Tranquility Science Duty Logs

Moderator: Kermie Mistwallow

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Ferre Flamand
Science - Lieutenant Commander
Science - Lieutenant Commander
Posts: 461
Joined: 211111.0543
Duty Post: Vice Chief Science Officer
Ship/Station Posted: SS Tranquility
Grid: Second Life
Location: Belgium
Has thanked: 226 times
Been thanked: 62 times
Contact:

230313.0414

Tranquility Station/Ops + Tranquility Science Lab - Stardate 230313.0235
Reporting Officer: LtCmdr Ferre Flamand
Other Officers on Duty: 6 NPC's

Duty Log - Daily Scientific and Observation Report

Surface environmental conditions

Nitrogen = 77.2 percent
Oxygen = 21.3 percent
Argon = 0.88 percent
Neon, Helium, Krypton = 0.0008 percent
Carbon dioxide = 0.22 percent
Water vapor = 0 - 4 percent

Daystar condition = Thermal radiation within acceptable margins. Three sunspot-groupings detected with rather minor flares. Minimal elevated interference can be expected. Warming-up sequence at normal rate within range.

Betelgeuse (Alpha Orionis) its variable magnitude intervals within range. Brightened with 0.4 magnitudes.

Orbital eccentricity is one of the basic planetary properties, whose distribution may shed light on the history of planet formation and evolution. Here, in a series of works on Planetary Orbit Eccentricity Trends (dubbed POET), we study the distribution of planetary eccentricities and their dependence on stellar/planetary properties. In this paper, the first work of the POET series, we investigate whether and how the eccentricities of small planets depend on stellar metallicities (e.g., [Fe/H]). Previous studies on giant planets have found a significant correlation between planetary eccentricities and their host metallicities. Nevertheless, whether such a correlation exists in small planets (e.g. super-Earth and sub-Neptune) remains unclear. Here, benefiting from the large and homogeneous LAMOST-Gaia-Kepler sample, we characterize the eccentricity distributions of 244 (286) small planets in single (multiple) transiting systems with the transit duration ratio method. We confirm the eccentricity-metallicity trend that eccentricities of single small planets increase with stellar metallicities. Interestingly, a similar trend between eccentricity and metallicity is also found in the radial velocity (RV) sample. We also found that the mutual inclination of multiple transiting systems increases with metallicity, which predicts a moderate eccentricity-metallicity rising trend. Our results of the correlation between eccentricity (inclination) and metallicity for small planet support the core accretion model for planet formation, and they could be footprints of self (and/or external) excitation processes during the history of planet formation and evolution.

-- end report --
User avatar
Ferre Flamand
Science - Lieutenant Commander
Science - Lieutenant Commander
Posts: 461
Joined: 211111.0543
Duty Post: Vice Chief Science Officer
Ship/Station Posted: SS Tranquility
Grid: Second Life
Location: Belgium
Has thanked: 226 times
Been thanked: 62 times
Contact:

230313.2322

Tranquility Station/Ops + Tranquility Science Lab - Stardate 230314.0019
Reporting Officer: LtCmdr Ferre Flamand
Other Officers on Duty: 6 NPC's

Duty Log - Daily Scientific and Observation Report

Surface environmental conditions

Nitrogen = 77.3 percent
Oxygen = 21.2 percent
Argon = 0.87 percent
Neon, Helium, Krypton = 0.0008 percent
Carbon dioxide = 0.24 percent
Water vapor = 0 - 4 percent

Daystar condition = Thermal radiation within acceptable margins. Three sunspot-groupings detected with rather minor flares. Minimal elevated interference can be expected. Warming-up sequence at normal rate within range.

Betelgeuse (Alpha Orionis) its variable magnitude intervals within range. Brightened with 0.11 magnitudes.



Today's study project : Dissipative Capture of Planets Into First-Order Mean-Motion Resonances.

