# HD 213885b: A transiting 1-day-period super-Earth with an Earth-like composition around a bright ($V=7.9$) star unveiled by TESS

## TL;DR

This paper reports the discovery and characterization of a bright, ultra-short period super-Earth with an Earth-like composition around a very bright star, including the detection of a second non-transiting planet, using TESS and radial velocity data.

## Contribution

It presents the first detailed characterization of HD 213885b, a bright ultra-short period super-Earth, and identifies a second non-transiting Neptune-mass planet in the system.

## Key findings

- HD 213885b has a mass of 8.8±0.6 M⊕ and radius of 1.74±0.05 R⊕.
- The planet's composition is similar to Earth's but enriched in iron.
- An additional 4.78-day signal indicates a second non-transiting planet, HD 213885c.

## Abstract

We report the discovery of the 1.008-day, ultra-short period (USP) super-Earth HD 213885b (TOI-141b) orbiting the bright ($V=7.9$) star HD 213885 (TOI-141, TIC 403224672), detected using photometry from the recently launched TESS mission. Using FEROS, HARPS and CORALIE radial-velocities, we measure a precise mass of $8.8\pm0.6$ $M_\oplus$ for this $1.74 \pm 0.05$ $R_\oplus$ exoplanet, which provides enough information to constrain its bulk composition, which is similar to Earth's but enriched in iron. The radius, mass and stellar irradiation of HD 213885b are, given our data, very similar to 55 Cancri e, making this exoplanet a good target to perform comparative exoplanetology of short period, highly irradiated super-Earths. Our precise radial-velocities reveal an additional $4.78$-day signal which we interpret as arising from a second, non-transiting planet in the system, HD 213885c (TOI-141c), whose minimum mass of $19.95\pm 1.4$ $M_\oplus$ makes it consistent with being a Neptune-mass exoplanet. The HD 213885 system is very interesting from the perspective of future atmospheric characterization, being the second brightest star to host an ultra-short period transiting super-Earth (with the brightest star being, in fact, 55 Cancri). Prospects for characterization with present and future observatories are discussed.