Jupiter’s melting heart sheds light on mysterious exoplanet

March 22, 2012 By Brian Jacobsmeyer

Credit: Forsetius via flickr

Scientists now have evidence that Jupiter’s core has been dissolving, and the implications stretch far outside of our solar system.

Jupiter might be having a change of heart. Literally.

New simulations suggest that Jupiter’s rocky core has been liquefying and mixing with the rest of the planet’s innards. With this new data, astronomers hope to better explain a recent puzzling discovery of a strange planet outside of our solar system.

“It’s a really important piece of the puzzle of trying to figure out what’s going on inside giant planets,” said Jonathan Fortney, a planetary scientist at the University of California Santa Cruz who was not affiliated with the research.

Conventional planetary formation theory has modeled Jupiter as a set of neat layers with a gassy outer envelope surrounding a rocky core consisting of heavier elements. But increasing evidence has indicated that the insides of gas giants like Jupiter are a messy mixture of elements without strictly defined borders.

This new research on a melting Jovian core bolsters a mixing model of gas giant planets and would provide another avenue for heavier elements to flow throughout the planet.

“People have been working on the assumption that these planets are layered because it’s easier to work on this assumption,” said Hugh Wilson, a planetary scientist at the University of California Berkeley and a coauthor of the new research appearing in Physical Review Letters.

Although scientists had previously toyed with the idea of melting cores in large planets, nobody sat down and did the necessary calculations, said Wilson.

Scientists have to rely on calculations of Jupiter’s core environment because the conditions there are far too extreme to recreate on Earth. Wilson and his UC-Berkeley colleague Burkhard Militzer used a computer program to simulate temperatures exceeding 7,000 degrees Celsius and pressures reaching 40 million times the air pressure found on Earth at sea level.

Those conditions are thought to be underestimates of the actual conditions inside Jupiter’s core.

Nonetheless, the authors found that magnesium oxide — an important compound likely found in Jupiter’s core — would liquefy and begin drifting into Jupiter’s fluid upper envelope under these relatively tame conditions.

Researchers believe that similarly-sized gas giant exoplanets — planets found outside of our solar system — probably have similar internal structures to Jupiter. Consequently, scientists were baffled earlier this year when they found a planet with approximately the same volume as Jupiter yet four to five times more mass.

Called CoRoT-20b, the new planet was announced in February, and its discoverers searched for a suitable explanation for its unusual density. Using conventional models, the astronomers calculated that the core would have to make up over half of the planet. For comparison, Jupiter’s core only represents about between 3-15 percent of the planet’s total mass.

With a core that large, CoRoT-20b presented a huge problem for traditional assumptions surrounding planet formation.

“It’s much easier to explain the composition of this planet under a model where you have a mixed interior,” said Wilson.

Even the team that discovered the planet noted that a mixing model could allow for a more palatable planet density. Wilson’s simulations not only add credence to the mixing model of giant planets but also suggest that this specific exoplanet’s core is probably melting just like Jupiter’s.

This melting may help explain why the exoplanet’s heavy elements are likely stirred up and distributed throughout its volume, said Wilson.

Santa Cruz’s Fortney agrees that most of the exoplanet’s heavy elements likely reside in the outer envelope. Nonetheless, he expects other factors played a larger role in how the planet’s interior became mixed: “It’s more of a planet formation issue.”

Several other events, such as two gas giants colliding together, might explain the ultra-high density of this new planet, Wilson admits. Certain processes may also limit the effectiveness of the melting and mixing process.

Liquefied parts of a gas giant’s core may have trouble reaching the outer envelope due to double diffusive convection — a process commonly found in Earth’s oceans. When salty water accumulates at the bottom of the ocean, its density keeps it from mixing thoroughly with the upper layers. In a similar fashion, the heavy elements in Jupiter’s core may have trouble gaining enough energy to move upward and outward.

