Atmospheric calcium spikes indicate potential meteor showers at Mercury

Chuck Bednar for redOrbit.com – Your Universe Online

A regular surge in exospheric calcium indicates that Mercury could be experiencing a regular meteor shower, possibly one associated with a comet that produces several similar events here on Earth, officials from the NASA Goddard Space Flight Center have revealed.

According to the US space agency, the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft detected regular seasonal surges in the element using its Mercury Atmospheric and Surface Composition Spectrometer instrument. Those surges have reportedly over each of the first nine Mercury years since MESSENGER arrived in March 2011.

Meteor showers occur when a planet passes through a patch of debris ejected from a comet or asteroid, NASA explained. The tiniest particles of dust, rock and ice feel the force of solar radiation, which causes them to be pushed away from the sun and creating a comet’s spectacular tail. The larger pieces of debris wind up being left behind like a trail of breadcrumbs along the comet’s orbit, creating a line of soon-to-be meteoroids.

“The possible discovery of a meteor shower at Mercury is really exciting and especially important because the plasma and dust environment around Mercury is relatively unexplored,” explained Rosemary Killen, a planetary scientist at the Greenbelt, Maryland-based NASA facility and lead author of research currently available online in the journal Icarus.

Researchers at Goddard believe that the cause of the spiking calcium levels is a shower of small dust particles that are colliding with the planet, causing molecules containing the element to break free. This process, which is known as impact vaporization, continually renews the gases in Mercury’s exosphere as meteoroids and interplanetary dust rain down upon the planet.

The periodic spikes is calcium cannot be explained solely by the general interplanetary dust content of the inner solar system, however, suggesting that there is occasionally a secondary source of the particles – a cometary debris field, for example. By examining the comets whose debris fields could potentially cross Mercury’s orbit, NASA determined that the likely culprit is comet Encke, which is also responsible for the Southern and Northern Taurids on Earth.

“If our scenario is correct, Mercury is a giant dust collector,” said Joseph Hahn, a planetary dynamist in the Austin, Texas, office of the Space Science Institute and co-author of the study. “The planet is under steady siege from interplanetary dust and then regularly passes through this other dust storm, which we think is from comet Encke.”

Killen, Hahn and their colleagues devised a series of computer simulations to test their hypothesis, and discovered that the calcium spikes detected by MESSENGER were offset somewhat from the anticipated results. They attributed this shift to changes in Encke’s orbit over time due to the gravitational pull of Jupiter and other planets.

“The variation of Mercury’s calcium exosphere with the planet’s position in its orbit has been known for several years from MESSENGER observations, but the proposal that the source of this variation is a meteor shower associated with a specific comet is novel,” noted Sean Solomon, MESSENGER Principal Investigator at the Lamont-Doherty Earth Observatory at Columbia University. “This study should provide a basis for searches for further evidence of the influence of meteor showers on the interaction of Mercury with its solar-system environment.”

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