Little Planet, Big Secrets Trivia Quiz

Answer: BepiColombo

Named for Italian Giuseppe "Bepi" Colombo, the Mercury mission to study Mercury and its magnetosphere is a joint effort between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA). The craft had its first flyby in 2021, capturing images of the planet, and is due to reach orbit in 2025.

The ESA will study the surface and interior of the planet, while JAXA will focus on the magnetosphere.

Answer: Wrinkles

A lobate scarp is a thrust fault that causes ridges and valleys on Mercury, and our moon. While neither of these celestial bodies have tectonic plates, the crust still lifts or collapses due to movement under the surface. While the moon's scarps are restricted to the highlands, Mercury's scarps are larger and are distributed across the entire planet.

The scarps on Mercury are sometimes linear and, on photos, resemble wrinkles.

Answer: Mostly solid iron

Mercury has a solid, dense core comprised of silica and iron and it contains more iron than any other planet. It was thought that the inner core was liquid iron, but data sent back from the MESSENGER analysis changed scientist's thinking. Planets that are closer to the sun comprise more iron due to the sun's magnetic field, and Mercury's high content makes it the second most dense planet. It has the proportionally largest core of any planet.

Answer: Cooling of its interior

Mercury has a solid crust and, as the inner metal core cools, it contracts. As the crust does not have tectonic plates, it cannot move to fit the smaller surface area. Eventually, gravity compresses the crust, causing it to buckle and wrinkle.

Answer: 58 days

A single rotation, or Mercury day, lasts for 58 Earth days, almost two months! For a long time it was thought that Mercury was tidally locked with the sun, where its rotation time equalled its orbit, but around 1965, close observation found that Mercury does rotate, but at a slightly different rate. Each day on Mercury is around 2/3 of its orbit, which means three Mercury days is equivalent to two years on Earth. The explanation for this slow rotation is the dense, heavy core, which slows the spin. Another hypothesis is that this slow rotation is causing Mercury to become tidally locked with the Sun.

Due to Mercury's elliptical orbit and the discrepancy in the 'normal' rate of rotation to orbit, it sometimes gives the impression that the sun is moving backwards.

Answer: Caloris Basin

The Caloris Basin, also called Caloris Planitia, was first seen in 1974 when the Mariner 10 probe photographed it during a fly by. At the time, the 1350km diameter Caloris was on the terminator (the demarkation betwen night and day), so it wasn't seen in its entirety until the MESSSENGER mission in 2008. The new images found the basin to larger than first thought. The rim of the crater is marked by a series of mountains, which also happen to be the highest on Mercury. Plains between the mountains are thought to have been gullies, later filled by volcanic ash and lava.

Answer: Spider

Inside the Caloris Basin, images from BepiColombo revealed a second impact crater, this one with 50 to 100 troughs or fissures radiating out from the central area. An impact crater like this has not been seen on any other planet, so there was some debate over the cause. It has been hypothesised that, instead of being caused by the initial impact, the troughs were caused by a resultant volcanic intrusion beneath the surface.

Answer: Transit

An orbital node is when the orbital planes of two celestial bodies intersect. When Earth and Mercury are on the same plane, Mercury can be seen as a black dot passing in front of the Sun. This is known as the Transit of Mercury and it normally occurs in May or November, around 14 times per century. The Transit of Mercury was predicted by Johannes Kepler in 1630, and the first recorded person to witness it was Pierre Gassendi in 1631. The next transit is predicted for November 2032.

Answer: Mercury has very little atmosphere

Mercury was thought to have no atmosphere, but Mariner 10 found that it does have an exosphere. This slight atmosphere is comprised of various elements like sodium and magnesium and traces of hydrogen and helium gasses. The energy released by the sun pushes these gases away from Mercury, creating a comet-like tail. During a mercury day, the surface facing the Sun can reach temperatures of over 400 degrees Celsius, while the dark side freezes to negative 170. The lack of atmosphere allows the heat to escape into space, thus cooling the planet slightly.

Answer: Weird Terrain

Also known as 'Chaotic Terrain' the area around the Petrach Crater is very hilly and lineated, whereas the rest of the planet looks much like our moon, with relatively flat craters. The Weird Terrain was first photographed by The Mariner 10 and its position found to be antipodal to the Caloris Basin. Since then, the hypothesis was that the impact of an asteroid caused shock waves to travel through Mercury's crust until they collided at the antipodal point, causing a violent uplifting of the crust into lineated hills. A recent scientific paper (published in 2020) has postulated that the terrain may instead be the result of the loss of volatile elements and compounds.

This theory states that these crust compounds have a low boiling point, and the constant heating and cooling of the planet has caused them to deteriorate and escape.

This has caused the surface to collapse into the lineated depressions.