A massive crater on Phobos, Mars' closest moon, known as Stickney Crater, may offer key insights into how the moon formed. Scientists are trying to determine whether Phobos originated from debris after a massive impact on Mars or if it was captured from the asteroid belt. The debate hinges on the age of the Stickney impact, with estimates ranging from 4.2 billion years ago for the impact scenario to 2.6 billion years ago for the capture theory. Phobos is unusually small and irregularly shaped, with a mean diameter of about 22.2 kilometers (13.8 miles). It orbits Mars every 7 hours and 39 minutes, making it the closest moon to its planet. A 2026 study published in The Monthly Notices of the Royal Astronomical Society suggested that Phobos may have a porous interior that could contain water ice. Scientists are especially interested in whether the Stickney impact created a denser region beneath the crater, which could be detected through detailed gravity mapping. Phobos is gradually spiraling toward Mars due to tidal forces, and it is expected to either crash into the planet or break apart in the future. This makes Phobos not only a relic of ancient events but also a dynamic system that is still evolving. Its irregular shape and composition resemble those of a "rubble pile" asteroid, which is made of loosely bound rock fragments. Japan's upcoming Martian Moons Exploration (MMX) mission, set for launch in late 2026, aims to study Phobos and return samples to Earth by mid-2031. The mission will attempt to operate in a quasi-stable orbit around Phobos, a challenging task due to the moon's weak gravity and Mars' strong gravitational pull. The spacecraft will use a core sampler and a pneumatic sampler provided by NASA to collect material from Phobos' surface. Understanding Phobos' gravitational field is crucial for mapping how mass is distributed inside the moon and for determining its origin. The MMX mission could provide the data and physical samples needed to resolve the long-standing mystery of how Phobos came to be in its current orbit around Mars.