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Finding common table salt — sodium chloride — on the surface of a moon is more than just a scientific curiosity when that moon is Europa, a potential abode of life.

If the salt came from the briny subsurface ocean of Europa, a satellite of Jupiter, that ocean may chemically resemble Earth's oceans more than previously thought. Because Europa's solid, icy crust is geologically young it has been suspected that whatever salts exist on the surface may come from the ocean below, which might host microorganisms.

Using visible-light spectral analysis, planetary scientists at Caltech and NASA's Jet Propulsion Laboratory discovered that the yellow color visible on portions of the surface of Europa is sodium chloride. They reached this conclusion with spectroscopic data from NASA's Hubble Space Telescope. Researchers were able to identify a distinct absorption in the visible spectrum which matches how salt would look when irradiated by the Sun.

Tara Regio is the yellowish area to left of center, in this NASA Galileo image of Europa’s surface. This region of geologic chaos is the area researchers identified an abundance of sodium chloride.

The finding was published in Science Advances on June 12.

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In order to grow to Jupiter size or larger, a gas giant planet must slurp large quantities of hydrogen and other gases from the disk in which it forms. Astronomers have looked for evidence of this process, but direct observations are challenging because planets become lost in the glare of their star. A team has succeeded in making ground-based observations of two planets accreting matter from a disk. It represents only the second multi-planet system to be directly imaged.

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The James Webb Space Telescope will open a new window on exoplanets, planets around other suns. With its keen infrared vision, Webb will observe them in wavelengths where they have never been studied before. One of the telescope’s first observation programs is to look at young, newly formed exoplanets and the systems they inhabit. Scientists will use all four of Webb’s instruments to observe three targets: A recently discovered exoplanet; an object that is either an exoplanet or a brown dwarf; and a well-studied ring of dust and planetesimals orbiting a young star. Webb will be vital for understanding how these objects form, and what these systems are like. These observations are part of a program that allows the astronomical community to quickly learn how best to use Webb’s capabilities, while also yielding robust science.

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One doesn't need a Ph.D. in astrophysics to recognize there is something odd-looking about this otherwise beautiful galaxy, NCG 4485. Like the Batman character Two-Face, one side looks normal, but the other side looks contorted with a firestorm of star formation going on. Why the colorful asymmetry in an island star city many thousands of light-years across? The clue is off the edge of the photo. It's another galaxy, NGC 4490, that swept by NGC 4485 millions of years ago. The gravitational taffy pull between the two galaxies compressed interstellar gas to trigger a flurry of new star birth as seen in the abundance of young blue stars and pinkish nebulas. So, out of a near-collision between two galaxies comes stellar renewal and birth. It's a trademark of our compulsive universe where even things as big as galaxies can go bump in the night.

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How far is far? And, how do you know when you get there? In 1995, astronomers decided to use the Hubble Space Telescope to conduct a bold and daring experiment to address this puzzle. For 10 consecutive days, Hubble stared at one tiny, seemingly empty patch of sky for 1 million seconds.

The gamble of precious telescope time paid off. Hubble captured the feeble glow of myriad never-before-seen galaxies. Many of the galaxies are so far away it has taken billions of years for their light to reach us. Therefore, the view is like looking down a "time corridor," where galaxies can be seen as they looked billions of years ago. Hubble became astronomy's ultimate time machine.

The resulting landmark image is called the Hubble Deep Field. At the time, the image won the gold medal for being the farthest peek into the universe ever made. Its stunning success encouraged astronomers to pursue a series of Hubble deep-field surveys. The succeeding surveys uncovered more galaxies at greater distance from Earth, thanks to new cameras installed on Hubble during astronaut servicing missions. The cameras increased the telescope's power to look even deeper into the universe.

These surveys provided astronomers with a huge scrapbook of images, showing how, following the big bang, galaxies built themselves up over time to become the large, majestic assemblages seen today in the nearby universe.

Among the most notable deep-field surveys are the Great Observatories Origins Deep Survey (GOODS), in 2003; the Hubble Ultra Deep Field (HUDF), in 2004; and the eXtreme Deep Field (XDF), in 2012.

