How big is the new world beyond Pluto?

Connecting observations

Rubin Observatory announced dwarf-planet candidate 2026 ED138 on 27 October. Linking 30 observations from 20 nights in March–July, plus older images back to 2016, helped establish its orbit.[1]

Why a range, rather than one diameter?

A 28 October preprint estimates a diameter of 612–1,530 km for assumed surface reflectivities of 0.25–0.04, rather than measuring a resolved edge.

A large dark ball can look as bright as a smaller white one. Similar brightness need not mean similar size. Learning more about reflectivity can narrow the estimate.[2]

With a one-metre Earth: about 4.8–12 cm

Shrink Earth’s rounded diameter of 12,742 km to 100 cm. ED138 becomes about 4.8–12.0 cm wide.

612 ÷ 12,742 × 100 ≈ 4.8 cm; 1,530 ÷ 12,742 × 100 ≈ 12.0 cm. These are diameter ratios, not distances. Picking a value inside the range would not make it confirmed.[2] [4]

Another discovery through motion

ScaleTrip synthesis of the two reports

On 19 October, ESA announced Euclid’s discovery of comet C/2026 S1. Software flagged moving streaks in galaxy-survey images; follow-up observations and Minor Planet Center confirmation followed.

Taken together, these stories show the value of repeat imaging and linking detections. That is ScaleTrip’s synthesis. Calling every detection program “AI discovering objects alone” would overstate the evidence.[3]

What remains uncertain?

ED138 remains a candidate. The cited manuscript was submitted to a journal; preprint release is not completed peer review. Further observations can refine its size. Read a number’s assumptions alongside the number.[2]