NASA Preps Mars Orbiters for Comet Close Encounter

While comet ISON will be making a flyby of Mars this week, this may be a dress rehersal for a much closer encounter with another comet late next year, as portrayed in this illustion. Credit: Courtesy of NASA
NASA and astronomers worldwide are preparing for Mars to have a close encounter with a comet in October this year, as portrayed in this illustration. Courtesy: NASA

A cometary near miss for Mars in a few months means meteor risks for NASA’s spacecraft orbiting the red planet.

On October 19, the comet Siding Spring will brush by Mars, passing so close that the space agency this week announced it has put together a special playbook filled with protective measures for its orbiters there.

While astronomers have ruled out a direct hit on the planet, the comet’s dusty coma (a cloud nearly as large as the Earth) will sweep directly across Mars, with the comet core buzzing within 85,600 miles (137,760 kilometers) of its surface—less than half the distance from the Earth to the moon.

Unlike NASA’s Mars rovers Curiosity and Opportunity, which will be perfectly safe and have amazing ringside seats to the sky show, the orbiters may be at risk of damage from a barrage of bullet-like cometary bits. Tiny dust particles traveling 125,200 miles per hour (201,490 kilometers per hour) could effectively sandblast the Mars spacecraft.

This chart shows the trajectory of Comet Siding Springs as it rounds the sun and passes by the planet Mars. Credit: JPL/NASA
This chart shows the trajectory of comet Siding Spring as it rounds the sun and passes by the planet Mars. Credit: JPL/NASA

At this point NASA has Mars Odyssey and the Mars Reconnaissance Orbiter circling the red planet, along with Mars Express, a joint mission with the European Space Agency. By the end of September a fourth orbiting probe will reach the red planet, the Mars Atmosphere and Volatile Evolution or MAVEN.

Computer simulations of the comet’s swing around Mars show that about 90 minutes after its closest approach to the planet, there is a specific 20-minute window that poses the most danger to the orbiters from the comet’s debris trail. So NASA plans to use the planet as a shield for its probes during those critical minutes, just in case.

But the orbiters won’t be shying away from this cosmic show—NASA hopes to be able to capture some amazing science in the hours and days before and after the comet’s closest approach.

Scientists believe that this comet has never entered the inner solar system before. If true, that means the comet is a pristine remnant of the solar system’s early formation. By directly taking a taste and sniff of the icy visitor, we may actually be able to collect data that harken back to the birth of the planets, including the Earth.

See for Yourself

By October 25, the comet will reach its point of closest approach to Earth, coming about 130 million miles (209 million kilometers) from the sun. But even then it’s not expected to be visible to the naked eye.

Instead, it’s a safe bet that both backyard and professional stargazers will be training their telescopes on the red planet on October 19, hoping to get a good view of the cosmic near-miss. Mars will be low in the southwest sky, near the constellation Sagittarius, at that time.

This sky chart shows the view of Mars and Comet Siding Springs on October 19th. Sky-watchers need to face the southwest after dusk, looking for the teapot star pattern of Sagittarius constellation as a guidepost for finding orange-hued Mars low in the sky.  Credit: Starry Night Software / A.Fazekas
This sky chart shows the position of Mars and comet Siding Springs on October 19. Sky-watchers need to face the southwest after dusk, looking for the teapot star pattern of the constellation Sagittarius as a guidepost for finding orange-hued Mars low in the sky. Courtesy: Starry Night Software/A. Fazekas

There is still hope that, starting around mid-September, Siding Spring may become visible in the evening skies through binoculars and backyard scopes for those in the Southern Hemisphere. The comet will then be gliding through the constellation Ophiuchus, in the southwestern sky at dusk.

Follow Andrew Fazekas, the Night Sky Guy, on TwitterFacebook, and his website.

Changing Planet

Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.