Now, astronomers are releasing a new deep-field image by weaving together exposures from several of these previous galaxy "fishing expeditions." Their efforts have produced the largest, most comprehensive “history book” of galaxies in the universe. The snapshot, a combination of nearly 7,500 separate Hubble exposures, represents 16 years' worth of observations. The ambitious endeavor is called the Hubble Legacy Field. The new view contains about 30 times as many galaxies as in the HUDF. The wavelength range stretches from ultraviolet to near-infrared light, capturing all the features of galaxy assembly over time.

The image mosaic presents a wide portrait of the distant universe and contains roughly 265,000 galaxies. They stretch back through 13.3 billion years of time to just 500 million years after the universe's birth in the big bang.

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There is something wrong with our universe. Or, more specifically, it is outpacing all expectations for its present rate of expansion.

Something is amiss in astronomers' efforts to measure the past and predict the present, according to a discrepancy between the two main techniques for measuring the universe's expansion rate – a key to understanding its history and physical parameters.

The inconsistency is between the Hubble Space Telescope measurements of today's expansion rate of the universe (by looking at stellar milepost markers) and the expansion rate as measured by the European Space Agency's Planck satellite. Planck observes the conditions of the early universe just 380,000 years after the big bang.

For years, astronomers have been assuming this discrepancy would go away due to some instrumental or observational fluke. Instead, as Hubble astronomers continue to "tighten the bolts" on the accuracy of their measurements, the discordant values remain stubbornly at odds.

The chances of the disagreement being just a fluke have skyrocketed from 1 in 3,000 to 1 in 100,000.

Theorists must find an explanation for the disparity that could rattle ideas about the very underpinnings of the universe.

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This Hubble image shows the results of two stellar companions in a gravitational waltz, several thousand light-years from Earth in the southern constellation Centaurus. The stellar duo, consisting of a red giant and white dwarf, are too close together to see individually in this view. But the consequences of their whirling about each other are two vast shells of gas expanding into space like a runaway hot air balloon. Both stars are embedded in a flat disk of hot material that constricts the outflowing gas so that it only escapes away above and below the stars. This apparently happens in episodes because the nebula has two distinct nested hourglass-shaped structures. The bubbles of gas and dust appear brightest at the edges, giving the illusion of crab legs. The rich colors correspond to glowing hydrogen, sulfur, nitrogen, and oxygen. This image was taken to celebrate Hubble's 29th anniversary since its launch on April 24, 1990.

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As the spiral galaxy ESO 137-001 plunges into a galaxy cluster, gas is being pulled off of it as though it faced a cosmic headwind. Within that gas, stars are forming to create the appearance of giant, blue tentacle-like streamers. Astronomers, puzzled that stars could form within such tumult, plan to use Webb to study this galaxy and its stellar offspring.

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NASA has selected 24 new Fellows for its prestigious NASA Hubble Fellowship Program (NHFP). The program enables outstanding postdoctoral scientists to pursue independent research in any area of NASA Astrophysics, using theory, observation, experimentation, or instrument development. Each fellowship provides the awardee up to three years of support.

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Astronomers once thought asteroids were boring, wayward space rocks that simply orbit around the Sun. These objects were dramatically presented only in science fiction movies.

But recent observations show that asteroids are anything but dull. In reality they are dynamic, active worlds that can ultimately disintegrate due to the long-term subtle effects of sunlight, which can slowly spin them up until they begin to shed material.

Several telescopes, including NASA's Hubble Space Telescope, have caught the gradual self-destruction of the asteroid (6478) Gault. Images from Hubble show two narrow, comet-like tails of dusty debris streaming from the diminutive asteroid.

For Gault, a mass of rubble a few miles across, mere sunlight set the stage for its gradual demise. The force of sunlight, in concert with Gault's own asymmetrical shape, speeded up the asteroid's rotation over a period of more than 100 million years. The estimated spin-up rate is 1 second every 10,000 years.

Today, the asteroid is rotating once every two hours, a speed so fast that it can no longer hold its surface material. The slightest disturbance — perhaps the impact of a pebble, or just a failure of the stressed material — may have set off a collapse. The dust left the asteroid's surface in gentle, short bursts, perhaps due to landslides lasting anywhere from a few hours to a few days. The particles are drifting away from Gault's surface at the speed of a strolling human. The gentle process is like scattering flour into the air, where wind — or sunlight, in the case of Gault — stretches the debris into a long streamer.

Astronomers will monitor the asteroid for future events. About 800,000 known asteroids reside between Mars and Jupiter, and they may fly apart at the rate of roughly one per year.

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