Scientific Method: Observation, Data, Hypothesis, Experimental Design and Testing
Scientific Method
-- Oklahoma State University, Department of
Zoology
1. Making hypotheses from data and testing with new data.
We can imagine Galileo Galilei first looking at Jupiter through that earliest of telescopes 1 2. He was amazed at what he saw: the bright prick of light resolved into a dim circular shape and beside it, in the inky blackness of the eternal night of space, smaller pinpoints of light, clearly arrayed in line with Jupiter's equatorial plane, like pearls on a strand.
His mind quickly made the powerful hypothesis, that these, in immediate and satisfying analogy to the Copernican theory of the solar system, were objects, planetesimals - moons - in orbit around the planet. As the moon orbited the earth and the earth and all the other planets orbited the sun, so too these were shepherded by the great planet.
As he charted the view through the telescope hour after hour and night after night, the hypothesis was made more and more robust by confirmatory data: that the moons would move to an extreme position at a distance furthest from Jupiter and then reverse their outward wandering and come back in toward the mighty planet. Surely they were in orbit!
But, wait, let's imagine alternative explanations. Despite the seductivity of the analogy to the earth and moon and to the Copernican theory of planets orbiting the sun, where was the warrant that these points of light were in fact orbiting Jupiter? Perhaps it was coincidental, perhaps these were heavenly bodies beyond Jupiter whose periodic motions just happened to intersect the earth-Jupiter line of sight.
Although the resolution of the following pictorial animation would have been beyond the capacity of Galileo's telescope, we might imagine that he would have been happy to have had its data, for it bears upon this issue and resolves the unquestionably the issue of whether or not the bodies orbit *around* Jupiter:
The idea here is that we can try to augment our original data with new data specific to the testing of a hypothesis.
2. The reliability of data and observation.
A classic case in point is the history of Mars astronomical observations from the period 1890 to 1910. The view through 20, 30 and 40 inch earth-bound refractor telescopes was far from ideal: the apparent disc under the best of circumstances was something on the order of two centimeters (example). Photographic equipment and techniques were mostly undeveloped and most of the recording of images was done by sketching.
Though the images seen through the period telescopes were indistinct, some features stood out. The Martian polar ice-caps were unambiguous and they were clearly observable as shrinking and expanding according to the seasons of the Martian year. Careful measurements had produced inferential data that Mars possessed an atmosphere of some sort and brightenings on the limbs and terminator were (correctly) interpreted as clouds. These features gave definitely the impression of a planet with earth-like characteristics.
The idea that Mars was vegetated had been proposed as early as the late 1700's and indeed, there seemed to be seasonal changes in the albedo (reflectivity) and coloration of vast areas on the observable Martian disc.
One of the period astronomers who had achieved considerable recognition as an astute and careful observer was the Italian Giovanni Schiaparelli. He was the first to suggest that Mars was networked with "canali". The Italian word has a first translation as "channels" but it was seized upon as "canals," a subtle distinction but one that implies artificial origin. The idea that intelligent Martians had created a vast web of canals to irrigate a dying world ran like wildfire through popular consciousness and it was taken up by many in the scientfic astronomical community. American astronomer Percival Lowell became the foremost proponent of the Martian canal hypothesis.
With the wisdom of hindsight, we are amazed at this egregious error. Looking at Lowell's map compared to Nasa's current Mars projection, the error is obvious - but this is not a fair comparison. Instead, view the same two maps "through a glass darkly," as it were and under these blurred conditions, the difference between conjecture and reality is not so obvious
3. Making deductions from physical evidence - made so as to lead to hypotheses for testing..
X marks the spot - X closer - Ice rafts - Closer - Closest -- Wedges area - Wedges drawing
Take the case of the Europa ice-fields in the so-called chaotic terrain. We can zoom in on the view from the Galileo orbiter in the sequence of images in the row above. In the third image, Ice rafts, it is not difficult to reason that what we are seeing are great huge chunks of ice that have fractured from having been united in a shelf. Now examine the shadows that are cast by the individual chunks. If you look closely (Closer), it is clear that some of the shadows are much longer than others: we know that shadow length varies as the height of the object casting the shadow, so therefore it is reasonable to deduce that these chunks, originally on a level with the other chunks, have shifted lengthwise and are up-ended, in a manner of speaking. This is something that can easily be modeled with e.g. cardboard and a light source, like a flashlight. Cut the cardboard into chunks, separate these slight and then position the light source so that the chunks are casting shadows. Now tilt one of the chucks and observe the shadow.
The "wedges" also illustrate this topic. The second image shows the hypothetical re-construction of the original topography of this area of Europa's surface. The power of the deduction is that it "explains" not just a single part of the image but provides a unitary, underlying mechanical explanation for all of the splits and rotations.
When we put these two cases together, we see that the hypothesis of an underlying liquid or semi-liquid layer of transport helps to tie the data together with one, coherent explanation.
