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ALMA Observations of Io Going into and Coming out of Eclipse

de Pater, Imke and Luszcz-Cook, Statia and Rojo, Patricio and Redwing, Erin and de Kleer, Katherine and Moullet, Arielle (2020) ALMA Observations of Io Going into and Coming out of Eclipse. . (Unpublished)

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We present 1-mm observations constructed from ALMA [Atacama Large (sub)Millimeter Array] data of SO₂, SO and KCl when Io went from sunlight into eclipse (20 March 2018), and vice versa (2 and 11 September 2018). There is clear evidence of volcanic plumes on 20 March and 2 September. The plumes distort the line profiles, causing high-velocity (≳500 m/s) wings, and red/blue-shifted shoulders in the line profiles. During eclipse ingress, the SO₂ flux density dropped exponentially, and the atmosphere reformed in a linear fashion when re-emerging in sunlight, with a "post-eclipse brightening" after ∼10 minutes. While both the in-eclipse decrease and in-sunlight increase in SO was more gradual than for SO₂, the fact that SO decreased at all is evidence that self-reactions at the surface are important and fast, and that in-sunlight photolysis of SO₂ is the dominant source of SO. Disk-integrated SO₂ in-sunlight flux densities are ∼2--3 times higher than in-eclipse, indicative of a roughly 30--50% contribution from volcanic sources to the atmosphere. Typical column densities and temperatures are N ≈ (1.5±0.3)×10¹⁶ cm⁻² and T ≈ 220−320 K both in-sunlight and in-eclipse, while the fractional coverage of the gas is 2--3 times lower in-eclipse than in-sunlight. The low level SO₂ emissions present during eclipse may be sourced by stealth volcanism or be evidence of a layer of non-condensible gases preventing complete collapse of the SO₂ atmosphere. The melt in magma chambers at different volcanoes must differ in composition to explain the absence of SO and SO₂, but simultaneous presence of KCl over Ulgen Patera.

Item Type:Report or Paper (Discussion Paper)
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URLURL TypeDescription Paper
de Pater, Imke0000-0002-4278-3168
de Kleer, Katherine0000-0002-9068-3428
Moullet, Arielle0000-0002-9820-1032
Additional Information:We are grateful for in-depth reviews by David Goldstein and one anonymous referee, which helped improve the manuscript substantially. This paper makes use of ALMA data ADS/JAO.ALMA#2017.1.00670.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The data can be downloaded from the ALMA Archive. This research was supported by the National Science Foundation, NSF grant AST-1313485 to UC Berkeley. PMR acknowledges support from ANID basal AFB170002.
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Subject Keywords:Galilean satellites, Planetary atmospheres, Radio astronomy
Record Number:CaltechAUTHORS:20201030-143700771
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106366
Deposited By: Tony Diaz
Deposited On:30 Oct 2020 23:17
Last Modified:30 Oct 2020 23:17

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