Relles'
- 'M. Rose'
- 'N. C. Santos'
- 'D. Ségransan'
- 'S. Shectman'
- 'A. Shporer'
- 'J. C. Smith P. Torres'
- 'S. Udry'
- 'J. Villasenor'
- 'J .G. Winters'
- 'G. Zhou'
bibliography:
- 'TOI134.bib'
title: 'A hot terrestrial planet orbiting the bright M dwarf L 168-9 unveiled by *TESS* [^1] ^,^[^2] ^,^[^3] '
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Introduction
============

The best planets for detailed characterization are transiting planets, first and foremost because they allow for the possibility of unambiguous mass measurement [e.g., HD209458b @Charbonneau2000; @Mazeh2000; @Henry2000]. From the Doppler effect we can determine the minimum mass of the planet ($m \sin i$), and from the transit light curve we can determine the planetary radius and the orbital inclination ($i$), thus yielding a measurement of the planet’s mass. Moreover, from this combination we can calculate the planet’s mean density, and shed light on its internal structure by comparison with models containing different amount of iron, silicates, water, hydrogen, and helium. Furthermore, transiting planets are unique because of the feasibility to characterize the upper atmosphere by spectroscopy during transits and occultations of a significant number of planets. The forthcoming *James Webb Space Telescope* [JWST, @Gardner2006] and the *Extremely Large Telescope* 