What They Didn't Teach You at School about Planet Mercury | NASA's MESSENGER Discoveries

The video introduces Mercury as the least explored terrestrial planet despite being known since ancient times. It invites viewers to learn about Mercury's characteristics, history, and the challenges of exploring it. The narrator, Alex McColgan, promises to teach everything about Mercury, starting with its physical resemblance to the Moon and its unique composition, which is more metallic than rocky, giving it the second-highest density in the solar system. The video also touches on Mercury's surface gravity, size comparison with Ganymede and Titan, and its geological features like the Caloris Basin and weird terrain.

This paragraph delves into Mercury's extreme temperature variations, ranging from minus 173 degrees Celsius to over 400 degrees Celsius, influenced by its lack of atmosphere and orbit/rotation dynamics. Mercury's exosphere is described as an unstable, extremely thin layer where atoms are continuously lost and replenished. The presence of water ice at the North Pole and Mercury's magnetosphere, weaker than Earth's but capable of deflecting solar wind, are also discussed. The video highlights Mercury's unique orbit and rotation, including its 3-2 spin-orbit resonance, which results in a solar day lasting two Mercurian years.

The paragraph outlines the historical context of space exploration, noting that Mercury was only visited after several other planets. It explains the challenges of reaching Mercury due to its extreme temperatures and proximity to the Sun, which requires advanced heat resistance and fuel efficiency. The MESSENGER probe's mission is introduced, highlighting its importance and the innovative trajectory designed by Chen-Wan Yen that involved multiple planetary flybys to slow the spacecraft enough to enter Mercury's orbit.

MESSENGER's journey and its scientific contributions to our understanding of Mercury are detailed. The probe's equipment is tested near Earth and Moon before its encounters with Venus and Mercury. A particular challenge during the third flyby of Mercury is mentioned, where the probe entered safe mode but later recovered. MESSENGER's successful entry into Mercury's orbit and its extensive data collection, including over 200,000 photographs, are highlighted. The information gathered helped create a high-resolution color map of Mercury's surface and provided insights into nearby comets and planets.

The paragraph discusses MESSENGER's findings on Mercury's magnetic field, which is generated by a dynamo effect in its molten core. The field's offset from the planet's center and its interaction with the solar wind are explained. The video also describes reconnection events and energetic electron bursts detected by MESSENGER. The use of spectrometers to analyze the exosphere and surface composition reveals volatile substances like potassium, magnesium, and chlorine, challenging previous solar system formation theories.

The video explores the source of hydrogen and helium in Mercury's exosphere, which is primarily the solar wind. It describes how the exosphere contains particles like sodium and potassium found on the surface, and how it is constantly replenished due to solar wind and light pressure. The seasonal nature of Mercury's tail, the presence of water vapor, and the discovery of water ice in permanently shadowed craters are also covered. The existence of hollows, unique geological features on Mercury, and the evidence of past volcanic activity are highlighted.

This section paints a picture of Mercury's past as a planet experiencing intense heat and volcanic activity. It discusses how the surface would have reached temperatures high enough to melt rock into magma, which could flow long distances due to its viscosity. The video describes the formation of smooth plains within craters like Raditladi, suggesting lava flows from volcanic eruptions or melting due to meteor impacts. The presence of volcanic ash and the possibility of explosive volcanic eruptions that left marks on the planet's surface are also mentioned.

The video describes the color variations on Mercury's surface, which include greys, creams, and beiges, and are believed to indicate different compositions, such as high levels of graphite. The prevalence of craters on Mercury's surface is noted, and it is explained that the sharpness of crater rims can indicate their relative age. The video also discusses the processes that shape Mercury's surface, including cooling, which causes the surface to crumple and form kilometer-long scarps, and slumping within craters.

The video explores the phenomenon of crater rays on Mercury, which are lighter-colored lines radiating from certain craters. It details the scientific mystery surrounding their formation and how it was eventually understood to be related to the roughness of the surface. The video also mentions the large ray systems that are a distinctive feature of Mercury, suggesting powerful impacts. It concludes with a discussion of the unusual fractures around the Apollodorus crater and the Pantheon Fossae, which may be related to volcanic activity from beneath the surface.

The final paragraph reflects on the many mysteries that remain about Mercury, despite the significant contributions from the MESSENGER mission. It highlights the unique surface features, such as the fractured glass appearance around Apollodorus and the radial fractures of Pantheon Fossae, which are not yet fully understood. The video anticipates further insights from the upcoming BepiColombo mission, set to arrive at Mercury in 2025, which will continue the study of the planet's magnetosphere, exosphere, geology, and composition.