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| Astronomy Essentials | Space on Sep 29, 2014

Comet Siding Spring’s close encounter with Mars

The icy core of Comet C/2013 A1 Siding Spring won’t strike Mars when it sweeps closest on October 19. But what a sight from Mars’ surface!

One of the most anticipated astronomical events of 2014 is the close passage of Comet C/2013 A1 Siding Spring to the planet Mars on October 19, 2014. The comet’s tiny nucleus, or core, will miss Mars by about 82,000 miles (132,000 kilometers). For comparison, Mars’s small outer moon Deimos orbits at a distance of about 15,000 miles (24,000 km). As comets travel through space, though, they leave behind a trail of dust particles, and this trail of debris might be wide enough to reach Mars and encounter its thin atmosphere … or might miss it, too. If the comet dust does reach Mars, it has the potential to damage our spacecraft in orbit there, which is why NASA has been taking steps to protect its Mars orbiters. As for the view from Mars itself … if only we could be there. Follow the links below to learn more:

Comet Siding Spring / Mars encounter on October 19, 2014

When did astronomers discover Comet C/2013 A1 Siding Spring?

How will the comet look from Mars?

Will I be able to see this comet in Earth’s night sky?

Animation via Near-Earth Object (NEO) office, NASA’s Jet Propulsion Laboratory.

Animation of Comet C/2013 A1 Siding Spring / Mars encounter via Near-Earth Object (NEO) office and NASA JPL.

An illustration of the inner part of the orbit of comet C/2013 A1 Siding Spring.  On October 19, 2014, the comet will have a close pass of the planet Mars.  Its nucleus will miss Mars by about 82,000 miles (132,000 kilometers). The comet's trail of dust particles shed by the nucleus might be wide enough to reach Mars or might also miss it.   Image via NASA/JPL.

An illustration of the inner part of the orbit of comet C/2013 A1 Siding Spring. Image via NASA/JPL.

Comet Siding Spring / Mars encounter on October 19, 2014 Hurtling through space at about 35 miles (56 kilometers) per second, this comet will come very close to Mars. It will be less than one-tenth the distance of any known previous Earthly comet flyby. The comet’s icy core, or nucleus, will not strike Mars, but the high speed of the comet relative to Mars means that even the smallest grain of dust from the comet could cause “significant damage” to our spacecraft, NASA says.

There are three live NASA spacecraft orbiting Mars now, and one mission from India. The Mars Reconnaissance Orbiter (MRO) and Mars Odyssey spacecraft have been in orbit around Mars for some time. MAVEN – the Mars Atmosphere and Volatile EvolutioN mission – arrived at Mars on September 21, 2014. The Mars Orbiter Mission (MOM) successfully entered Mars’ orbit on September 24, 2014, making India the first Asian country to reach the Red Planet. I don’t know what India plans for MOM during the Comet Siding Spring flyby, but NASA plans to have all three of it orbiters positioned on the opposite side of Mars from the comet, when the comet passes by. Rich Zurek, chief scientist for the Mars Exploration Program at NASA’s Jet Propulsion Laboratory in Pasadena, California, said in a NASA release on July 25:

Three expert teams have modeled this comet for NASA and provided forecasts for its flyby of Mars. The hazard is not an impact of the comet nucleus, but the trail of debris coming from it. Using constraints provided by Earth-based observations, the modeling results indicate that the hazard is not as great as first anticipated. Mars will be right at the edge of the debris cloud, so it might encounter some of the particles — or it might not.

NASA says the period of greatest risk will come not when the comet is closest to Mars, but about 90 minutes later. Space engineers expect the risk period to last about 20 minutes, during which time Mars will come closest to the center of the widening dust trail left behind by Comet Siding Spring. NASA said on July 25:

NASA’s Mars Reconnaissance Orbiter (MRO) made one orbit-adjustment maneuver on July 2 as part of the process of repositioning the spacecraft for the Oct. 19 event. An additional maneuver is planned for Aug. 27. The team operating NASA’s Mars Odyssey orbiter is planning a similar maneuver on Aug. 5 to put that spacecraft on track to be in the right place at the right time, as well.

NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft was on its way to the Red Planet when NASA was adjusting the orbits of its other Mars craft, in preparation for the comet flyby. The MAVEN team is planning to conduct a precautionary maneuver on October 9, prior to the start of the mission’s main science phase in early November.

Follow the orbit of Comet Siding Spring with this orbit simulator from JPL

NASA’s NEOWISE mission captured this image of the comet on Jan. 16, 2014 when it was 355 million miles (571 million km) from the sun. - See more at: http://astrobob.areavoices.com/2014/01/29/nasa-considers-precautions-for-upcoming-mars-comet-encounter/#sthash.BgScjNxZ.dpuf

NASA’s NEOWISE mission captured this image of the comet about a year after its discovery, on January 16, 2014. At that time, the comet was 355 million miles (571 million km) from the sun. Image via NASA/JPL-Caltech.

NEOWISE caught these four different shots of Comet Siding Spring around July 28, 2014 and combined them into this single image.  Read more about this image from NASA.

