New comet's potential Mars collision in 2014 explained

Comet Siding Spring will actually be the second close shave of Mars by a passing comet within a time span of just over a year.

By Joe Rao, SPACE.com
Tue, Mar 05 2013

A newfound comet is apparently on course to have an exceedingly close call with the planet Mars in October 2014, and there is a chance — albeit small — that the comet may even collide with the Red Planet.

The new comet C/2013 A1 (Siding Spring) was discovered Jan. 3 by the Scottish-Australian astronomer Robert H. McNaught, a prolific observer of both comets and asteroids who has 74 comet discoveries to his name.

McNaught is a participant in the Siding Spring Survey a program that hunts down asteroids that might closely approach the Earth. He discovered the new comet using the 0.5-meter Uppsala Schmidt Telescope at Siding Spring Observatory, New South Wales, Australia.

Pre-discovery images of the comet from Dec. 8, 2012 by the Catalina Sky Survey in Arizona were quickly found. Because the comet was discovered as part of its survey for asteroids, it bears the name of the observatory, Siding Spring. Officially it is catalogued as C/2013 A1.

When it was discovered, Comet Siding Spring was 669 million miles (1.07 billion kilometers) from the sun. Based on its orbital eccentricity, it is apparently a new or "virgin" comet, traveling in a parabolic orbit and making its very first visit to the vicinity of the sun. It is expected to pass closest to the sun (called perihelion) on Oct. 25, 2014 at a distance of 130 million miles (209 million km).

But, less than a week earlier, on Oct. 19, 2014, the comet — whose nucleus is estimated to be anywhere from 5 to 30 miles (8 to 50 km) in diameter — is projected to cross the orbit of Mars and pass very close to that planet. Preliminary calculations suggest that nominally at closest approach, Comet Siding Spring will come to within 63,000 miles (101,000 km) of Mars.

However, because the comet is currently very far out in space and has been under scrutiny for less than three months, the circumstances of its orbit will likely need to be refined in the coming weeks and months. As such, the comet's approach to Mars might ultimately end up being farther or closer than what current predictions suggest. In fact, last Wednesday (Feb. 27) observations made by Leonid Elenin, a reputable Russian astronomer who works at the Keldysh Institute of Applied Mathematics,suggested that the comet could pass even closer — just 25,700 miles (41,300 km) from the center of Mars.

According to Elenin: "On the 19th October 2014, the comet might reach apparent magnitude of -8 to -8.5, as seen from Mars!” (This would make the comet 15 to 25 times brighter than Venus). "Perhaps it will be possible to acquire high-resolution images from the Mars Reconnaissance Orbiter (MRO)," he added.

Then there is also the small possibility that the comet could collide with Mars.

Moving at 35 miles (56 km) per second, such a collision could create an impact crater on Mars up to ten times the diameter of the comet's nucleus and up to 1.25 miles (2 km) deep, with an energy equivalent up to of 2 x 10^10 megatons!

Most readers will recall Comet Shoemaker-Levy's plunge into Jupiter in July 1994 which left dark telltale scars on Jupiter’s cloud tops for many months thereafter.

Collision or not, Comet Siding Spring will definitely come extremely close to Mars less than 20 months from now. Incredibly, this will actually be the second close shave of Mars by a passing comet within a time span of just over a year.

On Oct. 1 of this year, the much awaited Comet ISON is due to pass 6.5 million miles (10.5 million km) from Mars on its way toward a grazing encounter with the sun in November. That rendezvous is close enough in its own right to be categorized as exceptional and yet, Siding Spring will approach about 100 times closer.

Comet (C/2010-X1) Elenin's Approach - March 30, 2011-Feb 13, 2012

Here's its trajectory and timetable in a snapshot

Massive Comet Impact Detected on Neptune

Smashup 200 years ago suggests crashes more frequent than thought. Rachel Kaufman for National Geographic News | July 23, 2010

Neptune was struck by a giant comet about two centuries ago, according to new research. The find adds to a growing body of evidence that cometary collisions with gas giant planets may be more common than astronomers thought.

On rocky planets with thin atmospheres, such as Mercury (pictures) and Mars, it's easy to count the craters made by impacts dating back millions of years, giving scientists a rough estimate of how frequently space rocks collide with other worlds.

