Mission to Mercury
BepiColombo
MIO - Mercury Magnetospheric Orbiter-

Humanity vs. Mercury
15-year development, 7-year cruise

Institute of Space and Astronautical Science
http://www.isas.jaxa.jp/e/

A project transcending both generations
and borders in the challenge to explore Mercury©ESA/ATG medialab

The Moon's Look-Alike
With a surface covered in craters, Mercury
closely resembles the Moon in appearance.
However, terrain has also been discovered"Finally, here we are. If this were a marathon, we would be standing on the starting line. We still

peculiar to Mercury and not seen on the Moon.

have a long way to go until we reach the goal of mission accomplished. However, I am looking

Many mysteries remain as to how this was created.

forward to the many unlocked mysteries and discoveries we will make upon arrival. "Hajime HAYAKAWA

600℃ Temperature Diﬀerence
Mercury is a planet with a very harsh environment. As

BepiColombo Project: the First Large-Scale International Cooperative Mission

the closest planet to the Sun, Mercury receives sunlight

BepiColombo is an international plan to explore Mercur y led byten times stronger than that on Earth. The surface

cooperation between the Japan Aerospace Exploration Agency (JAXA)

temperature of Mercury reaches as much as 430 ℃

and the European Space Agency (ESA). This challenge of this large-scale

during the day. at night the temperature drops to about

Mercury,

minus 170℃, because of heat escaping into space duein the Solar System

Mercury is the smallest planet in the Solar System, with

the nearest planet to the Suninternational cooperative mission is to simultaneously send two spacecraft
to orbit Mercury ̶MPO (the Mercury Planetary Orbiter) led by ESA andto the lack of a thick atmosphere such as on Earth.
©ESA

Rocky Planet Like Eartha size less than half that of the Earth. Despite its smallsize, the density of Mercury is roughly equal to that ofthe Earth and it is thought that the interior contains a

MIO (previously called MMO, the Mercury Magnetospheric Orbiter)
managed by JAXA̶ to conduct a comprehensive study of Mercury.

The Ariane 5 rocket will launch BepiColombo from French Guiana in October 2018 and, following a total of nine
planetary swing-by maneuvers, is scheduled to enter orbit around Mercury in December 2025.

Development Period: 15 Years

The Origin of
the Name BepiColombo

huge iron core extending to three-quarters of the radius

In Japan, discussions regarding the exploration ofThis project was named after the Italian astronomerof the planet.

Mercury began in 1997, with BepiColombo commencing

Giuseppe Colombo, who proposed that Mercury's orbital

as a project in 2003. Following a development period

and rotational periods were locked into a 3:2 resonance.

of 15 years, we are all now eagerly anticipating

He also pioneered using swing-by maneuvers in

the moment of the BepiColombo lift-off! MIO's key

planetary probe navigation and designed the trajectory

Mercury also possesses a magnetic ﬁeld with a strength

observation technique has been enhanced throughof the first probe to explore Mercury, Mariner 10. We

of around 1/100th of that of the Earth's. A ﬂowing liquidJapanese explorations for the Earth's magnetosphere.

can say that Colombo made the exploration of Mercury

Magnetic Field Like EarthAphelion

0.47 AUPerihelion

0.31 AU

Diameter

4,880 kmAveraged Density

5.43 g/cm3inner core is necessary for a planet to generate a

To demonstrate Japan's technical advantages, thepossible. Commemorating such achievements, weOrbital Period

88 daysmagnetic ﬁeld. Why Mercury, the smallest and easiest

researchers and engineers developed MIO with fervent

named our mission as 'BepiColombo,' adding hisRotation Period

59 daysplanet to cool and solidify, still has a magnetic ﬁeld is aenthusiasm.

nickname, 'Bepi.'

Length of Mercury Day

176 daysgreat mystery.

©NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

MIO

MPO

Mercury Magnetospheric Orbiter

Mercury Planetary Orbiter

MIO's objective is to study Mercury's surrounding

In addition to design choices to improve the eﬃciency

The MPO's objective is to study Mercury's surface

toward the strong sunlight. Thus, the orbiter is designed

environment in detail, including its magnetic field,of heat dissipation into space, MIO is covered with(terrain, minerals/chemical composition) and interior

to maintain a low temperature for equipment thatplasma, thin atmosphere, and dust. In addition tomirrors on the sides permanently exposed to sunlight.

