Institute of Astronomy

Mr Alan Jackson


Office: Hoyle H29
Office Tel: (01223) 766645
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Research Themes: Star Formation and Exoplanets

Research Keywords: Planets, Solar System


I study the formation and evolution of planetary systems, both massive planetary bodies and belts of small material, working primarily with Dr Mark Wyatt.

At the moment I am particularly working on the era of giant impacts thought to be the final stage of terrestrial planet formation, in which planetary embryos 2000-3000 km in size undergo mutual collisions eventually forming Earth-sized planets.  Giant impacts have been used to explain a number of the features of the terrestrial planets in our own solar system; how Earth came to have such a large moon, why the Martian Northern hemisphere is depressed relative to the Southern hemisphere (Martian hemispheric dichotomy) and why Mercury is so dense.
Much recent work has shown that although giant impacts are expected to be common in the late stages of terrestrial planet formation they are not very efficient.  Often the two bodies have a grazing encounter, and get slightly disrupted, but otherwise continue on their separate ways afterwards (called 'hit-and-run' encounters).  All giant impacts will produce significant amounts of dust and debris regardless of what happens to the large bodies so if many giant impacts are hit-and-runs more impacts are needed before big terrestrial planets can be formed and the total amount of debris produced during the planet forming process increases.  This debris forms disks around the host star that are generally much easier to detect than the forming terrestrial planets meaning a better way of looking for terrestrial planet formation might be to look for dust.  Comparisons between hot dust found by infrared surveys and planets found by experiments such as the Kepler mission then provide an important test for theories of terrestrial planet formation

I have also worked on the evaporation of very close orbiting gas giants by X-ray emissions from their host star.  Young sun-like stars rotate more rapidly, have stronger magnetic fields and more active coronae that have much stronger X-ray emission.  X-rays are strongly absorbed in the upper atmosphere and strong X-ray irradiation can heat the upper atmosphere so much that it simply boils away.  For a giant planet close enough to its host star this can lead to a large fraction of the envelope being stripped off.

Selected papers

  • Debris from terrestrial planet formation: the Moon-forming collision
    Jackson A.P., Wyatt M.C., 2012, MNRAS, 425, 657
  • Planetary evaporation by UV & X-ray radiation: basic hydrodynamics
    Owen J.E., Jackson A.P., 2012, MNRAS, 425, 2931
  • The coronal X-ray-age relation and its implications for the evaporation of exoplanets
    Jackson A.P., Davis T.A., Wheatley P.J., 2012, MNRAS, 422, 2024


2010 - present: PhD student, Institute of Astronomy, Cambridge University


2010 - MPhys  (Hons) Oxford University

Page last updated: 30 May 2013 at 11:11