Exploration of Mercury
Encyclopedia
The exploration of Mercury
has taken only a minor role in the space interests of the world. It is the least explored inner planet
. As of 2011, the Mariner 10
and MESSENGER
missions have been the only missions that have made close observations of Mercury. MESSENGER
made a flyby of Mercury on 14 January 2008, to further investigate the observations made by Mariner 10 in 1975. A third mission to Mercury, BepiColombo
, is to include two probes
. BepiColombo is a joint mission between Japan
and the European Space Agency
. MESSENGER and BepiColombo are intended to gather complementary data to help scientists understand many of the mysteries discovered by Mariner 10’s flybys.
Compared to other planets, Mercury is difficult to explore. The increased speed required to reach it is relatively high, and due to the proximity to the Sun, orbits around it are rather unstable. MESSENGER is the first probe to orbit Mercury.
and spins
on its own axis very slowly, its surface temperature varies from 427 °C (801 °F) to -173 °C (-279 °F). There is discussion of the possibility of terraforming
Mercury and inhabiting the poles
of the planet, but this possibility lies far in the future, being significantly less practical than terraforming Mars
. The current interest in Mercury is derived from the unexpected observations of Mariner 10. Before Mariner 10, it was thought that the planet simply revolved around the sun in a highly elliptical orbit
. The planet had been observed through ground-based telescope
s, and scientists felt that they were able to draw a great many inferences from such observations. Mariner 10 provided data that contradicted many of these.
Another reason why so few missions have targeted Mercury is that it is very difficult to obtain a satellite orbit
around the planet on account of its proximity to the Sun, which causes the Sun’s gravitation
al field to pull on any satellite that would be set into Mercury's orbit
. Furthermore, spacecraft naturally accelerate as they approach the greater gravitational pull of the Sun, but must slow down in order to orbit Mercury, so this entails considerable fuel requirements. This is different with planets beyond Earth’s orbit where the satellite works against the pull of the Sun. Mercury's lack of an atmosphere
poses further challenges because a probe attempting to land on Mercury would not be able to aerobrake or use a parachute type device. Thus it requires a great amount of energy to reach and observe the planet.
Mariner 10
was a probe
whose primary objective was to observe the atmosphere, surface, and physical characteristics of Mercury and Venus
. It was a low-cost mission completed for under $
98 million. Mariner 10 was launched at 21:45 PST
on November 2, 1973, from Cape Kennedy
. Since Mercury is so close to the Sun it was too difficult to incorporate an orbit around Mercury in the route so Mariner 10 orbited the Sun. In order to reach its destination, the satellite was accelerated with the gravity field
of Venus. It then passed close to Mercury on March 29, 1974, as it flew towards the Sun. This was the first observation made of Mercury at close range. After the encounter Mariner 10 was in an orbit around the Sun such that for every one of its orbits Mercury made two, and the spacecraft and the planet would be able to meet again. This allowed the probe to pass by Mercury two additional times before completing the mission; these encounters were made on September 21, 1974, and March 16, 1975. However, since the same side of Mercury was illuminated during each of the flybys, at the conclusion of the mission Mariner 10 had only photographed 45% of its surface. The mission was terminated by simply stopping contact with Mariner 10 on March 24, 1975. This was forced by a loss of fuel.
The close observations collected two important sets of data. The probe detected Mercury’s magnetic field
, which is very similar to Earth’s. This was a surprise to scientists, because Mercury spins so slowly on its axis. Secondly, visual data was provided, which showed the high number of craters
on the surface of the planet. The visual data also allowed scientists to determine that Mercury had “not experienced significant crustal modification
”. This also added to the mystery of the magnetic field, as it was previously believed that the magnetic fields are caused by a molten dynamo effect, but since there was little crustal modification this undermined that idea. The visual data also allowed scientists to investigate the composition and age of the planet.
is a NASA
probe in orbit of Mercury. MESSENGER stands for MErcury Surface, Space ENvironment, GEochemistry, and Ranging. It was launched from Cape Canaveral
on August 3, 2004, after a two-day delay due to bad weather. To correct the speed of the satellite it undertook gravitational slingshot flybys of planets several times. It passed by the Earth in February 2005 and then Venus in October 2006 and in October 2007. The total travel time before entering orbit is about six and a half years.
