It's an interesting question.
Mars may have had life. There are serious ideas it could have evolved there, and reached Earth with the collision that created the Moon when it seems Mars was stripped of water. See The Giant Impact Hypothesis. This could help explain how life began no less than 0.1 billion years after the Earth formed a solid crust, which seems very quick. It could help elucidate life on Earth as resulting from particularly hard steps, helping solve the Fermi Paradox. This would be grouped under the Rare Earth hypothesis. Now, the evidence for this might be very difficult to find. Introducing bacteria to Mars, and terra forming it, could very reasonably obscure it forever. Is there then a moral concern, to changing Mars?
No. Because there aren't moral subjects there currently. It is a question of scientific priority. But that has to be contrasted with other competing concerns, like getting humans established on Mars who can do research. Similarly, Enceladus, the water-moon of Saturn, could have already produced a separate incidence of abiogenesis, or it could do in the future given time. That is very scientifically interesting. But until we find moral subjects there, it is not a moral concern.
We can make an argument about the moral concern of future humans. Polluting the Moon, could limit it's used as a base to move out into the Solar System. Creating a liveable environment on Mars could help ensure human and Earth-biosphere survival in the case of nuclear war, or a powerful comet impact, or other events.
You have to look at the drivers of climate ethics. Moral subjects. Social contract with the unborn. The Golden Rule. Power and wealth inequalities in impacts and policy making. Irreversability of most extinctions, and the role of biodiversity in creating a stable healthy biosphere. The capacity for species to attain sentience in the future or already to have it, like dolphins and orangutans, that are being affected.
Earth will be fine, the biosphere will evolve and adapt. There is almost no imaginable event that could wipe out life on Earth, certainly not a human-caused one. Humanity, could possibly get wiped out, and certainly could have their long-term interests devasted. We find it difficult to see how profound the impacts happening in our own lives are, to see the consequences of just the changes of behaviour that have happened in our own generation. 30% of species on Earth went extinct in the last 50 years, and insects have declined by 75%, the 2020 Global Living Planet Index shows an average 68% fall in populations of mammals, birds, amphibians, reptiles and fish between 1970 and 2016. Change has never been this fast, even the comet impact at Chicxulub that generated the C-P boundary didn't have impacts so quickly (they mainly followed from the consequent long dark winter).
People often say we are entering the Anthropocene geological era, we are not, instead it is an extinction event, meeting the formal definition because in addition to rapid biodiversity loss, it is also marked by global deposition of a boundary layer, of micro plastics, literally from pole to pole, Chumalungma to the Marianas Trench. The Anthropocene is an extinction event.