(gravity and magnetic ﬁelds) in detail. An attitude control

requires cooling.

receiving sunlight around ten times as powerful as on

The reflection can reduce heat absorption as muchsystem will ensure that the heat shield is always faced

Earth when in orbit around Mercury, MIO must also beas possible. Instruments have not been attached toable to withstand heat radiated from the surface, where

the rear of the solar cells, as this surface is black andthe daily temperature reaches as much as 430℃.

inevitably heats up.

Ingenuity was needed to enable observations inMercury

s severe thermal environment.

©ESA/ATG medialab©ESA/ATG medialab

Scientiﬁc Instruments onboard MIO

Objectives

MPPE
With seven sensors, MPPE measures electrons and ions
(Mercury Plasma Particle Experiment) at diﬀerent energies and high-speed neutron particles.
MGF(Magnetic Field Investigation)

Measures the magnetic ﬁeld of Mercury,its magnetosphere and the solar wind.

Scientiﬁc Instruments onboard MPO

PWIObserves the electric ﬁeld and electromagnetic waves
in Mercury s magnetosphere and the solar wind.

(BepiColombo Laser Altimeter)

MDM

Detects interplanetary dust and that released from
Mercury within the Mercurian orbit

MSASI

Takes spectral images of the distribution and variationof Mercury s thin sodium atmosphere.

(Plasma Wave Investigation)(Mercury Dust Monitor)(Mercury Sodium Atmosphere Spectral Imager)

Attitude Control

Spin stabilized, with a rotation rate of 15 RPM

Shape and Size

Octagonal prism, measuring 1.8 meters between
opposing faces and with an overall height of 2.4 meters
including the antenna. Four 15 meter wire-antennas andtwo 5 meter masts are extended in orbit around Mercury.

Weight255kg

Attitude Three-axis stabilization

BELAMOREISA

PHEBUS

MPO-MAGSERENA

MERTISSIMBIO-SYSMGNSSIXS(Italian Spring Accelerometer)(Magnetic Field Investigation)(Mercury Radiometer and Thermal Imaging Spectrometer)(Mercury Gamma-Ray and Neutron Spectrometer)

MIXS(Mercury Imaging X-ray Spectrometer)(Mercury Orbiter Radio science Experiment)(Probing of Hermean Exosphere by Ultraviolet Spectroscopy)(Search for Exosphere Reﬁlling and Emitted Neutral Abundances)(Spectrometers and Imagers for MPO BepiColombo Integrated Observatory)(Solar Intensity X-ray and particle Spectrometer)

Control
Shape 2.4 x 2.4 x. 1.7 meters.
andThe solar array paddles

Size(7.5 meters) are extended
after the lift-oﬀ

Weight 1230kg

Voyage to Mercury
An Exploration Packed
with Challenges
Mercury is tough planet to explore and requires anenormous amount of energy to visit. As a result, only
two explorers, Mariner 10 and MESSENGER, have
travelled to Mercury so far. In order to save propellant,
BepiColombo faces a difficult journey to Mercury
and will perform a total of nine planetary swing-by©NASA/Johns Hopkins University Applied Physics Laboratory/
Carnegie Institution of Washington

maneuvers.

Mercury swing-by
4. Oct. 2, 2021
5. Jun. 23, 2022
6. Jun. 20, 2023
7. Sept. 5, 2024
8. Dec. 2, 2024
9. Jan. 9, 2025
Nine planetary swing-by
maneuvers in total©ESA/ATG Media Lab

On December 5, 2025, the Orbital Insertion©ESA▲ Ariane 5

Oct. 2018 - launch

Earth swing-by
1. Apr. 13, 2020

©JAXA

Venus swing-by
2. Oct. 16, 2020
3. Aug. 11, 2021

Why does it take as long as 7 years to arrive at

A spacecraf t can change direction, accelerate

Mercury? The reason lies in the number of swing-or decelerate when passing close to a planetaryby maneuvers that must be performed. To ensurebody due to its gravitational field. The navigationalcorrect alignment with the planet, the spacecraft mustmaneuver for utilizing a planets gravity to change

sometimes orbit the Sun many times to wait for thes speed is called a swing-by. A

correct timing for the swing-by. The 7 years is not due

spacecraft can adjust its course without propellants

to Mercury being far from the Earth, it is down to thewhen using a swing-by. Nowadays, many planetary

waiting times for the swing-bys.

a spacecraf t

missions use swing-by maneuvers to reach their※ As of Aug. 2018

Why Does it Take 7 years?

