Turnover of the cold classical TNO luminosity function at faint magnitudes

Determine whether the differential absolute-magnitude distribution dN/dH of cold classical trans-Neptunian objects turns over at faint absolute magnitudes.

Background

The paper combines bright, ground-based, Hubble Space Telescope, and James Webb Space Telescope observations to constrain the cold classical trans-Neptunian-object absolute-magnitude distribution over approximately 5 < H_r < 13. Several analytic forms—including lognormal, generalized-Gamma, and double-power-law models—fit the observed distribution comparably well within the measured range.

Because these fitted forms diverge toward fainter magnitudes, the available observations do not establish whether the luminosity function merely flattens or eventually decreases, or instead turns upward for objects below the current detection limit. Resolving whether a faint-end turnover exists is important for determining the abundance of small bodies and assessing the possible contribution of an unobserved reservoir to the total mass of the cold classical belt.

References

It remains unclear if dN/dH turns over at faint H.

— The size and mass distribution of cold classical TNOs for $5<H<13$  (2609.09063 - Bernstein et al., 8 Sep 2026) in Abstract

The number of TNOs to be discovered depends on the area covered by the survey, the true magnitude (or size) distribution of the TNOs (which is not known!), and the detection limit.

— The Luminosity Function of Ultra-Faint Trans-Neptunian Objects Detected by JWST  (2609.09044 - Eduardo et al., 8 Sep 2026) in Section 2, Observing Strategy

However, and only reached magnitudes as faint as $H_r \sim 8.3$ ($\sim 75$ km), while extended to $H_r \sim 10.5$ ($\sim 27$ km), leaving the faint-end consistency of the SI+PCC model still uncertain.

— The Luminosity Function of Ultra-Faint Trans-Neptunian Objects Detected by JWST  (2609.09044 - Eduardo et al., 8 Sep 2026) in Section 1, Introduction