Jupiter's Core Disrupted by a planetoid impact!
The giant planets of the Solar System (Jupiter, Saturn, Uranus and Neptune) differ from the
so-called "terrestrial" ones (Mercury, Venus, Earth and Mars), not so much for their larger
size, as for their composition, which is largely dominated by light elements such
as hydrogen and helium. Therefore, they are not simply enlarged copies of the Earth, nor
homogeneous spheres of gas, since their interior is characterized by a very articulated structure.
The diversity of gaseous planets to terrestrial ones is a problem that only recently is finding
partial solutions, especially thanks to the observational contribution of
interplanetary probes in recent years. Many pieces of the mosaic are going to their
place, while other mysteries are thickening even more, or old certainties are being questioned:
such as the solid and rocky nature of Jupiter's nucleus.
Astronomers thought so far that Jupiter was born as a rocky and icy planetary embryo,
which later would form its huge gaseous envelope by attracting hydrogen and helium
from the solar nebula by its enormous gravity. This would mean that there
was a relatively clear delineation between the solid core and the gas surrounding it.
However, the visit of the Juno probe was enough to force astronomers to reconsider the whole issue,
so that the real composition of the nucleus, as well as the properties of the materials that
constitute it, and even its very existence, are all returned to be the subject of speculation.
But at this point it comes just to ask: what has discovered Juno so important on Jupiter?
To understand that, we must first do a brief review of the origins of gas giants!
Jupiter... eleven times larger than Earth in diameter, 318 times
more massive, 1300 times more voluminous... In our Solar System, it is the planet of excess
in all its manifestations, the planet where everything is big, heavy, colorful and stormy.
All qualities that apparently contrast with its delicate constitution,
very similar to the gaseous one of the Sun. Jupiter is in fact largely formed by the
same elements that make up our star: hydrogen and helium. This makes it a planet that as a
whole is just 1.3 times denser than water, and more than four times less dense than our Earth!
On an imaginary journey from the outside to the center,
you would first encounter a layer of hydrogen and helium clouds, with traces of methane and
ammonia. The density of the atmosphere in the uppermost layers is about ten times less than
Earth's, but the gases become increasingly dense as you descend toward the center of the planet.
At about 10,000 km depth, the gas becomes so dense that hydrogen ionizes, turning into
metallic hydrogen, a superconductor that has also recently been synthesized in Earth's laboratories.
At about 20,000 km depth we would find that helium condenses into rain. And in the inner depths,
where pressures are about 10 million times higher than at Earth's surface,
scientists think the gas exists as a thick soup dotted with heavy metal rocks.
But why is Jupiter so different from the innermost planets, which are characterized by a very dense,
solid mass covered by a very thin gaseous envelope? The answer lies in
the formation processes of the Solar System. According to most of the current theories,
Jupiter is the planet whose nucleus must have formed first, well before the residual gas of the
primordial nebula was moved away from the solar wind that began to blow when the Sun started the
process of nuclear fusion. the Sun, in fact, began at that time to emit light and energy,
also generating a strong wind of ionized particles that pushed towards the periphery away most of the
dust and gas still present, differentiating them in this way: the denser and heavier material,
such as dust, remained available to the inner planets that were forming,
while the lighter gases, such as hydrogen, were pushed further away,
towards the current region of the outer planets. In the innermost region, the gravitational
attraction between the particles of solid material favored the aggregation of a considerable amount
of larger and larger objects, which in a continuous process of collisions and mergers
have then given rise to the inner planets as we know them today:
rocky bodies, relatively massive and high density. In the more distant areas, large quantities of
gas flowed in; both from the inner areas of the Solar System (due to the effect of the solar wind)
and from the periphery (due to the attraction of gravity exerted by the newly formed star). In this
area, starting roughly from the orbit of Jupiter, it was also able to condense the water ice, which
was impossible in areas closer to the Sun due to the too high temperature. And just around these
ice nuclei, mixed with rock, began to collect - faster and faster, as the mass grew - the gases
that have then "swollen" the diameter of the outer planets up to the size we know today.
Another theory, however, suggests that there was no need for a solid core; and that Jupiter,
like its siblings, simply formed from the cloud of gas and dust that surrounded the Sun.
In that chaotic environment it could, in fact, happen that random thicknesses of matter were
formed; some of which, more resistant than the others and therefore able to attract to themselves
ever larger quantities of matter, were then enlarged up to the current size
The Sun itself was formed in this way, without any need to use a solid core as an aggregator of
matter. And we must not forget that if Jupiter had reached a mass about ten times higher
than the one it has nowadays, in its nucleus would have reached pressures and temperatures
such to trigger the thermonuclear fusion reactions that happen in the Sun. Jupiter,
in short, would have lit up like a star, and our solar system, like so many others in space,
would now have two suns. That it has come close to this outcome is demonstrated by
the fact that Jupiter is currently radiating twice the energy it receives from the Sun:
a sign that it still has an internal heat source due to contraction processes still in place.
