Possible Signs of Water and Differentiation in a Rocky Exoplanetary Body

Abstract

Spitzer observations reveal the presence of warm debris from a tidally destroyed rocky and possibly icy planetary body orbiting the white dwarf GD 61. Ultraviolet and optical spectroscopy of the metal-contaminated stellar photosphere reveal traces of hydrogen, oxygen, magnesium, silicon, iron, and calcium. The nominal ratios of these elements indicate an excess of oxygen relative to that expected from rock-forming metal oxides, and thus it is possible that water was accreted together with the terrestrial-like debris. Iron is found to be deficient relative to magnesium and silicon, suggesting the material may have originated as the outer layers of a differentiated parent body, as is widely accepted for the Moon.

Evidence for Water in the Rocky Debris of a Disrupted Extrasolar Minor Planet

“…Although this makes little difference in the case of GD 61, where the parent body material appears distinctly mantle-like (26), there are at least two cases where metallic iron is a major (and even dominant) mass carrier within the parent bodies of circumstellar debris observed at white dwarfs (27). Overall, these data strongly suggest the material observed in and around polluted white dwarfs had an origin in relatively massive and differentiated planetary bodies.…”

“…it does not have a detectable disk), and without this information, the atmospheric oxygen could be consistent with that contained in dry minerals common in the inner Solar System (25). In the case of GD 61, elemental abundance uncertainties have previously prevented a formally significant detection of oxygen excess (26 3) The remaining oxygen exceeds that which can be bound in FeO, and the debris is interpreted to be water-rich. We find oxygen in excess of that expected for anhydrous minerals in the material at an H 2 O mass fraction of 0.26 ( Table 1, Fig.…”

An Asteroid Belt Interpretation for the Timing Variations of the Millisecond Pulsar B1937+21

“…Accretion of asteroids is thought to pollute atmospheres and cause anomalously high metallicity in some WDs (Koester & Wilken 2006;Farihi et al 2011). Tidal disruption of asteroids is hypothesized to cause dust disks around other WDs (Debes & Sigurdsson 2002).…”

ALMA and Herschel observations of the prototype dusty and polluted white dwarf G29-38

“…The elemental abundances in disk-polluted white dwarfs are universally depleted in volatile elements (especially carbon and hydrogen), and have a refractory rich pattern that broadly mimics the terrestrial material of the inner Solar System (Jura & Young 2014;Gänsicke et al 2012;Zuckerman et al 2007). All data acquired to date are consistent with rocky parent bodies that formed interior to a snow line (Farihi et al 2013;, including evidence for differentiation (Jura et al 2013;Gänsicke et al 2012;Zuckerman et al 2011;Farihi et al 2011). …”