According to a new study, the planet Mercury experiences regular meteor showers at roughly the same time each year, as it moves through a trail of dust thrown off by the ancient comet Encke. The work was presented at the annual Meeting of the Division of Planetary Sciences of the American Astronomical Society at National Harbor, Maryland.
On any given night you stand a decent chance of catching sight of a meteor – one of countless tiny grains of dust that are thrown off in the wake of a passing comet, that burn up in our atmosphere, creating a visible streak of light that has given birth to the moniker, shooting star.
Earth is not the only planet to be showered with extraterrestrial materials. In October 2014, MAVEN recorded the effects of tons of comet material raining down on the Martian atmosphere from Siding Spring.
For planets like Earth, that boast very thick atmospheres, the phenomenon is relatively inconsequential, but for other bodies, like Mercury – which is shrouded by a tenuous cloud of atomic particles known as a surface boundary exosphere – the passing of a comet can have a significant impact on atmospheric composition.
The recent study focused on an analysis of data collected by NASA's MErcury Surface Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft as it orbited the planet from March 2011 up to its demise in April this year. Over the course of its operational life, MESSENGER was able to observe the interaction between dust particles thrown off by the comet Encke, and the altering composition of the planet's fragile surface boundary exosphere.
It was discovered that there was a clear pattern in Mercury's atmospheric calcium levels that repeated each year at around the same time. It was theorized that dust thrown off by Encke over thousands of years was striking Mercury as it swept through the comet's orbital path, throwing up calcium from the planet's surface.
However, the timing of the closest point of interaction between the orbits of Mercury and Encke occurred roughly a week after the yearly calcium peak observed by MESSENGER. This meant that the comet's dust trail must have somehow deviated from Encke's extremely stable orbital path, which brings it within 31 million miles (50 million km) of the Sun once every 3.3 years.
To solve the mystery, a team of researchers ran complex computer simulations taking in to account the most accurate estimations of Encke's orbital path over thousands of years, and the behaviour of the dust stream this would have created. From the simulations, it appears likely that the deviation is likely the result of the subtle force exerted on particles by sunlight from our star.
Based on this analysis, it is theorized that the dust particles currently striking Mercury measure around 1 mm in size, and where dispersed by Encke between 10 – 20 thousand years ago. These particles would have been just the right size for the influence from the Sun to shift their orbit to the correct location to account for the calcium spikes.
The study of comets has been a popular subject of late thanks to the incredible success of ESA's Rosetta mission, and research of the type outlined above provides a wider viewing lens for some of the more subtle impacts that the celestial wanderers have on the planets that make up our solar system.