GSFC: Mercury Gets a Meteoroid Shower from Comet Encke

[bystander]

Mercury Gets a Meteoroid Shower from Comet Encke
NASA Goddard Space Flight Center | 2015 Nov 10

[img3="Mercury appears to undergo a recurring meteoroid shower when its orbit crosses the debris trail left by comet Encke. (Artist's concept) (Credits: NASA/Goddard)"]http://www.nasa.gov/sites/default/files ... trail3.jpg[/img3][hr][/hr]

The planet Mercury is being pelted regularly by bits of dust from an ancient comet, a new study has concluded. This has a discernible effect in the planet’s tenuous atmosphere and may lead to a new paradigm on how these airless bodies maintain their ethereal envelopes.

The findings are to be presented at the annual Meeting of the Division of Planetary Sciences of the American Astronomical Society at National Harbor, Maryland, this week, by Apostolos Christou at the Armagh Observatory in Northern Ireland, Rosemary Killen at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and Matthew Burger of Morgan State University in Baltimore, working at Goddard.

Earthlings are no strangers to the effects of cometary dust on a planet and its environment. On a clear, moonless night we witness the demise of countless such dust grains as they burn up in the Earth’s atmosphere in the form of meteors or “shooting stars.” At certain times of the year, their numbers increase manyfold, creating a natural fireworks display: a meteor shower. This is caused by the Earth passing through a stream of dust particles left behind by certain comets. ...

Bodies such as the moon and Mercury are typically thought of as airless, yet we have known since the time of the Apollo moon landings that they are surrounded by clouds of atomic particles either launched from the surface or brought in by the solar wind. Though tenuous by comparison to the dense atmospheres of the Earth or Mars, the observational record has revealed these “surface boundary exospheres” to be complex and dynamic entities, fascinating to study in their own right.

NASA’s MErcury Surface Space ENvironment, GEochemistry, and Ranging (MESSENGER), the first spacecraft to orbit Mercury, measured how certain species in the exosphere vary with time. Analysis of the data by Burger and colleagues found a pattern in the variation of the element calcium that repeats from one Mercury year to the next. To investigate, Killen teamed up with Joe Hahn of the Space Science Institute, based in Austin, Texas, to understand what happens when Mercury ploughs through the so-called zodiacal cloud of interplanetary dust around the sun and its surface is pelted by high-speed meteoroids. ...

Mercury Gets A Meteoroid Shower From Comet Encke
Armagh Observatory | 2015 Nov 10

The meteoroid stream of comet Encke at Mercury: Implications for MErcury Surface, Space ENvironment,
GEochemistry, and Ranging observations of the exosphere - Apostolos A. Christou, Rosemary M. Killen, Matthew H. Burger

• Geophysical Research Letters 42(18):7311 (28 Sep 2015) DOI: 10.1002/2015GL065361

[neufer]

[b][size=125][color=#0000FF]Did the intersection of Encke's Comet perihelion with Mercury result in the bi-modal bifurcated Northern & Southern Taurids :?: [/color][/size][/b]

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[b][color=#0000FF]A Han Dynasty silk comet atlas, featuring drawings of comets believed by Victor Clube and Bill Napier to be related to the breakup of Encke's Comet in the past[/color][/b]

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<<The Taurids are an annual meteor shower associated with the comet Encke. They are named after their radiant point in the constellation Taurus, where they are seen to come from in the sky. Because of their occurrence in late October and early November, they are also called Halloween fireballs. During the week ending November 4, 2005, the large number of fireballs seen all over the world led some to suggest UFO visitations. These fireballs may have been space junk or the Taurids.

Encke and the Taurids are believed to be remnants of a much larger comet, which has disintegrated over the past 20,000 to 30,000 years, breaking into several pieces and releasing material by normal cometary activity or perhaps occasionally by close encounters with the gravitational field of Earth or other planets (Whipple, 1940; Klačka, 1999). In total, this stream of matter is the largest in the inner solar system. Due to the stream's size, the Earth takes several weeks to pass through it, causing an extended period of meteor activity, compared with the much smaller periods of activity in other showers. The Taurids are also made up of weightier material, pebbles instead of dust grains. Typically, Taurids appear at a rate of about 7 per hour, moving slowly across the sky at about 27 kilometers per secondr. If large enough, these meteors may become bolides, with spectacular light shows and even audible sound.

Due to the gravitational effect of planets, especially Jupiter, the Taurids have spread out over time, allowing separate segments labeled the Northern Taurids and Southern Taurids to become observable. Essentially these are two cross sections of a single, broad, continuous stream in space. The Beta Taurids, encountered by the Earth in June/July and which many astronomers consider the cause of the Tunguska event, are also a cross section of the stream. Beta Taurids approach from the Earth's daytime side; so cannot be observed visually in the way the (night-time) Northern and Southern Taurids of October/November can.

The Taurid stream has a cycle of activity that peaks roughly every 2500 to 3000 years, when its core passes nearer to Earth and produces more intense showers. In fact, because of the separate "branches" (night-time in one part of the year and daytime in another; and Northern/Southern in each case) there are two (possibly overlapping) peaks separated by a few centuries, every 3000 years. Some astronomers note that dates for megalith structures such as Stonehenge are associated with these peaks. The next peak is expected around 3000 AD.

Some consider the Bronze Age breakup of the originally larger comet to be responsible for ancient destruction in the Fertile Crescent, perhaps evidenced by a large meteor crater in Iraq. However the Bronze Age was c. 6000 years ago and the original break up of the parent comet, as mentioned above, occurred long before that. Ancient peoples may have been used to Tunguska Class impacts which occur approximately every 300 years as calculated by Eugene Shoemaker and Krakatoa type eruptions both of which have widespread climatic effects and which would dwarf any climatic effects from the slight increase in upper atmospheric dust caused by bolides due to passing through the tail of Comet Encke.

An impact event was observed by NASA scientist Rob Suggs and astronomer Bill Cooke while testing out a new 10-in telescope and video camera they had assembled to monitor the moon for meteor strikes. After consulting star charts they concluded that the impact body was probably part of the Taurid meteor shower. This may well be the first recording of this type of lunar event which some have claimed to have witnessed in the past.>>

• A probable Taurid meteor hit the Moon on Sept. 11, 2013.