Seeing dust particles left behind by a passing comet burn up in a planet’s atmosphere is hardly a rare occurrence, as it occurs frequently on Earth and even happened on Mars last year, but a new study from NASA has found that even the largely airless planet Mercury experiences meteor showers.
In research presented at this week’s annual meeting of the American Astronomical Society’s Division of Planetary Sciences, experts from Armagh Observatory in Northern Ireland, NASA’s Goddard Space Flight Center, and Morgan State University reported that they found evidence that the planet was being pelted by particles from Comet Encke.
According to Universe Today, the researchers analyzed data collected by the Mercury Surface Space Environment Geochemistry and Ranging (MESSENGER) spacecraft, which orbited the planet until late April of this year—the first probe to ever do so. Their published their findings a recent edition of the bi-weekly science journal Geophysical Research Letters.
The researchers analyzed the MESSENGER data and uncovered a regular pattern of calcium variation that repeated at roughly the same time every year. They set out to determine what happened when Mercury travelled through the cloud of interplanetary dust surrounding the sun—called the zodiacal cloud—and was pelted by fast-moving meteoroids.
Determining how and why Comet Encke causes this calcium variation
Goddard’s Rosemary Killen, Morgan State’s Matthew Burger, and their colleagues determined that both the observed amounts of the element and its pattern of variation could be explained in terms of the material ejected from the planet’s surface by the impacts. However, they also found that the calcium emissions peaked right after Mercury’s closest approach to the sun.
A model developed by Killen’s team predicted that this peak would have occurred just before the planet’s perihelion, which indicated that they were still missing something.
That’s where Comet Encke enters the picture. Comet Encke has the shortest period of any known comet, returning to perihelion at a distance of 31 million miles (50 million kilometers) every 3.3 years.
Since its orbit is so stable, over the course of several millennia, any dust particles it gave off would have formed a dense dust stream. Killen and her colleagues proposed that the dust from this comet impacting Mercury would have caused more calcium to be lost from the surface, and explain MESSENGER’s observations. There were still some discrepancies, however.
As the study authors explained, Encke is actually closest to Mercury’s orbit about one week after the calcium peak. However, they explained that this is due to the dust stream spreading out along the comet’s current orbit over the course of several thousand years, then being affected by forces known as Poynting-Robertson drag, causing it to encounter Mercury at the observed location.
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Feature Image: NASA/Goddard
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