BD+05 4868 is a binary star consisting of a K-dwarf and an M-dwarf. Around the primary one rocky planet is detected. This planet, called BD+05 4868Ab, orbits the star so close that it disintegrates, creating a large comet-like tail, seen in transits.^[1]

BD+05 4868 was first cataloged in the Bonner Durchmusterung^[4] and in 1961 the star was identified as a proper motion star by Giclas et al.^[5] In 1984 its spectrum was observed for the first time, identifying it as a K5: type star.^[6] The star was first identified as a binary from Gaia data. The common proper motion and parallax indicate that the pair is physically bound. The binary was also detected with the Las Cumbres Observatory Global Telescope (LCOGT) 2 m Faulkes Telescope North and with Keck NIRC2.^[1]

The planet BD+05 4868Ab was discovered with TESS in transits. The transits are unusually deep with variable depths of 0.8-2.0%. The transits are also asymmetric, with a short ingress followed by a long egress. The researchers were also able to detect the transits in ground-based ASAS-SN and LCOGT 2m telescope data. Seven spectra of the primary were obtained with the WIYN 3.5m Telescope, detecting no radial velocity signal larger than a few m/s.^[1]

The researchers interpret the transits as a disintegrating rocky planet, similar to Kepler-1520b, KOI-2700b and K2-22b. The difference is that BD+05 4868Ab is around a relative bright (V=10.16 mag) host star and the transits are consistently deep. Other disintegrating rocky planets show weaker transits (~0.5% transit depth) that are also variable. This makes BD+05 4868Ab a compelling target for transmission spectroscopy, which could characterize exoplanet mineralogy.^[1]

The planet also has a relative low equilibrium temperature of 1,820±45 K, which could lead to differences in dust properties, when compared to other disintegrating planets. The transit shows both a leading and a trailing tail, which helped to constrain the grain sizes to be at around 1–10 μm. Comparisons to models suggest that the planet began with a mass that could be larger than the mass of Mercury. The planet lost mass due to the evaporation of minerals on the surface over several billion years. The current mass and radius of the planet is not known, but the researchers assume a mass of about 0.02 M_E (about lunar-mass) and a radius of 2,000 km (about that of Kepler-37b) in their modelling. Currently the mass-loss rate is at 10 M_E per billion years, meaning it will evaporate in about 2 million years.^[1]