Lowest Earth's atmosphere layers probed during a lunar eclipse

TL;DR

This study used high-resolution spectra during a lunar eclipse to analyze Earth's atmospheric layers, detecting specific gases and estimating the lowest altitude sunlight passes through, aiding future exoplanet atmosphere studies.

Contribution

First detailed high-resolution transmission spectra of Earth's atmosphere during a lunar eclipse, revealing the lowest atmospheric layer sunlight penetrates and providing a test case for exoplanet atmosphere analysis.

Findings

Detected O2 and H2O absorption lines in Earth's transmission spectra.

Estimated the lowest atmospheric altitude for sunlight transmission at about 10 km.

Indicated the presence of clouds blocking sunlight below this altitude.

Abstract

We report the results of detailed investigation of the Earth's transmission spectra during the lunar eclipse on UT 2011 December 10. The spectra were taken by using the High Dispersion Spectrograph (HDS) mounted on the Subaru 8.2 m telescope with unprecedented resolutions both in time and wavelength (300 s exposure time in umbra and 160,000 spectral resolution, respectively). In our penumbra and umbra data, we detected the individual absorption lines of O2 and H2O in transmission spectra and found that it became deeper as the eclipse became deeper. It indicates that the sunlight reaching the Moon passed through lower layers in the Earth's atmosphere with time because we monitored a given point on the Moon during the full eclipse duration. From the comparison between the observed and theoretically constructed transmission spectra, the lowest altitude at which the sunlight actually passed through the atmosphere is estimated to be about 10 km from the ground, which suggests the existence of sunlight blocking clouds below that altitude. Our result would be a test case for future investigations of atmospheric structure of Earth-like exoplanets via transmission spectroscopy including the refraction effect of the planetary atmosphere.