Letter to the Editor

A scenario of planet erosion by coronal radiation^*

J. Sanz-Forcada¹, I. Ribas², G. Micela³, A. M. T. Pollock⁴, D. García-Álvarez^5,6, E. Solano^1,7 and C. Eiroa⁸

¹ Laboratorio de Astrofísica Estelar y Exoplanetas, Centro de Astrobiología / CSIC-INTA, LAEFF Campus, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain e-mail: jsanz@cab.inta-csic.es
² Institut de Ciènces de l'Espai (CSIC-IEEC), Campus UAB, Fac. de Ciències, Torre C5-parell-2 planta, 08193 Bellaterra, Spain
³ INAF – Osservatorio Astronomico di Palermo G. S. Vaiana, Piazza del Parlamento, 1, 90134 Palermo, Italy
⁴ XMM-Newton SOC, European Space Agency, ESAC, Apartado 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁵ Instituto de Astrofísica de Canarias, 38205 La Laguna, Spain
⁶ Grantecan CALP, 38712 Breña Baja, La Palma, Spain
⁷ Spanish Virtual Observatory, Centro de Astrobiología/CSIC-INTA, LAEFF Campus, Madrid, Spain
⁸ Dpto. de Física Teórica, C-XI, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain

Received: 14 November 2009
Accepted: 8 February 2010

Abstract

Context. According to theory, high-energy emission from the coronae of cool stars can severely erode the atmospheres of orbiting planets. No observational tests of the long-term erosion effects have been made yet.

Aims. We analyze the current distribution of planetary mass with X-ray irradiation of the atmospheres to make an observational assessment of the consequences of erosion by coronal radiation.

Methods. We studied a large sample of planet-hosting stars with XMM-Newton, Chandra, and ROSAT, carefully identified the X-ray counterparts, and fit their spectra to accurately measure the stellar X-ray flux.

Results. The distribution of the planetary masses with X-ray flux suggests that erosion has taken place. Most surviving massive planets (M_p sin i > 1.5 M_J) have been exposed to lower accumulated irradiation. Heavy erosion during the initial stages of stellar evolution is followed by a phase of much weaker erosion. A line dividing these two phases could be present, showing a strong dependence on planet mass. Although a larger sample will be required to establish a well-defined erosion line, the distribution found is very suggestive.

Conclusions. The distribution of planetary mass with X-ray flux is consistent with a scenario in which planet atmospheres have suffered the effects of erosion by coronal X-ray and EUV emission. The erosion line is an observational constraint for models of atmospheric erosion.