Before entering orbit in 2011, the probe made three passes of Mercury. The first two flybys took place on January 14 and October 6, 2008. There was a third encounter on September 29, 2009. During these flybys, enough data was collected to produce images of over 95% of Mercury's surface. MESSENGER uses a “chemical bi-propellant system both to reach Mercury and brake into orbit”. MESSENGER's scheduled orbital insertion took place successfully on March 18, 2011. The mission is scheduled to end sometime in 2012, when there will no longer be enough fuel to maintain the probe's orbit.
The information collected by MESSENGER will be used to try to answer six questions about Mercury:
. The European Space Agency and Japan are working in conjunction on BepiColombo and will each provide one of the orbiters. The ESA will provide MPO, while Japan will provide MMO. The BepiColombo was designed with 12 specific objectives:
Like Mariner 10 and MESSENGER, BepiColombo will use gravity slingshots from Venus and Earth. BepiColombo will use solar electric propulsion and then also use similar manoeuvres at the Moon, Venus, and Mercury. These techniques will slow the orbiters as they approach Mercury. It is essential to avoid using fuel to slow the orbiters as they get closer to the Sun to minimize the gravitational influence of the Sun.
BepiColombo is set for launch in August 2014. It is scheduled to enter orbit around Mercury in August 2019. It will then gather data for one, or possibly two years.
The MPO will have a circular orbit much closer to Mercury. The reason for this orbit is that the MPO will be taking photos of Mercury, and the close orbit will aid picture quality. On the other hand, the MMO and MESSENGER will take largely elliptical orbits. This is because of the stability of the orbit and the lower amount of fuel required to obtain and maintain the orbit. Another reason for the different orbits of MMO and MESSENGER is to provide complementary data. The data of the two combined satellites will provide more accurate measurements.
These constitute the major differences in the two missions. It is notable that some of the questions that BepiColombo is seeking answers for are very similar to those of MESSENGER. The inexplicably strong magnetic field, for example, is of interest to both missions. A more detailed discussion of differences is provided by An international program for Mercury exploration: synergy of MESSENGER and BepiColombo.
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
has taken only a minor role in the space interests of the world. It is the least explored inner planet
Terrestrial planet
A terrestrial planet, telluric planet or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun...
. As of 2011, the Mariner 10
Mariner 10
Mariner 10 was an American robotic space probe launched by NASA on November 3, 1973, to fly by the planets Mercury and Venus. It was launched approximately two years after Mariner 9 and was the last spacecraft in the Mariner program...
and MESSENGER
MESSENGER
The MErcury Surface, Space ENvironment, GEochemistry and Ranging space probe is a robotic NASA spacecraft in orbit around the planet Mercury. The spacecraft was launched aboard a Delta II rocket in August 2004 to study the chemical composition, geology, and magnetic field of Mercury...
missions have been the only missions that have made close observations of Mercury. MESSENGER
MESSENGER
The MErcury Surface, Space ENvironment, GEochemistry and Ranging space probe is a robotic NASA spacecraft in orbit around the planet Mercury. The spacecraft was launched aboard a Delta II rocket in August 2004 to study the chemical composition, geology, and magnetic field of Mercury...
made a flyby of Mercury on 14 January 2008, to further investigate the observations made by Mariner 10 in 1975. A third mission to Mercury, BepiColombo
BepiColombo
BepiColombo is a joint mission of the European Space Agency and the Japan Aerospace Exploration Agency to the planet Mercury, due to launch in 2014. The mission is still in the planning stages so changes to the current description are likely over the next few years...
, is to include two probes
Space probe
A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...
. BepiColombo is a joint mission between Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and the European Space Agency
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...
. MESSENGER and BepiColombo are intended to gather complementary data to help scientists understand many of the mysteries discovered by Mariner 10’s flybys.
