The atomic nucleus isn't a frozen ball but a seething collective of protons and neutrons. They whirl, collide, and arrange themselves into patterns that physicists see as "bands"—ladders of energy levels. In niobium and technetium nuclei, four such ladders have been found, but the last one stubbornly refused to fit the calculations.
The three lower bands have long been understood: the ground state, the first and second "side" bands, like three floors of a house. But the fourth behaved strangely: by the brightness of transitions between levels, it couldn't be the third side band, though it seemed to suggest itself. The authors applied a model where the nucleus is allowed to have three different axes (like a potato, not an orange), and found that the fourth band is the second side band, but with a different "character."
The calculation predicted the energy of this band for all nine isotopes of niobium and technetium. Now that the puzzle is solved, physicists can more accurately describe how nuclei behave far from stability — for example, in stellar explosions.
The niobium-103 nucleus has a shape resembling a triaxial ellipsoid, like a potato with all three dimensions different.