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Title: Lyα transit spectroscopy and the neutral hydrogen tail of the hot Neptune GJ 436b

To date, more than 750 planets have been discovered orbiting stars other than the Sun. Two sub-classes of these exoplanets, ''hot Jupiters'' and their less massive counterparts ''hot Neptunes'', provide a unique opportunity to study the extended atmospheres of planets outside of our solar system. We describe here the first far-ultraviolet transit study of a hot Neptune, specifically GJ 436b, for which we use Hubble Space Telescope/Space Telescope Imaging Spectrograph Lyα spectra to measure stellar flux as a function of time, observing variations due to absorption from the planetary atmosphere during transit. This analysis permits us to derive information about atmospheric extent, mass-loss rate from the planet, and interactions between the star and planet. We observe an evolution of the Lyα lightcurve with a transit depth of GJ 436b from 8.8% ± 4.5% near mid-transit, to 22.9% ± 3.9% ∼2 hr after the nominal geometric egress of the planet. Using data from the time-tag mode and considering astrophysical noise from stellar variability, we calculate a post-egress occultation of 23.7% ± 4.5%, demonstrating that the signature is statistically significant and of greater amplitude than can be attributed to stellar fluctuations alone. The extended egress absorption indicates the probable existence of amore » comet-like tail trailing the exoplanet. We calculate a mass-loss rate for GJ 436b in the range of 3.7 × 10{sup 6}-1.1 × 10{sup 9} g s{sup –1}, corresponding to an atmospheric lifetime of 4 × 10{sup 11}-2 × 10{sup 14} yr.« less
Authors:
; ;  [1] ;  [2]
  1. Center for Astrophysics and Space Astronomy, University of Colorado, 593 UCB Boulder, CO 80309-0593 (United States)
  2. JILA, University of Colorado and NIST, 440 UCB Boulder, CO 80309-0440 (United States)
Publication Date:
OSTI Identifier:
22356942
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 786; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ASTROPHYSICS; FAR ULTRAVIOLET RADIATION; FLUCTUATIONS; LIFETIME; LYMAN LINES; MASS TRANSFER; NEPTUNE PLANET; PLANETARY ATMOSPHERES; SATELLITE ATMOSPHERES; SOLAR SYSTEM; SPACE; SPECTRA; SPECTROSCOPY; STELLAR WINDS; SUN; TELESCOPES; TIME DEPENDENCE