# A Visible Imaging Doppler Spectrometer dedicated to Uranus' Atmospheric Dynamics and Internal Structure

F.X. Schmider¹, P. Gaulme²,³,⁴, T. Guillot¹, S. Markham¹, T. Douçot¹, J. Jackiewicz³, C. Sanchez³ and R. .Morales-Juberías⁴,

¹Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, CS 34229 F-06304 NICE Cedex (schmider@oca.eu), ²Thüringer Landessternwarte Tautenburg, Germany, ³New Mexico State University, NM, USA, ⁴New Mexico Institute of Mining and Technology, NM, USA

**Introduction:** In the context of a possible mission to Uranus, the measurement of line-of-sight velocities of the planet would bring unique information about its atmospheric dynamics and internal structure. Firstly, line-of-sight velocities would allow us to retrieve zonal, meridional, and vertical motion, which would not be possible with classical cloud-tracking techniques [1]. Secondly, periodic fluctuations of the vertical motion caused by global acoustic modes would allow to perform seismic studies and extract the deep internal profiles of the sound-speed and the differential rotation [2]

**Method:** High precision Doppler measurements could be performed by a visible imaging spectrometer, a.k.a. Doppler imager, onboard a spacecraft orbiting the system, with techniques that have been successfully employed with solar missions for the past 30 years: MDI/SOHO, HMI/SDO, or PHI/Solar Orbiter. In this presentation, we give an overview of the proposed technique, and we report early results obtained on Jupiter with a ground-based version the proposed instrument, JIVE/JOVIAL [3], which was mounted at the Dunn solar telescope (USA). Our observations validate the instrumental concept and demonstrate our ability to measure wind fields with such a technique. We will also discuss an alternative instrumental concept that has been able to provide wind measurements on Jupiter from the ground [4], and could be suitable for a Uranus mission as well.

Regarding wind measurements, having an instrument on a spacecraft, i.e., moving with respect to the planet, represents a unique opportunity to disentangle the components of the atmospheric circulation (zonal, meridional, vertical), which is not possible from a fixed observation site [5].

Regarding the search for global acoustic oscillations, we present the expected detection level with this technique, as compared to gravity field variations [6]. We show that a successful seismology experiment conducted by a Doppler imager on board a Uranus orbiter breaks intrinsic degeneracies in Uranus interior structure models. [7].

**Conclusion:** A Doppler imager placed on an orbiter around Uranus has a unique capability to answer several deep scientific questions about its atmospheric

dynamics, its internal composition and about the interaction between the interior and the atmosphere and should be considered for further payload study.

<figure><img src="image_1.png" /><figcaption>Figure 1. Planisphere of the zonal winds recorded on Jupiter from ground-based observations with the JOVIAL Doppler Imager. Data were obtained during 11 nights at the Dunn Solar Telescope in New Mexico. Jupiter's Great Red Spot is clearly identified at around lat. -20°, long. 280°. Right panel: Mean zonal wind profile.</figcaption></figure>

## References:

[1] Guillot T., Fortney J., Rauscher E., Marley M.S., Parmentier V. et al; White Paper #244, BAAS Vol. 53; Issue 4 (2021)

[2] Jackiewicz, J., Nettelman N., Marley M., Fortney, J., Icarus, 220, 844 (2012)

[3] Gonçalves, I., Schmider, F. X., Gaulme, P., Morales-Juberías, R., Guillot, T., et al, Icarus, 319, 795-811 (2019)

[4] Shaw, C. L., Gulledge, D. J., Swindle, R., Jefferies, S. M., and Murphy, N., Frontiers in Astronomy and Space Sciences, vol. 9, (2022)

[5] Gaulme, P., Schmider, F.-X. & Gonçalves, I., A&A 617, A41 (2018).

[6] Friedson J., Philosophical Transactions of the Royal Society A, 378, Issue 2187, 20190475 (2020)

[7] Markham, S., this meeting (2023)