"In this year" versus "this year"

"In this year": Can anyone argue that the preposition in is unnecessary here, maybe even a hypercorrection? (Are there any situations where in is necessary?)

Edits

Some examples:

• How many days are left in this year? How many days are left this year?

• In this year, Tommy has grown 12 inches. This year, Tommy has grown 12 inches.

To stir up some debate, is in this year a prepositional phrase with year as the object? If so, how does this change with the phrase this year?

A construct such as "In this year's [some event], [this occurred]." makes sense because the phrase automatically becomes prepositional: in the [event] while year's becomes some kind of adjective. I'm not asking about this situation.

I suppose I'm interested in knowing whether in this year is grammatically correct. Can every sentence containing the phrase in this year be shortened to the one containing this year? (Do any grammar rules govern this?)

Solution 1:

In this year is a prepositional phrase with this year as the object. This year by itself is a noun phrase.

Both can be used to place an event within the current year, but this year is much more natural. (I don't think in this year is a hypercorrection.)

In this year, Tommy has grown 12 inches. (odd)

This year, Tommy has grown 12 inches. (ok)

But if we're not talking about something happening but counting the number of days in a particular span of time, the preposition is necessary.

She left him this year. (ok - she left him denotes an event)

How many days are left this year? (very odd - left is an adjective)

How many days are left in this year? (ok)

Expressions telling when are sometimes prepositional phrases (during exams), sometimes adverbs with or without modifiers (later, very soon now), and sometimes noun phrases (next Tuesday, this year).