The earliest known recorded observations of Mercury are from the
Mul.Apin
tablets. These observations were most likely made by an
Assyrian
astronomer around the 14th century BC.
[1]
The
cuneiform
name used to designate Mercury on the Mul.Apin tablets is
transcribed
as Udu.Idim.Gu\u
4
.Ud ("the jumping planet").
[b]
[2]
Babylonian records
of Mercury date back to the 1st millennium BC. The
Babylonians
called the planet
Nabu
after the messenger to the gods in
their mythology
.
[3]
The
ancient Greeks
of
Hesiod
's time called Mercury Στ?λβων (
Stilbon
), meaning "the gleaming", and ?ρμ?ων (
Hermaon
).
[4]
Later Greeks called the planet
Apollo
when it was visible in the morning sky, and
Hermes
when visible in the evening. Around the 4th century BC, however, Greek astronomers came to understand that Apollo and Hermes both
referred
to the same body. The Romans named the planet after the fast Roman messenger god,
Mercury
(Latin
Mercurius
) which they
equated
with the Greek
Hermes
, because it moves across the sky faster than any other planet in the solar system.
[5]
[6]
The Roman-Egyptian astronomer
Ptolemy
wrote about the possibility of planetary transits across the face of the Sun in his work
Planetary Hypotheses
. He suggested that no transits had been observed either because planets such as Mercury were too small to see, or because the transits were too infrequent.
[7]
Ibn al-Shatir
's model for the appearances of
Mercury
, showing the multiplication of
epicycles
using the
Tusi-couple
, thus eliminating the Ptolemaic eccentrics and
equant
.
In
ancient China
, Mercury was known as
Chen Xing
(辰星), the Hour Star. It was associated with the direction north and the phase of water in the
Wu Xing
.
[8]
Hindu mythology
used the name
Budha
for Mercury, and this god was thought to preside over
Wednesday
.
[9]
The god
Odin
(or Woden) of
Germanic paganism
was associated with the planet Mercury and
Wednesday
.
[10]
The
Maya
may have represented Mercury as an owl (or possibly four owls; two for the morning aspect and two for the evening) that served as a messenger to the
underworld
.
[11]
In ancient
Indian astronomy
, the
Surya Siddhanta
, an Indian astronomical text of the 5th century, estimates the diameter of Mercury as 3,008 miles, an error of less than 1% from the currently accepted diameter of 3,032 miles. However, this estimate was based upon an inaccurate guess of the planet's
angular diameter
as 3.0
arcminutes
.
In
medieval Islamic astronomy
, the
Andalusian
astronomer
Ab? Ish?q Ibr?h?m al-Zarq?l?
in the 11th century described the deferent of Mercury's geocentric orbit as being oval, like an egg or a
pignon
, although this insight did not influence his astronomical theory or his astronomical calculations.
[12]
[13]
In the 12th century,
Ibn Bajjah
observed "two planets as black spots on the face of the Sun," which was later suggested as the
transit of Mercury
and/or Venus by the
Maragha
astronomer
Qotb al-Din Shirazi
in the 13th century.
[14]
(Note that most such medieval reports of transits were later taken as observations of
sunspots
.
[15]
)
In India, the
Kerala school
astronomer
Nilakantha Somayaji
in the 15th century developed a planetary model in which Mercury orbits the Sun, which in turn orbits the Earth, similar to the
Tychonic system
later proposed by
Tycho Brahe
in the late 16th century.
[16]
Ground-based telescopic research
[
change
|
change source
]
Transit of Mercury
. Mercury is the small dot in the lower center, in front of the Sun. The dark area on the left of the solar disk is a
sunspot
.
The first
telescopic
observations of Mercury were made by
Galileo
in the early 17th century. Although he observed
phases
when he looked at Venus, his telescope was not powerful enough to see the phases of Mercury. In 1631
Pierre Gassendi
made the first telescopic observations of the
transit
of a planet across the Sun when he saw a transit of Mercury predicted by
Johannes Kepler
. In 1639
Giovanni Zupi
used a telescope to discover that the planet had
orbital
phases similar to Venus and the Moon. The observation demonstrated conclusively that Mercury orbited around the Sun.
