Third flyby images more of unseen parts of Mercury

William Atkins
Wednesday, 04 November 2009 18:41

Science - Space

All three flybys also saw a neutral sodium tail tailing behind the planet. The first two flybys revealed dramatic tails, while this third flyby saw a diminished size for the tail.

The tail increases and decreases in size as the planet moves around the Sun (in its elliptical orbit) and variations in solar radiation pressure occur.

The NASA article goes into further details about the comet-like tail trailing Mercury in its travels around the Sun.

For additional information and images on the MESSENGER mission (and the third flyby), please go to the NASA website "MESSENGER: Unlocking the Secrets of Mercury."

The Mercury tail is described on the NASA MESSENGER website. In part the website states, "All the material in the exosphere is accelerated in the anti-sunward direction by radiation pressure; atoms and molecules at high enough altitudes for this force to overcome the gravitational influence of the planet enter Mercury’s neutral tail."

"Neutral constituents in the tail either escape the Mercury system or are ionized by solar radiation. The ionized material can also escape along open magnetic field lines but some of the ions are returned to the surface by Mercury’s magnetosphere."

And, "... emission from neutral sodium in Mercury’s tail, which extends away from the planet in the anti-sunward direction, was a factor of 10-20 less than during the second flyby. This difference is due to variations in the pressure that solar radiation exerts on the sodium as Mercury moves in its orbit."

"During the third flyby, the net effect of radiation pressure was small, and the sodium atoms released from Mercury’s surface were not accelerated anti-sunward as they were during the first two flybys, resulting in a diminished sodium tail. These predictable changes lead to what are effectively “seasonal” effects on the distribution of exospheric species."