In December 2004, the Huygens probe descended through Titan's dense ______ detached from the Cassini orbiter three weeks earlier, the...

Sentence Structure

• In December 2004,
  • the Huygens probe
    • descended through Titan's dense atmosphere
      • [?] detached from the Cassini orbiter
        • three weeks earlier,
  • the probe
    • transmitted detailed data
      • that transformed scientists' understanding of Saturn's largest moon.

Understanding the Meaning

Let's start reading:

In December 2004,
the Huygens probe descended through Titan's dense atmosphere

This tells us:

• A space probe called Huygens
• Made a descent through the atmosphere of Titan (Saturn's largest moon)
• This happened in December 2004

This is where we have the blank. Let's look at the choices:

• They differ in punctuation before 'having'
  • Period and capital H
  • Comma and lowercase h
  • 'and' with lowercase h
  • No punctuation with lowercase h

To see what works here, let's read the rest of the sentence and understand what it's saying!

The sentence continues:

• 'detached from the Cassini orbiter three weeks earlier'
  • This is background information
  • The probe had separated from the larger Cassini spacecraft
  • This happened three weeks before the descent

Then:

• 'the probe transmitted detailed data that transformed scientists' understanding of Saturn's largest moon'
  • This is another main action
  • The probe sent back data
  • This data changed how scientists understood Titan

What do we notice about the structure here?

We actually have TWO complete thoughts (independent clauses):

• First: 'the Huygens probe descended through Titan's dense atmosphere'
  • Subject = the probe
  • Main verb = descended
• Second: 'the probe transmitted detailed data...'
  • Subject = the probe
  • Main verb = transmitted

Between these two complete thoughts, we have:

• 'Having detached from the Cassini orbiter three weeks earlier'
  • This provides background information
  • It tells us something that happened before the main events
  • It's not a complete thought on its own - it's a descriptive phrase

Here's the key: Two independent clauses (complete thoughts) cannot be joined by just a comma - that creates a run-on sentence. They need a stronger separation.

The correct structure is:

• First complete thought ends with a period
• Then the background phrase 'Having detached...' introduces the second sentence
• This phrase is followed by a comma, then the second complete thought

So we need: atmosphere. Having

This creates two proper sentences:

• Sentence 1: 'In December 2004, the Huygens probe descended through Titan's dense atmosphere.'
• Sentence 2: 'Having detached from the Cassini orbiter three weeks earlier, the probe transmitted detailed data...'

Grammar Concept Applied

Separating Independent Clauses and Using Introductory Phrases

When you have two independent clauses (complete thoughts that could stand alone as sentences), you cannot join them with just a comma. You need:

• A period (or semicolon) to create separate sentences, OR
• A comma + coordinating conjunction (and, but, or, etc.)

When you use a period to create two sentences, the second sentence can begin with an introductory phrase (called a participial phrase in grammar terms) that provides background information:

Pattern:

• Independent clause 1. [Period creates sentence boundary]
• [Introductory phrase providing background], independent clause 2.

Example 1:

• The team celebrated their victory. Having trained for months, they felt the win was well-deserved.
  • First complete thought: 'The team celebrated their victory'
  • Period separates
  • 'Having trained for months' = background information about the team
  • Second complete thought: 'they felt the win was well-deserved'

Example 2:

• The detective solved the case. Having examined all the evidence carefully, she identified the culprit.

In our question:

• First complete thought: 'the Huygens probe descended through Titan's dense atmosphere'
• Period separates (Choice A)
• 'Having detached from the Cassini orbiter three weeks earlier' = background about when the probe separated
• Second complete thought: 'the probe transmitted detailed data...'

The word 'Having' signals that this action (detaching) happened before the main action (transmitting data), providing important context.