![]() Mercury’s early history was likely dominated by giant impacts (similar to those that might have formed the Moon), which blasted large amounts of its silicate mantle into space. It’s believed that the young Sun had a solar wind about 100 times stronger than today, which is what makes the work in today’s paper possible. Parker’s other major discovery was the spiraling solar magnetic field. ![]() Parker’s solar wind is composed of supersonic protons traveling at 400 km/s, and it dominates the interplanetary environment as far as the heliopause. His solution was so revolutionary it took three tries to get published: the solar corona is not static but constant expands into space. At very far distances, he found a discontinuity - the pressure was much lower than realistically possible. In 1957, Eugene Parker realized something funny happened when he tried to solve the fluid equations to understand how the Sun’s atmosphere works. Specifically, they hypothesize that as asteroid impacts knocked pieces of Mercury’s mantle into orbit, the powerful solar wind removed the debris before it could coalesce back onto the surface. It is, in fact, a corollary of the first theory that the authors of today’s paper tested. The fact that many close-in exoplanets have been found over the last decade with rocky mantles casts considerable doubt on the latter theory. A third theory states that high temperatures took over after Mercury formed, vaporizing its mantle but not the iron core. Another puts forth that as the planets formed from the protoplanetary disk orbiting the Sun, high temperatures sorted out the silicates and iron, so Mercury formed in a region of the disk bereft of silicates to begin with. One idea is that Mercury formed with a silicate mantle that was blasted away by asteroid impacts. Many theories have been proposed to explain how Mercury ended up as the planet with the largest core compared to its size. Under the surface, Mercury has an iron core that extends to more than 80% of its radius, compared with just 50% for Earth. Because of its proximity to the Sun, Mercury doesn’t have an atmosphere, only a “ surface-bound exosphere” of gas particles on ballistic trajectories. Mercury is a bit of an oddball compared to the other terrestrial planets. ![]() Adamsįirst Author’s Institution: Yale University Title: The Solar Wind Prevents Reaccretion of Debris after Mercury’s Giant ImpactĪuthors: Christopher Spalding and Fred C. We hope you enjoy this post from astrobites the original can be viewed at. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. Editor’s note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. ![]()
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