polarimetry Archives - Astrobiology

The reflectance spectrum detailing features from O2, O3, H2O, CO2, and CH4 of a modern Earth-like planet from 0.2 - 2 µm, similar in range expected from HWO (adapted from Westall & Xiao (2024)). -- astro-ph.IM

Astrochemistry, Astronomy & Telescopes, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Status Report

The Power Of Polarimetry For Characterising Exoplanet Atmospheres, Clouds, And Surfaces With NASA’s Habitable Worlds Observatory

by Keith CowingFebruary 9, 2026February 9, 2026

The Habitable Worlds Observatory (HWO), planned for launch in the 2040s, represents the next major step in exoplanet characterisation. HWO will, for the first time, enable detailed studies of the […]

Polarization degree (Pr) and polarization position angle (θr) of 3I/ATLAS as a function of phase angle, measured in five bands (RC, IC, J, H, and Ks). Colored symbols denote our visible and near-infrared imaging polarimetric data obtained with different instruments, while orange symbols show previously published measurements of 3I/ATLAS (Z. Gray et al. 2025; M. Zheltobryukhov et al. 2025). Gray symbols represent polarimetric measurements of Solar System comets compiled in the Database of Comet Polarimetry (DBCP; N. Kiselev et al. 2017), and the pink triangles indicate the PPC of the interstellar comet 2I/Borisov (S. Bagnulo et al. 2021). The dashed curves show the best-fit linear–exponential models (Equation 1) to our data. -- astro-ph.EP

Astrochemistry, Astrogeology, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Comets and Asteroids, Icy Worlds, Imaging & Spectroscopy, Status Report

Dust Properties of the Interstellar Object 3I/ATLAS Revealed by Optical and Near-Infrared Polarimetry

by Keith CowingJanuary 15, 2026January 15, 2026

We present independent polarimetric observations of the interstellar object 3I/ATLAS, including the first near-infrared polarimetric measurements. Using imaging polarimeters, we measured the degree of linear polarization from the visible RC […]

Raw B band polarization measurements of HD 189733 obtained at Gemini North on UT 1 to 7 Aug 2018, which are dominated by observations on the last night (gold points). Top left: Stokes q (linear polarization) modulation as a function of parallactic angle. Telescope linear polarization is modulated by parallactic angle with amplitude ∆(qTP, uTP) = 0.2620±0.0034% (Wiktorowicz et al. 2023), where the best fit curve from Equation 2a is shown in black. Uncertainties in most data points are smaller than the size of the data points. Top right: Same as at top left but for Stokes u (linear polarization, Equation 2b). Bottom left: Same as at top left but for Stokes v (circular polarization, Equation 2c). Bottom right: Temporal variation of parallactic angle, which rotates rapidly as the target crosses the meridian (black dashed lines) around 20:00 LST. This rapid meridian crossing provides the bulk of the telescope polarization modulation necessary for accurate calibration. -- astro-ph.EP

Astronomy & Telescopes, Atmospheres, Climate, Weather, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report

A Scatter of Light from a Polarized World

by Keith CowingSeptember 25, 2025

Many known exoplanets harbor clouds, which lead to degeneracies in spectroscopic models between particle composition and size. Polarimetry, however, provides independent assessment.

To understand where the measured flux from the planet is coming from we need to capture both reflected and thermal components of the light from the planet. This requires broad wavelength coverage from 1 micron. Predicted planetary reflected signal vs. thermal emission for archetypal planets (letters correspond to planet properties shown in the inset plot) identified by Mayorga et al. (2019). Top: the total planetary flux as measured in flux units. Bottom: the percent contribution of reflected light to the total flux as a function of wavelength (R 300). Colored bands in the top panel show the photometric (hashed) and spectroscopic (solid) coverage from current and future facilities over this wavelength range. Figure courtesy of L. C. Mayorga. -- astro-ph.EP

Astrogeology, Atmospheres, Climate, Weather, Biochemistry & Organic Chemistry, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report

Characterizing the Dynamics and Chemistry of Transiting Exoplanets with the Habitable World Observatory

by Keith CowingJuly 2, 2025July 2, 2025

The primary scientific objective of this Habitable Worlds Observatory (HWO) Science Case Development Document (SCDD) is to measure planetary rotation rates of transiting exoplanets to determine the structure, composition, circulation, […]

Polarization of planetary phase functions for the cases of two cloud cap configurations and for a cloud-free atmosphere to illustrate the effect of locally obscured limb polarization on the net phase function at wavelengths of 𝜆 = 550 nm. The three panels show the spatially resolved normalized Stokes parameters 𝑞(𝛼) and 𝑢(𝛼) for selected phase angles 𝛼 of spatially resolved planetary disks. -- astro-ph.EP

Astronomy & Telescopes, Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Mapping, Geodesy, Cartography, Bathymetry, Status Report, Stellar Cartography

Feasibility Study on Retrieving Exoplanetary Cloud Cover Distributions Using Polarimetry

by Keith CowingMay 22, 2024May 22, 2024

Context. As a new growing field, exocartography aims to map the surface features of exoplanets that are beyond the resolution of traditional observing techniques. While photometric approaches have been discussed […]