But the gas giants—Jupiter, Saturn, Uranus, and Neptune—are planets that are almost all roiling atmosphere with just tiny cores of rock, making it much harder to find evidence of past impacts.

In 1994 the comet Shoemaker-Levy 9 broke apart and smashed into Jupiter, and several space probes, including Voyager 2, Galileo, and the Hubble Space Telescope, were able to document the rare event.

Using what they'd learned about chemicals left in Jupiter's atmosphere after the comet crash, scientists from the French observatory LESIA and the Max Planck Institutes in Germany analyzed the composition of Neptune's atmosphere with the European research satellite Herschel.

The data show that the amount of carbon monoxide in Neptune's upper atmosphere is higher than in the planet's lower atmosphere. Since gas would normally thin out as it reaches higher atmospheric layers, the extra gas had to come from some outside source, the scientists say.

A comet, which carries carbon monoxide in its icy tail, is the "main explanation," said study co-author Paul Hartogh of the Max Planck Institute for Solar System Research.

Comet Also Smashed Saturn?

The researchers estimate the comet that struck Neptune was 1.2 miles (2 kilometers) wide, which would have made its impact very powerful.

The first fragment of Shoemaker-Levy 9 was just half the size of the unnamed Neptune comet. When the fragment struck Jupiter, it released energy equal to 225,000 megatons of TNT and created a plume 621 miles (1,000 kilometers) high.

In addition, a similar technique used earlier this year found evidence for a comet crash on Saturn 300 years ago.

Adding the Neptune find to the relatively recent Saturn and Jupiter smashups implies that comet collisions might be more frequent than astronomers had thought.

A 1997 study estimated that comets about a mile (1.6 kilometers) wide hit Jupiter once every 6,000 years. And mathematical models for Neptune have suggested that a major comet hits the gas giant planet every 8,000 years, Hartogh said.

Based on the old calculations, he said, "statistically, it's not so probable" that Neptune, Jupiter, and Staurn would each suffer a major impact event within a 300-year period—suggesting a new estimate may be in order.

"Maybe there are more impacts than we think."

Near-Earth Object 2010 AL30

Near-Earth Object 2010 AL30



Photographer: Patrick Wiggins; Patrick's Web Site
Summary Author: Kurt Fisher; Patrick Wiggins
March 2010 Earth Science Picture of the Day Viewer's Choice

Most North Americans slept through the morning of January 13, 2010 as near-Earth object (NEO) 2010 AL30 silently moved across the night sky. Its path brought it to an altitude of about 122,000 km, which is one third of the distance to the Moon. 2010 AL30 is an asteroid approximately 10 to 15 m across. As shown above, Patrick Wiggins followed its passage using a 35 cm telescope and CCD camera. 2010 AL30 is estimated to be part of a NEO population of several thousand similar objects. On average, one 10-15 m diameter asteroid passes within one lunar distance of the Earth about once a week. If 2010 AL30 had entered the Earth's atmosphere, it would have created an air burst equivalent to between 50 kT and 100 kT (kilotons of TNT). The Nagasaki "Fat Man" atom bomb had a yield between 13-18kT.

On January 22, 2010, the National Research Council of the National Academy of the Sciences released its final report as requested by the United States Congress. This report recommended an optimal approach to complete the census of NEOs larger than about 140 m as well as an optimal approach for deflecting a NEO that threatens impact with the Earth. The report recommended that the census of NEOs be expanded to include NEOs between 30 and 50 m in diameter. NASA's NEO program estimates that "with an average interval of about 100 years, rocky or iron asteroids larger than about 164 ft (50 m) would be expected to reach the Earth's surface and cause local disasters or produce the tidal waves that can inundate low lying coastal areas." A NEO with a diameter of 50 m can create a blast equivalent to one megaton of TNT.

There have not been a significant number of deaths caused by asteroids in historical times due to the infrequency of the major events. When such events do occur they are more likely to happen over unpopulated regions such as oceans. Noting that without better surveys, accurate estimates of the risk of NEO impacts cannot be made, the report made best current estimates for the global risk of death by shark at 3-7 persons per year, death by asteroid at 91 persons per year and death by automobile at 1,200,000 persons per year.