Identifying and Correcting Passive Voice
Two elements are present in passive sentences:
A form of the verb 'to be' (those are: is, are, am, was, were, has been, have been, had been, will be, will have been and being) + a past participle, which is a verb in the past tense.
The planet example shows, the 'to be' verb is 'has been' and the past participle is 'located.' The direct object that has been found is the 'planet.' Hence, the sentence is in passive voice.
The preposition 'by' is another simpler hint in this sentence that it's in passive voice. If you see 'by', there is a deep chance that the sentence is in passive voice.
However, 'A large planet moving in the space has been located by the scientific group’ could be written as also,
'A large planet moving in the space has been located,' and it would still be a passive sentence even it is without preposition. So, it's a good hint but it's not the essential element to evaluate if a sentence is in the passive voice.
To avoid calamity change the voice of sentence,
'The scientific group located the large planet moving in the space.'
First-Person Sentences
It's said that the first person sentences ‘I or we’, can't be passive. So for instance I'm searching it,
Here,it can't be unclear who's performing the action, right?
For instance, 'I was beached on the sea by the storm' is passive. You're not beaching yourself on the sea. The storm is performing the action of beaching you. Let make it active:
'The storm beached me on the sea.'