Terra Hunting - extreme precision mass-measurements of Earth-like worlds


Despite the fact that astronomers have discovered over 4,000 extrasolar planets orbiting other stars, none of these planets resemble our own Earth. The reasons for this are many. For example, the detection methods needed to detect and fully characterise Earth-analogues are biased towards high-mass, large-radius planets in short orbits. In addition, surface motions and magnetic activity on the host star introduce signals larger than those expected when employing the Doppler wobble technique to measure the mass of an Earth-analogue. Finally, only recently (with the commissioning of ESPRESSO) have instruments reached the precisions needed to measure the mass of an Earth-analogue alien planet.

Nonetheless, we are rapidly detecting ever smaller and less-massive terrestrial (rocky) worlds in increasingly long orbits. Looking to the medium-term, the ~€600M European Space Agency PLATO (PLAnetary Transits and Oscillations) mission is specifically designed to detect the tiny dips of light caused by the transits of Earth-sized planets orbiting in the habitable zones around other Sun-like stars. Due to launch in ~2027, PLATO will discover the locations of these Earth-analogue candidates. However, only by determining the masses of exoplanets via the Doppler wobble method can these discoveries be confirmed, and their densities and compositions ascertained. Unfortunately, astrophysical noise sources (due to signatures of stellar activity such as star spots and plage) as well as other surface inhomogeneities (e.g. granulation and meridional flows) can mask the Doppler signatures of such planets. Indeed, such astrophysical signals are now what fundamentally limits our ability to confirm Earth-2.0 - not the quality of our instruments.

This project

The aim of this PhD is to quantify and understand the effects of stellar activity on Doppler wobble measurements - performing cutting edge science crucial to the discovery of Earth-sized planets as well as for studying the evolution of planetary systems. At QUB, we have discovered a new set of hundreds of stellar-activity indicators - hitherto unrealised. These new activity indicators contain a wealth of information on the location, size, and physical nature of the stellar activity on the observed star. We wish to now use these new indicators to track and predict the amplitude of the astrophysical signals they produce, and remove these from the observed Doppler wobble measurements needed to determine planetary masses. This fits into a global effort exploiting a number of world-class facilities in which QUB plays a prominent role. For example, we have recently joined the Terra Hunting Experiment, an ambitious decade-long intense Doppler wobble survey of ~40 stars led by the 2019 Nobel prize winner Prof. Didier Queloz. We are also one of 3 UK members of the HARPS-N (High Accuracy Radial-velocity Planet Searcher) international consortium (including Harvard and Geneva), and also have access to the HARPS-N Solar telescope, which provides exoplanet observation-grade Doppler wobble measurements of our own Sun. It is expected that the PhD student will contribute to these projects as a natural by-product of his/her work.


The PhD student will develop skills that are highly sought after within the astronomical community, including experience in the reduction of high-resolution spectroscopic data, and obtaining an understanding of atmospheric processes and planet evolution. We would also anticipate trialling machine-learning algorithms - though previous experience of such techniques is not required. The project will give the student a competitive edge in astronomy, having developed a track record in a blossoming research area, while the computational and analytical aspects of this project will instil skills highly sought after in industry and business.

More info

Supervisor: Dr. Chris Watson c.a.watson@qub.ac.uk

public/phds2020/2020_watson.txt · Last modified: 2020/01/13 09:30 by Chris Watson

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