There are no known stars between Sol and Proxima Centauri that are closer to Earth. Given the space telescopes currently in use that can see both visible and infrared light, and the further sky surveys that would have been done prior to launching the Arks, one might strongly expect that a dwarf star or dwarf binary system would be known and charted. It either shouldn't exist or should already be on their charts.
The Ark stops at a star system to refuel. But Proxima is the closest star to Earth (hence the name). There are no stars in between Sol and Proxima.
As stated, star charts of the region of space would have been established. In screenwriting circles, this is an illustration of a technique called a plot device, as in it advances the story forward.
Brice and Eva on the shuttle couldn't find any U235 or Acid substance on the planet, it was revealed later that the two things were on another Ark behind the dwarf planet. When the instruments on the shuttle couldn't detect the two things as the Ark 3 was shadowed behind the dwarf planet, how does the mother ship's instrument detect the same two elements because Ark 3 was shadowed behind the dwarf planet from mother ship also.