Professor Wordsworth's research is focused on the processes that shape planetary climate and habitability, both in the Solar System and around other stars. Currently active research topics include the nature of Mars' atmosphere and hydrological cycle during the late Noachian (ca. 3-4 billion years ago), the rate of water loss from Earth and Venus soon after their formation, and the extent to which molecules like O2 can be treated as markers for carbon-based life in the atmospheres of rocky planets around other stars.
R. Wordsworth, in prep. 2014: What determines the nitrogen content of Earth's atmosphere?
R. Wordsworth, L. Kerber, R. Pierrehumbert, F. Forget and J. Head, under review 2014: Global constraints on the climate of early Mars from the global distribution of valley networks
S. Guerlet et al., Icarus 2014: Global climate modeling of Saturn's atmosphere. Part I: Evaluation of the radiative transfer model
B. Charnay, F. Forget, G. Tobie, C. Sotin and R. Wordsworth, Icarus 2014: Titan's past and future: 3D modeling of a pure nitrogen atmosphere and geological implications
R. Wordsworth and R. Pierrehumbert, ApJ Letters 2014: Abiotic oxygen-dominated atmospheres on terrestrial habitable zone planets
In this note, we showed that oxygen-dominated atmospheres can appear on Earth-like exoplanets if their atmospheric nitrogen inventory is low. This poses a challenge for extraterrestrial life hunters, because oxygen is generally regarded as a good potential indicator of the presence of life (biosignature).
J. Leconte, F. Forget, B. Charnay, R. Wordsworth and A. Pottier, Nature 2013:
Increased insolation threshold for runaway greenhouse processes on Earth-like planets
This paper addressed the runaway greenhouse problem using the previously developed 3D climate model with a new scheme for moist convection. An interesting positive feedback was found when radiatively active clouds were included.
R. Wordsworth and R. Pierrehumbert, ApJ 2013: Water loss from terrestrial planets with CO2-rich atmospheres
The aim of this paper was to investigate the evolution of water-rich planets (which may be common in the galaxy). Contrary to previous work, we found that causing water loss to space by adding CO2 to the atmosphere is very difficult in general. This suggests that many Earth-mass exoplanets could therefore have ocean-covered surfaces and CO2-rich atmospheres. Further work on interior processes is needed to confirm this, but the potential implications are big, because any geochemical or biological cycles on ocean planets would be radically different from those we are used to on Earth.
B. Charnay, F. Forget, R. Wordsworth, J. Leconte, E. Millour and F. Codron, JGR 2013:
The faint young Sun problem and the possible climates of the Archean Earth with a 3D GCM.
This paper found that CO2-rich atmospheres appear to be pretty effective at warming the young Earth (unlike the case for early Mars).
R. Wordsworth and R. Pierrehumbert, Science 2013: Hydrogen-nitrogen greenhouse warming in Earth's early atmosphere
Here we showed that for terrestrial planets, H2 and N2 can have a significant greenhouse effect in large quantities, because their collision-induced absorption blocks emission from the 8-12 um water vapour window. If early Earth's atmosphere was hydrogen and nitrogen rich, this would have helped save it from runaway glaciation (snowball Earth). The mechanism also means that hydrogen-rich exoplanets could sustain surface liquid water even if they're far from their host stars, because neither N2 nor H2 condense nearly as easily as CO2.
K. E. Scanlon, James W. Head, J.-B. Madeleine, R. Wordsworth, and F. Forget, GRL 2013: Orographic precipitation in valley network headwaters: Constraints on the ancient Martian atmosphere.
J. Leconte, F. Forget, B. Charnay, R. Wordsworth, F. Selsis, E. Millour and A. Spiga, A&A 2013: 3D climate modeling of close-in land planets: Circulation patterns, climate moist bistability, and habitability
L. Kerber, F. Forget, J.-B. Madeleine, R. Wordsworth, J. Head and L. Wilson, Icarus 2013: The effect of atmospheric pressure on the dispersal of pyroclasts from martian volcanoes
R. Wordsworth, F. Forget, E. Millour, J. Head, J.-B. Madeleine and B. Charnay, Icarus 2012: Global modelling of the early Martian climate under a denser CO2 atmosphere: Water cycle and ice evolution
F. Forget, R. Wordsworth, E. Millour, J.-B. Madeleine, L. Kerber, J. Leconte, E. Marcq and R.M. Haberle, Icarus 2012: Global modelling of the early Martian climate under a denser CO2 atmosphere: Temperatures and CO2 ice clouds
In these two papers we described the first simulations of the water cycle and climate on early Mars using a realistic 3D climate model. Forget et al. focused on the dry case and confirmed our suspicions from 1D modelling: no matter how much CO2 you put in the atmosphere, early Mars would have been freezing cold.
In the second paper, we included a full water cycle, and found something very interesting: due to adiabatic surface cooling, ice tends to migrate to highland regions when the atmosphere is thicker. This led us to propose a new paradigm for the early Martian climate that we dubbed the 'icy highlands' hypothesis. I'm currently working with geologists and surface modelers to see the extent to which this hypothesis can explain surface features such as the dendritic valley networks and open-basin crater lakes.
R. Wordsworth, Icarus 2012: Transient conditions for biogenesis on low-mass exoplanets with escaping hydrogen atmospheres
In this paper I proposed that transient hydrogen-rich atmospheres on young rocky planets could lead to surface conditions where life could form. The idea is speculative, but if it's correct the implications are pretty important, because conditions for biogenesis could be common. In my mind, the question of when conditions for life to begin occur is probably much more important than that of habitabilty as usually defined. However, it's far more rarely considered in exoplanet research.
- *E-PSCI 160. Space Science and Engineering: Theory and Applications
- Engineering Sciences 237: Planetary Radiation and Climate
Gladys Prins (617) 384-8069