The Cirrus Cloud Greenhouse on Early Mars: An Explanation, The Explanation, or No Explanation for Rivers and Lakes?
Abstract
Observations at Gale crater and elsewhere show that precipitation-fed rivers and lakes formed on Mars as late as the Late Hesperian and Amazonian. Bolide-impact energy does not account for these data, so we need a climate-warming mechanism that can operate under Late Hesperian and Amazonian conditions - presumably including a relatively thin atmosphere. One candidate warming mechanism is the H2O-ice-cloud greenhouse, proposed by Urata & Toon (Icarus, 2013) and also by Haberle et al. (LPSC, 2012). Although H2O-ice clouds can produce extremely strong warming on early Mars under ideal conditions, this hypothesis remains controversial; for example, some modelers find little or no warming due to a lack of H2O-cloud formation at high altitudes (Wordsworth, Annual Reviews, 2016). We have reproduced the cirrus-cloud greenhouse in the MarsWRF GCM. At the conference, we will discuss the strength and duration of the corresponding warming. We will also discuss how the cloud greenhouse depends on orbital conditions - and on the size and albedo of the ice cap that acts as the surface water vapor source. Finally, we will combine the spatial resolution of the GCM with constraints on the history of Mars' obliquity to assess the likelihood that the cloud greenhouse can explain the geologic record of late-stage rivers and lakes on Mars.
Author contributions: E.S.K. and L.J.S. designed the work. L.J.S. set up and carried out the model runs. L.J.S. and E.S.K. interpreted the results. M.A.M. supplied his fork of the MarsWRF model.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.P51F2942K
- Keywords:
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- 5210 Planetary atmospheres;
- clouds;
- and hazes;
- PLANETARY SCIENCES: ASTROBIOLOGYDE: 5225 Early environment of Earth;
- PLANETARY SCIENCES: ASTROBIOLOGYDE: 6207 Comparative planetology;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTSDE: 6296 Extra-solar planets;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS