TOI-561 b is an ultra-short period super-Earth exoplanet orbiting TOI-561, a Sun-like star. The innermost planet in its planetary system, it orbits extremely close to its star, completing an orbit within 11 hours. This results in a dayside temperature exceeding 2000 Kelvin. With a radius of around 1.4 Earth radii and a mass of around 2 Earth masses, this planet has a relatively low density for ultra-short period planets, possibly suggesting iron-poor composition and/or a envelope of low density materials, the latter of which is supported by the detection of a volatile-rich atmosphere which transports heat from the dayside to the nightside.