The emergence of orbital resonances among planets is a natural consequence of the early dynamical evolution of planetary systems. While it is well-established that convergent migration is necessary for mean-motion commensurabilities to emerge, recent numerical experiments have shown that the existing adiabatic theory of resonant capture provides an incomplete description of the relevant physics, leading to an erroneous mass scaling in the regime of strong dissipation. In this work, we develop a new model for resonance capture that self-consistently accounts for migration and circularization of planetary orbits, and derive an analytic criterion based upon stability analysis that describes the conditions necessary for the formation of mean-motion resonances. We subsequently test our results against numerical simulations and find satisfactory agreement. Our results elucidate the critical role played by adiabaticity and resonant stability in shaping the orbital architectures of planetary systems during the nebular epoch, and provide a valuable tool for understanding their primordial dynamical evolution.

-- end report --
User avatar
Ferre Flamand
Science - Lieutenant Commander
Science - Lieutenant Commander
Posts: 461
Joined: 211111.0543
Duty Post: Vice Chief Science Officer
Ship/Station Posted: SS Tranquility
Grid: Second Life
Location: Belgium
Has thanked: 226 times
Been thanked: 62 times
Contact:

230315.0007

Tranquility Station/Ops + Tranquility Science Lab - Stardate 230315.0100
Reporting Officer: LtCmdr Ferre Flamand
Other Officers on Duty: 6 NPC's

Duty Log - Daily Scientific and Observation Report

Surface environmental conditions

Nitrogen = 77.4 percent
Oxygen = 21.1 percent
Argon = 0.87 percent
Neon, Helium, Krypton = 0.0008 percent
Carbon dioxide = 0.23 percent
Water vapor = 0 - 4 percent

Daystar condition = Thermal radiation within acceptable margins. Two sunspot-groupings detected with rather minor flares. Minimal elevated interference can be expected. Warming-up sequence at normal rate within range.

Betelgeuse (Alpha Orionis) its variable magnitude intervals within range. Brightened with 0.07 magnitudes.

Additional reporting : LtCmdr Otsuka performed test flights in the neighbourhood of SS Tranquility, taking care not to damage the station while making some spectacular flight passes. Post flight inspections revealed no damage.



Today's study project : The Low-Altitude Ionosphere of the Ice Giant Planets.

The study of atmospheric electricity of the lower stratosphere and upper troposphere of the ice giant planets can help to understand several physical phenomena such as cloud formation, lightning generation, aerosols growth, or chemical composition. At these depths, galactic radiation is the main energy source able to ionize the atmospheric constituents and to produce a low altitude ionospheric layer that can be similar in magnitude to the upper ionosphere produced by solar radiation and auroral electrons. The presence of aerosols affects the ion-neutral chemistry by capturing electrons and ions depending on the aerosol size and number density. Here, we present a new one dimensional ionospheric model of Uranus and Neptune able to calculate the number densities of electrons and ions as well as the charging of aerosols between 100 Pa and 4 × 105 Pa. Since the results depends upon the amount and size of the atmospheric aerosols, as well as on the flux of the incoming cosmic radiation, several aerosol models, solar-cycle conditions, and the effect of the intrinsic magnetic field are considered.

-- end report --
User avatar
Ferre Flamand
Science - Lieutenant Commander
Science - Lieutenant Commander
Posts: 461
Joined: 211111.0543
Duty Post: Vice Chief Science Officer
Ship/Station Posted: SS Tranquility
Grid: Second Life
Location: Belgium
Has thanked: 226 times
Been thanked: 62 times
Contact:

230316.0026

Tranquility Station/Ops + Tranquility Science Lab - Stardate 230316.0120
Reporting Officer: LtCmdr Ferre Flamand
Other Officers on Duty: 6 NPC's

Duty Log - Daily Scientific and Observation Report

Surface environmental conditions

Nitrogen = 77.2 percent
Oxygen = 21.3 percent
Argon = 0.88 percent
Neon, Helium, Krypton = 0.0008 percent
Carbon dioxide = 0.20 percent
Water vapor = 0 - 4 percent

Daystar condition = Thermal radiation within acceptable margins. Two sunspot-groupings detected with rather minor flares. Minimal elevated interference can be expected. Warming-up sequence at normal rate within range.