[17]
A very rare event in astronomy is the passage of one planet in front of another (
occultation
), as seen from Earth. Mercury and Venus occult each other every few centuries, and the event of May 28, 1737 is the only one historically observed, having been seen by
John Bevis
at the
Royal Greenwich Observatory
.
[18]
The next occultation of Mercury by Venus will be on December 3, 2133.
[19]
The difficulties inherent in observing Mercury mean that it has been far less studied than the other planets. In 1800
Johann Schroter
made observations of surface features, claiming to have observed 20 km high mountains.
Friedrich Bessel
used Schroter's drawings to erroneously estimate the rotation period as 24 hours and an axial tilt of 70°.
[20]
In the 1880s
Giovanni Schiaparelli
mapped the planet more accurately, and suggested that Mercury’s rotational period was 88 days, the same as its orbital period due to
tidal locking
.
[21]
This phenomenon is known as
synchronous rotation
and is shown by Earth’s Moon. The effort to map the surface of Mercury was continued by
Eugenios Antoniadi
, who published a book in 1934 that included both maps and his own observations.
[22]
Many of the planet's surface features, particularly the
albedo features
, take their names from Antoniadi's map.
[23]
In June 1962
Soviet
scientists at the
Institute of Radio-engineering and Electronics
of the
USSR Academy of Sciences
lead by
Vladimir Kotelnikov
became first to bounce
radar
signal off Mercury and receive it, starting radar observations of the planet.
[24]
[25]
[26]
Three years later radar observations by Americans
Gordon Pettengill
and R. Dyce using 300-meter
Arecibo Observatory
radio telescope
in
Puerto Rico
showed conclusively that the planet’s rotational period was about 59 days.
[27]
[28]
The theory that Mercury’s rotation was synchronous had become widely held, and it was a surprise to astronomers when these radio observations were announced. If Mercury were tidally locked, its dark face would be extremely cold, but measurements of radio emission revealed that it was much hotter than expected. Astronomers were reluctant to drop the synchronous rotation theory and proposed alternative mechanisms such as powerful heat-distributing winds to explain the observations.
[29]
Italian astronomer
Giuseppe Colombo
noted that the rotation value was about two-thirds of Mercury’s orbital period, and proposed that the planet’s orbital and rotational periods were locked into a 3:2 rather than a 1:1 resonance.
[30]
Data from Mariner 10 subsequently confirmed this view.
[31]
This means that Schiaparelli's and Antoniadi's maps were not "wrong". Instead, the astronomers saw the same features during every
second
orbit and recorded them, but disregarded those seen in the meantime, when Mercury's other face was toward the Sun, since the orbital geometry meant that these observations were made under poor viewing conditions.
[20]
Ground-based observations did not shed much further light on the innermost planet, and it was not until the first space probe flew past Mercury that many of its most fundamental properties became known. However, recent technological advances have led to improved ground-based observations. In 2000, high-resolution
lucky imaging
observations were conducted by the
Mount Wilson Observatory
1.5 meter
Hale telescope
. They provided the first views that resolved surface features on the parts of Mercury which were not imaged in the Mariner mission.
[32]
Later imaging has shown evidence of a huge double-ringed impact basin even larger than the
Caloris Basin
in the non-Mariner-imaged hemisphere. It has informally been dubbed the
Skinakas Basin
.
[33]
Most of the planet has been mapped by the Arecibo radar telescope, with 5 km resolution, including polar deposits in shadowed craters of what may be water ice.
[34]
Reaching Mercury from Earth poses significant technical challenges, since the planet orbits so much closer to the Sun than does the Earth. A Mercury-bound spacecraft launched from Earth must travel over 91 million kilometers into the Sun’s
gravitational
potential well
. Mercury has an
orbital speed
of 48 km/s, while Earth’s orbital speed is 30 km/s. Thus the spacecraft must make a large change in
velocity
(
delta-v
) to enter a
Hohmann transfer orbit
that passes near Mercury, as compared to the delta-v required for other planetary missions.
[35]
The
potential energy
liberated by moving down the Sun’s
potential well
becomes
kinetic energy
; requiring another large delta-v change to do anything other than rapidly pass by Mercury. To land safely or enter a stable orbit the spacecraft would rely entirely on rocket motors.
Aerobraking
is ruled out because the planet has very little atmosphere. A trip to Mercury requires more rocket fuel than that required to
escape
the Solar System completely. As a result, only two space probes have visited the planet so far.
