A bad day on Venus gets even worse

Contrary to its alluring name, Venus is the planet from hell, with an atmosphere so hot, toxic and heavy that any visitor would risk being simultaneously melted, suffocated and crushed.

But not just that: the second planet from the Sun turns on its axis so slowly that, for any survivor, a Venusian day would seem interminable, for it is the equivalent of 243 days on Earth.

To make things worse, a day on Venus is getting even longer, French astronomers have discovered.

A team from the Paris Observatory analysed data from a spectrometer aboard a European orbiter, the Venus Express.

Called VIRTIS, the gadget measures infrared and visible light and is used to scan the planet's surface beneath the thick, roiling atmosphere.

The astronomers were stunned when they checked landmarks against the last mapping of Venus, carried out between 1990 and 1994 by the US probe Magellan.

At a given point in the Venusian day, landmarks were a full 20 kilometers (12 miles) behind where they should have been.

The team, publishing in the journal Icarus, say they have been over the observations again and again.

"After eliminating possible sources of error, we believe that the duration of the Venusian day must have changed over the 16 years," they said in a press release.

Their calculation is that an extra six and a half terrestial minutes have been added to the Venusian day during this time.

"On the astronomical scale, this is a major change," said VIRTIS investigator Pierre Drossart.

Pierre Drossart is depicted here in an ESA Video on the Venus Express, along with his ESA collegues, explaining the thinking behind the Venus Express mission.

The astronomers' hypothesis is that friction by Venus' atmosphere is braking the movement of the terrain below.

That sounds bizarre until one realises that the atmosphere is 100 kms (60 miles) thick, with extremely dense clouds of 96 percent carbon dioxide, driven by superwinds reaching some 350 kilometres (210 miles) per hour.

Atmospheric pressure at the surface is 92 times that of Earth -- the equivalent of being more than 900 metres (3,000 feet) below the ocean.

"A braking effect from the atmosphere also occurs erratically on Earth, but the discrepancy is only a matter of a few tenths of a second and it is imperceptible," Drossart told AFP.

So will Venus eventually stop spinning -- or even go into reverse rotation?

"It's difficult to say, given that we only have two points of measurement," said Drossart.

"But theoretical models suggest that this is probably just a cyclical phenomenon. If the atmosphere speeds up, the planet slows. Then the energy goes into reverse, in a pendulum effect."

Jupiter's Eroding Core: Large Exoplanets Have no Cores

A new study indicates that the hydrogen and helium gases that made Jupiter a gas giant are destroying the planet's very core, leading astronomers to believe that most massive extrasolar planets have no cores at all and changing the view scientists have long held of these distant worlds.

Jupiter has been called a gas giant because it consists mostly of hydrogen and helium surrounding a central core of iron, rock, and ice.

The core, which weighs roughly 10 times as much as Earth, is a small component in a planet that weighs 318 Earths.

These same gases are causing the solid rock in Jupiter's core to dissolve into liquid, the researchers said.

Planetary scientists Hugh Wilson and Burkhard Militzer of the University of California, Berkeley, performed quantum mechanical calculations on the outcome if magnesium oxide (MgO), which is a key ingredient in the rock of Jupiter's core, is submerged in a hydrogen-helium fluid at the planet's heart.

According to the researchers, with MgOs high solubility, the core's temperature, which is hotter than the sun at approximately 16,000 degrees Kelvin, will make the solid rock in Jupiter's core melt into liquid.

In a paper submitted to Physical Review Letters, the scientists said that although the exact rate of erosion is unknown, it is also calculated that the ice in the core also dissolves, so Jupiter's present core may not be as large as it was when the planet formed.

While the new findings are important, a planetary scientist, Jonathan Fortney, said the big question is whether the convection in Jupiter's interior is vigorous enough to dredge up dissolved core material and toss it into the hydrogen-helium envelope.

Fortney said that if this was the case, then Jupiter's core could be smaller today than it was at birth; if not, the dissolved rock and ice will simply remain at Jupiter's center although the boundary between the core and mantle may not be so distinct.

