So if portals didn't have a distance maximum, assuming that they twist through some higher dimension or into an alternate universe and back or something like that, it would make sense that you could open a portal on Earth and on Mars and anything you push through that portal would maintain its velocity relative to Earth.

Which could result in some hilarious events where things basically detonate the instant they are pushed through as they are slammed into the surface of Mars at potentially ten of thousands of miles an hour depending on the Earths and Mars' relative velocities.

Despite that, there would also undoubtedly be times where their velocities synchronize due to their varying rotational locations and orbital velocities around the solar system, during which times you could conceivably quite easily step from Earth to Mars in a single go.

The safe thing to do though would be to decant from the Earth into a portal that is in orbit around Mars far enough away that at the worst you would experience some relatively gentle abrasion from the smattering of hydrogen atoms in the space surrounding Mars and then parachute down from orbit.