantly high polarization degree of the very low-albedo asteroid (152679) 1998 KU2

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732086 ◽

2018 ◽

Vol 611 ◽

pp. A31 ◽

Cited By ~ 2

Author(s):

Daisuke Kuroda ◽

Masateru Ishiguro ◽

Makoto Watanabe ◽

Sunao Hasegawa ◽

Tomohiko Sekiguchi ◽

...

Keyword(s):

Solar System ◽

Polarization Degree ◽

Polarimetric Observation ◽

High Polarization ◽

Planetary Satellites ◽

Large Phase ◽

Solar Phase ◽

Phase Angles ◽

Similar Phase ◽

Geometric Albedo

We present a unique and significant polarimetric result regarding the near-Earth asteroid (152679) 1998 KU2, which has a very low geometric albedo. From our observations, we find that the linear polarization degrees of 1998 KU2are 44.6 ± 0.5% in theRCband and 44.0 ± 0.6% in theVband at a solar phase angle of 81.0°. These values are the highest of any known airless body in the solar system (i.e., high-polarization comets, asteroids, and planetary satellites) at similar phase angles. This polarimetric observation is not only the first for primitive asteroids at large phase angles, but also for low-albedo (<0.1) airless bodies. Based on spectroscopic similarities and polarimetric measurements of materials that have been sorted by size in previous studies, we conjecture that 1998 KU2has a highly microporous regolith structure comprising nano-sized carbon grains on the surface.

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