Compared to other planets, Mercury is difficult to explore. The increased speed required to reach it is relatively high, and due to the proximity to the Sun, orbits around it are rather unstable. MESSENGER is the first probe to orbit Mercury.
Interest in Mercury
Mercury has not been a primary focus of many space programs. Since the planet is so close to the SunSun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
and spins
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
on its own axis very slowly, its surface temperature varies from 427 °C (801 °F) to -173 °C (-279 °F). There is discussion of the possibility of terraforming
Terraforming
Terraforming of a planet, moon, or other body is the hypothetical process of deliberately modifying its atmosphere, temperature, surface topography or ecology to be similar to those of Earth, in order to make it habitable by terrestrial organisms.The term is sometimes used more generally as a...
Mercury and inhabiting the poles
Geographical pole
A geographical pole is either of the two points—the north pole and the south pole—on the surface of a rotating planet where the axis of rotation meets the surface of the body...
of the planet, but this possibility lies far in the future, being significantly less practical than terraforming Mars
Terraforming of Mars
The terraforming of Mars is the hypothetical process by which the climate, surface, and known properties of Mars would be deliberately changed with the goal of making it habitable by humans and other terrestrial life, thus providing the possibility of safe and sustainable colonization of large...
. The current interest in Mercury is derived from the unexpected observations of Mariner 10. Before Mariner 10, it was thought that the planet simply revolved around the sun in a highly elliptical orbit
Elliptic orbit
In astrodynamics or celestial mechanics an elliptic orbit is a Kepler orbit with the eccentricity less than 1; this includes the special case of a circular orbit, with eccentricity equal to zero. In a stricter sense, it is a Kepler orbit with the eccentricity greater than 0 and less than 1 . In a...
. The planet had been observed through ground-based telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
s, and scientists felt that they were able to draw a great many inferences from such observations. Mariner 10 provided data that contradicted many of these.
Another reason why so few missions have targeted Mercury is that it is very difficult to obtain a satellite orbit
Orbital spaceflight
An orbital spaceflight is a spaceflight in which a spacecraft is placed on a trajectory where it could remain in space for at least one orbit. To do this around the Earth, it must be on a free trajectory which has an altitude at perigee above...
around the planet on account of its proximity to the Sun, which causes the Sun’s gravitation
Gravitation
Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their mass. Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped...
al field to pull on any satellite that would be set into Mercury's orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
. Furthermore, spacecraft naturally accelerate as they approach the greater gravitational pull of the Sun, but must slow down in order to orbit Mercury, so this entails considerable fuel requirements. This is different with planets beyond Earth’s orbit where the satellite works against the pull of the Sun. Mercury's lack of an atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
poses further challenges because a probe attempting to land on Mercury would not be able to aerobrake or use a parachute type device. Thus it requires a great amount of energy to reach and observe the planet.
Mariner 10
Mariner 10
Mariner 10 was an American robotic space probe launched by NASA on November 3, 1973, to fly by the planets Mercury and Venus. It was launched approximately two years after Mariner 9 and was the last spacecraft in the Mariner program...
was a probe
Space probe
A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...
whose primary objective was to observe the atmosphere, surface, and physical characteristics of Mercury and Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
. It was a low-cost mission completed for under $
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
98 million. Mariner 10 was launched at 21:45 PST
Pacific Time Zone
The Pacific Time Zone observes standard time by subtracting eight hours from Coordinated Universal Time . The clock time in this zone is based on the mean solar time of the 120th meridian west of the Greenwich Observatory. During daylight saving time, its time offset is UTC-7.In the United States...
on November 2, 1973, from Cape Kennedy
Kennedy Space Center
The John F. Kennedy Space Center is the NASA installation that has been the launch site for every United States human space flight since 1968. Although such flights are currently on hiatus, KSC continues to manage and operate unmanned rocket launch facilities for America's civilian space program...
