* Astronomy

Exploring Mercury by Spacecraft: The MESSENGER Mission

The third lecture in the 2011 Exploring Space Lecture Series featured Sean C. Solomon, the Principal Investigator for the MESSENGER mission and the Director of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington.
Until recently, Mercury was the least explored of the terrestrial planets, visited only by Mariner 10 in the 1970s. MESSENGER flybys in 2008 and 2009 revealed terrain seen by spacecraft for the very first time. In March 2011, as MESSENGER went into orbit, it opened a new era of comprehensive observation and study of the innermost planet, and continues to contribute to our understanding of the nature of Mercury and why it is different from its planetary neighbours. See Mercury in a new light as Sean Solomon guides us through the latest images and results.
Presented as a live webcast on Thursday, May 12, 2011 at 8pm ET at the National Air and Space Museum in Washington, DC.

Mercurys Magnetic Mysteries - MESSENGER  results after six months in orbit

MESSENGER scientists will highlight the latest results on Mercury from MESSENGER observations obtained during the first six months (the first Mercury solar day) in orbit. These findings will be presented October 5 in 30 papers and posters as part of a special session of the joint meeting of the European Planetary Science Congress and the Division for Planetary Sciences of the American Astronomical Society in Nantes, Frances.
Scientists will also look ahead to MESSENGER observations still to come and to the dual-spacecraft BepiColombo mission of the European Space Agency and the Japan Aerospace Exploration Agency's later this decade.
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Title: Mercury and frame-dragging in light of the MESSENGER flybys: conflict with general relativity, poor knowledge of the physical properties of the Sun, data reduction artifact, or still insufficient observations?
Authors: Lorenzo Iorio

The Lense-Thirring precession of the longitude of perihelion of Mercury, as predicted by general relativity by using the value of the Sun's angular momentum S = 190 x 10^39 kg m^2 s^-1 from helioseismology, is -2.0 milliarcseconds per century, computed in a celestial equatorial reference frame. It disagrees at 4-{\sigma} level with the correction 0.4 ±0.6 milliarcseconds per century to the standard Newtonian/Einsteinian precession. It was recently determined in a global fit with the INPOP10a ephemerides to a long planetary data record (1914-2010) including also 3 data points collected in 2008-2009 from the MESSENGER spacecraft. The INPOP10a models did not include the solar gravitomagnetic field at all, so that its signature might have partly been removed in the data reduction process. On the other hand, the Lense-Thirring precession may have been canceled to a certain extent by the competing precession caused by a small mismodeling in the quadrupole mass moment of the Sun, actually modeled, of the order of (0.1-0.2) x 10^-7. Future analysis of more observations from the currently ongoing MESSENGER mission will shed further light on such an issue which, if confirmed, might potentially challenge our present-day picture of the currently accepted laws of gravitation and/or of the physical properties of the Sun.

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Ed ~ Deriving any meaningful frame-dragging data from MESSENGER flybys will be very difficult, due to a host of other forces constantly affecting the spacecrafts trajectory, the time scale, and mission constraints.

MESSENGER performed a successful Earth flyby a year after launch, on August 2, 2005, with the closest approach at 19:13 UTC at an altitude of 2,347 kilometres over central Mongolia.
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