ANDY RIDGWAY IS A SENIOR LECTURER IN SCIENCE
COMMUNICATION AT THE UNIVERSITY OF THE WEST OF ENGLAND.20,000°C,” says Eggert.
Gregoryanz points out another problem, saying
that while the pressures created using the shockwaves
are “absolutely surreal”, getting usable data is even
more of a challenge than with diamond anvil cells.
“They can create these pressures but they can’t really
measure anything yet,” he explains. “Even the
measurement of pressure is a little bit contentious.”
Despite the challenges, Eggert says he has been
making progress using shockwaves. In yet to be
published research conducted at the LLE, he and his
colleagues have been investigating what happens to
m ixtures of hydrogen and helium at high pressures.
By pre-compressing the mixture using a diamond
anvil cell, they were able to keep a lid on the
temperature after the shockwave.
The experiments show that because of the
temperature and pressure distributions in Saturn,
these gases are much more likely to stop mixing and
‘phase separate’ at high pressure than in the
conditions found in Jupiter. So inside Saturn, much
of the hydrogen and helium wil l have separated.
“The extra energy of the helium falling into the
centre of the planet might be what’s heating it,” says
Eggert. If helium is falling and creating heat by
friction, it would answer one of the biggest mysteries
of Saturn – why it emits 80 per cent more energy
than it absorbs from sunlight given that there should
be no residual heat after its formation.IMMINENT ARRIVAL
But we don’t just have experiments here on Earth
that can tell us about the inner workings of gas
giants. In 1995, NASA sent a probe from the Galileo
spacecraft into Jupiter’s atmosphere. Beforedisintegrating under the intense pressure and heat, it
made some intriguing discoveries, including that
there was much less water vapour than expected (see
‘Journey into the unknown’, above). Finding out
why this is the case is one of the main targets of
NASA’s Juno spacecraft, which will reach Jupiter in
July and start building a more detailed picture.
Juno’s microwave instrument will try to determine
whether there is water lurking inside Jupiter’s core. It
would provide evidence for the leading theory of
how gas giants like Jupiter form; a core of ice
developing that gets so large it draws in hydrogen.
But it’s not just where the water is hiding that will
provide us with clues about how gas giants develop.
Understanding how hydrogen behaves now, and
where it changes between its different phases within
a gas giant as the pressure ramps up with increasing
depth, wil l also al low us to work backwards to the
birth of these planets.
All this could not have come at a better time. The
huge planets first spotted by Kepler are much closer
to their stars than the prevailing models of solar
system formation would predict. So a better
knowledge of planetary formation will come in
handy as we realign our models to our new
knowledge of other solar systems.
It’s perhaps no sur pr ise then, with so many big
questions to be answered, that physicists around the
world are prepared to endure the sound of a few
cracking diamonds. ßJuno, seen here being
assembled, was
launched in August 2011
and will reach Jupiter
later this yearJOURNEY INTO
THE UNKNOWN
When Juno reaches Jupiter later this year, it willcarry on the vital work started by Galileo
On its way to Jupiter,
Galileo also paid a visit
to our MoonOnitswaytoJupiter,There were many questions
about the inner workings of
Jupiter until the Galileo
spacecraft paid it a visit.
Launched aboard the Space
Shuttle Atlantis in 1989, this 2.5
tonne lump of finely tuned
instruments took six years to
reach the Solar System’s
largest planet.
On the day Galileo arrived, aprobe was flung into Jupiter’s
dense atmosphere. During the
first two minutes of descent,
the air temperature was twice
as hot as the Sun’s surface.
Despite such brutal conditions,
the probe’s instruments
provided tantalising
information about this
planetary behemoth.
As well as detecting lightningbolts more powerful
than those on Earth, the
probe provided intriguing
data about the planet’s
composition. It showed there
to be far less helium than
expected. It also revealed
there to be less water vapour
– a characteristic that will be
investigated further when Juno
reaches Jupiter in July.PHOTOS: NASA X2, LLNL