Liquid Ocean Sloshes under Saturn Moon’s Icy Crust, Cassini Evidence Shows

http://www.scientificamerican.com/article/liquid-ocean-saturn-moon-enceladus/

Apr 3, 2014 |By Clara Moskowi

A liquid-water ocean hides under the frozen surface of Saturn’s moon Enceladus, new evidence confirms. The presence of this water boosts Enceladus’ ranking among the top places in the solar system to look for extraterrestrial life, scientists say.

Enceladus has intrigued researchers since 2005, when NASA’s Cassini probe discovered water-rich plumes spewing from the moon’s south pole, raising the possibility that they were venting from a buried liquid sea. The same probe has now bolstered the sea hypothesis by measuring Enceladus’ gravitational field. Scientists carefully monitored how the moon deflected Cassini off course and determined that Enceladus must have more mass at its south pole than meets the eye. Because liquid water is denser than ice, a buried ocean could contribute this hidden mass, the investigators reasoned. “It’s very difficult to come up with any explanation for the data that does not involve a thick layer of liquid water beneath the ice,” says California Institute of Technology planetary scientist David Stevenson, a co-author of a paper reporting the finding that will appear in the April 4 Science. Although the gravity data provides no proof that the liquid is water and not something else, water is the likeliest explanation because it is plentiful on Enceladus (albeit mostly seen in the form of ice) and because rock in its place would not produce the gravitational pattern seen, Stevenson explains.

Although plumes could form from the melting of surface ice, a connection to an underground source of water is also likely. And the fact that Enceladus’s plumes stem from its south pole, the same location where the putative ocean resides, is another factor in favor of the water ocean explanation. “These new results are like the point in a detective story where finding the fingerprints confirms the hypothesis based on motive and opportunity,” says Larry Esposito, a planetary scientist at the University of Colorado Boulder who was not involved in the study. Stevenson himself admits to having been skeptical until now. “Before these results I personally thought it was not at all clear that Enceladus had an ocean,” Stevenson told reporters during a teleconference on Wednesday. “You can make water just by rubbing ice blocks together, so it wasn’t clear to me that you had a huge volume. We now know that we do.”

Cassini’s data imply a subsurface ocean about 10 kilometers deep that covers an area about the size of Lake Superior. It would be buried underneath roughly 50 kilometers of frozen ice. Such a reservoir could theoretically host some form of life, which is thought to rely on liquid water. “There are terrestrial organisms that would be perfectly comfortable in that environment,” said study co-author Jonathan Lunine, a planetary scientist at Cornell University. “It makes the interior of Enceladus potentially a very attractive place to look for life.”

Enceladus is not the only solar system body that may host an underground ocean. Jupiter’s moon Europa, another prime target for extraterrestrial life searches, is thought to contain a global ocean underneath its surface ice, and the other Jovian satellites, Callisto and Ganymede, also show evidence of subsurface seas. Whereas Ganymede’s ocean probably sits on a deeper layer of ice, the water on Enceladus would lie atop the moon’s silicate core. Because silicate could provide some of the chemicals necessary for life—such as salts, phosphorus and sulfur—this arrangement may offer the chance for those chemicals to mix with liquid water and brew life, Lunine said.

The latest findings required researchers to painstakingly track Cassini’s motion by monitoring minute changes in the frequency of the signal it sent back to Earth, called Doppler shifts. “It’s the same thing they’re using for the Malaysian plane but we can do it more accurately,” Stevenson says. After collecting data during three passes Cassini made near Enceladus, scientists could estimate the moon’s gravity field well enough to determine that some extra mass is beneath Enceladus’s surface. “If correct, it provides important new information about what might be going on well below the vents,” says University of Idaho planetary scientist Matthew Hedman, who was not involved in the research. “One important question that I think still needs answering is how such an ocean connects up with the surface to produce the plumes.” Another question is why Enceladus’s north pole so far shows no sign of plume activity or an ocean. Scientists think gravitational tides from Saturn could be heating the moon’s interior, melting ice to form the ocean. This heating would likely be greatest at the poles. “I don’t know why it is only at the south,” Stevenson says.

