Jupiter Was Formerly Twice Its Current Size and Had a Much Stronger Magnetic Field (phys.org) 38
A new study reveals that about 3.8 million years after the solar system's first solids formed, Jupiter was twice its current size with a magnetic field 50 times stronger, profoundly influencing the structure of the early solar system. Phys.Org reports: [Konstantin Batygin, professor of planetary science at Caltech] and [Fred C. Adams, professor of physics and astronomy at the University of Michigan] approached this question by studying Jupiter's tiny moons Amalthea and Thebe, which orbit even closer to Jupiter than Io, the smallest and nearest of the planet's four large Galilean moons. Because Amalthea and Thebe have slightly tilted orbits, Batygin and Adams analyzed these small orbital discrepancies to calculate Jupiter's original size: approximately twice its current radius, with a predicted volume that is the equivalent of over 2,000 Earths. The researchers also determined that Jupiter's magnetic field at that time was approximately 50 times stronger than it is today.
Adams highlights the remarkable imprint the past has left on today's solar system: "It's astonishing that even after 4.5 billion years, enough clues remain to let us reconstruct Jupiter's physical state at the dawn of its existence." Importantly, these insights were achieved through independent constraints that bypass traditional uncertainties in planetary formation models -- which often rely on assumptions about gas opacity, accretion rate, or the mass of the heavy element core. Instead, the team focused on the orbital dynamics of Jupiter's moons and the conservation of the planet's angular momentum -- quantities that are directly measurable.
Their analysis establishes a clear snapshot of Jupiter at the moment the surrounding solar nebula evaporated, a pivotal transition point when the building materials for planet formation disappeared and the primordial architecture of the solar system was locked in. The results add crucial details to existing planet formation theories, which suggest that Jupiter and other giant planets around other stars formed via core accretion, a process by which a rocky and icy core rapidly gathers gas. The findings have been published in the journal Nature Astronomy.
Adams highlights the remarkable imprint the past has left on today's solar system: "It's astonishing that even after 4.5 billion years, enough clues remain to let us reconstruct Jupiter's physical state at the dawn of its existence." Importantly, these insights were achieved through independent constraints that bypass traditional uncertainties in planetary formation models -- which often rely on assumptions about gas opacity, accretion rate, or the mass of the heavy element core. Instead, the team focused on the orbital dynamics of Jupiter's moons and the conservation of the planet's angular momentum -- quantities that are directly measurable.
Their analysis establishes a clear snapshot of Jupiter at the moment the surrounding solar nebula evaporated, a pivotal transition point when the building materials for planet formation disappeared and the primordial architecture of the solar system was locked in. The results add crucial details to existing planet formation theories, which suggest that Jupiter and other giant planets around other stars formed via core accretion, a process by which a rocky and icy core rapidly gathers gas. The findings have been published in the journal Nature Astronomy.
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Define "untestable hypothesis".
Re: (Score:2, Funny)
A hypothesis that cannot be tested.
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Most hypotheses cannot be tested, but inferred.
You cannot TEST how the primitive people lived their lives, for example.
Same goes for extrapolating various events into the future, especially those happening at very large scales.
If your answer to all of those is "so what?", well, the problem is you, then.
Re:another untestable hypothesis (Score:1)
What's the alternative? Stop guessing? History usually leaves clues, and we can make a best guess based on such clues.
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Learning about the universe may lead to new breakthroughs and insights. For example, learning about cosmic rays helped us build more reliable computers because cosmic rays can flip bits.
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another "untestable hypothesis" is that Jupiter would have forced the Earth to be ejected out of the Solar System were it not for the gravitational influence of Saturn.
i guess the Greek myths got it backwards
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The falsifiability of a large Jupiter hypothesis is possible.
WTF happened to all that mass? (Score:2)
...I demand a Congressional investigation!
Ionization of the atmosphere via the planet's then extra strong magnetic field? That's a lot of material to ionize away. There should be lots of residue left over somewhere. If it blew inward, our moon should have a record. If it blew outward, then we'd have to land on rocky bodies out there to get samples. Could all that "stuff" be what formed the Oort cloud or Kuiper Belt?
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Who said anything about missing mass? The abstract of the paper says that it was accreting mass, not losing it.
Nothing happened to it (Score:5, Insightful)
I presume Jupiter simply cooled down and it shrank. Shame the article doesn't have anything to say on it though.
Re:Nothing happened to it (Score:5, Funny)
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It says the gravity was stronger. Hard to shrink something down and then expect the same amount of mass to have less gravity.
Re:Nothing happened to it (Score:4, Informative)
It says no such thing. It says the magnetic field was stronger.
We all shrink when we age (Score:2)
It's normal.
Re:We all shrink when we age (Score:5, Funny)
Not around the middle. Let's just say our aspect ratio changes.
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Because you keep fucking your delux vacuum cleaner.
Re: We all shrink when we age (Score:2)
Citation for the original paper (Score:4, Funny)
Batygin, K., and Adams, F.C. You Think Jupiter's Big Now: Lemme Tell You, Back In MY Day. In Nat Astron (2025).
Hey Jupiter, you look great, have you lost weight? (Score:4, Funny)
Jupiter spins slowly so they can see it all and quietly thanks the weight loss jab.
I was so .. gassy .. before, always bloated. I feel great.
Re:Hey Jupiter, you look great, have you lost weig (Score:5, Interesting)
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Obviously that's because it shrunk so much...
https://www.youtube.com/watch?... [youtube.com]
What would it have taken for it to ignite? (Score:2)
Re:What would it have taken for it to ignite? (Score:4, Interesting)
Estimates are about 10 to 15x Jupiter's size to become a "brown dwarf" star, so 2x wouldn't do it. I wonder how bright a brown dwarf at Jup's distance would look from Earth? I guesstimate about as bright as the moon, and it probably wouldn't stand out in the day.
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A "brown dwarf" isn't really a "star". Its just a class of object where we start considering it too big to be considered a planet. Jupiter would need about ~65 to 70x its current *mass* (not size) to become the smallest type of star (red dwarf).
Also in this class of object its very, very important to distinguish between mass and size, because they stop scaling anything close to linearly at that scale.
Jupiter and Saturn are very similar in size. Saturn is 84.3% of the *size* of Jupiter (as it relates to d
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I think it would have been a cool looking "star" that comes and goes.
Sure. Having 6 months of light 24/7, like in the poles ... Hard to sleep!
Re:What would it have taken for it to ignite? (Score:5, Funny)
It won't ignite for a number of reasons
The most important being the absence of a monolith in orbit around it.
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Bear in mind the theory here is about size (volume), not mass. So it could have been the size of the solar system and still been less likely to turn into a star because there wouldn't have been enough mass for that to happen.
Ob. (Score:5, Funny)
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I came here for the 'yo mum' jokes. She was also twice the size of jupiter, but still is - and is just as gassy.
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"Does this asteroid belt make my Uranus look big?"