Space Friday: Comet 67P, Pluto Pics, and Early Galaxies

The Siren-Song of a Star-Struck Space-Ducky

Comet 67P/Churyumov-Gerasimenko is famous for several things: its tongue-twisting (for non-Russians) name and its endearing “rubber ducky” shape, but also the fact that the European Space Agency’s Rosetta spacecraft continues to orbit the comet and that Rosetta’s Philae lander remains undiscovered somewhere on the comet’s icy surface. But 67P now has another claim to fame: it “sings.” Sort of.

In August 2014, Rosetta’s magnetometer instrument detected a rapid series of clicks caused by oscillations in the comet’s magnetic field. The “sound” was picked up when Rosetta drew to within 60 miles (100 kilometers) of the comet. Involving frequencies far too low to be detected by the human ear, the oscillations had to be sped up about 10,000 times to be heard, and the resulting trill sounds like a science fiction sound effect.

In a research paper appearing in the European Geosciences Union’s journal Annales Geophysicae, Rosetta’s plasma team, led by principal investigator Karl-Heinz Glassmeier, suggests that a stream of charged particles from the Sun—the solar wind—is interacting with the gas-dust environment around the comet and inducing a magnetic field around a body that typically generates no such field of its own. That field oscillates due to interactions with a stream of solar plasma moving through it (plasma is the fourth state of matter, basically an electrically conductive gas).

At perihelion—the comet’s closest approach to the Sun—the “song” was nearly overwhelmed by a cacophony of other sounds representing increased activity as the comet reacted to the Sun’s heat. As the comet now distances itself from the Sun, scientists are eager to observe how its song changes, indicating changes in the magnetic field interaction. –Bing Quock

Plenty More Pluto Pics!

The treasure-trove of images from the New Horizons flyby of Pluto last July is beginning to trickle in, and the images are spectacular! Where mid-July’s encounter gave us a glimpse of the tiny world and its moons, the new images reveal stunning details to a resolution of a half-mile (0.8 kilometers). The interface between the nitrogen ice tundra of Tombaugh Regio—the famously-endearing “heart” of Pluto—and its more rugged “shoreline” reveal, side-by-side, some of Pluto’s oldest, crater-strewn topography along with some of its newest—flat, crater-free, and showing signs of fluid flow. In contrast is a region of “chaos terrain,” which looks just like what its name suggests—a chaotic jumble of landforms, similar to what has been seen on Mars and another frozen world, Europa. Another view shows what appear to be compression ridges, suggesting folding of Pluto’s frozen crust. More dazzling images reveal Pluto’s backlit atmosphere, more layered than expected, suggesting surprising complexity. There’s so much going on in these images, scientists are giddy with excitement.

Because of the distance of New Horizons, the volume of data, and the limitations of the spacecraft’s transmitting capabilities, the entire download of Pluto imagery will take 16 months, so we can look forward to more than a year of incoming, exciting images of this alien landscape. –Bing Quock

Early Galaxies

As techniques improve to look deeper into space—and farther back in time—astronomers are discovering galaxies almost as old as the Universe. Two recent publications have uncovered galaxies only a few hundred million years younger than the Big Bang.

In a research paper published this week in Nature Communications, University of California scientists and their colleagues describe the use of a new statistical method to analyze Hubble Space Telescope data captured during lengthy sky surveys. The method enabled the team to tease out signals from the noise in Hubble’s deep-sky images, providing the first estimate of the number of small, primordial galaxies in the early Universe, just 500 million years after the Big Bang. The researchers concluded that there are close to 10 times more of these galaxies than were previously detected in deep Hubble surveys.

“For this research, we had to look closely at what we call ‘empty pixels,’ the pixels between galaxies and stars,” says UC Irvine’s Asantha Cooray. “We can separate noise from the faint signal associated with first galaxies by looking at the variations in the intensity from one pixel to another. We pick out a statistical signal that says there is a population of faint objects. We do not see that signal in the optical [wavelengths], only in infrared. This is confirmation that the signal is from early times in the Universe.”

Cooray thinks these primordial galaxies were very different from the well-defined spiral and disc-shaped galaxies currently visible in the Universe. They were more diffuse and populated by giant stars. He notes that more observational proof for his team’s findings will be possible with the launch of the James Webb Space Telescope in 2018. “These galaxies are very faint,” he says, “so if we have a bigger telescope, like James Webb, we'll be able to go very deep and see them individually.”

Late last month another team of astronomers, including scientists from Caltech, described evidence for a 13.2 billion year-old galaxy called EGS8p7. First detected by Hubble working with the Spitzer Space Telescope, the researchers used the multi-object spectrometer for infrared exploration (MOSFIRE) at the W.M. Keck Observatory in Hawaii, to determine the galaxy’s redshift. Redshift results from the stretching of spacetime as the Universe expands, and the larger the redshift, the more distant the galaxy.

Redshift works well to estimate distances to most galaxies, but it’s difficult to measure when looking at the Universe’s most distant—and thus earliest—objects. “If you look at the galaxies in the early Universe, there is a lot of neutral hydrogen that is not transparent to this emission,” says the study’s lead author, Adi Zitrin. “We expect that most of the radiation from this galaxy would be absorbed by the hydrogen in the intervening space.”

But EGS8p7 is special, says Caltech’s Sirio Belli. The team was able to observe its Lyman-alpha line—the spectral signature of hydrogen gas that has been heated by ultraviolet emission from new stars. “EGS8p7 may be powered by a population of unusually hot stars, and it may have special properties that enabled it to create a large bubble of ionized hydrogen much earlier than is possible for more typical galaxies at these times,” Belli says.

And its detection may require some rewriting of cosmological history. “We are currently calculating more thoroughly the exact chances of finding this galaxy and seeing this emission from it, and to understand whether we need to revise the timeline of the reionization, which is one of the major key questions to answer in our understanding of the evolution of the Universe,” Zitrin says. –Molly Michelson

Image: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute