Expert: Courtney Seligman - 3/16/2010

Question
QUESTION: Christ!!! That wave from the asteroid that took out the dinosaurs to sweep over all the carribean islands and even reach Nebraska which is basically the centre of the US (presumming the layout of north and south america has basically the same form as today, correct??) must of been gigantic. We must be talking of a wave many miles high? I'm so interested in this phenomina, but it gives me a shiver down the spine. My guess though of a mile wide asteroid at high speed hitting some sea or ocean would at least create a sky-scraper high wave. Enough to sweep inland, many, many miles.

Courtney, here's a video simulation of an asteroid impact that's on youtube. You might find it interesting, it's pretty good.
http://www.youtube.com/watch?v=u4Mtac3HAJg

Is it true that until the the comet shoemaker-levy 9 hit Jupiter in 1996 there was much sceptism in the scientific community on to how much damage a comet or asteroid impact would cause?

We talked about impacts with the potensial to knock the earth of it's regular orbit. The planet that hit the very early earth which led to today's moon was a mars sized object. Is it known whether this alterted the earth's current orbit at the time at all? I know it did'nt hit straight on, more that it sliced at an angle. Someone said to be once this impact could of created the crater/trench what is now the pacific ocean as there wasn't water, seas or oceans on the earth at this time period. Is there any truth to this?

Thanks Courtney.

I see you are a Professor of Astronomy at a college. What do you need whether it be physics or any other sciences to start learning astronomy at your college? Obviously I'm from the Uk, but I'm interested.

ANSWER: (Note added March 16)

I reread your question, and realized I forgot to answer the last part of it -- what you need to know to learn astronomy. That would depend upon whether you want to learn it just for the fun of it, in which case you don't need much background at all, or with the idea of becoming an astronomy major, in which case you need some background, or even a lot.

Astronomy is the application of the laws of nature as we know them on Earth, to the objects we observe in the sky. As such, the more you know about the laws of nature, the better you can understand astronomy. Basic physics, some understanding of algebra and geometry, a little chemistry and some geology go a long way in following the discussions in introductory astronomy textbooks. Students without a background in science have more difficulty following things, and more often misunderstand what they think they followed, while those with some background understand things more easily, and more correctly.

For lower division courses for majors, a little more math and physics are useful, but not absolutely necessary. For upper division courses, two years of basic college-level physics and/or mathematics would be a prerequisite. For graduate work, an advanced degree in physics or mathematics might not be enough to thoroughly understand a topic, without considerable background in a particular field of astronomy.

In other words, you can jump right in without any previous training, at the introductory level. But if you want to do more advanced work, the more background you have the better, and sometimes, even the best background may not fully prepare you for a specialized field (e.g., in theoretical cosmology or astrophysics).

(previous post below)
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Sorry about the delay in answering -- I've been out all day, and just checked my email.

I think the tidal wave for the 65-million year event was estimated as a mile high near the impact, and shallower as it spread out. Going over the tops of the islands was partly due to its height, and partly just 'breaking' against them, and spraying upwards. Still, debris was deposited all over them.

I watched the video, which seemed interesting, but my system has no sound, so I couldn't hear any commentary that might have accompanied it. It appeared that the asteroid involved was hundreds of miles across. An impact that large would actually produce far more devastation than shown in the video, but is not likely to ever happen. Impacts like that were common around 4+ billion years ago, but it appears that since then, the largest impactors on any planetary surface have been in the range of ten miles diameter (the craters produced are of course much larger).

I don't believe Shoemaker-Levy changed opinions about the risks or dangers involved with asteroid or comet impacts. The evidence favoring a large impact around 65 million years ago was well accepted long before then, and the question of how often such impacts might occur was already being addressed, although with uncertainty about the quality of various calculations.

There is no way of knowing how much 'our' orbit was affected by the impact which presumably completed the Earth and created the Moon. If the impactor had a very different orbit, it could have altered the orbit by as much as 20%, but it probably had a similar orbit to the proto-Earth, in which case the change in the orbit would have been much smaller. However, that impact had nothing to do with the Pacific Ocean basin. Speculation about the Pacific Ocean partly underlay Darwin's suggestion that the Moon might have broken off the Earth, which is where the comments you've heard probably originated; but the Pacific Ocean is not that old -- just a few hundred million years, even if you count the pre-Pangaen oceans.

In any event, the impact that created the Moon occurred so early on that the melting and differentiation of the Earth wouldn't have been over, so after the two objects collided, they would have completely melted, thoroughly mixed, and formed a new, essentially molten object. After a few tens of millions of years, what is now the Earth would have formed a crust very similar to that of the Moon, which would have covered the entire surface of the planet. Impacts during the period ending about 3.9 billion years ago might have punched holes in the crust here and there, but none of them would have had anything to do with the Pacific or any other present ocean.

