Detectability of Artificial Lights from Proxima b: A Feasibility Study with JWST

Table of Contents

1. Introduction

Proxima b, an Earth-mass exoplanet in the habitable zone of Proxima Centauri (our nearest stellar neighbor at 4.2 light-years), represents a prime target in the search for extraterrestrial life. Its likely tidal locking creates a permanent dayside and nightside. This Letter investigates the detectability of artificial illumination on the planet's dark side as a potential technosignature of an advanced civilization. We assess the feasibility using light curve simulations and signal-to-noise calculations for the James Webb Space Telescope (JWST).

2. Methods

2.1. Proxima b Lightcurves

Light curves for Proxima b were calculated using the Exoplanet Analytic Reflected Lightcurves (EARL) model (Haggard & Cowan, 2018). A uniform albedo map (spherical harmonic $Y_0^0$) was assumed. The reflected flux is given by:

$F_0^0 = \frac{1}{3\pi^{3/2}} (\sin w - w \cos w)$

where $w$ is the angular width of the illuminated crescent. Key planetary parameters include: radius (~1.3 $R_\oplus$), orbital period (11 days), semi-major axis (~0.05 AU), albedo (~0.1, analogous to the Moon), and an orbital inclination estimated from data on Proxima c ($i = 2.65 \pm 0.43$ radians).

2.2. Error Analysis & Signal-to-Noise

Detection feasibility was evaluated using the JWST Exposure Time Calculator (ETC). We considered two artificial light scenarios: 1) Broad-spectrum light matching common Earth LEDs. 2) A much narrower spectrum containing the same total power as Earth's current artificial illumination. The analysis assumes photon-limited precision for JWST's NIRSpec instrument.

3. Results

Our simulations indicate that JWST could detect artificial lights on Proxima b's nightside under specific conditions:

• LED-type lights: JWST could detect an artificial light source contributing 5% of the host star's reflected light power with 85% confidence.
• Earth-level illumination: To detect the equivalent of Earth's current total artificial illumination, the emission would need to be concentrated into a spectral band $10^3$ times narrower than a typical LED spectrum. This represents a significant technological constraint for detection.

These predictions are contingent on optimal performance from JWST's NIRSpec instrument.

4. Discussion & Implications

The study highlights the extreme challenge of detecting technosignatures like city lights, even for the nearest exoplanet with a premier telescope like JWST. While detection of very powerful, inefficient (broad-spectrum) lighting might be marginally feasible, identifying a civilization using energy-efficient lighting (like modern Earth) is currently beyond JWST's capability. This work underscores the need for future, more powerful observatories (e.g., LUVOIR, HabEx) and refined search strategies to pursue such subtle signatures.

5. Original Analysis & Expert Critique

Core Insight: This paper isn't about finding aliens; it's a sobering reality check on the limits of our current flagship technology. The authors effectively demonstrate that JWST, often hailed as a revolutionary tool for biosignatures, operates at the very edge of plausibility for detecting even blatant, wasteful technosignatures like broad-spectrum night-side lighting on our closest exoplanetary neighbor. The core takeaway is that the "Great Filter" for technosignature detection might be our own instrumental sensitivity, not the absence of civilizations.

Logical Flow: The logic is admirably clear and quantitative. They start with a well-defined target (tidally-locked Proxima b), establish a plausible technosignature (artificial illumination), model its photometric signal using established exoplanet light curve formalisms, and finally run the numbers through the JWST instrument simulator. The step where they contrast "wasteful LED" light with "efficient Earth-like" light is particularly clever, framing the detection problem not just in terms of power, but of spectral strategy—a concept familiar from signal processing and communications theory, as seen in works like the seminal CycleGAN paper (Zhu et al., 2017) which deals with mapping between domains, analogous to extracting a signal from noise.

Strengths & Flaws: The major strength is its grounding in real, upcoming observatory capabilities (JWST ETC), moving beyond theoretical musings. However, the analysis has significant, acknowledged flaws. It assumes optimal, photon-limited performance—a best-case scenario rarely achieved in practice due to systematics. It also simplifies the exoplanet to a uniform albedo sphere, ignoring potential confounding factors like atmospheric variability, starspots on Proxima Centauri, or natural nightside airglow, which studies from institutions like NASA's Exoplanet Exploration Program caution can mimic artificial signals. The 5% threshold is enormous; for context, Earth's total artificial light at night is orders of magnitude fainter than sunlight reflected by the dayside.

Actionable Insights: For the SETI community, this paper is a mandate to look beyond photometry. The future lies in high-resolution spectroscopy to hunt for artificial atmospheric constituents (e.g., CFCs) or combined temporal-spectral anomalies, as suggested by research from the Breakthrough Listen initiative. For mission planners, it's a strong pitch for the larger apertures of LUVOIR-class telescopes. For theorists, it suggests modeling more realistic emission profiles—perhaps a network of city lights creating a specific, non-uniform photometric fingerprint during rotational phases. The work effectively closes one narrow avenue of inquiry while forcefully arguing for the investment to open wider ones.