The new evidence and the questions it raises are only making scientists more eager to devote some of Cassini’s remaining time at Saturn to studying Enceladus. The spacecraft arrived at the ringed planet in 2004 and is due to die a spectacular death by plunging into the Saturnian atmosphere in 2017. Before then, Cassini has three more targeted flybys of Enceladus scheduled. Hopefully, more discoveries await.

Fierce 2012 magnetic storm barely missed Earth

http://www.astronomy.com/news/videos/2014/03/fierce-2012-magnetic-storm-barely-missed-earth
RELATED TOPICS: SOLAR SYSTEM | SOLAR FLARES | SUN

According to scientists, a rapid succession of coronal mass ejections sent a pulse of magnetized plasma barreling into space and through Earth’s orbit.

By University of California, Berkeley | Published: Wednesday, March 19, 2014

According to University of California, Berkeley, and Chinese researchers, a rapid succession of coronal mass ejections — the most intense eruptions on the Sun — sent a pulse of magnetized plasma barreling into space and through Earth’s orbit. Had the eruption come nine days earlier, it would have hit Earth, potentially wreaking havoc with the electrical grid, disabling satellites and GPS, and disrupting our increasingly electronic lives.

The solar bursts would have enveloped Earth in magnetic fireworks matching the largest magnetic storm ever reported on Earth, the so-called Carrington event of 1859. The dominant mode of communication at that time, the telegraph system, was knocked out across the United States, literally shocking telegraph operators. Meanwhile, the northern lights lit up the night sky as far south as Hawaii.

In a paper, Ying D. Liu from China’s State Key Laboratory of Space Weather, Janet G. Luhmann from the University of California, Berkeley, and their colleagues report their analysis of the magnetic storm, which was detected by NASA’s STEREO A spacecraft.

“Had it hit Earth, it probably would have been like the big one in 1859, but the effect today, with our modern technologies, would have been tremendous,” said Luhmann.

A study last year estimated that the cost of a solar storm like the Carrington event could reach $2.6 trillion worldwide. A considerably smaller event March 13, 1989, led to the collapse of Canada’s Hydro-Quebec power grid and a resulting loss of electricity to 6 million people for up to nine hours.

“An extreme space weather storm — a solar superstorm — is a low-probability, high-consequence event that poses severe threats to critical infrastructures of the modern society,” warned Liu. “The cost of an extreme space weather event, if it hits Earth, could reach trillions of dollars with a potential recovery time of 4–10 years. Therefore, it is paramount to the security and economic interest of the modern society to understand solar superstorms.”

Based on their analysis of the 2012 event, Liu, Luhmann and their STEREO colleagues concluded that a huge outburst on the Sun on July 22 propelled a magnetic cloud through the solar wind at a peak speed of more than 1,200 miles (2,000 kilometers) per second — four times the typical speed of a magnetic storm. It tore through Earth’s orbit, but, luckily, Earth and the other planets were on the other side of the Sun at the time. Any planets in the line of sight would have suffered severe magnetic storms as the magnetic field of the outburst tangled with the planets’ own magnetic fields.

The researchers determined that the huge outburst resulted from at least two nearly simultaneous coronal mass ejections (CMEs), which typically release energies equivalent to that of about a billion hydrogen bombs. The speed with which the magnetic cloud plowed through the solar wind was so high, they concluded, because another mass ejection four days earlier had cleared the path of material that would have slowed it down.

“The authors believe this extreme event was due to the interaction of two CMEs separated by only 10 to 15 minutes,” said Joe Gurman from NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

One reason the event was potentially so dangerous, aside from its high speed, is that it produced a long-duration, southward-oriented magnetic field, Luhmann said. This orientation drives the largest magnetic storms when they hit Earth because the southward field merges violently with Earth’s northward field in a process called reconnection. Storms that normally might dump their energy only at the poles instead dump it into the radiation belts, ionosphere, and upper atmosphere and create aurorae down to the tropics.

