Magma on Mars likely ascends in a similar manner to that on Earth. It rises through the lower crust in diapiric bodies that are less dense than the surrounding material. As the magma rises, it eventually reaches regions of lower density.

Is Mars covered in lava?

Mars has some of the largest volcanoes in the solar system, but they've apparently been inactive for millions of years. No plumes of ash or flowing streams of lava are seen on Mars today. ... According to these scientists, this finding could mean Mars is still volcanically active even today, at least underground.

Do other planets have magma?

The short answer is no. Take Mercury for example in this comparison of Earth Mercury core. Mercury is thought to have a liquid outer core and solid inner core.