NASA’s got answers.

For some reason, ever since it was first discovered last December, Comet Elenin has been surrounded by a lot of misinformation regarding the danger it poses to Earth. True, it will be swinging around the Sun in a path that takes it “relatively” close to Earth and the other inner planets in October, but remember that in astronomical terms “relatively” close can still mean very, very far away. Like, 22 million miles far away. That’s 90 times the distance between Earth and the Moon! (Or, put another way, just over a quarter the distance from here to the Sun.)

Far. Very far. Especially for a chunk of ice and loose rubble most likely less than 7 miles wide.

I mean sure, you wouldn’t want it to smash into Earth by any means… but it won’t. They’re 99.999% sure of that (and I’m even being conservative on that percentage.)

Still there’s a lot of junk news being spread around about this little visitor from the outer solar system, ranging from the merely misinformed (its non-existent magnetic field cannot cause an earthquake) to the outright outrageous (a fleet of alien spaceships hiding behind it? Really??) so NASA has decided to recruit JPL’s Near-Earth Object specialist Don Yeomans and David Morrison of the NASA Astrobiology Institute to answer some common questions about Comet Elenin.

Since it’s their job to know this stuff, which they do very well, I tend to defer to their judgment on such things…

When will Comet Elenin come closest to the Earth and appear the brightest?

Comet Elenin should be at its brightest shortly before the time of its closest approach to Earth on Oct. 16, 2011. At its closest point, it will be 22 million miles (35 million kilometers) from us.

Will Comet Elenin come close to the Earth or between the Earth and the moon?

Comet Elenin will not come closer to Earth than 22 million miles (35 million kilometers). That’s more than 90 times the distance to the moon.

“Any approximate alignments of comet Elenin with other celestial bodies are meaningless, and the comet will not encounter any dark bodies that could perturb its orbit, nor will it influence us in any way here on Earth.”

– Don Yeomans, JPL

Can this comet influence us from where it is, or where it will be in the future? Can this celestial object cause shifting of the tides or even tectonic plates here on Earth?

There have been incorrect speculations on the Internet that alignments of comet Elenin with other celestial bodies could cause consequences for Earth and external forces could cause comet Elenin to come closer. “Any approximate alignments of comet Elenin with other celestial bodies are meaningless, and the comet will not encounter any dark bodies that could perturb its orbit, nor will it influence us in any way here on Earth.”

“Comet Elenin will not only be far away, it is also on the small side for comets,” said Yeomans. “And comets are not the most densely-packed objects out there. They usually have the density of something akin to loosely packed icy dirt.

“So you’ve got a modest-sized icy dirtball that is getting no closer than 35 million kilometers [about 22 million miles),” said Yeomans. “It will have an immeasurably miniscule influence on our planet. By comparison, my subcompact automobile exerts a greater influence on the ocean’s tides than comet Elenin ever will.”

I’ve heard about three days of darkness because of Comet Elenin. Will Elenin block out the sun for three days?

“As seen from the Earth, comet Elenin will not cross the sun’s face,” says Yeomans.

But even if it could cross the sun, which it can’t, astrobiologist David Morrison notes that comet Elenin is about 2-3 miles (3-5 kilometers) wide, while the sun is roughly 865,000 miles (1,392,082 kilometers) across. How could such a small object block the sun, which is such a large object?

Let’s think about an eclipse of the sun, which happens when the moon appears between the Earth and the sun. The moon is about 2,500 miles (4,000 kilometers) in diameter, and has the same apparent size as the sun when it is about 250,000 miles (400,000 kilometers) away — roughly 100 times its own diameter. For a comet with a diameter of about 2-3 miles (3-5 kilometers) to cover the sun it would have to be within 250 miles (400 kilometers), roughly the orbital altitude of the International Space Station. However, as stated above, this comet will come no closer to Earth than 22 million miles.

I’ve heard NASA has observed Elenin many times more than other comets. Is this true, and is NASA playing this comet down?

NASA regularly detects, tracks and characterizes asteroids and comets passing relatively close to Earth using both ground- and space-based telescopes. The Near-Earth Object Observations Program, commonly called “Spaceguard,” discovers these objects, characterizes a subset of them and predicts their paths to determine if any could be potentially hazardous to our planet. For more information, visit the NASA-JPL Near Earth objects site at http://neo.jpl.nasa.gov/ .

However, neither NASA nor JPL is in the business of actively observing Elenin or any other comet. Most of the posted observations are made by amateur astronomers around the world. Since Elenin has had so much publicity, it naturally has attracted more observers.

(There’s more too… read more of Don and David’s responses on Universe Today.)

These guys have a lot of answers, and that’s because near-Earth objects like asteroids – and the occasional comet – are their specialty. I’ve also posted about this topic before, as have other bloggers on many other very reputable sites. Really, there’s nothing to worry about from this comet… if anything, astronomers will get a nice look at a member of our solar system as it passes and maybe learn a little more about these enigmatic icy travelers.

Update: here’s a video commentary from David Morrison about Elenin, released on August 18. He touches on many of the questions above and addresses a few others as well. Check it out:

Vodpod videos no longer available.