Landing on the Red Planet is one of the biggest challenges in spaceflight, so hard that the problem is referred as the Great Galactic Ghoul.
NASA's Journey to Mars might be officially dead. That is, the agency doesn't seem likely to land an astronaut on the Red Planet in the 2030s, and NASA's associate administrator for human exploration, William H. Gerstenmaier, recently said that NASA does not have the funding for a crewed Mars mission in the current timeline. Gerstenmaier also addressed the underlying problem: The agency just doesn't know how to land something as heavy as a crewed spacecraft on Mars.
"I can't put a date on humans on Mars, and the reason really is the other piece is, at the budget levels we described, this roughly two percent increase, we don't have the surface systems available for Mars," said Gerstenmaier at a meeting of the American Institute for Aeronautics and Astronautics. "And that entry, descent, and landing is a huge challenge for us for Mars."