BepiColombo is set to begin its long journey to one of the least studied of Earth's seven neighboring planets. It is hoped the probe will offer insights into how our solar system was formed.
The Mercury Planet Orbiter (left) is designed to separate from the Magnetospheric Orbiter Image: EADS Astrium
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A seven-year journey to Mercury, one of the solar system's least studied planets, is about to get underway.
The space probe duo BepiColombo, named after Italian engineer and mathematician Giuseppe Colombo, is considered one of the most demanding space missions the European Space Agency (ESA) has ever undertaken.
This might sound surprising, because at first glance the project appears to be a simple one — at least when compared to missions such as Rosetta's landing on comet Chury in 2014.
After all, it's just an orbiter probe — albeit one with two components — like many others before it that have visited planets in our solar system.
But getting a probe to Mercury is not as easy as it sounds. ESA has teamed up with the Japanese space agency JAXA for this technically challenging mission. Extreme climatic conditions around the planet will add an element of difficultly to the study, as Mercury has virtually no atmosphere.
At the same time, it is the planet closest to the sun. As a result, the planet can heat up to around 430 degrees Celsius (806 degrees Fahrenheit) during the extremely long days that prevail there. At night, it drops to temperatures as low as minus 180 degrees Celsius.
Little is known about Mercury. Its conditions make it inhospitable and with a diameter of 4,878 kilometers (3,031 miles), it is only slightly larger than our Earth's moon.
Only two NASA probes — the Mariner in 1975 and Messenger between 2011 and 2015 — have ever visited the planet named for the Roman deity and messenger of the gods. Messenger's main focus was on the planet's northern hemisphere. Now BepiColombo is to fill the gap and provide data for the southern hemisphere.
BepiColombo spacecraft launches quest to survey Mercury
Humans still know very little about Mercury, the planet closest to the Sun. It's hoped the BepiColombo space probe will reveal the planet's secrets. Here is what we do already know about Mercury.
Image: DLR/ESA
Meet the BepiColombo space probe
The BepiColombo spacecraft is scheduled to start its journey on October 20, 2018. It is a joint project of the European Space Agency (ESA) and the Japanese Space Agency (JAXA). BepiColombo consists of two satellites — the European Mercury Planetary Orbiter (MPO) and the Japanese Mercury Magnetospheric Orbiter (MMO). They will explore Mercury on different orbits starting in early 2026.
Image: DLR/ESA
Unknown beauty
To date, only two space probes have come close to Mercury. The last one was the successful NASA probe, Messenger. It orbited the planet more than 4,000 times and sent over 250,000 images back to Earth. A planned crash landing in 2015 due to lack of fuel saw the end of the Messenger mission.
Image: picture-alliance/dpa
Long nights
Mercury probes must be able to withstand a lot. Above all, the extreme temperature differences pose great challenges to engineers and manufacturers here on Earth. Mercury is uninhabitable for another reason — the sun rises there once every 176 Earth days. Yes, you read correctly.
Image: picture-alliance/dpa
Hot, hot, hot — but no atmosphere
On Mercury it is hot, but not it's as bad as one would expect from a planet so close to the Sun. Its neighbor, Venus, experiences much hotter conditions. The reason: Mercury, in contrast to Venus, has no atmosphere and heat leaves the planet in the form of radiation. Temperatures vary from 430 degrees Celsius (806 degrees Fahrenheit) to minus 180 C.
Image: Reuters/NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Unstable and eccentric
Mercury is the smallest planet in our solar system and is closest to the Sun. Its orbit around the Sun is unstable, and is growing larger all the time because Jupiter is slowly pulling Mercury out of its orbit. At some point, this could see Mercury colliding with Earth. But fear not, that won't happen for many millions of years.
Image: Getty Images/AFP/IAU
Similarities to the moon
The surface of Mercury is scarred and filled with craters like those on our moon. Many meteorites and asteroids have violently smashed into the planet in the past. Some craters are several hundred kilometers in diameter.
Image: NASA, JHU APL, CIW
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BepiColombo: Two orbiters traveling together
BepiColombo consists of two orbiters, which will only separate from each other as it approaches Mercury. The first, Mercury Planet Orbiter (MPO), will investigate the surface and composition of the planet with the aim of obtaining a complete three-dimensional image.
While the Mercury Magnetospheric Orbiter (MMO) will measure magnetism. Both probes will also collect data on solar winds and examine the interactions between the Sun and Mercury.
