Tag Archives: gas giants

Jupiter’s Supersonic Stratospheric Winds Make it a Unique Beast

Using the aftermath of a comet collision in 1994 astronomers have measured the winds blowing across Jupiter‘s stratosphere for the first time. The team has discovered that these winds raging around the middle atmosphere of the solar system’s largest planet are incredibly powerful–reaching speeds of up to 400 metres per second at the poles.

The team’s findings represent a significant breakthrough in planetary metrology and mark the gas giant out as what the team are describing as a ‘unique metrological beast in the solar system.’

This image shows an artist’s impression of winds in Jupiter’s stratosphere near the planet’s south pole, with the blue lines representing wind speeds. These lines are superimposed on a real image of Jupiter, taken by the JunoCam imager aboard NASA’s Juno spacecraft. (ESO/L. Calçada & NASA/JPL-Caltech/SwRI/MSSS)

To conduct the research the astronomers diverged from the usual methods used to measure the winds of Jupiter. Previous attempts to measure the gas giant’s winds have hinged on measuring swirling clouds of gas–seen as the planet’s distinctive red and white bands–but this method is only effective in measuring winds in the lower atmosphere. Whereas, by using aurorae at Jupiter’s poles researchers have been able to model winds in the upper atmosphere. But, both of these methods, even when used in conjunction, have left the winds in the middle section of the gas giant’s atmosphere–the stratosphere– something of a mystery.

That is until now. This team of astronomers used the Atacama Large Millimetre Array (ALMA) to track molecules left in Jupiter’s atmosphere by the collision with the comet Shoemaker-Levy 9 in 1994.

“We had to use ALMA’s ability to quickly map Jupiter’s spectral emission at very high spatial and spectral resolution in the submillimeter and observe the Doppler shifts induced by the winds on the spectral line we targeted,” team leader Thibault Cavalié,  Laboratoire d’Astrophysique de Bordeaux, France, exclusively tells ZME Science. “We could deduce the wind speeds just like you could deduce the speed of a passing fire engine by the change in frequency of its siren. This spectral line is formed in the stratosphere, giving us access to the winds at this altitude.

“It is the first time we achieve measuring directly winds in the stratosphere of Jupiter, which lacks visual tracers such as clouds.”

Thibault Cavalié,  Laboratoire d’Astrophysique de Bordeaux, France.

Cavalié explains that the team had to use ALMA’s ability to quickly map Jupiter’s spectral emission at very high spatial and spectral resolution in the submillimeter and observe the Doppler shifts induced by the winds on the spectral line they targeted.

“We could deduce the wind speeds just like you could deduce the speed of a passing fire engine by the change in frequency of its siren,” the researcher continues. “This spectral line is formed in the stratosphere, giving us access to the winds at this altitude.”

What the astronomers discovered was powerful winds in the middle atmosphere of Jupiter in two different locations. One set of winds conformed to expectations, but the other came as a surprise.

Jupiter’s ‘Supersonic Jet’ Winds

Cavalié explains that the team first found a 200 metres per second eastward jet just north of the equator in ‘super-rotation–meaning that the wind rotates faster around the planet than the planet rotates itself. “Winds at such latitudes were expected from models and previous temperature measurements at these low latitudes,” the astronomer adds.

But, not everything observed by the team conformed to expectations.

“Most surprisingly, we identified winds located under the main UV auroral emission near Jupiter’s poles. These winds have velocities of 300 to 400 meters per second,” Cavalié says. “While the equatorial winds were kind of anticipated, the auroral winds and their high speed were absolutely unexpected.”

To put this into perspective, the fastest winds ever recorded on earth reached a speed of just 103 metres per second–measured at the Mount Washington Observatory in 1931. These auroral winds even beat the winds recorded in Jupiter’s Great Red Spot–an ongoing raging storm on the surface of the gas giant–which have been clocked at around 120 metres per second.

The speed of these jets isn’t their only intimidating quality, however. The jets seem to behave like a giant vortex with a diameter around four times that of our entire planet, reaching a height of around 900 kilometres.

“A vortex of this size would be a unique meteorological beast in our Solar System.”

Thibault Cavalié,  Laboratoire d’Astrophysique de Bordeaux, France.

The team’s measurements and stunning discovery, documented in a paper published in the latest edition of Astronomy & Astrophysics, wouldn’t have been possible without a violent incident in Jupiter’s recent history.

Shoemaker-Levy 9 Still has Impact

The impact of Shoemaker-Levy 9 upon the surface of Jupiter was an event–or more precisely a series of events– that had already made history before its effects made this research possible.

The comet broke up in the planet’s atmosphere resulting in a series of impacts that had never been studied prior to 1994, and its somewhat ironic that thanks to this study, Shoemaker-Levy 9 is still having an impact today. The comet left traces of hydrogen cyanide swirling in Jupiter’s atmosphere which the team was able to track.

