Kepler-408 b is the smallest planet known to orbit at a steep tilt to its star's spin. It is a hot planet a little smaller than Earth, about 0.86 times its width, that circles its star every 2.5 days. The star, a little hotter than the Sun, is about 290 light-years away.
Most planets orbit roughly in line with their star's equator, as the planets of the solar system do. Measuring that alignment is usually done during a transit, by watching which side of the spinning star the planet blocks, but that works only for large planets. Kepler-408 b is far too small. Instead, a team led by Shoya Kamiaka used asteroseismology: the star vibrates, and the pattern of those vibrations in NASA's Kepler data reveals how its spin axis is tilted toward us. Earlier studies had reached conflicting answers, and in 2019 the team traced the disagreement to how each had modelled background noise in the data.
With that resolved, they found the star's spin axis tilted about 42 degrees toward us. Because the planet transits, its orbit is seen nearly edge-on, so the planet's orbit and the star's spin must be badly out of line. The team called Kepler-408 b by far the smallest planet known to have a significantly misaligned orbit. How it ended up that way is an open question. It is far too hot for liquid water, receiving about 1,500 times the light Earth gets from the Sun, according to the NASA Exoplanet Archive.