Research project Homing in on Earth-like planets
Planets around other stars than the Sun are collectively called “Exoplanets”. The first exoplanets were discovered in the late 1990s, and since then, the field has rapidly developed, with thousands of exoplanets known to date.
However, the instruments and techniques used to discover and characterize exoplanets are not yet sensitive enough to discover true Earth analogs. Such planets are of particular interest since they are thought to be prime sites for life to arise and evolve. This research project aims to develop and use methods for detecting temperate planets like the Earth, in order to prepare the ground for detection of Earth analogs in the future.
Project description
Most exoplanets that have been discovered to date were found by carefully studying the brightness and spectra of stars to study how they vary over time. If a planet passes in front of a star as seen from Earth, the star momentarily looks a little bit fainter, since the planet blocks out some of the light that would otherwise have reached us. Thus, if a star displays periodical dips in brightness, this can be a sign of a planet periodically passing on front of the star. This technique for discovering planets is called the ”transit method”. Meanwhile, as a planet orbits around a star, its gravitational influence on the star causes a reflex motion in the star. When the star moves toward or away from an observer at Earth as a result of this motion, the frequency of the light it emits changes, similar to the Doppler effect that causes the apparent pitch of an ambulance to shift as the ambulance moves relative to the listener. Measuring this frequency shift in stars to discover planets is called the “radial velocity method”.
Both radial velocity and transits are excellent for discovering planets that are close to their host stars, but they are much less sensitive to planets in larger orbits. For the purpose of characterizing Earth analogs (planets with similar properties to the Earth, orbiting stars similar to the Sun) in particular, they have clear limitations. For this purpose, there are two other techniques with much more promising prospects: Astrometry, and Direct Imaging. Astrometry operates on the same physical principles as radial velocity, but instead of measuring frequency shifts, it measures the actual motion of the star in the plane of the sky. Direct imaging uses so-called high-contrast techniques to separate the stellar light from reflected or thermal planetary light - i.e., instead of using indirect techniques to find planets, it simply images the planets themselves. This research project works on developments in both astrometry and direct imaging, in order to prepare the ground for being able to detect and carefully study Earth analogs in the future.
In the field of astrometry, the project includes developing the “STARE” concept, which is a conceived microsatellite that is estimated to be sensitive enough to discover Earth analogs around alpha Centauri A or B, which are the two closest Sun-like stars outside of the Solar system. As part of the project, we have developed an optical component which functions as a beam splitter with unprecedented thermal stability, and is intended to be the central component of STARE. STARE is developed for the purpose of fitting into the Swedish microsatellite program run by the Swedish National Space Agency.
For direct imaging purposes, the project deals with several aspects of high-contrast imaging and spectroscopy. For imaging purposes, techniques using time-domain correlations in imaging data series have been developed as part of the project. In on-sky experiments, several new planets have been detected within the project. Current developments include a new technique for optimizing contrast in data with high spectral resolution. The project also includes software developments for the METIS instrument, which will be one of the first instruments on the ~40 meter diameter E-ELT telescope that is currently being built in Chile. METIS will be the first instrument with the capacity to potentially image the first Earth-like planets in the habitable zones of nearby stars, if they exist in sufficiently nearby system. For this purpose, it is also necessary to know when and where in the system to focus the observational efforts. Astrometry with STARE would be able to provide the necessary information for this purpose.
Project members
Project managers
Markus Janson
Professor
Members
Markus Janson
Professor
Gayathri Viswanath
PhD student
Simon Ringqvist
PhD student