arXiv subjects

Maarten H. Versteeg

Publications and source records attributed to Maarten H. Versteeg.

8 recordsLinked to original sources

arXiv2026

The Ultraviolet Spectrograph on ESA's Jupiter Icy Moons Explorer Mission (JUICE-UVS)

The Jupiter Icy Moons Explorer (JUICE) mission, led by ESA, has an Ultraviolet Spectrograph (JUICE-UVS) contributed by NASA and built at Southwest Research Institute. JUICE-UVS is designed to provide a diversity of measurements to further our understanding of the potential habitability of icy ocean worlds at Jupiter and to study Jupiter and the Jovian system as an archetype for gas giants. JUICE-UVS observes photons in the 50-204 nm wavelength range at moderate spectral and spatial resolution along a 7.5 deg slit composed of 7.3 deg x 0.1 deg and 0.2 deg x 0.2 deg contiguous sections. JUICE-UVS performs a comprehensive study of icy satellite atmospheres, plumes, surfaces, and local space environments; Jupiter's atmosphere and aurora; Io and its Io Plasma Torus; and other Jupiter system targets (rings, small moons, etc.) as available. The variety of observational techniques employed include: nadir push-broom imaging, disk scans, limb stares, stellar and solar occultations, Jupiter transit observations, and neutral cloud/plasma torus stares and scans. This paper describes the UVS investigation's science plans, instrument details, concept of operations, and data formats in the context of the JUICE mission's habitability and Jupiter system goals.

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arXiv2023

The Io, Europa and Ganymede auroral footprints at Jupiter in the ultraviolet: positions and equatorial lead angles

Jupiter's satellite auroral footprints are a consequence of the interaction between the Jovian magnetic field with co-rotating iogenic plasma and the Galilean moons. The disturbances created near the moons propagate as Alfvén waves along the magnetic field lines. The position of the moons is therefore "Alfvénically" connected to their respective auroral footprint. The angular separation from the instantaneous magnetic footprint can be estimated by the so-called lead angle. That lead angle varies periodically as a function of orbital longitude, since the time for the Alfvén waves to reach the Jovian ionosphere varies accordingly. Using spectral images of the Main Alfvén Wing auroral spots collected by Juno-UVS during the first forty-three orbits, this work provides the first empirical model of the Io, Europa and Ganymede equatorial lead angles for the northern and southern hemispheres. Alfvén travel times between the three innermost Galilean moons to Jupiter's northern and southern hemispheres are estimated from the lead angle measurements. We also demonstrate the accuracy of the mapping from the Juno magnetic field reference model (JRM33) at the completion of the prime mission for M-shells extending to at least 15RJ . Finally, we shows how the added knowledge of the lead angle can improve the interpretation of the moon-induced decametric emissions.

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arXiv2023

Enhanced C$_2$H$_2$ absorption within Jupiter's southern auroral oval from Juno UVS observations

Reflected sunlight observations from the Ultraviolet Spectrograph (UVS) on the Juno spacecraft were used to study the distribution of acetylene (C$_2$H$_2$) at Jupiter's south pole. We find that the shape of the C$_2$H$_2$ absorption feature varies significantly across the polar region, and this can be used to infer spatial variability in the C$_2$H$_2$ abundance. There is a localized region of enhanced C$_2$H$_2$ absorption which coincides with the location of Jupiter's southern polar aurora; the C$_2$H$_2$ abundance poleward of the auroral oval is a factor of 3 higher than adjacent quiescent, non-auroral longitudes. This builds on previous infrared studies which found enhanced C$_2$H$_2$ abundances within the northern auroral oval. This suggests that Jupiter's upper-atmosphere chemistry is being strongly influenced by the influx of charged auroral particles and demonstrates the necessity of developing ion-neutral photochemical models of Jupiter's polar regions.

