For a career in traditional astronomy/astrophysics, the foundational major of physics (on the bachelor’s level) may be preferred to one in astronomy/astrophysics, in that a physics curriculum may offer the more rigorous preparation for this field (with a minor in astronomy adding range). This principle might extend to your goals in astrobiology as well, and in your case your preferred path might depend even more specifically on your interests. For example, one of the founders of astrobiology, Frank Drake (of the famous equation), was principally an astronomer. However, he sought support from specialists in foundational fields such as chemistry, biology and planetary science (which itself relies on foundational fields) for his SETI investigations. All of these scientists helped develop the field of, and determine the conceptual branches of, astrobiology. It seems that, for undergraduate study, one of these foundational majors, or one of their interdisciplinary variants, could be optimal for your interests (accompanied by an astronomy minor). Based on what you have written, you seem most oriented toward biology / biochemistry / molecular biology, but this yet may be to be determined.
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