Betelgeuse (Alpha Orionis) its variable magnitude intervals within range. Brightened with 0.01 magnitudes.



Today's study project : Migration of pairs of giant planets in low-viscosity discs.

When considering the migration of Jupiter and Saturn, a classical result is to find the planets migrating outwards and locked in the 3:2 mean motion resonance (MMR). These results were obtained in the framework of viscously accreting discs, in which the observed stellar accretion rates constrained the viscosity values. However, it has recently been shown observationally and theoretically that discs are probably less viscous than previously thought. Therefore, in this paper, we explore the dynamics of pairs of giant planets in low-viscosity discs. We performed two-dimensional hydrodynamical simulations using the grid-based code FARGOCA. In contrast to classical viscous discs, we find that the outer planet never crosses the 2:1 resonance and the pair does not migrate outwards. After a wide parameter exploration, including the mass of the outer planet, we find that the planets are primarily locked in the 2:1 MMR and in some cases in the 5:2 MMR. We explain semi-analytically why it is not possible for the outer planet to cross the 2:1 MMR in a low-viscosity disc. We find that pairs of giant planets migrate inwards in low-viscosity discs. Although, in some cases, having a pair of giant planets can slow down the migration speed with respect to a single planet. Such pairs of slowly migrating planets may be located, at the end of the disc phase, in the population of exoplanets of 'warm Jupiters'. However, the planets never migrate outwards. These results could have strong implications on the Solar System's formation scenarios if the Sun's protoplanetary disc had a low viscosity.

-- end report --
User avatar
Ferre Flamand
Science - Lieutenant Commander
Science - Lieutenant Commander
Posts: 461
Joined: 211111.0543
Duty Post: Vice Chief Science Officer
Ship/Station Posted: SS Tranquility
Grid: Second Life
Location: Belgium
Has thanked: 226 times
Been thanked: 62 times
Contact:

230317.0256

Tranquility Station/Ops + Tranquility Science Lab - Stardate 230317.0050
Reporting Officer: LtCmdr Ferre Flamand
Other Officers on Duty: 6 NPC's

Duty Log - Daily Scientific and Observation Report

Surface environmental conditions

Nitrogen = 77.2 percent
Oxygen = 21.3 percent
Argon = 0.88 percent
Neon, Helium, Krypton = 0.0008 percent
Carbon dioxide = 0.22 percent
Water vapor = 0 - 4 percent

Daystar condition = Thermal radiation within acceptable margins. Three sunspot-groupings detected with rather minor flares. Minimal elevated interference can be expected. Warming-up sequence at normal rate within range.

Betelgeuse (Alpha Orionis) its variable magnitude intervals within range. Brightened with 0.4 magnitudes.

Today's project : Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) VIII. Nondetection of sodium in the atmosphere of the aligned planet KELT-10b