This image, taken with the MPG/ESO 2.2-metre telescope and the IRAC instrument, shows comet Shoemaker–Levy 9 impacting Jupiter in July 1994. (ESO)

“The team measured the Doppler shift of hydrogen cyanide molecules — tiny changes in the frequency of radiation emitted by the molecules — caused by their motion driven by stratospheric winds on Jupiter,” says Thomas K Greathouse, Senior Research Scientist at Southwest Research Institute (SwRI), responsible for the development of the study and analysis of the observational results. “

“The high spectral and spatial resolution and the exquisite sensitivity of the observations at the wavelengths covered by ALMA allowed us to map such small Doppler shifts caused by the winds in the stratosphere all along the limb of Jupiter.”

Thomas K Greathouse, Senior Research Scientist at Southwest Research Institute (SwRI).

The fact that the team was able to obtain all the measurements they did with just 30 minutes of operating time with ALMA is a striking testament to the power and precision of the 66 antennas that make up the telescope array located in the Atacama Desert of Nothern Chile, currently the most powerful radio telescope on Earth.

“It was the availability of ALMA that made these measurements possible.  Previous radio observatory facilities did not have the combination of spectral and spatial resolution along with the high sensitivity needed to measure the winds as was done in this study,” Greathouse tells ZME Science. “Making further observations using ALMA to capture Jupiter at different orientations will allow us to study these winds in more detail and allow us to look for temporal variability in them as well. 

“Additionally, more extensive measurements will be possible from the JUICE mission and its Submillimetre Wave Instrument slated for launch in 2022.”

The Future of Jupiter Investigations

JUICE or JUpiter ICy moons Explorer is the first large-class mission in the European Space Agency’s (ESA) Cosmic Vision program and will arrive at Jupiter in 2029 when it will begin a three-year mission observing the gas giant in intense detail.

“This is why science is so much fun.  We have worked hard to understand a system–Jupiter’s stratosphere in this case–as best we can, we make our predictions about something–stratospheric wind behaviour–and then go test those predictions. If we are right, fantastic, we move on to the next problem, but if we are wrong we have learned something new and unique and can then continue making further studies to come to a more complete understanding of the system.”

Thomas K Greathouse, Senior Research Scientist at Southwest Research Institute (SwRI).
Amazing image of Jupiter taken in infrared light on the night of 17 August 2008 with the Multi-Conjugate Adaptive Optics Demonstrator (MAD) prototype instrument mounted on ESO’s Very Large Telescope. This false colour photo is the combination of a series of images taken over a time span of about 20 minutes, through three different filters. 9ESO/F. Marchis, M. Wong, E. Marchetti, P. Amico, S. Tordo)

For Cavalié, who has been involved with the measurement of Jupiter’s winds since 2009, the future is bright for such investigations and what they can tell us about the solar system’s largest planet and gas giants in general. “We now want to use ALMA again to characterize the temporal variability of the equatorial winds,” the astronomer says. “It is expected from temperature measurements and models that the direction of the equatorial winds should oscillate from eastward to westward with a period of about 4 years.”

The scientist is also clear, just because he and his colleagues have achieved a first, that doesn’t mean they are prepared to rest on their laurels. There are a lot of exciting developments on the way, and thus a lot of work to be done.

“We also want to observe the auroral winds during a Juno perijove pass to compare our data with observations of the poles by the spacecraft to better understand their origin and what maintains them,” he explains. “In addition, this study is a stepping stone for future investigations to be conducted using the same technique with JUICE and its Submillitre Wave Instrument.”

In addition to these missions, the ESO’s Extremely Large Telescope (ELT)–due to start operations later this decade–will also join investigations of Jupiter and should be capable of providing highly detailed investigations of the gas giant’s atmosphere.

“Jupiter and the giant planets are fascinating worlds. Understanding how these planets formed and how they work is a source of daily motivation, especially when working with world-class observatories like ALMA and participating in space missions to explore Jupiter and its satellites.”

Thibault Cavalié,  Laboratoire d’Astrophysique de Bordeaux, France.



Juno captures the closest-ever pictures of Jupiter we’ve seen — and its hair-raising voice

NASA has just shared the data from Juno’s flyby of Jupiter last week, containing the most detailed images of the gas giant that humans have ever seen. The new information surprised even the specialists who didn’t expect how unique the largest planet in the Solar System would prove to be up-close.

The Romans never regarded Jupiter as a merciful god. This infrared picture of the giant’s southern aurora certainly doesn’t seem to contradict them.
Image credits NASA / JPL-Caltech.

Following a five-year journey through space, the Juno probe entered Jupiter’s orbit in July. Last week, it got closer to the planet than any other spacecraft in history and managed to take some breathtaking snaps of the giant. It took NASA one and a half days to download the treasure trove of images from this historical six-hour flyby. The pictures revealed previously unseen storm and weather systems, and Jupiter’s never-before-seen north pole.

