* Auroras: Auroras are caused by charged particles from the Sun interacting with a planet's magnetic field. Without a magnetic field, there would be no auroras.

* Protection from solar wind: A magnetic field acts as a shield, deflecting the harmful radiation and charged particles from the Sun's solar wind. Without a magnetic field, the solar wind would directly bombard the planet's atmosphere and surface, potentially stripping away the atmosphere and causing radiation damage.

* A stable atmosphere: The solar wind can strip away a planet's atmosphere if it's not protected by a magnetic field. This would make it difficult for life to exist on the planet.

* A global ocean: Without a magnetic field, a planet's atmosphere and water could be stripped away by the solar wind. This would make it difficult for liquid water to exist on the planet's surface.

It's worth noting that the absence of a magnetic field doesn't necessarily mean a planet is completely uninhabitable. Some planets may have other protective mechanisms, like a thick atmosphere or a strong gravitational field. However, the absence of a magnetic field would certainly be a significant challenge for life to evolve and thrive.