Scientists don’t know how much this hindrance will affect potential mixing inside Jupiter, and many other questions remain to be answered about the melting process.

“The next question is, ‘How efficient is this process?'” said Fortney.

Researchers will have more tools to answer this question once NASA’s Juno probe reaches Jupiter in 2016. With the spacecraft’s instruments carefully analyzing Jupiter’s composition, Wilson believes that there will be signatures of mixing and core erosion.

Source: Inside Science News Service

Jupiter’s melting heart sheds light on mysterious exoplanet.


Scientists discover a Saturn-like ring system eclipsing a Sun-like star

The object at the center of the ring system is either a very low-mass star, a brown dwarf, or a planet.

By University of Rochester, New York — Published: January 13, 2012

Saturn-like ring system eclipsing a Sun-like star.
Credit: Michael Osadciw/Univ. of Rochester

A team of astrophysicists from the University of Rochester, New York, and Europe has discovered a ring system in the constellation Centaurus that invites comparisons to Saturn.

The scientists, led by Eric Mamajek from Rochester and the Cerro Tololo Inter-American Observatory, used data from the international Wide Angle Search for Planets (SuperWASP) and All Sky Automated Survey (ASAS) project to study the light curves of young Sun-like stars in the Scorpius-Centaurus association — the nearest region of recent massive star formation to the Sun.

The basic concept of the research is straightforward. Imagine yourself sitting in a park on a sunny afternoon when a softball passes between you and the Sun. The intensity of light from the Sun would appear to weaken for just a moment. A bird then flies by, causing the intensity of the sunlight to again weaken — more or less than it did for the baseball, depending on the size of the bird and how long it took to pass. That’s the principle that allowed the researchers to discover a cosmic ring system.

A light curve is a graph of light intensity over time, and one star in particular showed dramatic changes during a 54-day period in early 2007. Mark Pecaut and Mamajek from Rochester discovered the unusual eclipse in December 2010. “When I first saw the light curve, I knew we had found a very weird and unique object,” said Mamajek. “After we ruled out the eclipse being due to a spherical star or a circumstellar disk passing in front of the star, I realized that the only plausible explanation was some sort of dust ring system orbiting a smaller companion — basically a ‘Saturn on steroids.’”

If a spherical object merely passed in front of the star, the intensity of the light would gradually dim and reach a low point before gradually increasing. That was not the case with the star identified as 1SWASP J140747.93-394542.6. The Rochester team discovered a long, deep, and complex eclipse event with significant on-and-off dimming. At the deepest parts of the eclipse, at least 95 percent of the light from the star was being blocked by dust.

The shape of the light curve was similar to that of a well-researched star (EE Cephei), suggesting similar traits in the companion objects. However, EE Cephei differs in that it appears to be a thick protoplanetary disk transiting — or passing in front of — a massive, hot star. “We suspect this new star is being eclipsed by a low-mass object with an orbiting disk that has multiple thin rings of dust debris,” said Mamajek. The star is similar in mass to the Sun, but it is much younger — about 16 million years old, or 1/300th the age of the solar system — and it lies about 420 light-years away.

“This marks the first time astronomers have detected an extrasolar ring system transiting a Sun-like star, and the first system of discrete, thin dust rings detected around a very low-mass object outside of our solar system,” said Mamajek, “But many questions remain about what exactly has been discovered.” He says the object at the center of the ring system is a very low-mass star, brown dwarf, or planet. The answer lies in the object’s mass.

In order to be a brown dwarf, the object would have to be between 13 Jupiter masses (MJ) and 75 MJ, insufficient to sustain the thermonuclear fusion reactions during its projected lifetime. If the object’s mass is less than 13 MJ, it would likely be a planet, making it similar to Saturn, whose rings have a similar optical depth.

Mamajek and colleagues will be proposing to use Southern Hemisphere telescopes to obtain radial velocity data for the star to detect the gravitational tug of the companion and to conduct non-redundant mask imaging experiments to try to detect light from the faint companion. The observations will help calculate the companion’s mass, which, in turn, will help determine its identity.