---------- FOLLOW-UP ----------

QUESTION: Thanks Courtney. I do learn astronomy for fun, there is nothing better than watching a good documentary on the subject, but I was very interested to know what you need to become someone like yourself. Some of my friends say to me I should go for it as I tell them certain facts about the universe, galaxies and stars etc, etc that they had no idea about themselves, but I understand there's stacks more stuff you need other than just having some good general knowledge on the subject.

Is there any particular area of astronomy that facinates you more than others?

Also, what's your opinion on other life advanced or not out there in the universe? When you consider how big the universe is, how many million galaxies and another many million stars there are in the galaxies, there must be other earth type planets that have been created and evloved. One thing that really captures my imagination is seeing another earth type planet with all the different land forms, (I mean seeing an earth with not the familiar North America, Europe, Asia continents etc that us Humans are so used to recognising). And imgaine coming across an animal on another earth type planet with something the equivilent to a lion. Obviously I doubt it would be any relation to a feline or even a mammal come to that, but an animal with similar intelligence and that how we look basic animals today.

Answer
I find almost all of astronomy interesting. I'm not as interested in the nuts and bolts -- how telescopes and other observing tools work -- as much as I am in the results of their observations. And I'm more interested in the big picture -- what's going on, what significance does that have, and how is it related to the rest of astronomy -- than some of the details of magnetic flux tube collapse, subsurface currents inside the Sun, and the like. But I can't think of any general area that I'm not interested in. I used to teach a survey course of astronomy, physics, chemistry, geology and meteorology, and to me, it was all astronomy, in the sense that every example I used of how you could apply a given science to the real world was a topic that I covered in my astronomy class, as well. You can't avoid geology and meteorology when you're talking about the planets, and you need physics and chemistry to talk about geology, and physics to talk about orbits, astrophysics, the structure of the Universe, and so on.

And of course you need a lot of math to do much in any professional field of astronomy, but I was always good at math, and in fact planned to major in math when I entered UCLA. I only enrolled in astronomy because I knew the head of the astronomy department, George Abell, and they had a double major in astronomy and math, so I could make him my advisor if I took that major (I did have a lifelong interest in astronomy, but hadn't actually thought of it as a career, before then). My only regret about what I studied was that the more you learn, the more you find there is to learn, so I could have used more physics (even though I ended up with a double major in astronomy and physics), and more math and geology (even though I took enough math classes for a minor in math, and nearly enough geology classes for a minor in that). And after forty years out of school, if I had to start over now, there are whole fields of astronomy that didn't exist back then, and math and physics and computer classes you'd need to take to properly deal with those fields. For instance, I remember taking a math class where all sorts of interesting functions were discussed, and how useful they might be if you could do anything with them; but using them would have required more than a lifetime of calculations, so they were just interesting tidbits. Now, with computers to do the calculations, many of those functions are used every day by astronomers, and are as fundamental to their work as basic calculus would have been, back then.

As far as life in the Universe: I suspect that some form of life is a fairly common 'disease' of planetary surfaces, as long as there conditions remotely suitable for life. With hundreds of billions of stars in a typical galaxy, all other things being equal, you might have hundreds of billions of planets with some form of life. There are, as it turns out, all sorts of things that make this unlikely -- some stars are so old that they don't have much besides hydrogen and helium, so it's hard to build small planets around them, some are so young that life might not have had a chance to get very far (to date), some are in regions where violent stellar events are common and might extinguish all life on nearby planets, and so on. As it happens, the Sun is in a region where life is more likely than elsewhere, just as the Earth is in a region (around the Sun) where life is more likely than elsewhere. So our being here isn't as much a matter of chance, as it is of suitability. And we just don't know how suitable things have to be, to get life forms that are fairly complex. On the Earth, it took more than four billion years to get to things much more complicated than slimes and sludges. That might be typical, slow, or unusually fast.

As a result, there is a wide range of opinion on the subject. Some people believe (or perhaps hope would be a more accurate word) that fairly advanced life forms are very common (tens of thousands of them in just our galaxy alone), and only the huge distances involved make travel and/or communication difficult or impossible. Others think we might be "it" in the entire Universe. I find both views too extreme to be very likely, but I'm not sure where I would want to place my peg, so to speak. There might be one or more advanced civilizations in almost every galaxy, or in only one galaxy in a million or more. There might be interesting life forms, such as lionlike or piglike creatures, on thousands of planets in any given galaxy, or in only one galaxy in ten. I tend to waver in my opinion, depending upon whether the most recent articles I've read are about the ability of life to survive in extreme conditions, or the spectacular catastrophes that occur here or there, now and then, in every galaxy. So I waffle on any answer I give about life elsewhere. It's likely, in some ways, but unlikely, in other ways, and which is more significant is unknown. I think simple life forms are probably extremely common. Things as complicated as pigs and lions are probably more rare than not. And conscious beings wondering where the heck everyone is may be incredibly rare. But with so many stars in so many galaxies, even incredibly rare may still be a lot of places.