HD 215152 - Four Super-Earths in Compact System

The HARPS search for southern extra-solar planets. XLIII. A compact system of four super-Earth planets orbiting HD 215152
https://arxiv.org/abs/1802.04631

Quote :

We report the discovery of four super-Earth planets around HD 215152, with orbital periods of 5.76, 7.28, 10.86, and 25.2 d, and minimum masses of 1.8, 1.7, 2.8, and 2.9 M_Earth respectively. This discovery is based on 373 high-quality radial velocity measurements taken by HARPS over 13 years. Given the low masses of the planets, the signal-to-noise ratio is not sufficient to constrain the planet eccentricities. However, a preliminary dynamical analysis suggests that eccentricities should be typically lower than about 0.03 for the system to remain stable. With two pairs of planets with a period ratio lower than 1.5, with short orbital periods, low masses, and low eccentricities, HD 215152 is similar to the very compact multi-planet systems found by Kepler, which is very rare in radial-velocity surveys. This discovery proves that these systems can be reached with the radial-velocity technique, but characterizing them requires a huge amount of observations.

It's worth noting two of these planets were found here by Mayor (2011). (forum thread).

Sirius_Alpha wrote:

It's worth noting two of these planets were found here by Mayor (2011). (forum thread).

Not sure why they felt it necessary to change the letters. Surely the new planets (the 5.76-day and the 25.2-day planets) should be designated d and e, with b and c left for the 7.28-day and 10.9-day planets?