. Since Mercury is so close to the Sun it was too difficult to incorporate an orbit around Mercury in the route so Mariner 10 orbited the Sun. In order to reach its destination, the satellite was accelerated with the gravity field
Gravitational field
The gravitational field is a model used in physics to explain the existence of gravity. In its original concept, gravity was a force between point masses...
of Venus. It then passed close to Mercury on March 29, 1974, as it flew towards the Sun. This was the first observation made of Mercury at close range. After the encounter Mariner 10 was in an orbit around the Sun such that for every one of its orbits Mercury made two, and the spacecraft and the planet would be able to meet again. This allowed the probe to pass by Mercury two additional times before completing the mission; these encounters were made on September 21, 1974, and March 16, 1975. However, since the same side of Mercury was illuminated during each of the flybys, at the conclusion of the mission Mariner 10 had only photographed 45% of its surface. The mission was terminated by simply stopping contact with Mariner 10 on March 24, 1975. This was forced by a loss of fuel.
The close observations collected two important sets of data. The probe detected Mercury’s magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
, which is very similar to Earth’s. This was a surprise to scientists, because Mercury spins so slowly on its axis. Secondly, visual data was provided, which showed the high number of craters
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
on the surface of the planet. The visual data also allowed scientists to determine that Mercury had “not experienced significant crustal modification
Geology of Mercury
The surface of Mercury is dominated by impact craters, and lava plains similar in some respects to the lunar maria. Other notable features include scarps and mineral deposits inside craters at the poles. Currently, the surface is presumed to be geologically inactive...
”. This also added to the mystery of the magnetic field, as it was previously believed that the magnetic fields are caused by a molten dynamo effect, but since there was little crustal modification this undermined that idea. The visual data also allowed scientists to investigate the composition and age of the planet.
MESSENGER
MESSENGERMESSENGER
The MErcury Surface, Space ENvironment, GEochemistry and Ranging space probe is a robotic NASA spacecraft in orbit around the planet Mercury. The spacecraft was launched aboard a Delta II rocket in August 2004 to study the chemical composition, geology, and magnetic field of Mercury...
is a NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
probe in orbit of Mercury. MESSENGER stands for MErcury Surface, Space ENvironment, GEochemistry, and Ranging. It was launched from Cape Canaveral
Cape Canaveral Air Force Station
Cape Canaveral Air Force Station is an installation of the United States Air Force Space Command's 45th Space Wing, headquartered at nearby Patrick Air Force Base. Located on Cape Canaveral in the state of Florida, CCAFS is the primary launch head of America's Eastern Range with four launch pads...
on August 3, 2004, after a two-day delay due to bad weather. To correct the speed of the satellite it undertook gravitational slingshot flybys of planets several times. It passed by the Earth in February 2005 and then Venus in October 2006 and in October 2007. The total travel time before entering orbit is about six and a half years.
Before entering orbit in 2011, the probe made three passes of Mercury. The first two flybys took place on January 14 and October 6, 2008. There was a third encounter on September 29, 2009. During these flybys, enough data was collected to produce images of over 95% of Mercury's surface. MESSENGER uses a “chemical bi-propellant system both to reach Mercury and brake into orbit”. MESSENGER's scheduled orbital insertion took place successfully on March 18, 2011. The mission is scheduled to end sometime in 2012, when there will no longer be enough fuel to maintain the probe's orbit.
The information collected by MESSENGER will be used to try to answer six questions about Mercury:
- Why is the planet so denseDensityThe mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
? - What is Mercury's geologic historyGeologic time scaleThe geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...
? - What is the structure of Mercury's corePlanetary coreThe planetary core consists of the innermost layer of a planet.The core may be composed of solid and liquid layers, while the cores of Mars and Venus are thought to be completely solid as they lack an internally generated magnetic field. In our solar system, core size can range from about 20% to...
? - What is the nature of Mercury's magnetic field?
- What are the unusual materials at Mercury's poles?
- What volatilesVolatilesIn planetary science, volatiles are that group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust and/or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, and methane, all compounds of C, H, O...
are important on Mercury?”
