Which planet takes about 88 Earth days to orbit the Sun?

Mercury, closest to the Sun and therefore fastest - which is what the name records, the Roman messenger god. Its year is 88 days and its day is 59, and the ratio between them is exactly 3:2, locked there by the Sun's tides. That produces something genuinely strange: it rotates three times for every two orbits, so a solar day on Mercury - noon to noon - lasts 176 Earth days, two full Mercurian years.

From some places on the surface the Sun appears to rise, stop, go backwards, and then resume, because near closest approach the planet's orbital speed briefly exceeds its rotation speed. There are two points on Mercury where the Sun rises and sets twice in the same day.

It was also the first evidence that Newton was incomplete. Mercury's orbit precesses - the whole ellipse rotates slowly - by a tiny amount more than Newtonian gravity predicts, and nineteenth-century astronomers were confident enough in the theory to propose an undiscovered planet, Vulcan, to explain it. There was no planet. Einstein's general relativity produced the observed figure exactly, with nothing adjusted to fit, and he later wrote that it gave him palpitations.