Read the Moon’s hidden weight.

Reconstruct two buried density contrasts from their gravity signature. Place one dense block (+) and one light block (−) at the right horizontal positions and depths. Match the gold observations, then test the unobserved stations.

Gravity traverse

● Observed stations— Your reconstruction◇ Withheld until validation

Observed RMS · goal <3%100%

Inventory placed0 / 2

Validation attempts0 / 3

Subsurface section

Each column = 10 km

WESTEXAGGERATED VERTICAL SCALEEAST

Cell labels: horizontal position / depth. Rows: 6 km / 12 km / 20 km. Colored markers are point-mass approximations of density contrast, not literal cubic rocks.

Model & source notes

This teaching model sums signed point masses on a spherical Moon of radius 1,737.4 km. Measurements are synthetic, collected 2 km above the surface. Each contrast has magnitude 3×10¹² kg. Positive and negative blocks represent excess or missing mass relative to a background crust. Many real subsurface distributions can explain similar observations; these puzzles restrict the model to two grid points.

JavaScript ports of Harmonica’s spherical point-mass summation, upward-gravity kernel and spherical-distance routine drive every plotted value. Source: fatiando/harmonica, BSD-3-Clause, commit a9cd4420, October 2026; 310 observed stars. Original puzzles, controls and GPT-generated lunar cutaway. License.