ALMA Observations of Io Going into and Coming out of Eclipse

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

Drift Rates of Major Neptunian Features between 2018 and 2021

Using near-infrared observations of Neptune from the Keck and Lick Observatories, and the Hubble Space Telescope in combination with amateur datasets, we calculated the drift rates of prominent infrared-bright cloud features on Neptune between 2018 and 2021. These features had lifespans of $\sim 1$ day to $\geq$1 month and were located at mid-latitudes and near the south pole. Our observations permitted determination of drift rates via feature tracking. These drift rates were compared to three zonal wind profiles describing Neptune's atmosphere determined from features tracked in H band (1.6 $\mu m$), K' band (2.1 $\mu m$), and Voyager 2 data at visible wavelengths. Features near $-70 \deg$ measured in the F845M filter (845nm) were particularly consistent with the K' wind profile. The southern mid-latitudes hosted multiple features whose lifespans were $\geq$1 month, providing evidence that these latitudes are a region of high stability in Neptune's atmosphere. We also used HST F467M (467nm) data to analyze a dark, circumpolar wave at $- 60 \deg$ latitude observed on Neptune since the Voyager 2 era. Its drift rate in recent years (2019-2021) is $4.866 \pm 0.009 \deg$/day. This is consistent with previous measurements by Karkoschka (2011), which predict a $4.858 \pm 0.022 \deg$/day drift rate during these years. It also gained a complementary bright band just to the north.Comment: 29 pages, 13 figures, accepted to Icaru

ALMA observations of Io going into and coming out of eclipse

We present mm observations constructed from Atacama Large (sub)Millimeter Array (ALMA) data of SO2, SO, and KCl when Io went from sunlight into eclipse (2018 March 20) and vice versa (2018 September 2 and 11). There is clear evidence of volcanic plumes on March 20 and September 2. The plumes distort the line profiles, causing high-velocity (≥500 m s-1) wings and red-/blueshifted shoulders in the line profiles. During eclipse ingress, the SO2 flux density dropped exponentially, and the atmosphere re-formed in a linear fashion when reemerging 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 selfreactions 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 two to three 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 noncondensible 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.Astrodynamics & Space Mission