6. Technical Details & Mathematical Framework

The core of the light curve modeling relies on the EARL framework's analytic solution for a uniformly reflecting sphere. The key equation (1) in the text, $F_0^0 = \frac{1}{3\pi^{3/2}} (\sin w - w \cos w)$, describes the reflected flux integrated over the visible crescent. The variable $w$ is derived from the planetary phase angle $\alpha$ and the angular radius of the planet as seen from the star. The signal from artificial lights is then added as an additional, constant nightside flux component, $F_{art}$, proportional to the civilization's total luminous power and its emission spectrum. The detectability criterion is set by comparing the differential flux between planetary phases (e.g., full phase vs. new phase) to the expected photometric noise $\sigma$ from JWST NIRSpec: $SNR = \Delta F / \sigma$, where $\Delta F$ includes the contrast from both reflected starlight and the artificial component.

7. Experimental Results & Chart Description

While the PDF excerpt does not contain explicit figures, the described results imply specific graphical outputs:

• Light Curve Plot: A simulated plot would show flux vs. orbital phase for Proxima b. The curve would have a primary peak at "full" phase (planet fully illuminated) and a minimum at "new" phase (dark side facing observer). The key result is that with artificial lights, the minimum flux level would be elevated compared to the natural case (zero reflected light from the nightside). The 5% detection threshold would correspond to a small but statistically significant bump in the light curve minimum.
• SNR vs. Artificial Light Power Plot: Another implied chart would plot the calculated Signal-to-Noise Ratio (SNR) for JWST observations against the fractional power of artificial lights (as a percentage of reflected stellar power). The curve would show SNR increasing with light power. The 85% confidence detection threshold (likely corresponding to SNR ~3-5) would be marked, intersecting the curve at the 5% power level for the broad-spectrum LED case.
• Spectral Bandwidth Requirement Chart: A diagram contrasting the wide emission spectrum of typical LEDs with an extremely narrow, idealized spectrum. The text indicates the narrow band must be $10^3$ times narrower to make Earth-level illumination detectable, visually emphasizing the immense spectral density required.

8. Analysis Framework: A Hypothetical Case Study

Scenario: A future study aims to re-analyze archival JWST time-series photometry of Proxima b, searching for an anomalous, phase-independent flux baseline.

Framework Steps:

1. Data Acquisition & Preprocessing: Obtain NIRSpec time-series data across multiple orbits. Perform standard calibration, cosmic-ray removal, and systematic correction (e.g., for telescope jitter) using pipelines like the JWST Science Calibration Pipeline.
2. Baseline Model Fitting: Fit the primary light curve using the EARL model (Eq. 1) for natural reflected light, with parameters for albedo, inclination, and radius as free variables. This establishes the expected "null" model with no artificial lights.
3. Residual Analysis: Subtract the best-fit natural model from the observed flux. Analyze the residuals as a function of orbital phase. The signature of artificial lights would be residual flux that does not correlate with phase, remaining constant or showing a different periodicity.
4. Hypothesis Testing: Formally compare the fit of the null model (no artificial light) to an alternative model that includes a constant flux offset parameter ($F_{art}$). Use a statistical test like the F-test or Bayesian Model Comparison to see if the added parameter is justified by a significant improvement in fit, given the increased model complexity.
5. Spectral Verification: If a photometric anomaly is found, the next step would be to obtain phase-resolved spectroscopy. The artificial light hypothesis predicts a nightside spectrum dominated by stellar light reflected from the dayside and atmosphere PLUS an emission spectrum with distinct features (e.g., sharp lines from sodium vapor lamps, a blackbody continuum from incandescent sources, or the broad hump of LEDs).

9. Future Applications & Research Directions

• Next-Generation Telescopes: The primary application is informing the design and science cases for post-JWST flagships. The paper explicitly mentions LUVOIR; its larger aperture (8-15m) would lower detection thresholds by an order of magnitude or more, potentially bringing Earth-like illumination levels into the realm of detectability.
• Spectral Signature Libraries: Future work must move beyond "LED-like" spectra. Research should compile detailed spectral templates for various hypothetical technologies: different lighting types (plasma, OLED, laser-based), industrial processes, and even deliberate beacon signals.
• Temporal & Spatial Signatures: Detectability could be enhanced by looking for non-uniform patterns. A network of cities would create a rotating modulation as the planet spins. Flashing or pulsed lights (for energy efficiency or communication) could be identified via Fourier analysis of high-cadence photometry.
• Atmospheric Technosignatures: A more promising near-term direction, compatible with JWST's strengths, is searching for artificial gases (e.g., chlorofluorocarbons, industrial pollutants) via transmission or emission spectroscopy, as proposed by studies from the Virtual Planetary Laboratory.
• Multi-Messenger Synergy: Combining photometric searches with radio (e.g., Breakthrough Listen) and optical laser SETI efforts could provide cross-validation. A faint photometric anomaly could be prioritized for follow-up with dedicated radio telescopes.

10. References

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4. Haggard, H. M., & Cowan, N. B. 2018, MNRAS, 478, 3711 (EARL model).
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11. NASA Exoplanet Exploration Program: https://exoplanets.nasa.gov
12. Breakthrough Listen: https://breakthroughinitiatives.org/initiative/1