“[We got our] first glimpse of Jupiter’s north pole, and it looks like nothing we have seen or imagined before,” says principal investigator of the Juno mission Scott Bolton, from the Southwest Research Institute in San Antonio.

“It’s bluer in colour up there than other parts of the planet, and there are a lot of storms.”

Far from the orderly striped appearance of Jupiter’s midsection, the north pole is a swirling mass of roiling hurricane-like storms.

Jupiter’s northern pole.
Image credits NASA / JPL-Caltech.

“There is no sign of the latitudinal bands or zone and belts that we are used to – this image is hardly recognisable as Jupiter,” says Bolton. “We’re seeing signs that the clouds have shadows, possibly indicating that the clouds are at a higher altitude than other features.”

One thing scientists expected to see but didn’t is a hexagonal formation over the north pole, a structure which other Solar System gas giants — such as Saturn — have.

“Saturn has a hexagon at the north pole,” says Bolton. “There is nothing on Jupiter that anywhere near resembles that. The largest planet in our Solar System is truly unique.”

Along with the images of the north pole, the Juno team used an infrared device – the Italian Space Agency’s Jovian Infrared Auroral Mapper (JIRAM) – to analyse Jupiter’s polar regions in infrared wavelengths. This revealed warm and hot spots all over the giant’s polar regions and also gave us our first glimpse of the planet’s southern aurora.

“JIRAM is getting under Jupiter’s skin, giving us our first infrared close-ups of the planet,” says researcher Alberto Adriani from the Istituto di Astrofisica e Planetologia Spaziali in Rome. “And while we knew that the first ever infrared views of Jupiter’s south pole could reveal the planet’s southern aurora, we were amazed to see it for the first time.”

During the flyby, Juno passed about 4,200 kilometres (2,600 miles) above Jupiter’s clouds and it activated all eight of its onboard data collection instruments. One of these, the Radio/Plasma Wave Experiment instrument (Waves), recorded radio emissions thought to be produced by Jupiter’s auroras.

By converting these signals into an audio frequency, NASA put together a recording of the rest of Jupiter’s “voice” — and it will make the hairs stand on the back of your head.

“Jupiter is talking to us in a way only gas-giant worlds can,” says Waves co-investigator Bill Kurth from the University of Iowa.

“Waves detected the signature emissions of the energetic particles that generate the massive auroras which encircle Jupiter’s north pole. These emissions are the strongest in the Solar System. Now we are going to try to figure out where the electrons come from that are generating them.”

NASA researchers have only now begun analysing the data from the probe’s first sweep of the planet, but with 35 more orbital flybys yet to come, one thing’s for sure: Juno’s only just started spilling Jupiter’s secrets.

“It’s going to be a flood,” Juno project scientist Steve Levin from NASA’s Jet Propulsion Laboratory told Amina Khan at the Los Angeles Times. “Like drinking from a fire hose.”

When the Gas Giants are streched beyond The Point Of No Return

gas giants
The quest for understanding planets and stars seems to be more intense than ever. Things we could not have imagined not years but months ago are proven valid today. The problem of really big planets has especially fascinated scientists for hundreds of years for numerous reasons.

gas giant is basically a large planet that is not comprised of rock or other solid matter. Now, planetary scientists at UCL have identified the point at which a star causes the atmosphere of an orbiting gas giant to become critically unstable, as reported in this week’s Nature (December 6). These planets which are similar with Jupiter have atmospheres which are either stable and thin, or unstable and rapidly expanding. They are using 3d models to find out how they are.

Tommi Koskinen of UCL’s Physics & Astronomy Department is lead author of the paper and says: “We know that Jupiter has a thin, stable atmosphere and orbits the Sun at five Astronomical Units (AU) – or five times the distance between the Sun and the Earth. In contrast, we also know that closely orbiting exoplanets like HD209458b – which orbits about 100 times closer to its sun than Jupiter does – has a very expanded atmosphere which is boiling off into space. Our team wanted to find out at what point this change takes place, and how it happens. “Our paper shows that if you brought Jupiter inside the Earth’s orbit, to 0.16AU, it would remain Jupiter-like, with a stable atmosphere. But if you brought it just a little bit closer to the Sun, to 0.14AU, its atmosphere would suddenly start to expand, become unstable and escape. This dramatic change takes place because the cooling mechanism that we identified breaks down, leading to the atmosphere around the planet heating up uncontrollably.”

This gives us an important clue about how they evolve and this meaning that according to this study every such planet at a point in its life goes to a point where it can not return from. They form as an ice core out in the cold depths of space before migrating in towards their host star over a period of several million years. We have traveled a long way in a short amount of time when you think that just about 15 years ago we had not discovered an extrasolar planet.