[lafroste]

models predict that the planet should be either rocky – like our Earth – or covered with oceans,” he said.

The last time I looked, the Earth was rocky AND covered with oceans. Why do they think it must be one or the other, but not both?

[Jedi Master Pikachu]

The author could have been getting at: it could be similar to Earth, or it could be completely covered in water.

[ukie55]

models predict that the planet should be either rocky – like our Earth – or covered with oceans,” he said.

The last time I looked, the Earth was rocky AND covered with oceans. Why do they think it must be one or the other, but not both?

They need a model to predict this?

They're just covering all the bases. That way, no matter what they find, they can say they were right.