Ariel Mission

Assessing Ariel’s Capabilities To Observe Free-floating Brown Dwarfs

By Keith Cowing

Status Report

astro-ph.EP

June 10, 2026

Filed under Ariel mission, astro-ph.EP, atmosphee, brown dwarf, exoplanet, hot jupiter, imaging, Spectroscopy

Assessing Ariel’s Capabilities To Observe Free-floating Brown Dwarfs — Simulated Ariel single-epoch spectral observations of 3 targets from our sample. Each target was observed with a 1-minute exposure — enough to capture rotational variability. The integration time could safely be increased to 5 minutes for higher SNR on fainter targets. Top: LSR J1826+3014, the brightest free-floating brown dwarf in the FGS2 bandpass, an L0 dwarf. Middle: SIMP J0136, a well-known variable T2.5 dwarf at the L/T transition. Bottom: WISE 0855-0714, the closest known Y dwarf. These targets emit 5.5×104, 0.36×104, and 270 photons/s/m2 respectively in the FGS2 band. Despite the high expected SNR with Ariel’s spectroscopic instruments, guiding on SIMP J0136 would require 2.5-second FGS2 readout (33.3 seconds for the Y dwarf). Additional analysis of the spacecraft stability and centroiding accuracy will be required to assess how much the guiding cadence can be decreased. SNRs reported on the plot are median values for each instrument. Black lines are smoothed spectra of corresponding theoretical models: Sonora Diamondback (Morley et al. 2024) for LSR J1826 and SIMP J0136, and Morley14 (Morley et al. 2014) for WISE 0855. — astro-ph.EP

The primary goal of the Ariel space telescope is to conduct the biggest spectroscopic survey of transiting exoplanets to characterize their atmospheres and weather.

We propose to extend the Ariel survey to another domain of alien atmospheres – rogue planets and free-floating brown dwarfs.

Their isolated nature means the observations are uncontaminated by light from a host star, and their short rotation periods, often similar to hot Jupiter orbital periods, provide an opportunity to study time-varying meteorology.

Phase curve observations would especially help scientists understand atmospheric dynamics at the L/T transition, where multiple cloud species at different altitudes influence the time-varying spectra of brown dwarfs.

Inferring timescales and length scales of these atmospheric features is key to understanding the meteorology of sub-stellar objects. We quantify how many isolated cool objects that Ariel’s fine guidance sensor (FGS) is able to guide on.

Among 2744 selected targets, none are bright enough under the planned 10 Hz FGS cadence; however, with a “slow” fine guidance mode of 1 Hz, Ariel could study 98 L0- to L5-type brown dwarfs. We simulate single-epoch and time-series spectroscopic observations of the brightest isolated brown dwarfs given currently known instrumental specifications.

We show that the resolution and sensitivity of Ariel instruments in the 1.1-7.8 micron regime can measure cloud-induced variability at the sub-percent level. A survey of brown dwarf phase curve observations, unavailable to ground-based telescopes, would be the perfect complement to Ariel’s survey of atmospheric variability in hot Jupiters.

Roman Akhmetshyn, Nicolas B Cowan, Sarah Casewell

Comments: Submitted to RASTI on May 22, 2026
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2605.28924 [astro-ph.EP] (or arXiv:2605.28924v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2605.28924
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Submission history
From: Roman Akhmetshyn
[v1] Wed, 27 May 2026 18:00:00 UTC (198 KB)
https://arxiv.org/abs/2605.28924

Astrobiology

Keith Cowing

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member 🖖🏻

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