October’s Talk

The BepiColombo mission to Mercury is a joint ESA/JAXA (Japan Aerospace Exploration Agency). The craft is named in honour of Giuseppe (Bepi) Colombo (1920-1984), an Italian scientist who first used the gravity assist (‘slingshot’) method of sending spacecraft across the solar system by bringing them close to other planets, thereby using their gravity to increase speed.

Mercury is odd in that it has a very dense large core with a total size not much different from that of Earth’s. This almost certainly came about when Mercury hit something massive while the solar system was still being formed. (What Prof Rothery calls ‘planetary embryo collisions’.) But where was Mercury’s embryo when it got bashed? He is intrigued why there is so much sulphur (2-5%) on the surface but the collision theory would also explain that away in that Mercury probably formed further out in the cooler parts of the solar system and was therefore mostly the hit and run impactor itself, and most of the lighter stuff from the two bodies was dumped into space, leaving the dense core.

Mercury’s surface has a rather dark grey, flat albedo, even lower than that of the Moon. There are areas of slight stepping, indicating tectonic thrusting as the surface cooled.

The Messenger spacecraft was busy orbiting and mapping Mercury from around 2011-15. Joint UK/Italian scientists are using the data to create 15 geological maps in total. As regards BepiColombo, the UK contribution is an x-ray spectrometer (see below) which sees the fluorescence on the surface. The Sun shines x-rays onto Mercury and the resulting fluorescence and reflected x-ray photons tells us what elements there are and the abundance thereof. The more active the Sun is the more fluorescence there is so you get more information.

Unfortunately the Messenger data did not cover the south pole. The north pole had much better coverage. The elements detected were silicon, sulphur, iron, magnesium, potassium, calcium, among others.

BepiColombo consists of two craft which will not be able to separate until they arrive. MMO (Mercury Magnetospheric Orbiter) is Japan’s half, MPO (Mercury Planetary Orbiter) is the ESA half. The UK and Finland have created MIXS (Mercury X-ray Imaging Spectrometer mentioned above).

Launch may go ahead next year. There will be two Venus flybys and five Mercury flybys to get it into orbit, and this is going to take 8-9 years. Once in position, MMO will fly very close in ellipses, so that its orbits will take 2 to 3 hours (400-1500km) and MPO will have a far more elliptical orbit, with its closest being 400km also.

It was amusing to hear Prof Rothery’s defence of the cost of the mission in the face of nasty comments from people on public media. The mission is likely to cost a total of 3.3 billion euros. Not that much when you consider about 8 billion dollars is likely to be spent on lipstick in the next year….

Clear Skies

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