We searched for potential atmospheric species in KELT-10b, focusing on sodium doublet lines (Na i; 589 nm) and the Balmer alpha line (H α; 656 nm) in the transmission spectrum. Furthermore, we measured the planet-orbital alignment with the spin of its host star. We used the Rossiter-McLaughlin Revolutions technique to analyze the local stellar lines occulted by the planet during its transit. We used the standard transmission spectroscopy method to probe the planetary atmosphere, including the correction for telluric lines and the Rossiter-McLaughlin effect on the spectra. We analyzed two new light curves jointly with the public photometry observations. We do not detect signals in the Na i and H α lines within the uncertainty of our measurements. We derive the 3-sigma upper limit of excess absorption due to the planetary atmosphere corresponding to equivalent height Rp to 1.8Rp (Na i) and 1.9Rp (H α). The analysis of the Rossiter-McLaughlin effect yields the sky-projected spin-orbit angle of the system λ = -5.2 ± 3.4 and the stellar projected equatorial velocity veqsini⋆ = 2.58 ± 0.12 km/s. Photometry results are compatible within 1 -sigma with previous studies. We found no evidence of Na i and H α, within the precision of our data, in the atmosphere of KELT-10b. Our detection limits allow us to rule out the presence of neutral sodium or excited hydrogen in an escaping extended atmosphere around KELT-10b. We cannot confirm the previous detection of Na i at lower altitudes with VLT/UVES. We note, however, that the Rossiter-McLaughlin effect impacts the transmission spectrum on a smaller scale than the previous detection with UVES. Analysis of the planet-occulted stellar lines shows the sky-projected alignment of the system, which is likely truly aligned due to tidal interactions of the planet with its cool (Teff < 6250 K) host star.


-- end log --

:communicator: LtCmdr Ferre Flamand
User avatar
Ferre Flamand
Science - Lieutenant Commander
Science - Lieutenant Commander
Posts: 461
Joined: 211111.0543
Duty Post: Vice Chief Science Officer
Ship/Station Posted: SS Tranquility
Grid: Second Life
Location: Belgium
Has thanked: 226 times
Been thanked: 62 times
Contact:

230320.0720

Tranquility Station/Ops + Tranquility Science Lab - Stardate 230320.0615
Reporting Officer: LtCmdr Ferre Flamand
Other Officers on Duty: 6 NPC's

Duty Log - Daily Scientific and Observation Report

Surface environmental conditions

Nitrogen = 77.2 percent
Oxygen = 21.3 percent
Argon = 0.88 percent
Neon, Helium, Krypton = 0.0008 percent
Carbon dioxide = 0.22 percent
Water vapor = 0 - 4 percent

Daystar condition = Thermal radiation within acceptable margins. Three sunspot-groupings detected with rather minor flares. Minimal elevated interference can be expected. Warming-up sequence at normal rate within range.

Betelgeuse (Alpha Orionis) its variable magnitude intervals within range. Brightened with 0.4 magnitudes.

Today's project : Assessing the spin-orbit obliquity of low-mass planets in the breaking the chain formation model.

The spin-orbit obliquity of a planetary system constraints its formation history. A large obliquity may either indicate a primordial misalignment between the star and its gaseous disk or reflect the effect of different mechanisms tilting planetary systems after formation. Observations and statistical analysis suggest that system of planets with sizes between 1 and 4 R⊕ have a wide range of obliquities (∼0−30∘), and that single- and multi-planet transiting have statistically indistinguishable obliquity distributions. Here, we revisit the ``breaking the chains'' formation model with focus in understanding the origin of spin-orbit obliquities. This model suggests that super-Earths and mini-Neptunes migrate close to their host stars via planet-disk gravitational interactions, forming chain of planets locked in mean-motion resonances. After gas-disk dispersal, about 90-99\% of these planetary systems experience dynamical instabilities, which spread the systems out. Using synthetic transit observations, we show that if planets are born in disks where the disk angular momentum is virtually aligned with the star's rotation spin, their final obliquity distributions peak at about ∼5 degrees or less, and the obliquity distributions of single and multi-planet transiting systems are statistically distinct. By treating the star-disk alignment as a free-parameter, we show that the obliquity distributions of single and multi-planet transiting systems only become statistically indistinguishable if planets are assumed to form in primordially misaligned natal disks with a ``tilt'' distribution peaking at ≳10-20 deg. We discuss the origin of these misalignments in the context of star formation and potential implications of this scenario for formation models.