By late July 2014, we could see the comet much better. That’s when NASA’s NEOWISE mission caught four shots of Comet Siding Spring, as it moved in front of the star background, and combined them into this single image. Read more about this image from NASA.

When did astronomers discover Comet C/2013 A1 Siding Spring? Astronomer Rob McNaught discovered the on January 3, 2013 using the Uppsala Schmidt Telescope at Siding Spring Observatory in Australia. At the time of discovery it was 7.2 AU (7.2 times Earth’s distance) from the sun. Shortly after its discovery, astronomers in Arizona confirmed the comet in images taken a month earlier as part of the Catalina Sky Survey. Those early observations, plus others from around the world, quickly showed that the comet has a highly inclined, retrograde orbit around the sun. We learned that the comet won’t come very close to the sun at its perihelion (closest point to the sun), no closer than 140 million miles (in contrast to Earth’s average distance of about 92 million miles). So the comet will not come near Earth. But its perihelion is just about at the orbit of Mars. This means the comet will be at its most active around the time it encounters Mars.

By the way, Comet C/2013 A1 Siding Spring probably took millions of years to come into the inner solar system from the Oort cloud. Once it passes closest to the sun and heads back out to deep space, we will not see it again.

Comet Lovejoy is visible near Earth's horizon behind airglow in this nighttime image photographed by NASA astronaut Dan Burbank, Expedition 30 commander, onboard the International Space Station on Dec. 22, 2011.

This is not Comet C/2013 A1 Siding Spring. It’s Comet Lovejoy, seen from the International Space Station in December 2011, near Earth’s horizon (behind airglow). How will Comet Siding Spring look from Mars on October 19, 2014? Maybe our spacecraft will get some images, but, since the craft aren’t designed for night sky imaging, they likely won’t look this awesome. Comet Lovejoy photo via NASA.

How will the comet look from Mars? If only we could transport ourselves there! The animation above looks more awesome if you view it in full scale at the website of its creators, solarsystemscope.com. It shows Comet Siding Spring moving among the stars (yes, Mars sees the same patterns of stars we do from Earth). It’s the comet as seen from the location of Curiosity rover on Mars, now at the base of Mount Sharp in Mars’ Gale Crater, during Comet Siding Spring’s close flyby on October 19. Michal Sadlon of solarsystemscope told EarthSky:

Length of the tail was calculated according available data: tail should be 12,000 miles long, distance of the comet from Mars is 82,000 miles = 8 degrees angular size.

But of course no one knows for sure how long the tail will be until the comet actually sweeps past Mars.

Sky & Telescope said in an article in March 2013:

… Comet Siding Spring is going to put on one helluva show as seen from Mars. As calculated by small-body aficionado Bill Gray, the comet will approach Mars from the south and sweep into its northern-hemisphere skies over just a few hours.

Hopefully, some of the NASA spacecraft will be able to capture its picture. Although Mars’ atmosphere is thinner than Earth’s, it is thick enough to protect the Opportunity and Curiosity rovers that are transmitting from Mars surface, NASA has said, “even if dust particles from the comet hit the atmosphere and form into meteors.” What a sight that would be! NASA also said:

Rover cameras may be used to observe the comet before the flyby, and to monitor the atmosphere for meteors while the comet’s dust trail is closest to the planet.

In the meantime, NASA also plans to study the comet with its orbiters in the days before and after the comet’s flyby. They’ll use instruments on the Mars orbiters to study the comet nucleus, the coma surrounding the nucleus, and the tail of Siding Spring, as well as the possible effects on the Martian atmosphere. MAVEN, in particular, will study gases coming off the comet’s nucleus into its coma as it is warmed by the sun. MAVEN also will look for effects the comet flyby may have on the planet’s upper atmosphere and observe the comet as it travels through the solar wind.

Roger Groom in Western Australia captured this photo of Comet C2013-A1-Siding Spring in early July, 2014, using a 12-inch telescope.  Copyright Roger Groom.  Used with permission.   See more astrophotography by Roger Groom.

Roger Groom in Western Australia captured this photo of Comet C/2013 A1 Siding Spring in early July, 2014, using a 12-inch telescope. Copyright Roger Groom. Used with permission. See more astrophotography by Roger Groom.

Will I be able to see this comet in Earth’s night sky? Despite the spectacular show from Mars, we on Earth will not be able to see this comet with the eye alone. However, southern hemisphere observers with telescopes have been seeing it for some time now, and some have captured the comet’s picture. Click here for info on the position of Comet C/2013 A1 Siding Spring.

On the other hand, on October 19, 2014 – the night of the comet’s Mars encounter – you will be able to see Mars. I’ll be up in the early evening, located more or less in the direction toward the center of our Milky Way galaxy. That’s a star-rich region of the heavens, but Mars’ reddish color should help you spot it. EarthSky’s planet guide will tell you more.

Bottom line: The tiny nucleus of Comet C/2013 A1 Siding Spring will not strike Mars when it comes closest on October 19, 2014. But material shed by the comet could damage our spacecraft in orbit around the Red Planet. NASA is taking steps now to prevent damage to its orbiting spacecraft.