This investigation is an observational study. The scientists are passively collecting data (light from distant stars) to find evidence of planets without manipulating or controlling the system they are studying. They are observing the celestial bodies in their natural state. This method is fundamental in fields like astronomy, where the subjects are inaccessible for direct experimentation. The use of an instrument like the Hubble Space Telescope is a hallmark of modern observational science.

A. Laboratory experiment: This involves manipulating variables in a controlled, artificial environment (a lab), which is not the case here.

B. Constructing a model: While the data gathered will be used to construct or refine models of planetary systems, the act of data collection itself is observation, not model building.

C. Controlled experiment: This requires the deliberate manipulation of an independent variable to observe its effect on a dependent variable, which is impossible to do with distant stars.

1. University of California, Berkeley. Understanding Science. "Types of scientific studies." This resource distinguishes between experimental and observational studies, noting that in fields like astronomy, scientists are often limited to observations because they cannot manipulate the variables (e.g., stars). Retrieved from: https://undsci.berkeley.edu/understanding-science-101/how-science-works/types-of-scientific-studies/

2. The Pennsylvania State University. STAT 507: Epidemiological Research Methods. "Lesson 1.2 - Types of Studies." This course material defines an observational study as one where the researcher does not control the variables of interest but observes them as they naturally exist. This directly applies to astronomers observing distant star systems.

3. NASA Science. Hubble Space Telescope. "About." The official documentation describes Hubble's mission as making observations of the cosmos. For example, the discovery of exoplanets is listed as a key scientific achievement based on observational data, such as using the transit method, which involves watching for a star's light to dim as a planet passes in front of it. This is a purely observational technique. (See "Hubble's Discoveries" sections on NASA's official site).