[36]
A proposed alternative approach would use a
solar sail
to attain a Mercury-synchronous orbit around the Sun.
[37]
The Mariner 10 probe, the first probe to visit the innermost planet
View of Mercury from Mariner 10
The first spacecraft to visit Mercury was
NASA
’s
Mariner 10
(1974?75).
[5]
The spacecraft used the gravity of
Venus
to adjust its orbital velocity so that it could approach Mercury, making it both the first spacecraft to use this
gravitational “slingshot”
effect and the first NASA mission to visit multiple planets.
[35]
Mariner 10 provided the first close-up images of Mercury’s surface, which immediately showed its heavily cratered nature, and revealed many other types of geological features, such as the giant scarps which were later ascribed to the effect of the planet shrinking slightly as its iron core cools.
[38]
Unfortunately, due to the length of Mariner 10's orbital period, the same face of the planet was lit at each of Mariner 10’s close approaches. This made observation of both sides of the planet impossible,
[39]
and resulted in the mapping of less than 45% of the planet’s surface.
[40]
On March 27, 1974, two days before its first flyby of Mercury, Mariner 10's instruments began registering large amounts of unexpected ultraviolet radiation near Mercury. This led to the tentative identification of
Mercury's moon
. Shortly afterward, the source of the excess UV was identified as the star 31
Crateris
, and Mercury's moon passed into astronomy's history books as a footnote.
The spacecraft made three close approaches to Mercury, the closest of which took it to within 327 km of the surface.
[41]
At the first close approach, instruments detected a magnetic field, to the great surprise of planetary geologists?Mercury’s rotation was expected to be much too slow to generate a significant
dynamo
effect. The second close approach was primarily used for imaging, but at the third approach, extensive magnetic data were obtained. The data revealed that the planet’s magnetic field is much like the Earth’s, which deflects the
solar wind
around the planet. However, the origin of Mercury’s magnetic field is still the subject of several competing theories.
[42]
On March 24, 1975, just eight days after its final close approach, Mariner 10 ran out of fuel. Since its orbit could no longer be accurately controlled, mission controllers instructed the probe to shut down.
[43]
Mariner 10 is thought to be still orbiting the Sun, passing close to Mercury every few months.
[44]
MESSENGER being prepared for launch
A second NASA mission to Mercury, named MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging), was launched on August 3, 2004, from the
Cape Canaveral Air Force Station
aboard a
Boeing Delta 2
rocket. It made a fly-by of the Earth in August 2005, and of Venus in October 2006 and June 2007 to place it onto the correct trajectory to reach an orbit around Mercury.
[45]
A first fly-by of Mercury occurred on January 14, 2008, a second on October 6, 2008,
[46]
and a third on September 29, 2009.
[47]
Most of the hemisphere not imaged by Mariner 10 has been mapped during these fly-bys. The probe will then enter an elliptical orbit around the planet in March 2011; the nominal mapping mission is one terrestrial year.
[46]
The mission is designed to clear up six key issues: Mercury’s high density, its geological history, the nature of its
magnetic field
, the structure of its core, whether it has ice at its poles, and where its tenuous atmosphere comes from. To this end, the probe is carrying imaging devices which will gather much higher resolution images of much more of the planet than Mariner 10, assorted
spectrometers
to determine abundances of elements in the crust, and
magnetometers
and devices to measure velocities of charged particles. Detailed measurements of tiny changes in the probe’s velocity as it orbits will be used to infer details of the planet’s interior structure.
[48]
The
European Space Agency
is planning a joint mission with
Japan
called
BepiColombo
, which will orbit Mercury with two probes: one to map the planet and the other to study its
magnetosphere
.
[49]
Once launched, the spacecraft bus is expected to reach Mercury in 2019.
[50]
The bus will release a
magnetometer
probe into an elliptical orbit, then chemical rockets will fire to deposit the mapper probe into a circular orbit. Both probes will operate for a terrestrial year.
[49]
The mapper probe will carry an array of spectrometers similar to those on MESSENGER, and will study the planet at many different wavelengths including
infrared
,
ultraviolet
,
X-ray
and
gamma ray
.
[51]
- ↑
Schaefer, Bradley E. (May 2007).
"The Latitude and Epoch for the Origin of the Astronomical Lore in Mul.Apin"
.
