Short-period comets need roughly 200 years or less to complete one orbit, long-period comets take more than 200 years, and single-apparition comets are not bound to the sun, on orbits that take them out of the solar system, according to NASA.
Yes, you can invest in both an IRA and a 401k (or a Roth 401k and a Roth IRA) at the same time, or any combination of those accounts. And in some cases, based on the fees in your 401k, an IRA might actually be a better place to invest your money.
The twin brother (ok, granted, they are not perfect twins) of the 401K is the IRA. If your employer doesn't offer a 401K, you can still open an IRA on your own, and do stuff very similar to what you would with a 401K.More info: http://www.fool.com/ira/ira.htm.f your employer doesn't offer a 401K, you can still open an IRA on your own, and do stuff very similar to what you would with a 401K. More info: http://www.fool.com/ira/ira.htm.