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arXiv2021

Meridional variations of C$_2$H$_2$ in Jupiter's stratosphere from Juno UVS observations

The UVS instrument on the Juno mission records far-ultraviolet reflected sunlight from Jupiter. These spectra are sensitive to the abundances of chemical species in the upper atmosphere and to the distribution of the stratospheric haze layer. We combine observations from the first 30 perijoves of the mission in order to study the meridional distribution of acetylene (C$_2$H$_2$) in Jupiter's stratosphere. We find that the abundance of C$_2$H$_2$ decreases towards the poles by a factor of 2-4, in agreement with previous analyses of mid-infrared spectra. This result is expected from insolation rates: near the equator, the UV solar flux is higher, allowing more C$_2$H$_2$ to be generated from the UV photolysis of CH$_4$. The decrease in abundance towards the poles suggests that horizontal mixing rates are not rapid enough to homogenize the latitudinal distribution.

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arXiv2021

Detection of a bolide in Jupiter's atmosphere with Juno UVS

The UVS instrument on the Juno mission recorded transient bright emission from a point source in Jupiter's atmosphere. The spectrum shows that the emission is consistent with a 9600-K blackbody located 225 km above the 1-bar level and the duration of the emission was between 17 ms and 150 s. These characteristics are consistent with a bolide in Jupiter's atmosphere. Based on the energy emitted, we estimate that the impactor had a mass of 250-5000 kg, which corresponds to a diameter of 1-4 m. By considering all observations made with Juno UVS over the first 27 perijoves of the mission, we estimate an impact flux rate of 24,000 per year for impactors with masses greater than 250-5000 kg.

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arXiv2020

Possible Transient Luminous Events observed in Jupiter's upper atmosphere

11 transient bright flashes were detected in Jupiter's atmosphere using the UVS instrument on the Juno spacecraft. These bright flashes are only observed in a single spin of the spacecraft and their brightness decays exponentially with time, with a duration of ~1.4 ms. The spectra are dominated by H2 Lyman band emission and based on the level of atmospheric absorption, we estimate a source altitude of 260 km above the 1-bar level. Based on these characteristics, we suggest that these are observations of Transient Luminous Events (TLEs) in Jupiter's upper atmosphere. In particular, we suggest that these are elves, sprites or sprite halos, three types of TLEs that occur in the Earth's upper atmosphere in response to tropospheric lightning strikes. This is supported by visible light imaging, which shows cloud features typical of lightning source regions at the locations of several of the bright flashes. TLEs have previously only been observed on Earth, although theoretical and experimental work has predicted that they should also be present on Jupiter.

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arXiv2018

The Lyman-α Sky Background as Observed by New Horizons

Recent observations of interplanetary medium (IPM) atomic hydrogen Lyman-α (Lyα) emission in the outer solar system, made with the Alice ultraviolet spectrograph on New Horizons (NH), are presented. The observations include regularly spaced great-circle scans of the sky and pointed observations near the downstream and upstream flow directions of interstellar H atoms. The NH Alice data agree very well with the much earlier Voyager UVS results, after these are reduced by a factor of 2.4 in brightness, in accordance with recent re-analyses. In particular, the falloff of IPM Lyα brightness in the upstream-looking direction as a function of spacecraft distance from the Sun is well-matched by an expected 1/r dependence, but with an added constant brightness of ~40 Rayleighs. This additional brightness is a possible signature of the hydrogen wall at the heliopause or of a more distant background. Ongoing observations are planned at a cadence of roughly twice per year.

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arXiv2016

The Atmosphere of Pluto as Observed by New Horizons

Observations made during the New Horizons flyby provide a detailed snapshot of the current state of Pluto's atmosphere. While the lower atmosphere (at altitudes <200 km) is consistent with ground-based stellar occultations, the upper atmosphere is much colder and more compact than indicated by pre-encounter models. Molecular nitrogen (N$_2$) dominates the atmosphere (at altitudes <1800 km or so), while methane (CH$_4$), acetylene (C$_2$H$_2$), ethylene (C$_2$H$_4$), and ethane (C$_2$H$_6$) are abundant minor species, and likely feed the production of an extensive haze which encompasses Pluto. The cold upper atmosphere shuts off the anticipated enhanced-Jeans, hydrodynamic-like escape of Pluto's atmosphere to space. It is unclear whether the current state of Pluto's atmosphere is representative of its average state--over seasonal or geologic time scales.

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