Along with the central object, Mamajek is interested in what is taking place in the two pronounced gaps located between the rings. Gaps usually indicate the presence of objects with enough mass to gravitationally sculpt the ring edges, and Mamajek thinks his team could be either observing the late stages of planet formation if the transiting object is a star or brown dwarf, or possibly moon formation if the transiting object is a giant planet.

If the dusty rings are similar to Saturn’s in terms of their mass per optical depth, then the total mass of the rings is only on the order of the mass of Earth’s Moon. The orbital radius of the outermost ring is tens of millions of kilometers, so the mass and size of the ring systems is substantially heftier than Saturn’s ring system. The four rings detected thus far have been dubbed “Rochester,” “Sutherland,” “Campanas,” and “Tololo” after the sites where the eclipsed star was first detected and analyzed.

Mamajek expects it will take at least a couple more years to piece everything together. However, with future all-sky monitoring surveys like the proposed Large Synoptic Survey Telescope being built in Chile, Mamajek expects that rare eclipses of young stars by moon-forming disks and large ring systems around young giant planets will be detectable over many years of searching. “Follow up observations of such eclipses may provide our first observational constraints on the formation and early evolution of moons around gas giant planets.”

Scientists discover a Saturn-like ring system eclipsing a Sun-like star – Astronomy Magazine.

Ice cavern ‘could support life’ on Jupiter’s moon Europa

7:30AM GMT 17 Nov 2011

An ice cavern containing as much water as the North American Great Lakes may provide a potential habitat for life on Jupiter’s moon Europa, scientists believe.

The salty “lake” is thought to be locked within Europa’s icy outer shell a few kilometres from the surface.

Other large pockets of liquid water are also likely to exist on the moon, it is claimed.

Scientists are excited by the discovery, which offers one of the best hopes yet of finding life beyond the Earth.

Evidence for the ice-covered lake in Europa’s Thera Macula region is seen in the shape of the terrain above it. The site appears to be marked by a fractured and collapsing “lid” of floating ice.

On Earth, similar features in the Antarctic are caused by briny seawater penetrating and weakening ice shelves. They are also present in Iceland, where glaciers are heated from below by volcanic activity.

Scientists have long suspected that a liquid or slushy ocean exists under Europa’s surface, warmed by the tidal forces of Jupiter’s powerful gravity.

Theoretically, a liquid water ocean could provide a suitable habitat for life – but only if it was not too far from the surface.

Experts disagree about how thick the layer of covering ice is. The new research, based on images from the Galileo probe, suggests that water “lenses” could lie as little as three kilometres below the bottom of the surface crust.

Lead scientist Dr Britney Schmidt, from the University of Texas, said: “One opinion in the scientific community has been, ‘If the ice shell is thick, that’s bad for biology – that it might mean the surface isn’t communicating with the underlying ocean’.

“Now we see evidence that even though the ice shell is thick, it can mix vigorously. That could make Europa and its ocean more habitable.”

The research, published today in the journal Nature, involved computer simulations based on observations of Europa and Earth.

Dr Schmidt’s team focused on two circular bumpy regions on Europa’s surface called “chaos terrains” .

The scientists produced a four-step model to explain the features which resolves several conflicting observations.

However, it can only infer the presence of the hidden lakes. Their existence will only be confirmed by a new space mission designed to probe Europa’s ice shell.

Such a mission, likely to employ ground-penetrating radar, is now under consideration by American space agency Nasa.

Commenting on the study, Dr Robert Pappalardo, senior research scientist at Nasa’s planetary science section, said: “It’s the only convincing model that fits the full range of observations. To me, that says ‘yes, that’s the right answer’.”

via Ice cavern ‘could support life’ on Jupiter’s moon Europa – Telegraph.