WASHINGTON — On Sunday, Oct. 19, Earthlings and a handful of spacecraft can witness an awesome celestial spectacle live as it happens.
Comet Siding Spring will pass only 87,000 miles from the surface of planet Mars at 2:27 p.m. EDT. Not since the impact of Comet Shoemaker-Levy 9 with the planet Jupiter in July 1994 have we had such a close encounter. Space history will be made as this will be the closest planetary flyby of a comet in recorded human history.
NASA, India and the European Space Agency (ESA) are gearing up to observe this historic event and protect their spacecraft in orbit around Mars from getting hit by zillions of comet bits.
Comets are left over debris from the formation of the solar system 4.6 billion years ago. These frozen icy dirtballs can be miles across; when they get close enough to the Sun, they begin to evaporate from the heat.
When this happens, a stream of dust, gases and water come off the comet’s solid core, called the nucleus. This expanding sphere of material forms a cloud around the nucleus, called the coma. Comets also grow a tail that streams away from the comet and can stretch for millions of miles across the solar system.
Comet Siding Spring was discovered in January 2013 and was found to be a first- time visitor to the inner solar system from the depths of the Oort Cloud, a vast repository of over an estimated trillion comets.
Last year’s Come t ISON, which got so much media coverage up until its disintegration from passing too close to the Sun, was also a first time visitor from the Oort Cloud.
Astronomers want to study these pristine comets whenever they can to learn about the birth of the solar system. Analyzing the coma and tail can provide important information about the composition of the comet and provide insight into conditions that existed where and when it formed.
But what made Comet Siding Spring so exciting was that when the orbit of this icy interloper from the depths of the solar system was calculated, astronomers were amazed.
The estimated half-mile across comet would pass a mere 87,000 miles from the surface of Mars. With two rovers on the surface of Mars and a fleet of Mars orbiting spacecraft, the opportunity to make up-close and personal observations of the comet would be available as never before in history.
But the closeness of the flyby also presented a clear and present danger to the spacecraft, especially the orbiters. All of the debris flying off the comet is traveling at a speed of 35 miles per second. Talk about a speeding bullet! Even the smallest fluff of dust could be catastrophic to an orbiting spacecraft. The two surface rovers, Opportunity and Curiosity, will be protected by the thin Martian atmosphere, which should be sufficiently dense to destroy any incoming bits.
To protect the orbiting Martian fleet, NASA’s Mars Odyssey, Mars Reconnaissance Orbiter, newly arrived Maven and Mars Orbiter Mission (India) and ESA’s Mars Express have changed their orbits so they can be on the opposite side of Mars when Siding Spring is at closest point of approach (CPA). It is hoped that the spacecraft will be out of harm’s way long enough for the bulk of the cometary debris to have passed.
The view from Mars should be awesome for the two rovers as seen in this NASA video. NASA has created a website for Earthlings to get the latest views and news from Mars during this historic encounter as it happens.
You can see Mars low in the western sky on the day of the encounter after sunset, but the comet is not visible to the unaided eye. You can watch Comet Siding Spring live on the Internet starting at 2:15 p.m. EDT.
We will learn a lot about comets during this fabulous flyby. We should also be witness to some incredible pictures from a variety of spacecraft and boots-on- the-ground rovers. We’ll have an update for you on WTOP at 7:10 p.m. EDT the day of the flyby.