“These gnarly, twisty ropes of magnetic field from coronal mass ejections come blasting from the Sun through the ambient solar system, piling up material in front of them, and when this double whammy hits Earth, it skews the Earth’s magnetic field to odd directions, dumping energy all around the planet,” Luhmann said. “Some of us wish Earth had been in the way; what an experiment that would have been.”

“People keep saying that these are rare natural hazards, but they are happening in the solar system even though we don’t always see them,” she said. “It’s like with earthquakes; it is hard to impress upon people the importance of preparing unless you suffer a magnitude 9 earthquake.”

All this activity would have been missed if STEREO A — the STEREO spacecraft ahead of us in Earth’s orbit and the twin to STEREO B, which trails in our orbit — had not been there to record the blast.

The goal of STEREO and other satellites probing the magnetic fields of the Sun and Earth is to understand how and why the Sun sends out these large solar storms and to be able to predict them during the Sun’s 11-year solar cycle. This event was particularly unusual because it happened during a calm solar period.

“Observations of solar superstorms have been extremely lacking and limited, and our current understanding of solar superstorms is very poor,” Liu said. “Questions fundamental to solar physics and space weather, such as how extreme events form and evolve and how severe it can be at the Earth, are not addressed because of the extreme lack of observations.”

Telescope captures view of gravitational waves

http://www.nature.com/news/telescope-captures-view-of-gravitational-waves-1.14876
Ron Cowen

Astronomers have peered back to nearly the dawn of time and found what seems to be the long-sought ‘smoking gun’ for the theory that the Universe underwent a spurt of wrenching, exponential growth called inflation during the first tiny fraction of a second of its existence.

Using a radio telescope at the South Pole, the US-led team has detected the first evidence of primordial gravitational waves, ripples in space that inflation generated 13.8 billion years ago when the Universe first started to expand.

The telescope captured a snapshot of the waves as they continued to ripple through the Universe some 380,000 years later, when stars had not yet formed and matter was still scattered across space as a broth of plasma. The image was seen in the cosmic microwave background (CMB), the glow that radiated from that white-hot plasma and that over billions of years of cosmic expansion has cooled to microwave energies.

The fact that inflation, a quantum phenomenon, produced gravitational waves demonstrates that gravity has a quantum nature just like the other known fundamental forces of nature, experts say. Moreover, it provides a window into interactions much more energetic than are accessible in any laboratory experiment. In addition, the way that the team confirmed inflation is itself of major significance: it is the most direct evidence yet that gravitational waves — a key but elusive prediction of Albert Einstein’s general theory of relativity — exist.

“This is a totally new, independent piece of cosmological evidence that the inflationary picture fits together,” says theoretical physicist Alan Guth of the Massachusetts Institute of Technology (MIT) in Cambridge, who proposed the idea of inflation in 1980. He adds that the study is “definitely” worthy of a Nobel prize.

Instant inflation
Guth’s idea was that the cosmos expanded at an exponential rate for a few tens of trillionths of trillionths of trillionths of seconds after the Big Bang, ballooning from subatomic to football size. Inflation solves several long-standing cosmic conundrums, such as why the observable Universe appears uniform from one end to the other. Although the theory has proved to be consistent with all cosmological data collected so far, conclusive evidence for it has been lacking.

Cosmologists knew, however, that inflation would have a distinctive signature: the brief but violent period of expansion would have generated gravitational waves, which compress space in one direction while stretching it along another (see ‘Ripple effect’). Although the primordial waves would still be propagating across the Universe, they would now be too feeble to detect directly. But they would have left a distinctive mark in the CMB: they would have polarized the radiation in a curly, vortex-like pattern known as the B mode (see ‘Cosmic curl’).

