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Topic Name: NASA Goddard Lunar Science on a Roll
Category: STAR (Space, Telecommunications & Radioscience)
Research persons: Dr. Stephen M. Merkowitz , Dr. Casey Lisse, Dr. Michael J. Mumma, Dr. Thomas Cravens , Dr. Michael Collier
Location: Suite 5K39, Washington, DC 20546-0001, United States
Details
Pack your bags because NASA Goddard's "suitcase
science" is taking off. Coming on the heels of two Lunar Sortie Science
Opportunities (LSSO) awards for NASA's
Goddard Space Flight Center in Greenbelt, Md. are two more, this time in the
field of astrophysics. As before, the awards are funded by NASA Headquarters for
studies that could result in simple, automated "suitcase science" instrument
packages deployed on the lunar surface by astronauts.
The first proposal, "Precision
Lunar Laser Ranging," is being led by Goddard astrophysicist Dr. Stephen
Merkowitz. The proposal could lead to suitcase-sized laser reflector arrays
and/or laser transponders at various locations on the moon so the distance from
Earth to the moon can be determined to the submillimeter level. The laser
transponders also could be eventually deployed on Mars for the same purpose.
Over the past 35 years,
laser ranging to retroreflector
arrays placed on the lunar surface have dramatically increased mankind's
understanding of gravitational physics along with Earth and
Moon geophysics,
geodesy, and dynamics. "Significant advances in these areas will require placing
modern retroreflectors and/or active laser ranging systems at new locations on
the lunar surface," Merkowitz said.
Retroreflectors
are extremely robust, do not require power, and will last for years. This
longevity is important for studying long-term effects such as a possible time
variation of the gravitational constant. However, to make a large leap in lunar
ranging accuracy and to precision range to planets such as Mars, an active laser
ranging system will be required. Over the next year, Merkowitz and his
colleagues will perform a concept study for a lunar ranging flight experiment
that will enable unprecedented tests of Einstein's theory of General Relativity
in addition to providing valuable data on the interior structure of the Moon and
Earth-Moon interactions.
The second proposal is for a
Lunar X-ray Observatory (LXO), and it began with the mysterious case of the
glowing comet. In 1996, a team of scientists including Goddard's Dr. Casey Lisse
(now at Johns Hopkins University) and Dr.
Michael Mumma observed comet Hyakutake with the ROSAT satellite. They were
surprised to see it glowing in soft (low-energy) X-rays. This was unexpected
because X-rays are usually given off by hot things in the universe, and comets,
being a lump of ice and dust, are cold.
It was actually the breath of the sun causing the glow,
according to Dr. Thomas Cravens of the University
of Kansas, Lawrence, a member of the LXO team. The sun continually blows a
thin gas of electrically charged particles (plasma) into space in all
directions. This is called the solar wind. Cravens knew that the solar wind
contains atoms with a lot of positive electric charge (oxygen and iron ions).
Since opposite electric charges attract, he reasoned that these positive solar
wind ions would steal negatively charged electrons from electrically neutral
atoms emitted by the comet as its surface vaporized. The ion with the stolen
electron would initially be highly energetic, but as it relaxed to a less
energetic state, it would get rid of the extra energy by emitting a soft X-ray.
This phenomenon, dubbed Solar Wind Charge Exchange, or SWCX, was responsible for
the mysterious
X-ray glow around the comet.
"The LXO team realized that since the solar wind blows through
the solar system, we should see X-rays from SWCX throughout the solar system,"
said Goddard's Dr. Michael Collier, Principal Investigator for LXO.
"Particularly exciting is the ability to see the boundary of the vast region of
space around Earth that's dominated by our planet's magnetic field, called the
magnetosphere."
Interaction between the solar wind and the boundary of the
magnetosphere causes space weather effects that can disrupt satellites, radio
communication, and power systems. "This boundary is not visible in the ordinary
light seen by our eyes, so typically spacecraft have to travel through it to get
measurements. But this area is huge, extending past the moon's orbit on Earth's
night side, and spacecraft exploring the
magnetosphere only give
us information about a single tiny point. However, by observing the soft X-rays
emitted from near the magnetosphere by SWCX, we can see the big picture – a
global view. An observatory on the moon provides a terrific vantage point."
