Is it possible for all planets in our solar system to align in a straight line?

Theoretically, no, as the plane of orbit of each planet is tilted slightly in relation to other planets. However, if we ignore the intra-orbital plane tilt, then the chance of all planets (eight now excluding Pluto) to be at the right ascension with respect to sun at same time would be once in 180 trillion years. For an exact alignment, when all the planets are inclined with respect to the ecliptic, we must factor the line-ofnodes recession into calculations, that makes the chance once in 86 billion trillion trillion trillion years (86 followed by 45 zeros). The odds strongly favour the fact that an exact planetary alignment will never occur within the lifetime of the solar system that now has only about 12 billion years left.