The closest planet to Earth is Venus. However, it's important to clarify that the distance between planets is constantly changing due to their orbits.

Here's the catch: While Venus is the closest planet on average, Mercury can actually be closer to Earth at certain points in their orbits.

Travel time:

* Current technology: There's no way to travel to Venus or Mercury in a human lifetime with our current technology. The fastest spacecraft ever launched, Parker Solar Probe, takes about 7 years to reach Venus.

* Hypothetical future: With future advancements, we could potentially reach Venus in a few months or even weeks, but it's still a long way off.

Important note: While Venus is close in astronomical terms, it's a hostile environment with extreme temperatures, crushing pressure, and a toxic atmosphere.