BepiColombo
This mission to Mercury is to include two satellites: the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO). Each orbiter has a distinct purpose: the MPO is to take images of Mercury, and the MMO is to study the magnetosphereMagnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
. The European Space Agency and Japan are working in conjunction on BepiColombo and will each provide one of the orbiters. The ESA will provide MPO, while Japan will provide MMO. The BepiColombo was designed with 12 specific objectives:
- What can we learn from Mercury about the composition of the solar nebulaSolar nebulaIn cosmogony, the nebular hypothesis is the most widely accepted model explaining the formation and evolution of the Solar System. There is evidence that it was first proposed in 1734 by Emanuel Swedenborg. Originally applied only to our own Solar System, this method of planetary system formation...
and the formation of the planetary systemPlanetary systemA planetary system consists of the various non-stellar objects orbiting a star such as planets, dwarf planets , asteroids, meteoroids, comets, and cosmic dust...
? - Why is Mercury's normalized density markedly higher than that of all other terrestrial planets, as well as the MoonMoonThe Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
? - Is the core of Mercury liquid or solid?
- Is Mercury tectonically active today?
- Why does such a small planet possess an intrinsic magnetic field, while Venus, Mars and the Moon do not have any?
- Why do spectroscopic observations not reveal the presence of any ironIronIron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
, while this elementChemical elementA chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
is supposedly the major constituent of Mercury? - Do the permanently shadowed craters of the polar regions contain sulfurSulfurSulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
or water ice? - What are the production mechanisms of the exosphereExosphereThe exosphere is the uppermost layer of Earth's atmosphere. In the exosphere, an upward travelling molecule moving fast enough to attain escape velocity can escape to space with a low chance of collisions; if it is moving below escape velocity it will be prevented from escaping from the celestial...
? - In the absence of any ionosphereIonosphereThe ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
, how does the magnetic field interact with the solar windSolar windThe solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
? - Is Mercury's magnetised environment characterized by features reminiscent of the auroraeAurora (astronomy)An aurora is a natural light display in the sky particularly in the high latitude regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere...
, radiation beltsVan Allen radiation beltThe Van Allen radiation belt is a torus of energetic charged particles around Earth, which is held in place by Earth's magnetic field. It is believed that most of the particles that form the belts come from solar wind, and other particles by cosmic rays. It is named after its discoverer, James...
and magnetosphericMagnetosphereA magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
substorms observed on Earth? - Since the advance of Mercury's perihelionApsisAn apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
was explained in terms of space-time curvature, can we take advantage of the proximity of the Sun to test general relativityGeneral relativityGeneral relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...
with improved accuracy?
Like Mariner 10 and MESSENGER, BepiColombo will use gravity slingshots from Venus and Earth. BepiColombo will use solar electric propulsion and then also use similar manoeuvres at the Moon, Venus, and Mercury. These techniques will slow the orbiters as they approach Mercury. It is essential to avoid using fuel to slow the orbiters as they get closer to the Sun to minimize the gravitational influence of the Sun.
BepiColombo is set for launch in August 2014. It is scheduled to enter orbit around Mercury in August 2019. It will then gather data for one, or possibly two years.
Comparison of MESSENGER and BepiColombo
BepiColombo was designed to complement the findings of MESSENGER and is equipped with far more measuring equipment than MESSENGER. BepiColombo is being sent to obtain a larger range of data. The orbit patterns of BepiColombo and MESSENGER are significantly different.The MPO will have a circular orbit much closer to Mercury. The reason for this orbit is that the MPO will be taking photos of Mercury, and the close orbit will aid picture quality. On the other hand, the MMO and MESSENGER will take largely elliptical orbits. This is because of the stability of the orbit and the lower amount of fuel required to obtain and maintain the orbit. Another reason for the different orbits of MMO and MESSENGER is to provide complementary data. The data of the two combined satellites will provide more accurate measurements.
These constitute the major differences in the two missions. It is notable that some of the questions that BepiColombo is seeking answers for are very similar to those of MESSENGER. The inexplicably strong magnetic field, for example, is of interest to both missions. A more detailed discussion of differences is provided by An international program for Mercury exploration: synergy of MESSENGER and BepiColombo.