The Pale Green Dot: A Method to Characterize Proxima Centauri b Using Exo-Aurorae

Journal Article · Wed Mar 01 04:00:00 EST 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA6040· OSTI ID:22869264

Luger, Rodrigo; Lustig-Yaeger, Jacob; Fleming, David P.; Agol, Eric; Meadows, Victoria S.; Deitrick, Russell; Barnes, Rory ^[1]

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1. Astronomy Department, University of Washington, Box 951580, Seattle, WA 98195 (United States)

We examine the feasibility of detecting auroral emission from the potentially habitable exoplanet Proxima Centauri b. Detection of aurorae would yield an independent confirmation of the planet’s existence, constrain the presence and composition of its atmosphere, and determine the planet’s eccentricity and inclination, thereby breaking the mass-inclination degeneracy. If Proxima Centauri b is a terrestrial world with an Earth-like atmosphere and magnetic field, we estimate that the power at the 5577 Å O i auroral line is on the order of 0.1 TW under steady-state stellar wind, or ∼100× stronger than that on Earth. This corresponds to a planet–star contrast ratio of 10{sup −6}--10{sup −7} in a narrow band about the 5577 Å line, though higher contrast (10{sup −4}--10{sup −5}) may be possible during periods of strong magnetospheric disturbance (auroral power 1–10 TW). We searched the Proxima Centauri b HARPS data for the 5577 Å line and for other prominent oxygen and nitrogen lines, but find no signal, indicating that the O i auroral line contrast must be lower than 2×10{sup −2} (with power ≲3000 TW), consistent with our predictions. We find that observations of 0.1 TW auroral emission lines are likely infeasible with current and planned telescopes. However, future observations with a space-based coronagraphic telescope or a ground-based extremely large telescope (ELT) with a coronagraph could push sensitivity down to terawatt oxygen aurorae (contrast 7×10{sup −6}) with exposure times of ∼1 day. If a coronagraph design contrast of 10{sup −7} can be achieved with negligible instrumental noise, a future concept ELT could observe steady-state auroral emission in a few nights.

• OSTI ID: 22869264
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 837; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
AURORAE
DETECTION
DISTURBANCES
EMISSION
FORECASTING
INCLINATION
MAGNETIC FIELDS
MASS
NITROGEN
OXYGEN
SATELLITE ATMOSPHERES
SATELLITES
SPACE
STARS
STEADY-STATE CONDITIONS
STELLAR WINDS
TELESCOPES