Comet Siding Spring provides close encounter for Earth
By Amanda Jermyn

On October 19th at about 2.30pm, Eastern Daylight Time, comet Siding Spring passed within 87,000 miles of the planet Mars, providing Earthlings with a unique opportunity to study primordial material from the birth of our solar system 4.6 billion years ago.

87,000 miles might not sound all that close, but it is only about one third the distance from the Earth to the moon, and the closest a comet has ever been observed to approach either the Earth or Mars.

A comet is comprised of rocky particles, dust, water ice and frozen gases. When it approaches the sun it heats up, releasing gas to form an atmosphere called a coma, and sometimes a trail of dust called a tail. Comet Siding Spring is about a mile wide and its coma is about 12,000 miles across. It was first discovered in January of 2013 by Robert McNaught at the Siding Spring Observatory in Australia. It formed in the Oort Cloud, a vast area of icy debris left over from the gas and dust that first formed our sun and planets, so studying it is of particular interest for the information it may reveal about the composition of our early solar system. As the Oort Cloud is well beyond Pluto’s orbit and half way to the nearest star, the comet has taken about a million years to reach its current position in the inner solar system, and it will be another million years before it makes its next orbit around the sun. Before its close fly-by of Mars, Jim Green, director of NASA’s Planetary Science Division said: “We’re going to observe an event that happens maybe once every million years.”

Fortunately for us, we had in place on the surface of Mars the rovers Curiosity and Opportunity, plus five spacecraft orbiting the planet: NASA’s Mars Reconnaissance Orbiter, Mars Odyssey and MAVEN, along with India’s Mars Orbiter Mission and the European Space Agency’s Mars Express orbiter. Farther out were the Hubble Space Telescope and ground-based telescopes at observatories around the world, all focused on monitoring the fly-by.

As it whizzed through space at 126,000 miles per hour, the comet created a meteor shower and shed debris that could potentially have damaged the orbiting spacecraft. Even a tiny grain of sand can cause major damage when traveling at such high speed. As a precaution, NASA moved its orbiters out of harm’s way during the critical period, and all survived just fine. The rovers were not in danger as they were protected by Mars’ atmosphere.

From observations taken by the various instruments we have begun to receive valuable information about the comet’s composition and its impact on the atmosphere of Mars. According to Jim Green of NASA’s Planetary Science Division, “The comet’s dust slammed into the upper atmosphere, creating a massive and dense ionospheric layer, and literally changed the chemistry of the upper atmosphere” of Mars. Too bad no one was there to witness the dazzling light show of shooting stars that resulted. More recently, with the arrival of the Rosetta Mission’s Philae lander on Comet 67P-Churyumov-Gerasimenko, we have another extraordinary opportunity to explore a comet. Exciting times, indeed!

Join the Springfield Stars Club on Tuesday, November 25th at 7pm (please note earlier starting time) at the Springfield Science Museum for a talk by amateur astronomer Tim Connolly on “Astro-Imaging, a father and son’s personal experience capturing images of the night sky and the sun.” Connolly will also demonstrate how to set up a telescope correctly and will show a selection of his and his son’s deep space images from inside and outside the Milky Way galaxy. Connolly is employed by Baystate Medical Center’s Pathology Department, performing diagnostic electron microscopy. He has a BS degree in biology, chemistry, physics and astronomy, and is active in the Springfield Stars Club and the Amherst area Amateur Astronomers Association. For more information please visit the Connolly father and son Facebook website: Refreshments will be served and the public is welcome. The meeting is free of charge for members, with a suggested donation of $2 per non-member.

Also, on Friday, December 5th at 7:30pm, the Stars Club and Springfield Science Museum will host “Stars over Springfield.” Amateur astronomer Paul Cardone will speak on “How to get to Pluto,” a history of Pluto plus the New Horizons Mission. A fee of $3 for adults and $2 for children under 18 will be charged.