How Big is Comet ISON?

“Images captured June 13 with Spitzer’s Infrared Array Camera indicate carbon dioxide is slowly and steadily “fizzing” away from the so-called “soda-pop comet,” along with dust, in a tail about 186,400 miles (300,000 kilometers) long.

“We estimate ISON is emitting about 2.2 million pounds (1 million kilograms) of what is most likely carbon dioxide gas and about 120 million pounds (54.4 million kilograms) of dust every day,” said Carey Lisse, leader of NASA’s Comet ISON Observation Campaign and a senior research scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. “Previous observations made by NASA’s Hubble Space Telescope and the Swift Gamma-Ray Burst Mission and Deep Impact spacecraft gave us only upper limits for any gas emission from ISON. Thanks to Spitzer, we now know for sure the comet’s distant activity has been powered by gas.”
NASA 07/23/2013

Comet ISON was emitting about 2.2 million pounds (1 million kilograms) of carbon dioxide gas per day in a tail about 186,400 miles (300,000 kilometers) long on June 13, 2013.

Here are some quick back-of-the-envelope numbers based on the information from June 13, 2013.

2.2 million pounds (1 million kilograms) equals 35,200,000 ounces.
As a comparison, a can of soda is roughly 12 ounces.

35200000/12 = 2,933,333.3 cans

3,074,186 = total population of Iowa estimated in 2012

(3074186*.235) = population under 18 years of age
3,074,186 - (3,074,186*.235) = 2,351,752 adults
2,933,333.3 - 2,351,752 = 581581.3

That’s the equivalent of 1 can of soda for every adult Iowan per day, with 581,581 having another serving.

As another example, an old vending machine can hold about 368 beverages.

2,933,333.3 /368 = 7971.01 vending machines

Keep in mind that the above example only uses the 2.2 million pounds (1 million kilograms) of carbon dioxide gas emitted by ISON. Comet ISON also ejects 120 million pounds (54.4 million kilograms) of dust.

The total mass of the Statue of Liberty is approximately 225 tons (or 450,000 pounds).

120 million pounds / 450,000 pounds = 266.66

That’s enough dust to weigh in the same as 266 Statues of Liberty per day.

Comet ISON is less than 3 miles (4.8 kilometers) in diameter, about the size of a small mountain, and weighs between 7 billion and 7 trillion pounds (3.2 billion and 3.2 trillion kilograms).

Let’s take the smaller number.

2.2 million pounds / 7 billion pounds * 100  = % of carbon dioxide emitted per day.
2.2 million pounds / 7 billion pounds * 100  = 0.0314%

Comet ISON emits less than 0.031% of its mass of carbon dioxide per day.

120 million pounds / 7 billion pounds * 100 = % of dust emitted per day
120 million pounds / 7 billion pounds * 100 = 1.714%

Comet ISON emits around 1.71% of its mass as dust per day, if we take the much smaller number.

If we take the much larger estimation of 7 trillion pounds, we get less than 0.000031% of its mass emitted as carbon dioxide per day.
If we also use the larger figure to compare the dust, we get less than 0.0017% of its mass emitted as dust per day.

Even though the larger estimation of 7 trillion pounds seems like a daunting amount, it’s fairly tiny in the scope of things here on Earth. In a May 2003 Outside magazine article, Roger Bilham, a geophysics professor at the University of Colorado, estimated that Mount Everest has a mass of around 357 trillion pounds.

Amazing!

Comet ISON is not a planet just a comet.

Let’s compare some sizes.

Size Comparisons
Saturn has a diameter of approximately 72,367 miles (116,464 km). That’s approximately 9.1 Earth diameters.
Jupiter has a diameter of approximately 86,881 miles (139,822 km). That’s approximately 10.9 Earth diameters.
Mars has a diameter of approximately 4,212 miles (6,779 km). That’s approximately 0.53 Earth diameters.

Earth has a diameter of approximately 7918 miles (12,742 km).
Earth’s moon has a diameter of approximately 2159.14 miles (3474.8 km). That’s larger than dwarf planet Pluto’s diameter of 1466.44 miles (2360 km) but smaller than Mercury’s diameter of 3032 miles (4879 km).

The diameter of Comet ISON's nucleus is approximately 3 miles (4.8 km).

The diameter of Comet ISON is approximately 3 miles (4.8 km).

Based on observations by NASA’s Spitzer Space Telescope, the nucleus, or body of Comet ISON was approximately 3 miles (4.8 km) on June 13, 2013. To put this into perspective, the diameter of the nucleus, the main rocky and icy body of Comet ISON would be the same distance as a drive in downtown Dallas, Texas. You can use Google Earth to plot a measurement on any major city to get an idea of what 3 miles (4.8 km) looks like.

Here’s another interesting comparison.

According to the USGS, all the water on Earth would create a sphere of water with a diameter of 860 miles. If you only took the drinkable liquid fresh water, you would have a sphere about 169.6 miles in diameter. If you only took the amount of fresh water in lakes and rivers, you would have a sphere with a diameter of 34.9 miles.

Comet ISON’s diameter of 3 miles (4.8 km) is less than 1/10th of that last amount.

Diagram of a Comet.

Diagram of a Comet.

Comet ISON’s coma, which is a cloud of gas, was approximately 3,100 miles across, or 1.2 times the width of Australia, based on observations from NASA’s Hubble Space Telescope on April 10, 2013.

Since Comet ISON is a comet and not a planet or a moon, it has a dust tail.

On January 30, 2013, NASA’s Swift Telescope observed that Comet ISON’s dust tail extended more than 57,000 miles.

A few months later on June 13, 2013, NASA’s Spitzer Space Telescope observed that Comet ISON’s dust trail extended more than 186,400 miles (300,000 kilometers) long.

Comet ISON is expected to become visible to the eye in mid-November as it approaches the sun and reaches perihelion on November 28, 2013.

As a comparison, Comet Halley’s tail was approximately 13.67 million miles (22 million km) on February 22, 1986, thirteen days after it reached perihelion on February 9, 1986.

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