Astronomical Journal

Uranus May Have Two Undiscovered Moons

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Written by Tara Roberts
University of Idaho Communications
For NASA Jet Propulsion Laboratory, Pasadena, California 
October 21, 2016 at 1:04 p.m. EDT

Uranus is seen in this false-color view from NASA’s Hubble Space Telescope from August 2003. The brightness of the planet’s faint rings and dark moons has been enhanced for visibility. Image credit: NASA/Erich Karkoschka (Univ. Arizona)

 

NASA’s Voyager 2 spacecraft flew by Uranus 30 years ago, but researchers are still making discoveries from the data it gathered then. A new study led by University of Idaho researchers suggests there could be two tiny, previously undiscovered moonlets orbiting near two of the planet’s rings.

Rob Chancia, a University of Idaho doctoral student, spotted key patterns in the rings while examining decades-old images of Uranus’ icy rings taken by Voyager 2 in 1986. He noticed the amount of ring material on the edge of the alpha ring — one of the brightest of Uranus’ multiple rings — varied periodically. A similar, even more promising pattern occurred in the same part of the neighboring beta ring.

“When you look at this pattern in different places around the ring, the wavelength is different — that points to something changing as you go around the ring. There’s something breaking the symmetry,” said Matt Hedman, an assistant professor of physics at the University of Idaho, who worked with Chancia to investigate the finding. 

Their results will be published in The Astronomical Journal and have been posted to the pre-press site arXiv.

 

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NASA Space Telescopes See Magnified Image of Faintest Galaxy from Early Universe

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This is a Hubble Space Telescope view of a very massive cluster of galaxies, MACS J0416.1-2403, located roughly 4 billion light-years away and weighing as much as a million billion suns. Image credit: NASA, ESA, and Pontificia Universidad Católica de Chile

 

 

Astronomers harnessing the combined power of NASA’s Hubble and Spitzer space telescopes have found the faintest object ever seen in the early universe. It existed about 400 million years after the big bang, 13.8 billion years ago.

The team has nicknamed the object Tayna, which means “first-born” in Aymara, a language spoken in the Andes and Altiplano regions of South America.

Though Hubble and Spitzer have detected other galaxies that are record-breakers for distance, this object represents a smaller, fainter class of newly forming galaxies that until now had largely evaded detection. These very dim objects may be more representative of the early universe, and offer new insight on the formation and evolution of the first galaxies.

“Thanks to this detection, the team has been able to study for the first time the properties of extremely faint objects formed not long after the big bang,” said lead author Leopoldo Infante, an astronomer at the Pontifical Catholic University of Chile. The remote object is part of a discovery of 22 young galaxies at ancient times located nearly at the observable horizon of the universe. This research means there is a substantial increase in the number of known very distant galaxies.

The results are published in the December 3 issue of The Astrophysical Journal.

The new object is comparable in size to the Large Magellanic Cloud, a diminutive satellite galaxy of our Milky Way. It is rapidly making stars at a rate 10 times faster than the Large Magellanic Cloud. The object might be the growing core of what will likely evolve into a full-sized galaxy.

The small and faint galaxy was only seen thanks to a natural “magnifying glass” in space. As part of its Frontier Fields program, Hubble observed a massive cluster of galaxies, MACS0416.1-2403, located roughly 4 billion light-years away and weighing as much as a million billion suns. This giant cluster acts as a powerful natural lens by bending and magnifying the light of far more distant objects behind it. Like a zoom lens on a camera, the cluster¹s gravity boosts the light of the distant proto-galaxy to make it look 20 times brighter than normal. The phenomenon is called gravitational lensing and was proposed by Albert Einstein as part of his General Theory of Relativity.

The galaxy’s distance was estimated by building a color profile from combined Hubble and Spitzer observations. The expansion of the universe causes the light from distant galaxies to be stretched or reddened with increasing distance. Though many of the galaxy’s new stars are intrinsically blue-white, their light has been shifted into infrared wavelengths that are measurable by Hubble and Spitzer. Absorption by intervening cool intergalactic hydrogen also makes the galaxies look redder.

