Expert: Ed - 4/30/2008

Question
I am nine years old, and have been interested in astronomy for about five years. I have a few questions regarding miscellaneous subjects. Number one; what exactly is dark matter? Does anybody know? Number two; if the universe goes on forever, like I've read many times in books, then how could it also be expanding? Number three; I have heard that there is a planet between Earth and ?Venus? called Mobius. I have doubted this because we would've had gravitational changes in Mercury and Venus. Does Mobius really exist?

Thank you for your time, I really appreciate it.

Answer
Ethan,

I think it's great that you are interested in astronomy already.  I hope you stay interested in it.  It has been one of my favorite interests in my life, since I myself was about 9 years old.

No one is sure what dark matter is.  They are working on it!  They know it is an important part of the universe, but they aren't sure what it is.  One leading candidate is WIMPs (weakly interacting massive particles).  Scientists are working on this right now.  This article is from just a few weeks ago.
http://www.sciencedaily.com/releases/2008/02/080228100731.htm

Here are a few good links to browse.  This website has a great collection of recent, authoritative articles, by real scientists studying dark matter.
http://www.sciencedaily.com/news/space_time/dark_matter/

This is a nice little overview of the topic, from a few months ago.  Articles that you read in astronomy should be as recent as possible, these days.  New discoveries are made all the time.
http://www.sciencedaily.com/releases/2007/10/071002100235.htm

The universe is expanding, yet infinite?!?!?  OK, this confuses everyone, including me.  There is a lot of ridicuous stuff on the internet, so be careful.  Here is a NASA website which could be helpful to you:
http://map.gsfc.nasa.gov/universe/uni_shape.html

as I understand it, the idea is that spacetime itself is expanding.  This means that there is nothing outside it to expand into.

I am not sure what you are talking about, regarding a planet between Earth and Venus called Mobius.  There is a "minor planet," also known as an asteroid, called 28516 Mobius.  Is that what you are thinking of?  Or, maybe planet Mobius from Sonic the Hedgehog is supposed to be between Earth and Venus?  I have no idea, but I know that that is science fiction, not science.

You are right to notice that if there was a planet between Venus and Earth, we would be able to see gravitational effects on other, relatively local planets.

I hope this is helpful.  Please get back to me if I am not writing clearly enough.

Keep Looking Up!
-Ed