-- end log --

:communicator: LtCmdr Ferre Flamand
User avatar
Ferre Flamand
Science - Lieutenant Commander
Science - Lieutenant Commander
Posts: 461
Joined: 211111.0543
Duty Post: Vice Chief Science Officer
Ship/Station Posted: SS Tranquility
Grid: Second Life
Location: Belgium
Has thanked: 226 times
Been thanked: 62 times
Contact:

230321.0114

Tranquility Station/Ops + Tranquility Science Lab - Stardate 230321.0110
Reporting Officer: LtCmdr Ferre Flamand
Other Officers on Duty: 6 NPC's

LtCol Sirena Rowley-wood paid a visit to the station and had a formal chat with her at Ops.

Duty Log - Daily Scientific and Observation Report

Surface environmental conditions

Nitrogen = 77.1 percent
Oxygen = 21.4 percent
Argon = 0.87 percent
Neon, Helium, Krypton = 0.0008 percent
Carbon dioxide = 0.24 percent
Water vapor = 0 - 4 percent

Daystar condition = Thermal radiation within acceptable margins. Two sunspot-groupings detected with rather minor flares. Minimal elevated interference can be expected. Warming-up sequence at normal rate within range.

Betelgeuse (Alpha Orionis) its variable magnitude intervals within range. Unchanged brightness the last 24 hrs.


Today's project : The energetic particle environment of a GJ 436 b-like planet

A key first step to constrain the impact of energetic particles in exoplanet atmospheres is to detect the chemical signature of ionisation due to stellar energetic particles and Galactic cosmic rays. We focus on GJ436, a well-studied M dwarf with a warm Neptune-like exoplanet. We demonstrate how the maximum stellar energetic particle momentum can be estimated from the stellar X-ray luminosity. We model energetic particle transport through the atmosphere of a hypothetical exoplanet at orbital distances between a=0.01−0.2au from GJ436, including GJ436b's orbital distance (0.028au). For these distances we find that, at top-of-atmosphere, stellar energetic particles ionise molecular hydrogen at a rate of ζStEP,H2∼4×10−10−2×10−13s−1. In comparison, Galactic cosmic rays alone lead to ζGCR,H2∼2×10−20−10−18s−1. At 10au we find that ionisation due to Galactic cosmic rays equals that of stellar energetic particles: ζGCR,H2=ζStEP,H2∼7×10−18s−1 for the top-of-atmosphere ionisation rate. At GJ436b's orbital distance, the maximum ion-pair production rate due to stellar energetic particles occurs at pressure P∼10−3bar while Galactic cosmic rays dominate for P>102bar. These high pressures are similar to what is expected for a post-impact early Earth atmosphere. The results presented here will be used to quantify the chemical signatures of energetic particles in warm Neptune-like atmospheres.


-- end log --

:communicator: LtCmdr Ferre Flamand
User avatar
Ferre Flamand
Science - Lieutenant Commander
Science - Lieutenant Commander
Posts: 461
Joined: 211111.0543
Duty Post: Vice Chief Science Officer
Ship/Station Posted: SS Tranquility
Grid: Second Life
Location: Belgium
Has thanked: 226 times
Been thanked: 62 times
Contact:

230322.0018

Tranquility Station/Ops + Tranquility Science Lab - Stardate 230322.0115
Reporting Officer: LtCmdr Ferre Flamand
Other Officers on Duty: 6 NPC's

Today I had an online meeting with some other UFS members where the future of AI was discussed.

Duty Log - Daily Scientific and Observation Report

Surface environmental conditions

Nitrogen = 77.0 percent
Oxygen = 21.5 percent
Argon = 0.86 percent (that's a huge drop)
Neon, Helium, Krypton = 0.0008 percent
Carbon dioxide = 0.22 percent
Water vapor = 0 - 4 percent

Daystar condition = Thermal radiation within acceptable margins. Two sunspot-groupings detected with rather minor flares. Minimal elevated interference can be expected. Warming-up sequence at normal rate within range.

Betelgeuse (Alpha Orionis) its variable magnitude intervals within range. Unchanged brightness the last 48 hrs.


