Who’d A- Thunk It? Mercury May Have Meteor Showers Too

Artist’s concept of Mercury crossing the debris trail of Comet Encke, sparking a recurring meteor shower. New evidence from the MESSENGER mission suggests the planet receives regular doses of Mercurial dust. Credit: NASA’s Goddard Space Flight Center

Of course, of course, it only makes sense. We’re so caught up in watching meteor showers on our own planet, who ever thinks about meteors at Mercury? Or Venus for that matter? This week NASA announced that regular spikes in the amount of calcium in Mercury’s upper atmosphere bespeak a cyclical source. The likely culprit? Comet 2P/Encke.

Like breadcrumbs dropped to mark a path, dust and fragile bits of rock are released through vaporization of a comet’s ice and pushed back by the pressure of sunlight to form a tail. The larger pieces are left behind to fan out along the comet’s orbit. If by good fortune Earth’s orbit happens to intersect the debris trail, we see a shower of meteors in the sky.

This photo, made by NASA’s Spitzer Space Telescope in infrared light, shows Comet Encke’s glowing nucleus/nuclear region and a trail of warm dust and pebbly debris shed by the comet along its orbital path. Credit: NASA

Most recently, the Geminids put on a great show, although their origin lies with the peculiar rock-shedding asteroid 3200 Phaethon.

Comet 109P/Swift-Tuttle brings us the familiar Perseid meteor shower, while 2P/Encke gives rise to several meteor streams – the Southern and Northern Taurids, showers that peak in October and November, and the daytime Beta Taurids in June and July.

Measurements taken by MESSENGER’s Mercury Atmospheric and Surface Composition Spectrometer have revealed seasonal surges of calcium that occurred regularly over the first nine Mercury years (1 year = 88 Earth days) since MESSENGER began orbiting the planet in March 2011. Just as we saw huge spikes in the amounts of metals like magnesium and iron in Mars’ upper atmosphere during Comet’s Siding Spring’s brush with the planet last October, MESSENGER’s instrument detected periodic spikes in the amount of calcium – although with a twist.

A color- enhanced view of Mercury, assembled from images taken at various wavelengths by the cameras on board the MESSENGER spacecraft, shows a cratered composed with a surface composed of a variety of minerals. The circular, orange area near the center-top of the disk is the enormous Caloris impact basin. Credit: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington

Mercury’s has only a whiff of an atmosphere, what astronomers term an exosphere, the last thing you could call an atmosphere before encountering the vacuum of space. The shower of small dust particles peppering interplanetary space pass right down to the surface and strike the planet’s rocks, knocking calcium-bearing molecules free from the surface, which are then free to rise to greater heights. This process, called impact vaporization, continually renews the gases in Mercury’s exosphere as interplanetary dust and meteoroids rain down on the planet.

These type of impacts happen all the time, but scientists noticed a pattern in the calcium spikes that pointed to a repeating source. Sounds like a perfect time for a comet to step in. Examination of the handful of comets in orbits that would permit their debris to cross Mercury’s orbit indicated that the likely source of the spikes was Encke.

The Jupiter family of comets were all once long-period objects in the Kuiper the orbits of which were changed to short-period by close passes by Jupiter. The green circle is Jupiter’s orbit, the purple is Earth’s. Notice that when farthest from the Sun, the comets about as far as Jupiter is from the Sun. Credit: Wikipedia with additions by the author

“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 coauthor 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.”

To test their hypothesis, Han and crew created detailed computer simulations and discovered that the MESSENGER were offset from the expected results but in a way that made sense due to changes in Encke’s orbit over time from the gravitational pull of Jupiter and other planets.

Pantheon Fossae – The striking troughs of Mercury’s Pantheon Fossae, the feature that MESSENGER scientists first called “The Spider” when they discovered it. Credit: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington

Comets get nudged by planets routinely, especially if they pass near Jupiter, the outer Solar System’s gravitational goliath. Jupiter, with the help of Neptune, has re-worked the orbits of countless bodies that once resided in the distant Kuiper Belt into shorter-period comets that swing around the Sun in 20 years or less. Called the Jupiter-family, there are about 400 known and Encke is one of them with an orbital period of just 3.3 years.

Who knows how many other meteor showers might pepper Mercury in a year, but scientists will be looking for potential signs of them in planet’s atmosphere in the months ahead. While they may not leave bold streaks of light as they do on Earth, they create something almost as amazing – a shower of particles that goes up instead of down.

8 Responses

  1. Edward M. Boll

    I have not seen Mercury in a while, but saw Venus the other evening, first time in months. It will be a nice spectacle in 15.

  2. Edward M. Boll

    Lovejoy may even be brighter than the optimistic predictions of the BAA. If this trend continues it may make magnitude 4 or brighter.

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