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Dark streaks that appear on the surface of Mars during warm seasons have been observed at the mid-latitudes and tentatively attributed to the flow of briny water. Imagery from the Mars Reconnaissance Orbiter over multiple Mars years suggests that these seasonally active features are also present in equatorial regions, where liquid surface water is not expected.
The Archaean rocks of Isua, West Greenland, contain graphite, but its origins are debated. Geochemical and microscopic analyses suggest that the graphite was formed from biologically formed carbon that was deposited at least 3.7 billion years ago.
In many planetary atmospheres, including that of Earth, the base of the stratosphere—the tropopause—occurs at an atmospheric pressure of 0.1 bar. A physically based model demonstrates that the pressure-dependence of transparency to infrared radiation leads to a common tropopause pressure that is probably applicable to many planetary bodies with thick atmospheres.
The Archaean Earth was much hotter than today. Numerical modelling shows that the base of thickened crust that formed at the time would have been so dense that it dripped back into the mantle.
Liquid water may lurk beneath the frozen surfaces of Jupiter's moon Europa and other icy worlds. Extending ocean science beyond Earth, planetary oceanographers are linking Europa's ocean dynamics to its enigmatic surface geology.
At mid-ocean ridges, the movements between rift segments are usually accommodated by transform faults that are oriented perpendicular to the rift axis. Analysis of seismic data from rift segments exposed in Iceland shows that such movements can also occur through the rotation of several small faults and crustal blocks that slip like books tilting on a shelf.
Great earthquakes in the Himalaya are thought to occur mostly along the range front. Field mapping and radiocarbon dating reveal earthquake rupture on a previously unrecognized fault in the interior of the western Himalaya, which forms part of a key structural component of the mountain range, implying that seismic risk evaluations should be revised.
On Jupiter’s icy moon Europa, enigmatic chaos terrain—where the icy crust is cut by a jumble of ridges and cracks—occurs most commonly at lower latitudes. Simulations of convection in the ocean underlying Europa’s icy crust suggest that ocean dynamics can control an enhanced flow of heat to Europa’s equatorial surface, and hence geological activity.
The volume of Archaean crust preserved at Earth’s surface today is low. Thermodynamic calculations and geodynamic modelling show that the thick, primary crust that would have formed on a much hotter Archaean Earth was denser than the underlying mantle, and would have therefore been recycled back into the mantle as drips.
The Chelyabinsk fireball highlighted the threat of asteroids and comets. But actually, for life on Earth, impacts may have once played the role of hero.
Significant quantities of the ozone and aerosol precursor isoprene are released into the atmosphere in densely forested regions of the world. Experimental observations suggest that the oxidation of isoprene in these pristine environments adds to the self-cleansing capacity of the atmosphere.
Following almost three decades of some certainty over how the Moon was formed, new geochemical measurements have thrown the planetary science community back into doubt. We are either modelling the wrong process, or modelling the process wrong.
Antarctic temperatures and atmospheric carbon dioxide levels generally co-varied at the end of glacial periods. Detailed analysis of an Antarctic ice core suggests a decoupling during the deglaciation 130,000 years ago, possibly linked to a strengthening of ocean circulation.
The Indian Ocean Dipole is a key mode of interannual climate variability influencing much of Asia and Australia. A Review suggests that in response to greenhouse warming, mean conditions of the Indian Ocean will shift toward a positive dipole state, but with no overall shift in the frequency of positive and negative events as defined relative to the mean climate state.