Last year, another telescope in Antarctica — the South Pole Telescope (SPT) — became the first observatory to detect a B-mode polarization in the CMB (see Nature http://doi.org/rwt; 2013). That signal, however, was over angular scales of less than one degree (about twice the apparent size of the Moon in the sky), and was attributed to how galaxies in the foreground curve the space through which the CMB travels (D. Hanson et al. Phys. Rev. Lett. 111, 141301; 2013). But the signal from primordial gravitational waves is expected to peak at angular scales between one and five degrees.

And that is exactly what John Kovac of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, and his colleagues now say they have detected, using an instrument dubbed BICEP2 that is located just metres away from its competitor, the SPT.

Detecting the tiny B mode required measuring the CMB with a precision of one ten-millionth of a kelvin and distinguishing the primordial effect from other possible sources, such as galactic dust.

“The key question,” says Daniel Eisenstein, an astrophysicist at the CfA, “is whether there could be a foreground that masquerades like this signal”. But the team has all but ruled out that possibility, he says. First, the researchers were careful to point BICEP2 — an array of 512 superconducting microwave detectors — at the Southern Hole, a patch of sky that is known to contain only tiny amounts of such emissions. They also compared their data with those taken by an earlier experiment, BICEP1, and showed that a dust-generated signal would have had a different colour and spectrum.

Furthermore, data taken with a newer, more sensitive polarization experiment, the Keck array, which the team finished installing at the South Pole in 2012 and will continue operating for two more years, showed the same characteristics. “To see this same signal emerge from two other, different telescopes was for us very convincing,” says Kovac.

“The details have to be worked out, but from what I know it’s highly likely this is what we’ve all been waiting for,” says astronomer John Carlstrom of the University of Chicago, Illinois, who is the lead researcher on the SPT. “This is the discovery of inflationary gravitational waves.”

Solid signature
Cosmologist Marc Kamionkowski adds: “To me, this looks really, really solid.” He was one of the first cosmologists to calculate what the signature of primordial gravitational waves should look like in the CMB. The findings are “on a par with dark energy, or the discovery of the CMB — something that happens once every several decades”, says Kamionkowski, who is at Johns Hopkins University in Baltimore, Maryland.

The strength of the signal measured by BICEP2, although entirely consistent with inflation, initially surprised the researchers because it is nearly twice as large as estimated from previous experiments. According to theory, the intensity of a B-mode signal reveals how fast the Universe expanded during inflation, and therefore suggests the energy scale of the cosmos during that epoch. The data pinpoint the time when inflation occurred — about 10–37 seconds into the Universe’s life — and its temperature at the time, corresponding to energies of about 1016 gigaelectronvolts, says cosmologist Michael Turner of the University of Chicago. That is the same energy at which three of the four fundamental forces of nature — the weak, strong and electromagnetic force — are expected to become indistinguishable from one another in a model known as the grand unified theory.

Because inflation took place in the realm of quantum physics, seeing gravitational waves arise from that epoch provides “the first-ever experimental evidence for quantum gravity”, says MIT cosmologist Max Tegmark — in other words, it shows that gravity is at heart a quantum phenomenon, just like the other three fundamental forces. Physicists, however, have yet to fully understand how to reconcile general relativity with quantum physics from a theory standpoint.

The researchers reported the findings on 17 March at a press briefing at the CfA, held just after they described their results to scientists in a technical talk. The team also released several papers describing the results. In so doing, it seems to have beaten the SPT and also several other groups racing to find the fingerprint of inflation using an assortment of balloon-borne and ground-based experiments and one satellite, the European Space Agency’s Planck spacecraft.

More-extensive maps of the B-mode polarization, and especially a full-sky survey, which the Planck telescope may be able to obtain later this year, should provide more clues about how inflation unfolded and what drove it. In addition to looking farther back in time than ever before, the discovery “is opening a window a trillion times higher in energy than we can access with the Large Hadron Collider”, the world’s premiere atom smasher, notes cosmologist Avi Loeb of the CfA, who is not part of the BICEP2 team.