Today's project : A Catalog of Exoplanets with Equilibrium Temperature less than 600 K

The UFS Exoplanet Archive was searched for planets with an equilibrium temperature below 600 K, mass uncertainty less than 27 percent, and radius uncertainty less than 8 percent. This search produced 93 planets with mass from 0.3 to 1680 ME; and 101 planets if the Solar System planets are included. The characteristics of the sample in this catalog are: (1) 94 percent of the Terrestrial planets have mass less than 2.9 ME and radius less than 1.4 RE, (3) The sample has a small drop in population consistent with the previously identified radius gap from 1.5 to 2.0 RE, (4) Planets in the radius range 1.50 to 2.25 RE are consistent with either a gas-rich Terrestrial composition or a rock-ice Terrestrial composition with a supercritical hydrosphere and water mass fraction less than 20 percent, (5) A super-Neptune radius desert is observed for the radius range 4.5 to 7.5 RE, (6) Saturn composition planets have masses from 15 to 170 ME and radii from 7.9 to 10.1 RE, (7) A nearly barren sub-Saturn mass-radius desert is found in the sample as indicated by a lack of planets with mass exceeding 20 ME and radii in the range 4.0 to 7.5 RE, (8) Most Jupiter composition planets have radii between 10.9 and 12.4 RE and mass exceeding 200 ME, (9) With few exceptions, planet radius can be used as a proxy for planet composition classification into Terrestrial, gas-rich Terrestrial or supercritical hydrosphere Terrestrial, Rock-Ice Giant, and Gas Giant composition classes for this sample of Teq less than 600 K planets. The characteristics of this sample are consistent with several predictions of the core accretion model including the predicted values for the critical core mass for gas accretion and runaway accretion, the pebble isolation mass, and the Saturn mass desert.


-- end log --

:communicator: LtCmdr Ferre Flamand
User avatar
Ferre Flamand
Science - Lieutenant Commander
Science - Lieutenant Commander
Posts: 461
Joined: 211111.0543
Duty Post: Vice Chief Science Officer
Ship/Station Posted: SS Tranquility
Grid: Second Life
Location: Belgium
Has thanked: 226 times
Been thanked: 62 times
Contact:

230323.0045

Tranquility Station/Ops + Tranquility Science Lab - Stardate 230323.0130
Reporting Officer: LtCmdr Ferre Flamand
Other Officers on Duty: 6 NPC's

Duty Log - Daily Scientific and Observation Report

Surface environmental conditions

Nitrogen = 77.0 percent
Oxygen = 21.4 percent
Argon = 0.88 percent (normalized again, could have been a glitch in the software)
Neon, Helium, Krypton = 0.0008 percent
Carbon dioxide = 0.23 percent
Water vapor = 0 - 4 percent

Daystar condition = Thermal radiation within acceptable margins. Two sunspot-groupings detected with rather minor flares. Minimal elevated interference can be expected. Warming-up sequence at normal rate within range.

Betelgeuse (Alpha Orionis) its variable magnitude intervals within range. Unchanged brightness the last 72 hrs.


Today's project : LRG-BEASTS: Evidence for clouds in the transmission spectrum of HATS-46 b

We have performed low-resolution ground-based spectroscopy of HATS-46 b in transmission, using the EFOSC2 instrument on the ESO New Technology Telescope (NTT). HATS-46 b is a highly-inflated exoplanet that is a prime target for transmission spectroscopy, having a Jupiter-like radius (0.95 RJup) but a much lower mass (0.16 MJup). It orbits a G-type star with a 4.7 d period, giving an equilibrium temperature of 1100 K. We observed one transit of HATS-46 b with the NTT, with the time-series spectra covering a wavelength range of 3900 - 9000 Angstrom at a resolution of R∼380. We achieved a remarkably precise transmission spectrum of 1.03 × photon noise, with a median uncertainty of 357 ppm for ∼200 Angstrom wide bins, despite the relative faintness of the host star with Vmag=13.6. The transmission spectrum does not show strong absorption features and retrievals favour a cloudy model, ruling out a clear atmosphere with 3.0σ confidence. We also place a conservative upper limit on the sodium abundance under the alternative scenario of a clear atmosphere. This is the eighth planet in the LRG-BEASTS survey, which uses 4m-class telescopes such as the NTT to obtain low-resolution transmission spectra of hot Jupiters with precisions of around one atmospheric scale height.


