Terra can mean a few things in Portuguese, depending on context:
In Esta terra é nossa, the most natural meaning is land or this land.
So the sentence is not usually understood as This planet is ours unless the context clearly points that way.
Because esta already works as a determiner before the noun.
In Portuguese, demonstratives like este / esta / esse / essa normally go directly before the noun:
You do not need a in front of terra here.
So:
Portuguese often uses the same possessive forms in slightly different ways.
So nossa can mean:
English changes the form:
Portuguese often does not:
Context and sentence structure show the difference.
Because the sentence means This land is ours, not Our land is this one.
These are related but not identical structures:
When Portuguese uses ser to link the subject to a description or identification, the possessive often comes after the verb:
Yes, and in everyday Brazilian Portuguese, that is very common.
Traditionally:
But in modern spoken Brazilian Portuguese, essa often replaces esta in many situations.
So:
It is more directly This land is ours.
Compare:
Both can be similar in meaning, but the structure is different.
The original sentence focuses on the land and says it belongs to us.
A simple approximate pronunciation is:
EH-sta TEH-ha eh NOH-sa
A few helpful notes:
So terra often sounds roughly like TEH-ha in many Brazilian accents.
In Portuguese spelling, rr and single r can sound different.
Between vowels:
So:
Likewise, terra is spelled with rr, and that affects pronunciation.
By itself, it is grammatically neutral, but it can sound strong or emphatic depending on context.
Esta terra é nossa could be used in:
Using esta instead of essa can also make it feel slightly more formal or literary in Brazilian Portuguese.