There isn't one single answer to the question "Which planet is missing in space?" The question is ambiguous and depends on the context. Several possibilities exist, based on the provided references:
1. Planet Nine/Planet X: A Hypothetical Missing Planet
A significant amount of research focuses on the potential existence of Planet Nine (also known as Planet X), a hypothetical planet far beyond Pluto's orbit within our solar system. A recently submitted study to The Astronomical Journal continues to search for this elusive planet. Its existence is inferred from gravitational effects on other celestial bodies, but it hasn't been directly observed yet.
2. Missing Planets in Exoplanetary Systems
Research also explores the missing populations of certain types of exoplanets. For example, the lack of super-Earths and mini-Neptunes in some systems is a topic of ongoing investigation. The mystery of these missing exoplanets may be due to planetary migration.
3. Missing Planetary Material
The formation of planets like Earth and Mars involved collisions of planetary embryos. Studies suggest that Earth and Mars formed from collisions that incorporated material potentially missing from the early solar system. This isn't a missing planet per se, but rather missing building blocks.
4. Misunderstandings and Fictional Contexts
The references also include examples unrelated to the actual missing planets in space, such as a missing tomato on the International Space Station or a fictional scenario in the Planet of the Apes series ("Icarus Lost in Space"). These instances are not relevant to the core question of missing planets in the astronomical sense.
In summary, the question of a "missing planet" can refer to various phenomena. The most scientifically relevant interpretation centers on the search for Planet Nine, while other contexts highlight gaps in our understanding of planetary formation and exoplanetary systems.
