The search for life on other planets has been a quest that has motivated human beings since the genesis of mankind. Are we alone in the universe? Is there any form of life elsewhere? are questions which have intrigued scientists for decades. The first discovered extrasolar planets opened an encouraging opportunity to finally pursue the answer to some of these fundamental questions.
Astronomers have conceived cunning techniques to detect extrasolar planets. In most cases, they rely on the influence of the planet on its parent star.
These techniques have allowed the discovery of several hundreds of extrasolar planets until now (for the most recent number count, see exoplanet.eu).
Briefly, some ways of detecting extrasolar planets are:
Radial velocity measurements: due to the mutual gravitational interaction between the planet and the star, the stellar radial velocity will change due to the motion of the star around the system’s center of gravity. Variations in the stellar spectral lines will show a small Doppler shift (the star will appear to move towards or away from the observer). Measuring these radial velocity changes allows to confirm or rule out the presence of planets. Radial velocity measurements permit to estimate the orbital period and the eccentricity, but only a minimum mass of the planet due to the unknown inclination of the system.
Astrometry: A star with a planetary companion orbits around the system’s center of mass. If the star’s position is measured very precisely over time, it is possible to model that orbit and discover the perturber planet.
Microlensing: when a massive foreground object passes very close to the line of sight of a background source star, it is possible to observe the deflection and magnification of the emission of the background source due to the gravitational potential of the foreground object. If the lens foreground object is a star with a planet, the presence of the planet may be detectable due to a brief disturbance in the lensing light curve. The microlensing technique allows to constrain the ratio of planet mass to stellar mass.
Pulsar timing: pulsars emit radio waves whose timing can be measured very precisely. Due to the extremely regular rotation of a pulsar, small changes in the timing of the radio pulses can be used to define the pulsar’s motion. If there is a planet orbiting the pulsar, it will interact gravitationally with the pulsar, and, therefore, influence its orbit. This method is so sensitive that is capable of detecting planets as small as a tenth the mass of Earth.
Direct imaging: A star’s light reflected off a planet can be imaged directly. To probe that the object is associated with the parent star, proper motion measurements are necessary too.
The TRANSIT METHOD is a very promising method to detect extrasolar planets and has more advantages compared to other techniques. When a system is observed nearly edge-on, it is possible to observe a periodic dim of the stellar light as the planet orbits.
A transiting system allows to study several important properties of the system such as planetary period, semimajor axis, radius, mass, and therefore also its density which is not possible to determine by any other methods. In combination with the radial velocity technique, the unknown inclination of the system can be resolved and the true planetary mass (not a minimum mass) can be estimated. In addition, during transits of exoplanets the light of the host star filters through the planet’s atmosphere, and atmospheric signatures from molecules and atoms get imprinted on the transmission spectrum, that allow a characterization of the exoplanetary atmospheres and make it possible to search for biosignatures in these alien worlds. In summary, for transiting systems it is possible to study the chemical composition, internal structure, formation, and evolution of planetary systems. Therefore, the transit method has proven a high scientific return delivering a rich list of astrophysical quantities.
Currently, we are performing a campaign to monitor some known interesting incompletely studied transiting planets using several telescopes in Chile including the IRIS system. These studies will help improving the knowledge of planetary systems.
Faculty member active in this area: Maximiliano Moyano