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We are so used to picturing us humans on
Earth's surface (and maybe soon Mars) that when we see a planet like Jupiter,
one of the first questions that comes to mind is "Can we stand on
it?" Let’s for a moment ignore the extreme conditions (gravity,
atmospheric pressure, high temperature, and winds) that are found on the giant
planet, and let’s just descend through the atmosphere.
What we’d really see is a spectacle like no
other. Far beneath Jupiter's atmosphere is a gigantic ocean of liquid metallic
hydrogen, which would look and behave like mercury except that hydrogen has 60
percent the density of water. So, you would have to sink for tens of thousands
of kilometers to reach a hot, molten, rocky core that's possibly solid.
The interior of Jupiter is not precisely
mapped – that is one of the scientific goals of the Juno mission, which has
just reached Jupiter. The probe will use precise gravitational and
electromagnetic measurements to map what goes on underneath Jupiter’s clouds.
I know that the answer so far is not really
satisfying, so let’s drop the pretense of a magical observer and let’s dive
into Jupiter with current technologies.
Jupiter is really warm, with the very top of
its atmosphere at about 900 Kelvins (630°C or 1,160°F). As we fly down through
the atmosphere, the temperature quickly drops as the pressure and wind speed increase.
Following what happened to the Galileo probe,
which dived into Jupiter in 1995, things start going badly for electronics 58
minutes into our exploration and 156 kilometers (97 miles) into the atmosphere.
For the Galileo probe, this combination of pressure (23 atmospheres) and
temperature (153°C or 307°F) proved deadly.
But it's been 20 years, so let's assume we can
continue down. At 500 kilometers (310 miles), the visibility is almost
completely gone and the thick ammonia clouds swirl all around us, with wind
speeds of around 100 meters (330 feet) per second.
Underneath the ammonia clouds, there are more
water clouds and more complex atmospheric effects that Juno will hopefully
clarify. Current technology will have been pulverized by now, and our remains
will now be traveling to a layer of supercritical fluid hydrogen – something
not quite a gas but not exactly a liquid either.
After about 2.5 hours of exploration, we will
have reached the liquid metallic hydrogen ocean. Heavy elements might reach the
center after many more hours of falling. So, you couldn't exactly stand on this
ocean. But below this, it's thought Jupiter may indeed have a rocky core,
perhaps somewhat similar to terrestrial planets. Juno will help answer this
question during its mission.
Jupiter has most of the planetary mass of the
Solar System, and could easily fit all the other planets in its interior.
There's a reason why it is the planetary king
of the Solar System.
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