This finding suggests that the very early universe will be rich in galaxy targets for the upcoming James Webb Space Telescope to uncover. Astronomers expect that Webb will allow us to see the embryonic stages of galaxy birth shortly after the big bang.

For more information, visit http://www.nasa.gov/hubble or http://www.nasa.gov/spitzer.

 

Icy Tendrils Reaching into Saturn Ring Traced to Their Source

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This collage, consisting of two Cassini images of long, sinuous, tendril-like features from Saturn’s moon Enceladus and two corresponding computer simulations of the same, illustrates how well the structures, and the sizes of the particles composing them, can be modeled by tracing the trajectories of tiny, icy grains ejected from Enceladus’ south polar geysers. Credit: NASA/JPL-Caltech/Space Science Institute

Long, sinuous, tendril-like structures seen in the vicinity of Saturn’s icy moon Enceladus originate directly from geysers erupting from its surface, according to scientists studying images from NASA’s Cassini spacecraft.

This result is published online today in a study in the Astronomical Journal, along with additional insights into the nature of the structures.

“We’ve been able to show that each unique tendril structure can be reproduced by particular sets of geysers on the moon’s surface,” said Colin Mitchell, a Cassini imaging team associate at the Space Science Institute in Boulder, Colorado, and lead author of the paper. Mitchell and colleagues used computer simulations to follow the trajectories of ice grains ejected from individual geysers. The geysers, which were discovered by Cassini in 2005, are jets of tiny water ice particles, water vapor and simple organic compounds.

Under certain lighting conditions, Cassini’s wide-view images showing icy material erupting from Enceladus reveal faint, finger-like features, dubbed “tendrils” by the imaging team. The tendrils reach into Saturn’s E ring — the ring in which Enceladus orbits — extending tens of thousands of miles (or kilometers) away from the moon. Since the tendrils were discovered, scientists have thought they were the result of the moon’s geysering activity and the means by which Enceladus supplies material to the E ring. But the ghostly features had never before been traced directly to geysers on the surface.

Because the team was able to show that tendril structures of different shapes correspond to different sizes of geyser particles, the team was able to zero in on the sizes of the particles forming them. They found the tendrils are composed of particles with diameters no smaller than about a hundred thousandth of an inch, a size consistent with the measurements of E-ring particles made by other Cassini instruments.

As the researchers examined images from different times and positions around Saturn, they also found that the detailed appearance of the tendrils changes over time. “It became clear to us that some features disappeared from one image to the next,” said John Weiss, an imaging team associate at Saint Martin’s University in Lacey, Washington, and an author on the paper.

The authors suspect that changes in the tendrils’ appearance likely result from the cycle of tidal stresses — squeezing and stretching of the moon as it orbits Saturn — and its control of the widths of fractures from which the geysers erupt. The stronger the tidal stresses raised by Saturn at any point on the fractures, the wider the fracture opening and the greater the eruption of material. The authors will investigate in future work whether this theory explains the tendrils’ changing appearance.

There is even more that can be extracted from the images, the scientists say. “As the supply lanes for Saturn’s E ring, the tendrils give us a way to ascertain how much mass is leaving Enceladus and making its way into Saturn orbit,” said Carolyn Porco, team leader for the imaging experiment and a coauthor on the paper. “So, another important step is to determine how much mass is involved, and thus estimate how much longer the moon’s sub-surface ocean may last.” An estimate of the lifetime of the ocean is important in understanding the evolution of Enceladus over long timescales.

Because of its significance to the investigation of possible extraterrestrial habitable zones, Enceladus is a major target of investigation for the final years of the Cassini mission. Many observations, including imaging of the plume and tendril features, and thermal observations of the surface of its south polar geyser basin, are planned during the next couple of years.

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA’s Jet Propulsion Laboratory in Pasadena, California, manages the mission for the agency’s Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology in Pasadena. The Cassini imaging operations center is based at the Space Science Institute in Boulder, Colo.

New images released today can be found at:

http://www.ciclops.org/view_event/205

More information about Cassini, visit:

http://www.nasa.gov/cassini

http://saturn.jpl.nasa.gov