According to the Wikipedia article on Juno, the data that Juno returns will sift through multiple competing theories for Jupiter's formation. However the more theories that one has, the more likely one of them will be "confirmed" by chance alone. Are there any theories that are highly expected to be true based on modelling Jupiter's formation, but previous spacecrafts did not test?

Edit: To back up what I meant by "the more likely one of them will be "confirmed" by chance alone". When they were searching for the Higgs boson, they had to correct for the look-elsewhere effect. They had to search a specific predicted bump in the data, but they had to look everywhere for that bump because they did not know where it would be. There was a possibility that said bump would occur by chance alone, and they had to correct for that. As explained by cms

The likelihood of finding something in the entire region you probed is greater than it would be if you had stated beforehand where the signal would be.

So I am asking is there one leading hypothesis that we are "stating beforehand". If not, then a follow up question would be how are they counteracting the multiple comparison problem? If they cannot counteract it, then: if we model the measurements as random variables with mean and variance values based on what we already know, what is the probability that none of these models will be validated? (Note I am willing to ask these follow up questions as separate questions).

  • $\begingroup$ "However the more theories that one has, the more likely one of them will be "confirmed" by chance alone." [citation needed] $\endgroup$ Commented Jul 4, 2016 at 16:46
  • $\begingroup$ @NathanTuggy Suppose $A$ and $B$ are the events that theories 1 and 2 are confirmed respectively. If theories 1 and 2 cannot be confirmed at the same time, then $P(A \text{ and } B) = 0$ and thus $P(A \text{ or } B) = P(A) + P(B) - P(A \text{ and } B) = P(A) + P(B)$, thus the more theories you add, the more likely one will be confirmed. $\endgroup$ Commented Jul 4, 2016 at 18:31
  • $\begingroup$ That is a very simplistic analysis that treats confirmation as random by assumption, which does nothing to address my strong disbelief in your assertion that theories are confirmed randomly. $\endgroup$ Commented Jul 4, 2016 at 18:48
  • $\begingroup$ @NathanTuggy Please see model selection and my favourite example about the null hypothesis and then the (sadly not so well explained) page on the null hypothesis $\endgroup$ Commented Jul 4, 2016 at 19:24
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    $\begingroup$ FWIW, I don't see how this question is really "primarily opinion-based". Surely the scientists who designed the experiments for Juno had some specific ideas of what theories (or hypothesis) they wanted to test and why, and designed the experiments to gather data that would help either confirm or falsify one or more of those theories. Asking what those theories were seems like a question that is likely to be answerable with facts, rather than personal opinions of the answerer. $\endgroup$
    – user
    Commented Jul 4, 2016 at 21:06

1 Answer 1


Juno is looking for how Jupiter formed, which would say a lot about how all planetary systems form, and all theories regarding that are on the line. First, determining how much water it has would help determine where and how fast it formed.

Oxygen is the 3rd most abundant element in the universe, including in our solar system, and its most common form is combined with hydrogen in water. Observation to date has indicated a range of possible values for water on Jupiter:

The latest analyses of data from the Voyager spacecraft that flew by Jupiter in 1979 have suggested a water abundance for the planet of twice the solar level (based on the Sun's oxygen content). Observations of the propagation of atmospheric waves across Jupiter's cloud tops from the Comet Shoemaker-Levy 9 impacts implied that Jupiter might have a water content of ten times the solar level. Actual probe measurements, while subject to scientific debate, suggest a level near that of the Sun. Scientists are left to wonder, "where is the oxygen?," "where is the water?,"

The Galileo probe detected levels much lower than the solar level of oxygen.

Juno will measure the water in the atmosphere below the troposphere using a microwave radiometer. The clouds are transparent to microwaves, while water absorbs them.

How much water is in this layer will help determine how Jupiter formed. One possible explanation for a low oxygen content is that water ice became depleted in the inner region of the cloud of gas our solar system formed from:

That Jupiter formed in a disk with C/O ∼1 implies that water ice was heterogeneously distributed over several AU beyond the snow line in the primordial nebula and that the fraction of water contained in icy planetesimals was a strong function of their formation location and time. The Jovian oxygen abundance to be measured by NASA's Juno mission en route to Jupiter will provide a direct and strict test of our predictions.

Or put another way on phys.org:

Steve Levin, Juno project scientist from NASA's Jet Propulsion Laboratory, said water figures are the most important ones that Juno is going to bring back. "If Jupiter formed far from the sun, where it is cold, out of blocks of ice... you would get a different amount of water inside Jupiter than if it formed closer to the sun than it is now."

But there are other possibilities, as one would expect for something as complex as the formation of a planet. There is a good summary in the final two sections of this article by Katharina Lodders. The two main ideas are first, the core accretion model in which a solid core forms slowly, and starts capturing gasses by its gravity once it is big enough, and second the disk instability model, in which slight differences in matter density in the protoplanetary disk cause matter to clump and quickly densify into a planet. How much water Jupiter has, and how that compares with the exact amounts it has of other elements heavier than hydrogen and helium, will give hints about which of the two it was, and how other mechanisms were involved, such as later capture of other objects by Jupiter.

To put it together, it is also crucial to know how big the core of Jupiter is, and whether it is solid or liquid. Some core accretion models predict a large solid core of metals, like Earth's but many times the mass of Earth. Others propose a small solid core could still accrete a planet like Jupiter. Those proposing that instead disk instability is the source of planet formation say that accretion can't be the explanation because study of other star systems indicates the protoplanetary disk doesn't last long enough for accretion to happen. They say Jupiter might not have a solid core at all, or have a much smaller one that gathered over a long time. It is also possible both mechanisms played a part, and there is also a completely different idea in which accretion happened through the medium of formation around a carbonaceous core, a tar ball. So knowing the size and density of the core won't immediately settle the matter, but has to be known to get any further.

Juno has a magnetometer to measure Jupiter's magnetic field and a nice big antenna so that Goldstone can map its gravity field, together this will tell us about Jupiter's core.

  • $\begingroup$ Is there any reasonable values (within 3 sigmas of what we already expect) for the measurement of the water quantities, the solid core size and magnetic field size for which none of these models will predict? $\endgroup$ Commented Jul 5, 2016 at 11:00
  • $\begingroup$ To be more precise, if we model the measurements as random variables with mean and variance values based on what we already know, what is the probability that none of these models will be validated? More or less, what is the probability that a null hypothesis would be shown to be false. $\endgroup$ Commented Jul 5, 2016 at 11:06
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    $\begingroup$ @StrategyThinker Estimates of the core size range between 0 and 20 Earth masses, water measurements have been between 0.6 and 10 times solar level. We have too few data points on these aspects of Jupiter to do a statistical analysis. In fact, the data Juno returns will not settle the matter at all, it will only add data to the debate. $\endgroup$
    – kim holder
    Commented Jul 5, 2016 at 14:24

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