Principal Investigator
Nuno C. Santos

Abstract
The present project has the overall goal of continuing the effort to build a strong national team doing frontier research in the field of extra-solar planets, and particularly focussed on the detection and study of other Earths.

The discovery 13 years ago of an extra-solar planet orbiting the solar-type star 51 Peg (Mayor & Queloz 1995) encouraged the launch of numerous search programs leading to a steadily increasing number of exoplanet detections. More than 300 other
planetary companions have been found to orbit solar-type stars. The very large majority of the exoplanets were found using the radial-velocity (RV) technique.

Although most exoplanets discovered to date are giant planets similar to Jupiter (see review by Udry & Santos 2007), since 2004 research teams using the RV technique have been making the headlines several times for their discoveries of low-mass extrasolar planets (e.g. Santos et ai. 2004a). Some of these have only a few times the mass of the Earth.

Present results from the HARPS programs (on which some of our team members participate) further suggest that the already published discoveries only represent the tip of the iceberg. A recent census of planetary candidates among stars of the "high-
precision" sub-program revealed 45 possible very low-mass planets orbiting with periods below 50 days. Statistically, this would mean that about 30% of solar-like stars do possess such close-in ice giants and super-Earths. These preliminary numbers are a strong indication that a whole new population of low-mass objects is now emerging. The existence of such a populations is also supported by current theoretical population synthesis calculations (e.g. Benz et ai. 2008).

These observational and theoretical results triggered a number of instrumentation projects to build new high precision spectrographs for planet searches, that may be able to attain radial-velocity precisions of a few cm/s. Such instruments would allow
to extensively explore the low-mass tail of the exoplanet distribution and to find rocky planets within the habitable zone (HZ) around other stars. The detection of terrestrial planets in the HZ will be one of the main scientific topics of the next decades in
Astronomy.

With this in mind, our team is participating in a consortium to build and use a new high resolution ultra-stable spectrograph for the VLT: ESPRESSO. The goals of this instrument are to achieve the 10 cm/s precision in radial-velocity. This precision will allow us to detect other Earth-mass planets orbiting nearby solar-tvpe stars. It is important to say that this project has recently been approved by ESO for Phase A study. If there are no major difficulties, this spectrograph will be mounted at the VLT site in 2014.

The present project has the goals of addressing for the first time a number of scientific challenges that are crucial to allow us to fully exploit current (e.g. HARPS) and future (e.g. ESPRESSO@VLT or CODEX@E-ELT) high-precision radial-velocity planet search projects aiming at the detection of Earth-like planets.

To optimize this goal, we propose to explore four important topics that are in the frontier between stellar astrophysics, N-body dynamics, and the search for extra-solar planets. These topics follow from a very successful FCT project that was financed in 2004 to our team (already finished), and include:

i) Participate in several state-of-the-art planet-search projects, both allowing us to participate in the discovery of new low-mass planets, but also to develop the research mentioned in the following points;

ii) Study the influence of stellar induced radial-velocity variations (due to the effect of stellar activity, oscillations, and granulation). These are of extreme importance if we want to achieve the radial-velocity precision that is necessary for the detection of Earth mass planets (e.g. Santos et aI. 2004a);

iii) Develop a number of tools to analyze the spectra and study the relation between the presence of a planet and the properties of its host star. This is particularly important at this point regarding stars hosting Neptunes and Super-Earths. Such relations may give us extremely important information to understand the processes of planet formation and evolution (e.g. Santos et ai. 2004b, Sousa et aI. 2008);

IV) Produce numerical simulations of multi-planet systems that will help us to better understand the origin and evolution of the discovered planets (Correia et aI. 2005). This includes the developement of analytical and numerical tools that will allow a better determination of the orbital parameters of multi-planetary systems.

All the mentioned studies will also be useful to the general community, and will have an impact that will extend well beyond the timeline of the current project.

The two institutions involved have the two main national groups involved in the study of exoplanets, both from the observational (CAUP) and theoretical (Aveiro) side.

Institutions involved in the project:
- Centro de Astrofísica da Universidade do Porto (CAUP/UP)
- Universidade de Aveiro (UA)

Project members in CAUP:
- Ana Soares
- Giancarlo Pace
- Isabelle Boisse
- João Gomes da Silva
- Mahmoudreza Oshah
- Marco Montalto
- Nuno Santos
- Pedro Figueira
- Sérgio Sousa
- Vasco Neves
- Xavier Dumusque

Project website
http://www.astro.up.pt/exoearths/

Start
1 April 2010
End
31 March 2013

Funding Institution
Fundação para a Ciência e a Tecnologia