4. Having a hypothesis, getting contradictory data - how to analyse
The Galileo mission to Jupiter was designed to have two main parts: the Orbiter and the Probe - the one to take up post as it were and send back pictorial and other data over many years - the other to make fiery descent into the gaseous upper levels of Jupiter and send back information about the chemical composition of the atmosphere.
The design of the Probe's mission and its instruments was a direct consequence of wanting to test hypotheses about the Jovian atmosphere. In mainstream scientific thinking, Jupiter's atmosphere represented a relic from the original solar "nebula": the gaseous proto-solar system that evolved into Sol, the nine planets, their numerous moons, the asteroids and comets. Data from studies of gas clouds throughout the galaxy fueled ideas of what could be expected from Jupiter's atmosphere's chemical makeup. Spectroscopic studies from space, in the main through the Hubble Space Telescope, provided confirmatory data for these ideas.
The data sent back from the Probe, though, was disconcertingly at odds with expectations. The amount of water vapor, for example, was a small fraction of what scientists "knew" had to be present in the Jupiterian atmosphere.
But the scientific method is not pursued as a black-or-white, all-or-nothing exercise. When discrepant data arises from experimentation, it demands that the source of the data be re-examined, to see if perhaps instrumentation misfunction could be at work. It was probably a fairly natural reaction on the part of the scientists seeing the probe data for the first time to imagine that an instrument was defective.
But there is at least one other possibility when you, qua practitioner of scientific method, are confronted with counter-hypothesis data. It may be that the sample that the data is coming from is not actually representative of the phenomenon that you thought you were sampling.
And that's what the Case of the Wierd Probe Data turned out to be. As it happened, the Probe descended into a pressure convection zone that had created a "hole" in Jupiter's cloud-layered atmosphere.
5. Serendipity - discovering the un-expected
I imagine the Galileo project scientist in charge of the Probe slapping his or her forhead and bemoaning the bad luck behind the Probe going down into a data-poor hole in the Jovian atmosphere. When you have an idea in mind, it's always a little depressing to have it go awry for random factors that you probably didn't have control over.
However, science is not something precision and gleaming and always-this-way-or-that. What's the saying? - "when life gives you Lemons, make Lemonade..."
It turns out that the "hole science" is kind of interesting. Imaging from the Orbiter and data from infra-red doppler analysis shows the hole to be surrounded by higher water-bearing clouds - with wind patterns circulating directly into the hole which is markedly drier.. This is quite analogous to earthian atmosphere "hydrodynamics" where moist air rises at the equator and then falls as dry air over the deserts.
And that right there illustrates an on-going science idea: that the physics and mechanics of phenomena are everywhere governed by the same laws. We are not surprised to find that these weather patterns on Jupiter are similar to those on Earth.
6. The argument for life
The argument, for Europa, is one on the basis of analogy: we have found those life outposts at the bottom of the ocean, totally lightless environment, living around the sulfur-spewing thermal out-gassing vents: sulfur-digesting bacteria, tubeworms living on them, spidercrabs living on them - non-photosynthetic foodweb, call it "chemosynthetic". They had to add to the classes of bacteria to describe these new guys and they tend to see them as relic and some have suggested that this may be where life actually started and then went on from there to evolve into the majority photosynthetic situation that we have now: in the earliest days, earth was still being bombarded by asteroidal flotsam and jetsam and it would have been a hard row to hoe for life on the surface or even in the upper layers of ocean (the photosynthetic layer) which was being boiled off with regularity by the severity of these cosmic strikes: we're talking around four billion years ago.
Anyway, if indeed Europa does have a watery ocean under the ice and there's one set of hi-res pictures showing up-ended iceburgy-type structures that have been analysed to suggest that the ice layer there is no more than perhaps a kilometer deep (i.e. under this slushy or liquid layer), then the question is, does it have volcanic processes that might have this deepsea vent business going on and the answer there is possibly and even probably: evidence of tectonic-type activity from crustal deformations and evidence of "hotspots" and "lobate-shaped" surface flows (like lava but watery stuff in this case). So... maybe down deep at the bottom of the Europan sea there are strange shadowy shapes a-wavin' in the dark...
Another thing to consider is that it's not impossible that Jupiter, which is quite hot now, was very nearly burning hot a couple billion years ago and conceivably generated enough local heat so that Europa was liquid to the top.
Then there's this whole big thing about the meteorite from Mars that has been scanning-electron-microscoped to show bacteria-looking shapes clustered around carbonate bubbles (the carbonate would have been food), chemically analysed to show organic chemical residues that could be from these bacteria, etc etc etc. On the other hand, there's a legion of legitimate nay-sayers who don't believe it for a minute and have many reasonable arguments agin it. Once again, looking back around three and a half billion years ago, there's a reasonable chance that Mars had an atmosphere *and* an ocean and would have easily been life-sustaining then. With rock being blown off planets by meteor strikes and making the circuit to nearby other planets (like the meteors from Mars that have landed on earth), life from one planet could have migrated to others in this fashion.