To sum up, until recently the controversy over the actual nature of the nucleus of Jupiter
moved within two very distinct hypotheses, the first of which claimed that Jupiter possesses
a solid and well-defined nucleus, and the second that Jupiter does NOT possess a nucleus.
All this until the speculations based on observations now dated and quite approximate
has not moved to the development of models based on the findings from the Juno probe,
launched by NASA in 2011 and arrived in the middle of the Jovian system in mid-2016.
The spacecraft is still orbiting the planet every 53 days,
reaching a minimum distance of 4,000 kilometers from its surface.
In astronomical terms it is a tiny distance, even considering the size of Jupiter.
“BE sure to join the “Insane Curiosity Channel”...
Click on the bell, you will help us to make products of ever higher quality!”
Thanks to Juno, we're learning a lot of new things about the giant of the Solar System.
The data collected in recent months have served astronomers to analyze the atmosphere
and the interior of Jupiter, discoveries that have been collected and reported in four major research
published in the scientific journal Nature. The most surprising of all is currently
the one concerning the core of the planet, a discovery that unexpectedly seems to disprove
both the hypotheses of the solid core and the one of the absent core... The mathematical
models built on the basis of the probe data, in fact, suggest the presence of heavy elements,
such as iron and silicates, but also say that these elements are not concentrated
in a compact and well-defined core, but they are diluted and scattered within a
region with blurred boundaries that extends for almost half the radius of the planet!
This means that probably the nucleus is not only made of rock and ice,
but is also mixed with hydrogen and helium, and that there is a very gradual transition
between the nucleus and its surroundings. Crucial in this discovery was the role of the KaT
instrument, which installed on board can measure the speed of Juno with extraordinary precision:
up to a few thousandths of a millimeter per second... a hundred times less than the speed
of a snail! Measuring these minute variations in speed means being able to understand how
the spacecraft moves in Jupiter's gravitational field; and from this, taking into account how the
spacecraft accelerates and slows down in response to variations in the planet's gravitational field,
it is then able to deduce how the mass is distributed in the depths of Jupiter.
The discovery of this very strange "fuzzy" core left researchers incredulous,
convinced that the probe's data would finally provide evidence of a dense, rocky or icy core.
What could have happened billions of years ago on Jupiter to reduce the core like that?
Immediately, various teams of astronomers have set in motion
to answer this question, and after thousands of simulations started each time with different
parameters, the only solution that can not contradict the observational data of Juno
seems to be the one that provides the hypothesis of a giant impact,
occurred about 4.5 billion years, between a large planetary embryo and proto-Jupiter.
According to this reconstruction, initially Jupiter was formed by a solid and compact core
of heavy elements with a mass equal to about a tens of Earth masses,
surrounded by an extended and massive atmosphere, roughly corresponding to the current one.
The very strong gravitational field of Jupiter must have perturbed the orbit of one of the many
large planetoids that probably populated the chaotic first period of formation of
the Solar System, with a solid core of about eight Earth masses and an atmosphere of two.
The enormous difference between the masses of the two celestial bodies
caused the protoplanet to rush headlong into Jupiter, heading like a bullet toward its core.
The resulting impact between the two cores of fairly similar size
would then have shattered them by mixing their material with that of the surrounding atmosphere.
Such an event would have seen Jupiter literally absorb the planetoid, causing the two cores
to combine and spread in a very short time, perhaps in no more than ten hours. Subsequently,
the strong cooling after the heat developed by the collision and the strong winds kicked up
would have swept upward some of the pulverized core, which would explain
Jupiter's incredible enrichment in elements such as carbon and nitrogen near its surface.
This scenario, the authors of the simulation warn, however,
has only a 40% chance of being realistic. Which means we certainly need to take it into account,
but also that it could be replaced or corrected by other information not currently available.
However, the duration of Juno's mission, originally planned until 2018,
seems to have been extended until 2025, which will allow the probe to make at least another thirty
close passes by Jupiter. Surely the instruments on board the spacecraft will have a way to confirm
or deny the data on the consistency of the core, or to indicate other solutions to the problem.
But not only that. The orbit of Juno will cross in the coming years also the orbits of three of
the largest moons of Jupiter: Ganymede, Europa and Io, and there will be close passes at 1,000
kilometers from Ganymede in mid-2021 and only 320 kilometers from Europa at the end of 2022.
Juno has already given us some truly incredible photographic shots of Jupiter, and now we can't
wait to see what it will be able to do with the fairy-tale landscapes of the Galilean moons.