-- end log --

:communicator: LtCmdr Ferre Flamand
User avatar
Ferre Flamand
Science - Lieutenant Commander
Science - Lieutenant Commander
Posts: 461
Joined: 211111.0543
Duty Post: Vice Chief Science Officer
Ship/Station Posted: SS Tranquility
Grid: Second Life
Location: Belgium
Has thanked: 226 times
Been thanked: 62 times
Contact:

230328.1156

Tranquility Station/Ops + Tranquility Science Lab - Stardate 230328.1245
Reporting Officer: LtCmdr Ferre Flamand
Other Officers on Duty: 6 NPC's

Duty Log - Daily Scientific and Observation Report

Surface environmental conditions

Nitrogen = 77.4 percent
Oxygen = 21.2 percent
Argon = 0.89 percent
Neon, Helium, Krypton = 0.0008 percent
Carbon dioxide = 0.21 percent
Water vapor = 0 - 4 percent

Daystar condition = Thermal radiation within acceptable margins. Two sunspot-groupings detected with rather minor flares. Minimal elevated interference can be expected. Warming-up sequence at normal rate within range.

Betelgeuse (Alpha Orionis) its variable magnitude intervals within range. Brightened with 0.2 magnitude.


Today's project : From exo-Earths to exo-Venuses: Flux and polarization signatures of reflected light

Context. Terrestrial-type exoplanets in or near stellar habitable zones appear to be ubiquitous. It is, however, unknown which of these planets have temperate, Earth-like climates or for example, extreme Venus-like climates.

Aims. Technical tools to distinguish different kinds of terrestrial-type planets are crucial for determining whether a planet could be habitable or incompatible with life as we know it. We aim to investigate the potential of spectropolarimetry for distinguishing exo-Earths from exo-Venuses.

Methods. We present numerically computed fluxes and degrees of linear polarization of starlight that is reflected by exoplanets with atmospheres in evolutionary states ranging from similar to the current Earth to similar to the current Venus, with cloud compositions ranging from pure water to 75% sulfuric acid solution, for wavelengths between 0.3 and 2.5 µm. We also present flux and polarization signals of such planets in stable but spatially unresolved orbits around the star Alpha Centauri A.

Results. The degree of polarization of the reflected starlight shows larger variations with the planetary phase angle and wavelength than the total flux. Across the visible, the largest degree of polarization is reached for an Earth-like atmosphere with water clouds due to Rayleigh scattering above the clouds and the rainbow feature at phase angles near 40°. At near-infrared wavelengths, the planet with a Venus-like CO2 atmosphere and thin water cloud shows the most prominent polarization features due to Rayleigh-like scattering by the small cloud droplets. A planet in a stable orbit around Alpha Centauri A would leave temporal variations on the order of 10−13 W m s−1 in the total reflected flux and 10−11 in the total degree of polarization as the planet orbits the star and assuming a spatially unresolved star-planet system. Star-planet contrasts are on the order of 10−10 and vary proportionally with planetary flux.

Conclusions. Current polarimeters appear to be incapable to distinguish between the possible evolutionary phases of spatially unresolved terrestrial exoplanets, as a sensitivity close to 10−10 would be required to discern the planetary signal given the background of unpolarized starlight. A telescope or instrument capable of achieving planet-star contrasts lower than 10−9 should be able to observe the large variation of the planets resolved degree of polarization as a function of its phase angle and thus be able to discern an exo-Earth from an exo-Venus based on their clouds unique polarization signatures.




-- end log --

:communicator: LtCmdr Ferre Flamand
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