The Tungus Event

The second theory offered for what caused the Tungus devestation:

“2. The object was a comet and thus produced minimal debris, since a comet’s head is mostly dust and ice. This theory remains popular…”

What is meant by “ice”? Would that be frozen water? From where?

I assume you’re referring to the column What caused the massive 1908 explosion in Tunguska, Siberia?
Yes, “ice” as in “frozen water”, which would come from the comet, whose head “is mostly dust and ice”.

It wouldn’t have to be all water ice, though that’s probably what most of it is. That’s water from oxygen and hydrogen. The elements don’t need a planet to become fused into a compound. But it could also have included ammonia ice, alcohol ice, or just about any other. (Most of the Galactic Core is made of beer, you know.)

BTW, if you lived on the surface of a star, you’d probably think of gold jewelry as “gold ice”, iron bars as “iron ice cubes”, and a set of Authentic Ginsu Knives as “popsicles”.

What I don’t understand is

What’s the distinction here between a comet and an asteroid? I thought it was their orbit, not their composition. Besides, couldn’t the Tunguska Object have been some median composition between them?

Comets are mostly ice. Asteroids are mostly rock and/or iron.

And it’s not implausible to suppose that an object might be half-and-half ice and minerals, but so far as I know, such a beast has never been discovered. And it doesn’t really make the event any easier to explain, either.

And don’t forget dry (carbon dioxide) ice, either, which I understand is the second most abundant component of comets.

Sorry, Owen, it is composition. A comet has a tail. The tail is formed by the blowing off of volatiles - i.e. the ice melting/sublimating off. Asteroids don’t have tails, because they are rocky minerals (including iron).

Chronos, I recall reading somewhere, such as a Planetary Society magazine, an article about asteroid-like comets and comet-like asteroids. Unfortunately, I don’t recall exactly where I read it or info to help me look it up. So call it an unconfirmed rumor.

You all seem to agree that a comet yes has ice, and it might be water ice, or is. Thanks!

But, despite the assertions, nobody told me how we kNOW it’s water (I know, I know…I didnt ask!) I have read elsewhere that we analyze light from the comet with a spectroscope, which is pretty accurate. In fact, Helium was first discovered on the SUN, not the Earth! Once we saw this new element out there, we began looking for it here.

Nobody tackled the second part, “From where?”
I dont know ANY place with water, other than EARTH!

Do you?
(Remember, because I read about Tunguska, I didnt know there was water in comets!)

Well, oxygen & hydrogen are found throughout the Universe. So, in theory, water ice can form where ever you find both.

And just look at how sharp Rogg has gotten, just over the course of one thread! We’ve got him remembering what he’s learned, & reasoning from that info! Only 38 posts on this site as I look at his info, and he’s sharp as a tack.

Another Straight Dope victory over ignorance!

The Oort cloud and the Kuiper belt are full of it.

Mars, according to recent observations (Mars Odyssey), is also full of it.

As a matter of fact, current thinking is that most of the water on Earth came from comets. Hydrogen is the most common element in the Universe, and oxygen is pretty high on the list, as well (fourth, I think), with the result that water is one of the most common compounds in the Universe (carbon monoxide and methane might be more common). It’s all over the place. Most of the satellites of outer planets are largely water ice, as well as Saturn’s rings and the Kuiper belt objects. And, of course, comets.

Europa, we hope-a.