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Bibcode
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Hunger, Hermann (1989). "MUL.APIN: An Astronomical Compendium in Cuneiform".
Archiv fur Orientforschung
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Staff (2008).
"MESSENGER: Mercury and Ancient Cultures"
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H.G. Liddell and R. Scott (1996).
Greek?English Lexicon, with a Revised Supplement
(9th ed.). Oxford: Clarendon Press. pp. 690 and 1646.
ISBN
0-19-864226-1
.
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5.0
5.1
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Antoniadi, Eugene Michel (1974).
The Planet Mercury
. Shaldon, Devon: Keith Reid Ltd. pp. 9?11.
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Goldstein, Bernard R. (February 1996), "The Pre-telescopic Treatment of the Phases and Apparent Size of Venus",
Journal for the History of Astronomy
,
27
: 1,
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10.1177/002182869602700101
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Kelley, David H. (2004).
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ISBN
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Pujari, R.M. (2006).
Pride of India: A Glimpse Into India's Scientific Heritage
. Samskrita Bharati.
ISBN
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Bakich, Michael E. (2000).
The Cambridge Planetary Handbook
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ISBN
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Milbrath, Susan (1999).
Star Gods of the Maya: Astronomy in Art, Folklore and Calendars
. University of Texas Press.
ISBN
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Samso, Julio; Mielgo, Honorino (1994).
"Ibn al-Zarq?lluh on Mercury"
.
Journal for the History of Astronomy
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(4): 289?96 [292].
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Hartner, Willy (1955). "The Mercury Horoscope of Marcantonio Michiel of Venice".
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Ansari, S. M. Razaullah (2002).
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Goldstein, Bernard R. (December 1969). "Some Medieval Reports of Venus and Mercury Transits".
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Ramasubramanian, K.; Srinivas, M. S.; Sriram, M. S. (1994).
"Modification of the Earlier Indian Planetary Theory by the Kerala Astronomers (c. 1500 AD) and the Implied Heliocentric Picture of Planetary Motion"
(PDF)
.
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).
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Sinnott, RW (1986).
"John Bevis and a Rare Occultation"
.
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.
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Ferris, Timothy (2003).
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20.0
20.1
Colombo, G. (1965).
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.
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Holden, E. S. (1890).
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Publications of the Astronomical Society of the Pacific
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Evans, J. V.; Brockelman, R. A.; Henry, J. C.; Hyde, G. M.; Kraft, L. G.; Reid, W. A.; Smith, W. W. (1965).
"Radio Echo Observations of Venus and Mercury at 23 cm Wavelength"
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Pettengill, G. H.; Dyce, R. B. (1965). "A Radar Determination of the Rotation of the Planet Mercury".
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Murray, Bruce C. (1977).
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Davies, Merton E.; et al. (October 1976).
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Dantowitz, R. F. (2000).
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35.0
35.1
Dunne, J. A. and Burgess, E. (1978).
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.
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.
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Leipold, M.; Seboldt, W.; Lingner, S.; Borg, E.; Herrmann, A.; Pabsch, A.; Wagner, O.; Bruckner, J. (July 1996). "Mercury sun-synchronous polar orbiter with a solar sail".
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Phillips, Tony (October 1976).
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Tariq Malik (August 16, 2004).
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Merton E. Davies; et al. (1978).
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Ness, Norman F. (March 1978).
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Dunne, J. A. and Burgess, E. (1978).
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.
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Grayzeck, Ed (April 2, 2008).
"Mariner 10"
.
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- ↑
46.0
46.1
"Countdown to MESSENGER's Closest Approach with Mercury"
. Johns Hopkins University Applied Physics Laboratory. January 14, 2008
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2008-05-30
.
- ↑
"MESSENGER Gains Critical Gravity Assist for Mercury Orbital Observations"
. MESSENGER Mission News. September 30, 2009
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).
- ↑
49.0
49.1
"ESA gives go-ahead to build BepiColombo"
.
European Space Agency
. February 26, 2007
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2008-05-29
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- ↑
Fleming, Nic (January 18, 2008).
"Star Trek-style ion engine to fuel Mercury craft"
. The Telegraph
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2008-05-23
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- ↑
"Objectives"
. European Space Agency. February 21, 2006
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2008-05-29
.