The Swing-By: the Key Techniquefor Arriving at Mercury

destinations.

MIO- Measure Mercury's environment(magnetic ﬁeld, plasma, dust, and atmosphere) precisely

MPO-Observe Mercury s surface(topology and minerals and chemical composition).
-Measure Mercury s interior(gravitational and magnetic ﬁelds) precisely.

Observations orbiting around Mercury
Placing the Two Satellites into Diﬀerent Orbits
Upon BepiColombo's arrival at Mercury, in a world's

MPO, separating from MMO sun-shield, will graduallyﬁrst the two satellites will ﬁnally be inserted into orbit.

reduce its altitude and enter into a low-altitude orbit.

The electric propulsion module, having completed its

From this point, the MIO and MPO will orbit the samerole, will be jettisoned and the spacecraft will enter

orbital plane at diﬀerent heights while performing theirinto orbit around Mercury, with the MIO ﬁrstly coming

respective scientiﬁc observations.

into an extended elliptical orbit with a high apoapsis(the furthest point in orbit from Mercury). Next, theThe advantage of 2 Probes
Observing Simultaneously

MIO's Observations
The plasma particle instruments, magnetometer, andIn order to know what is occurring in the interior ofplasma wave and electric field instruments, mounted

Mercury, it is important to precisely measure the planet's

on the MIO, will work together to understand themagnetic ﬁeld. Meanwhile, the harsh solar winds aroundvarious physical phenomena occurring in the Mercury's

Mercury cause disturbances in the electromagnetic ﬁeld

magnetosphere.

and interfere in the measuring of the magnetic field.

A sodium atmosphere spectral imager will study

The combination of the MPO and MIO enables us to

Mercury's thin sodium atmosphere's luminescence

discriminate the Mercury's own magnetic ﬁeld from thatto shed light on the mysteries of the atmosphere'sof the solar wind. Thus, we can obtain more precise

production mechanisms. The Mercury dust monitor will

information on the interior of Mercury.

observe the dust of the Solar System's innermost edge of which about hardly anything is known.

Science Objectives ofBepiColombo
Understanding Geographical Features
Despite being the closest planet to the Sun, it wasdiscovered that the mineral composition of Mercury's
surface contains far more volatile elements thanexpected. Furthermore, the MESSENGER probe
discovered strange depressions peculiar to Mercury.
It is thought that maybe these depressions wereformed when volatile elements escaped from thesurface. These results may indicate that Mercury
was once larger than it is now and could hold thekey to a re-examination of the planet formation
theory.
©NASA/JHUAPL/CIW

Understanding theMagnetic Field

Based on research of the Earth, scientists believethat a planet with its own magnetic field mustpossess a liquid metal core which generates
electric currents through circulating. Why Mercury,the smallest and which should be the easiest planet
to cool and solidify in the Solar System, still has
a liquid core remains a huge mystery. Moreover,observations of the MESSENGER probe revealed

Understanding the Surrounding Environmentthat the center of Mercury's magnetic field isactually north of its equator.

The planets in the Solar System are constantly

such an environment different to that of Earth's, weWhat kind of internal structure causes such an

bombarded by solar winds. While magnetic ﬁelds likewill clarify what role the planetary magnetic fieldasymmetric magnetic field? BepiColombo will

Earth's are thought to perform the role of a barrierplays in relation to the solar winds. And in the future,

reveal the interior of Mercury through detailed

against solar winds, Mercury's magnetic field isresearchers believe that such an understanding

magnetic ﬁeld observations from the two satellites

about 100 times weaker than the Earth's as well as

will help in the search for the possibility of life on

a n d d e c i p h e r t h e i nf o r m at i o n o n p l a n et a r ybeing subject to far stronger solar winds. Throughexoplanets.

evolution.

understanding what kinds of phenomena occur in