[meteorite-list] MESSENGER Finds Evidence of Ancient Magnetic Field on Mercury

[Ron Baalke]

http://messenger.jhuapl.edu/news_room/details.php?id=285

MESSENGER Mission News
May 7, 2015

MESSENGER Finds Evidence of Ancient Magnetic Field on Mercury

Mercury's magnetic field, generated by a dynamo process in its outer core, 
has been in place far longer than previously known, a paper by MESSENGER 
Participating Scientist Catherine Johnson reports.

About 4 billion years ago, Mercury's magnetic field could have been much 
stronger than today, as indicated by low-altitude observations made by 
NASA's MESSENGER spacecraft that revealed evidence of magnetization of 
ancient crustal rocks on Mercury.

The MESSENGER spacecraft crashed onto Mercury last week after running 
out of fuel, but the mission provided a trove of new information on the 
planet closest to the Sun.

"From MESSENGER and Mariner 10 observations we already knew that Mercury 
has had a global magnetic field today and 40 years ago," said Johnson, 
a senior scientist at the Planetary Science Institute and lead author 
of "Low-altitude Magnetic Field Measurements by MESSENGER Reveal Mercury's 
Ancient Crustal Field," published today in the journal Science. Johnson 
is also a Professor of Geophysics at the University of British Columbia, 
Vancouver.

With MESSENGER orbiting Mercury closer than 100 kilometers from the planet's 
surface, the spacecraft's Magnetometer instrument that measures magnetic 
field strength and direction was able to resolve signals too small to 
be detected earlier at higher altitudes. The observed decrease in signal 
strength measured with changes in altitude from 15 to 80 kilometers confirms 
that the signals are due to the presence of magnetized crustal rocks, 
Johnson said.

Mercury is the only inner solar system body other than Earth that currently 
possesses a global magnetic field generated by a dynamo in a fluid metallic 
outer core. In Mercury, as in Earth, the outer core is molten iron.

"Magnetized rocks record the history of the magnetic field of a planet, 
a key ingredient in understanding its evolution," Johnson said. "We already 
know that around 3.7 to 3.9 billions years ago Mercury was volcanically 
and tectonically active. We now know that it also had a magnetic field 
at around that time."

"If we didn't have the recent very low-altitude observations, we would 
never have been able to discover these signals," said Johnson. "Mercury 
has just been waiting to tell us its story."

Visit http://www.psi.edu/news/mercurymagnetism for some images relating 
to Johnson's research. See also 
http://news.ubc.ca/2015/05/07/messenger-reveals-mercurys-magnetic-field-secrets/ .

Media Contact: Alan Fischer, Planetary Science Institute, 520-382-0411, 
520-622-6300, fischer at psi.edu .

Science Contact: Catherine Johnson, Senior Scientist, 619-846-9566, cjohnson at psi.edu.

--------------------------------------------------------
MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) 
is a NASA-sponsored scientific investigation of the planet Mercury and 
the first space mission designed to orbit the planet closest to the Sun. 
The MESSENGER spacecraft launched on August 3, 2004, and entered orbit 
about Mercury on March 17, 2011 (March 18, 2011 UTC), to begin a study 
of its target planet. After more than four years in orbit about Mercury, 
MESSENGER crashed into the planet on April 30, 2015. Dr. Sean C. Solomon, 
the Director of Columbia University's Lamont-Doherty Earth Observatory, 
leads the mission as Principal Investigator. The Johns Hopkins University 
Applied Physics Laboratory built and operated the MESSENGER spacecraft 
and manages this Discovery-class mission for NASA.