CAN GROUND-BASED TELESCOPES DETECT THE OXYGEN 1.27 μm ABSORPTION FEATURE AS A BIOMARKER IN EXOPLANETS?

Abstract

The oxygen absorption line imprinted in the scattered light from the Earth-like planets has been considered the most promising metabolic biomarker of the exo-life. We examine the feasibility of the detection of the 1.27 µm oxygen band from habitable exoplanets, in particular, around latetype stars observed with a future instrument on a 30 m class ground-based telescope. We analyzed the night airglow around 1.27 µm with IRCS/echelle spectrometer on Subaru and found that the strong telluric emission from atmospheric oxygen molecules declines by an order of magnitude by midnight. By compiling nearby star catalogs combined with the sky background model, we estimate the detectability of the oxygen absorption band from an Earth twin, if it exists, around nearby stars. We find that the most dominant source of photon noise for the oxygen 1.27 µm band detection comes from the night airglow if the contribution of the stellar PSF halo is suppressed enough to detect the planet. We conclude that the future detectors for which the detection contrast is limited by photon noise can detect the oxygen 1.27 µm absorption band of the Earth twins for ∼ 50 candidates of the late type star. This paper demonstrates the importance of deploying small inner working angle efficient coronagraph and extreme adaptive optics on extremely large telescopes, and clearly shows that doing so will enable study of potentially habitable planets.

Biosignature False Positives

“…JWST will be best equipped to obtain such data for larger worlds, but its sensitivities may allow it to detect the largest absorption features on a small number of nearby Earth-like worlds in orbit around cool, low-mass stars (Deming et al 2009). Greater sensitivities for this kind of observation -likely fine enough for biosignature searches -will be enabled by extremely large ground-based telescopes such at the Giant Magellan Telescope (GMT), the European-Extremely Large Telescope (E-ELT), and the Thirty Meter Telescope (TMT) (Kawahara et al 2012;Snellen et al 2013Snellen et al , 2015Rodler and López-Morales 2014;Lovis et al 2017). A second generation of instruments for these telescopes may include coronagraphs that could directly image such worlds and obtain reflected-light spectroscopy which would allow assessment of deeper layers of the exoplanet's atmosphere.…”

On high-contrast characterization of nearby, short-period exoplanets with giant segmented-mirror telescopes

“…I adopt a baseline observing wavelength of 1.2 µm (J band), where future AO systems should achieve good correction and which provides good angular resolution. Observations at J band are also interesting because of their potential to descry the 1.27 µm O 2 band expected in oxygen-rich planetary atmospheres (e.g., Turnbull et al 2006;Kawahara et al 2012). In terms of astrophysical parameters, the baseline scenario assumes that 1−2 R ⊕ and 2−4 R ⊕ planets occur with equal frequencies (as described in Sect.…”

“…Kawahara et al (2012) have presented an excellent first step toward this goal with their recent determination that GSMTs will allow low-resolution spectroscopy of small planets at 1.27 µm in just a few hours. Further such work at both shorter and longer wavelengths will help determine whether spectroscopy will be possible, or whether characterization will be limited to broadband photometry.…”

ERIS: the exoplanet high-resolution image simulator for CHARIS

“…5 Direct imaging will also be a critical component for characterizing Earth-like planets that may be able to support life. 6 Integral field spectrographs (IFSs) are well purposed for taking spectra of exoplanets. The purpose of an integral field spectrograph (IFS) is to simultaneously image the spectrum of the full two-dimensional field of view.…”