The famed Hubble Telescope of the National Aeronautics and Space Administration (NASA) did not disappoint when comet Siding Spring passed within a short distance from Mars earlier this month.

The Hubble has captured an image of the mountain sized comet, also known as C/2013 A1, as it approached the Red Planet, a phenomenon that has never been seen before and which scientists said occurs only once in a million years.

Comet Siding Spring got nearest Mars on Oct. 19 at 2:28 PM EDT at a distance of about 87,000 miles. At the time of this close encounter, comet Siding Spring and the Red Planet were about 149 million miles away from the planet Earth.

Hubble's image of the rare event, which the U.S. space agency shared on its website, is spectacular with planet Mars and the comet being highlighted against the dark backdrop of space speckled with smaller and seemingly less-impressive lights from the background stars.  

Mars glows red and the bright nucleus and diffuse tail of Comet Siding Spring stand out against the rest of the cosmic objects in the image.  

The photo was actually the result of combining separate images of the Red Planet and comet Siding Spring that were taken from Oct.18 at 8:06 a.m. to Oct. 19 at 11:17 p.m. The Hubble also captured a separate image of planet Mars on Oct. 18 at 10:37 P.M.

As to why a composite image was rendered, NASA explained that a single exposure of Mars and comet Siding Spring with their stellar background would pose some problems because the red planet is significantly brighter than the comet by up to 10,000 times.

"Mars actually is 10,000 times brighter than the comet, so it could not be properly exposed to show detail in the Red Planet," NASA said in a statement.

The two cosmic bodies were also moving relative to each other. Thus, they could not be simultaneously imaged in one exposure without having one of them getting motion blurred.

Scientists had to program the Hubble so it would track comet Siding Spring and the Red planet separately in two observations.

Comet Siding Spring came from a cold and remote region of the Solar System known as Oort cloud. It is the first comet from this region to be studied by scientists up close. Scientists hope that by studying Comet Siding Spring, they can learn more about how planets form. 

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