The team will be able to string X-ray images from the LXO
together to make movies that show how the boundary between the magnetosphere and
the solar wind reacts to changes in the solar wind. "Energy transport across
this boundary, called the magnetopause, is responsible for the disruptive space
weather phenomena. The ability to see this happen on a global scale is key to a
better understanding of space weather," said Collier.
The team will also use LXO to improve
astrophysics
observations. Astrophysicists are trying to determine the nature and extent
of the Local Hot Bubble, a region around our solar system and nearby stars where
the interstellar gas is unusually thin. (One theory is that it was cleared by a
shock wave from an exploding star.) However, soft X-rays from SWCX in our solar
system interfere with observations of soft X-rays emitted by the bubble.
Astronomers have a hard time determining if the soft X-ray came from our own
solar system, or from the distant regions of the bubble. "Our observations with
LXO will help improve understanding of SWCX and allow astrophysicists to correct
for its interference," said Collier.
LXO will also observe the solar wind as it hits the lunar
surface. The solar wind, along with the sun's ultraviolet radiation, causes the
lunar surface on the day side to become positively charged and the night side to
become negatively charged. The different charges cause
electrostatic dust
transport – dust moves between the day and night side.
This electrically charged dust could stick to spacesuits and
machinery. Since the moon has almost no atmosphere, countless tiny meteorites
have hit the lunar surface over billions of years, forming dust that is jagged
and sharp. If this dust becomes embedded in spacesuits and machinery, it could
cause them to fail over time. "By observing how much the solar wind contributes
to surface charging, we can estimate how significant the dust hazard will be to
explorers," said Collier.
"The LXO has many applications, from plasma physics to astronomy
to lunar and planetary exploration. It takes a very rare organization like
Goddard, with experts in all these areas, to successfully undertake such a
project," said Collier.
The LXO LSSO study team includes members from Goddard, the
University of Kansas, the Johns Hopkins University, Baltimore, Md., the
University of Maryland, Baltimore County, Leicester University, United Kingdom,
and the Institute for Atmospheric Physics, Academy of Science, Czech Republic.
About Researhcer:
Dr. Stephen M. Merkowitz
Astrophysics Science Division
NASA/GSFC
Code 663, Gravitational Astrophysics Laboratory
Greenbelt, MD 20771
tel: 301-286-9412
fax: 301-286-1684
e-mail: Stephen.M.Merkowitz @ nasa.gov
Dr. Casey Lisse
Email:
carey.lisse@jhuapl.edu
Dr. Michael J.
Mumma
NASA/GSFC, Code 690
Greenbelt, MD 20771
Phone: (301) 286-6994
Fax: (301) 286-0212
Voice: (410) 544-1273(home)
Email: mmumma@lepvax.gsfc.nasa.gov
PRESENT
POSITION:
Chief Scientist, Planetary and Astrophysical Sciences
Laboratory for Extraterrestrial Physics
NASA/Goddard Space Flight Center
EDUCATION:
A.B. (Physics, with Honors - 1963) Franklin and Marshall College
Ph.D. (Physics - 1970) University of Pittsburgh
Assorted Management Training Workshops and Courses (1975-1984)
NASA Management Education Program (1981
Dr. Thomas Cravens
3093 Malott Hall
TEL: (785) 864-4739
FAX: (785) 864-5262
Email: cravens@ku.edu
HomePage:
http://www.ku.edu/~kuspace/tec.html
PROFESSIONAL BACKGROUND
1991-present, Professor: University of Kansas
1988-1991 Associate Professor: University of Kansas
1975: Ph.D. Astronomy, Harvard University
1970, B.S. Physics, Summa Cum Laude, State University of New York at Stony Brook
Related Online Resources:
http://www.nasa.gov/goddard/
http://www.physorg.com/news106838029.html
http://www.ion-development.com/suitcase-science-c-41.html
http://www.csr.utexas.edu/mlrs/
http://www.csr.utexas.edu/mlrs/dda.html
http://www.retroreflectors.com/
http://www.planetary.org/explore/topics/chandra/
http://www.nasa.gov/
http://www.nasa.gov/centers/goddard/news/topstory/2007/lsso2.html
http://www.gsfc.nasa.gov/
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