What would happen if we could make Jupiter many times more massive but not make it so massive that it became a star? This is a question that in a certain ideal view of science could only be answered by an experiment. Since we can’t add several Jupiter’s of mass Astronomers must observe the sky and see if such objects exist. They do and they are known as Brown Dwarfs. Objects discovered relatively recently which are the smallest objects that might fairly be called a type of star and or the largest objects that could be called a planet. The paper “Revealing the Vertical Cloud Structure of a young low-mass Brown Dwarf, an analog to the beta-Pictoris b directly-imaged exoplanet, through Keck I/MOSFIRE spectro-photometric variability” by Manjavacas et al. (1) is a great example of the application of theory based on the doable experiments to understand the natural, and undoable experiment that is a Brown dwarf. By careful observation of what would to the eye appear to be a mere dot of light we learn about the physical properties of things we may never ever approach much less touch.
Observations of Beta Pictoris b. A brown dwarf in orbit of a main sequence star. The paper reported on here claims that the brown dwarf they studied is roughly analogous to Beta Pictoris b. Image courtesy of Wikipedia, credit ESO/Lagrange/SPHERE consortium - https://www.eso.org/public/images/potw1846a/
I , your humble correspondent, am a theoretical astrophysicist so I will not pretend to understand all the intricate details of this. Observational astronomers work to confirm and test theories with their observations, I solve equations that I hope describe nature. To know the most details read either their paper or their very friendly website. Here’s the gist of it.
They Used Spectroscopic Data And Applied Theory.
The spectrum of an object tells us much more than a mere image. We can learn the objects chemical composition. Since each chemical element and compound have a characteristic set of lines in the spectrum (invisible light a spectrum is basically a rainbow). What direction and velocity it is moving at, measure vibrations in the object using the Doppler effect, use the vibrations we observe via the spectrum and the Doppler effect to understand “seismographicly” how vibrations in the object propagate through the object. We do this with our very own Sun to measure “Sun Quakes” which allow us to understand the internal layered structure of the Sun (Which built on how we know the internal layered structure of the Earth. Indirect, “theory based” analysis of earthquakes.)
In the current study an instrument called MOSFIRE which can observe an object of interest and calibration objects at the same time was used. By doing so they can filter out spectroscopic noise from the contamination of Earth’s atmosphere to take very detailed, error corrected, observations of an object’s spectrum. The vertical cloud structure of the Brown Dwarf which is analogous to Beta Pictoris b was then inferred from a computer model based on the physics and chemistry we know, and what we have observed about gas planets in our solar system.
This is an artist conception of a cross section of the atmosphere of free-floating brown dwarf called 2MASS J22081363+2921215 based on the obervations in 1.) Credit: NASA, ESA, STScI, Andi James (STScI)
I guarantee that there are some theoretical planetary scientists who have various models of these Brown dwarfs who are either very happy their predictive models fit this data or working hard to modify their models based on observation.
Theory Is Itself Science Unless It Is not.
Theory is nothing more or less than a framework and toolset via which data can be interpreted which makes testable predictions about what will happen next. In physical science that toolset and framework can be stated with mathematics most of the time.
What makes a “theory” science or social science isn’t weather it can be tested practically or legally and ethically but in principle. The condition that it predicts must either exist or not exist in nature, in some realm of validity, under some circumstances. Even if those circumstances are rare and would be hard to achieve. This is how we know everything from the existence of Black holes which were not directly observable until we had gravitational waves from them, or the psycho-neurological and genetic reasons behind being LGBT which were not observable until our MRI technology and DNA technology had advanced.
Now a theory that proclaims it cannot be tested, even in principle, even indirectly via observations, in its most formidable steel manned understanding of it, and not a straw man version of it, is one which is not science of any kind and should not be called a theory.