"I think we've made much more progress in the past year than people had made in the previous 20 years," said Fortney, adding that those calculations have implications far beyond Jupiter since many of the planets orbiting other stars are more massive than Jupiter, so their cores are even hotter.

"For these planets, core erosion would be faster," says Militzer, which could support the theory that gas giants several times heavier than Jupiter might be completely coreless.

In 2016, NASA's Juno spacecraft will start orbiting Jupiter, which could provide data on the planet's interior by measuring its gravitational field.

Hot Jupiters: Stars that steal give birth to backwards planets

Stealing gas from their siblings could leave stars with a motley crew of planets – including ones with backwards orbits.

Our solar system is thought to have formed from a collapsing cloud of gas and dust that flattened out as it spun, rather like pizza dough. 

This explains why the planets all orbit the sun in the same direction as the sun itself spins, and share the same plane.

Exoplanets tell a different story, with some tilted at jaunty angles and others orbiting their stars backwards. Planet-on-planet violence is one explanation, but Ingo Thies of the University of Bonn in Germany and colleagues suggest the culprit is the star itself, before its planets are born.

The team made a computer model of stars forming in a cluster. The stars started out forming proto-planetary discs in the usual way. But if a star veered too close to another clump of matter, like another star's disc or a cloud of gas that hadn't formed a star yet, it sucked huge streams of gas – up to 30 times the mass of Jupiter – from its neighbours and into its own nascent disc.

Hot Jupiters

In the model, this stolen material tilted the disc. And when the angle and the mass of material were just right, the final disc ended up spinning in the opposite direction to the star. Any planets that formed in that disc did the same. The work will appear in Monthly Notices of the Royal Astronomical Society.

The influx of gas could also compress the inner part of the disc, making planets form there more quickly. These may be more susceptible to violent crashes, leading to further eccentric orbits.

This in turn could help explain why, unlike our solar system, which keeps the smallest and rockiest planets closest to the sun, many exoplanet systems have bloated gas giants, known as "hot Jupiters", as their innermost planets. When the smaller planets get flung out of the inner part of the disc, an overall conservation of angular momentum means these gas giants could get drawn in closer.

Reference: arxiv.org/abs/1107.2113

NASA Scientists Cook Up Jupiter's Atmosphere on Earth

Close-up of Jupiter's Great Red Spot as seen by a Voyager spacecraft.
CREDIT: NASA/JPL-Caltech

On a rooftop in downtown Atlanta, a group of scientists are cooking up alien atmospheres.

Their results will help astronomers understand the data that NASA's Juno spacecraft will send back from Jupiter in 2016.

Jupiter's cloudy bands and great red spot are visible with an amateur telescope but the elements that compose them are more challenging to detect.

The Juno spacecraft launched on Aug. 5, will spend the next five years journeying to Jupiter, the largest planet in the solar system.

Using myriad instruments, the craft is expected to help scientists come to a greater understanding of the origins and composition of the gas giant.

Photos: NASA's Juno Mission to Jupiter

Hot Gas Giants go Through Phases

A SUPER-HOT planet 1500 light years away has been seen waxing and waning like the moon. The discovery hints that hot gas giants come in two varieties.

The phases of Corot 1b were detected by a team at Leiden Observatory in the Netherlands, who analysed changes in the amount of red light from the system. A small component of the light smoothly dims and brightens as the planet orbits. This is probably alternation between the dark of Corot 1b's relatively cool night side and the glow of its red-hot day side, which permanently faces its star and reaches a temperature of about 2400 kelvin (Nature, DOI: 10.1038/nature08045).

The stark temperature difference contrasts with previous observations of another gas planet, HD 189733b, using the Spitzer Space Telescope, which found a fairly even temperature around the planet of about 1000 kelvin.

The theory is that fierce winds carry solar heat around HD 189733b, whereas on Corot 1b, metal oxides appear to absorb heat high in the stratosphere and quickly re-radiate it before it can be spread around. "What we observe really fits into the idea that there are two different types of planet in this range", says Leiden team member Ignas Snellen.