Some highlights from the AGU journals

The AGU have published a few research highlights from recent copies of the Journal of Geophysical Research – Atmospheres and Geophysical Research Letters. Some of these have some interest for astrophysics, and these include:

More evidence ice is common on the Moon. Researchers using archived data from Lunar Prospector, launched on the 7th of January 1998 and which ran for 570 days, to determine an estimate for the amount of water ice present. LP had a Neutron Spectrometer that was able to detect a signal from hydrogen. Since the confirmation that at least some of the hydrogen is in the form of water ice in shadowed craters, researchers returned to these proxy results and compared where they said the hydrogen was to the actual terrain of the Moon. The LP results show the detected hydrogen existed mostly in shadowed craters, lending credence to the idea that it is indeed locked into water ice. The spectrometer works by measuring the number of cosmic ray neutrons that have undergone elastic collisions with hydrogen and therefore transferred all kinetic energy over, leaving just thermal energy behind. The spectrometer had a sensor that was shielded from these low energy particles and one that wasn’t, the difference in signal indicating hydrogen amounts.

The thermosphere has contracted. The outer layer of the neutral atmosphere, the Thermosphere, has contracted and now has the lowest mass density at any time during the space age. The low solar activity has reduced the amount of EUV radiation absorbed and therefore heating up the thermosphere, the increased amounts of carbon dioxide have cooled the thermosphere more than average, but a significant amount of the contraction is thought to be due to chemical and dynamical effects in the mesosphere. This is good news for satellites, which now experience less drag at a given altitude than ever before.

Solar wind laps against Mercury’s magnetosphere. When two liquids pass over one another, waves form between them called Kelvin-Helmholtz waves. As the solar wind passes around Earth, these undulations can allow charged particles moving faster than them in one of the plasmas to pass into another, mass loading the Earth’s magnetosphere with particles from the solar wind. The MESSENGER spacecraft presently at Mercury performed a number of passes from solar wind dominated areas to areas controlled by the magnetic field of Mercury (its magnetosphere). Data gathered from these passes show the characteristic signature of Kelvin-Helmholtz waves operating at the magnetopause boundary, suggesting a similar mechanism for loading solar wind particles could be happening at Mercury too.


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