Unique measuring instruments
Sixteen measuring instruments are on board two probes.
"With some of them, we can even take a look beneath the planet's surface and learn about the minerals there — iron-sulfur compounds, for example," ESA project scientist Johannes Benkhoff told DW in an interview.
The German Aerospace Center (DLR) is directly involved with three of the instruments: A laser altimeter (BELA), a magnetometer (MPO-MAG) and a combined radiation measuring device with an infrared spectrometer (MERTIS).
The instruments had to be specially designed to withstand the temperature fluctuations and radiation.
For example, the sensor for the MERTIS radiation measuring device is tiny — 1 by 3 millimeters (0.04 by 0.12 inches) in size. It was made from a single piece of silicon and at the same time serves as a tiny opening for the spectrometer with which it's combined. The outer part of the instrument must be able to withstand the temperature extremes.
The inside of the probe is less extreme. It is encased in a specially developed 6-centimeter-thick insulating layer. This is intended to cool the central devices to a moderate 20 degrees Celsius.
It's hoped BepiColombo will complement these infrared images provided by NASA's Messenger probe Image: Reuters/NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Long, complicated approach
The probe also has to have enough energy to fuel its long journey.
"We need a lot of energy to reach Mercury," says planetary researcher Benkhoff. "We obtain this energy in two ways. First, we have solar-electric propulsion that is very energy-efficient. But solar energy alone is not enough to reach Mercury. Secondly, we must get help from the planets."
BepiColombo will perform a series of swing-by maneuvers to gain the necessary speed. But the planetary constellation must be just right for this, meaning the journey will take some time. The probe will fly past Earth once and past Venus twice. "In total, BepiColombo must orbit the Sun 18 times before it reaches Mercury," says Benkhoff.
To be able to complete its journey, BepiColombo has to be slowed down too. Swing-by maneuvers are also used here — six times on Mercury itself. Only in this way can the probe reach its desired orbit around the planet.
On the outbound flight, BepiColombo will collect data from Earth and Venus. After the probe begins operations in early 2026, its two orbiters will collect data for about a year, before sending the information back to Earth.
A tiny planet Mercury before the huge sun
One of the smallest planets in our solar system is passing across the sun's face. This is a rare event to observe: it only happens every thirteen to fourteen years on average.
Image: NASA/JHUAPL/Carnegie Institution of Washington
Everybody's looking for the little black dot
A tiny black spot - this is how Mercury looks in front of the solar disk, which it passed on Monday. It took the planet more than seven hours to travel the entire length.
Image: picture-alliance/dpa/K.-J. Hildenbrand
View from Bavaria
An astronomer took those pictures with an 800mm telescope from Kempten in the Allgäu region of Bavaria. The sun is shining with such intensity that the planet is reduced to a small shadow. Even this picture could only be taken because the telescope has been darkened with a special sunray-filter.
Image: picture-alliance/dpa/S. Jansen
Zooming in
This picture is from 2006. Italy's National Institute of Astrophysics took it during a previous Mercury flyby. At least here it is easy to distinguish between the planet and frequently ocurring sunspots, or coronal mass ejections, which also appear as dark spots on the surface of the sun. The planet, however, is clearly round with sharp edges before the background of solar flares.
Image: picture-alliance/dpa/INAF
How to get even closer
Only a spacecraft will do. NASA's spacecraft Messenger took the best pictures of Mercury so far. The probe circled the planet from 2011 to 2015 until it finally crashed there.
Image: picture-alliance/dpa
Just like the Moon?
Messenger found a planet with a surface which does not look too differently from our Earth-Moon - at first glance: rock, sand, gravel and lots of craters left behind by meteorite impacts. But there are big differences, too: temperatures on Mercury are much more extreme. Because there is practically no atmosphere, it can get icy cold. On the other hand, the sun can make it extremely hot.
Image: NASA, JHU APL, CIW
Mercury in all its beauty
This picture is a composite from thousands of pictures taken by different spectrometers in the course of countless orbits around the planet. For the first time, there is a really high-resolution image of Mercury.
Image: Reuters/NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Messenger's final resting place
This area shows the eventual crash site where Messenger came down in 2015. Clearly visible: meteorite impact craters of all sizes.
Image: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Highland plains in sunshine
The astronomers who have watched Monday's Mercury flyby did not see pictures like this. The photo taken by Messenger shows an area of plains formed by volcanic activity. The different colors indicate different rock materials.
Image: NASA/JHUAPL/Carnegie Institution of Washington
