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Cosmic Space

Slush on Ceres widens hopes for water worlds

Even before NASA’s Dawn probe mapped Ceres in detail in 2015, scientists suspected that the dwarf planet was a water world. Now they’ve traced Ceres’ upwellings of salty slush and mud to reservoirs deep beneath the surface.

The details came out this week in a package of papers published by Nature Astronomy, Nature Geoscience and Nature Communications. The findings serve as a fitting coda to an 11-year mission that almost didn’t happen, but ultimately succeeded in solving many of the mysteries surrounding Ceres as well as its sister asteroid Vesta.

For example, consider the bright spots in Ceres’ Occator Crater, which some have likened to “alien headlights.” The reflectivity is due to a crust of sodium carbonate, a salt left behind by the evaporation of briny water that percolated up to the surface.

Gravity readings gathered during the latter days of Dawn’s mission led scientists to conclude that the brine came from a reservoir that’s 25 miles deep and hundreds of miles wide.

In one of the bright spots, known as Cerealia Facula, Dawn’s instruments detected a concentration of hydrated salt compounds. The fact that those compounds are still hydrated suggest that they must have reached the surface relatively recently — perhaps within the past few centuries. That suggests that the transfer of liquid material from Ceres’ deep reservoir is continuing.

“For the large deposit at Cerealia Facula, the bulk of the salts were supplied from a slushy area just beneath the surface that was melted by the heat of the impact that formed the crater about 20 million years ago,” Dawn principal investigator, Carol Raymond, explained in a news release. “The impact heat subsided after a few million years; however, the impact also created large fractures that could reach the deep, long-lived reservoir, allowing brine to continue percolating to the surface.”

Dawn’s scientists saw additional evidence for Ceres’ active, slush-based geology in the presence of conical hills reminiscent of earthly features known as pingos. On Earth, pingos are formed when pressurized groundwater freezes beneath the surface and pushes up the soil above. Similar geological structures have been observed on Mars.

On icy moons such as Europa, Enceladus and Titan, geological activity is primarily driven by gravitational interactions with their parent planets. The fact that Ceres is geologically active, even though its crust is not being flexed by a nearby planet, widens the possibilities for finding slush or liquid water deep within ice-rich worlds in the main asteroid belt, the Kuiper Belt and elsewhere.

The data-gathering phase of Dawn’s mission ended in 2018, and the dead spacecraft is now silently circling Ceres. But decades or centuries from now, the scientific findings resulting from the mission just might guide explorers to new kinds of interplanetary watering holes.

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Solar system’s farthest-out known object is … Farout

Farout
An artist’s conception shows the distant object known as 2018 VG18 or “Farout.” (Carnegie Institution for Science Illustration / Roberto Molar Candanosa)

Astronomers say they’ve discovered the most distant body ever observed in our solar system, a potential dwarf planet that’s about 11 billion miles from the sun.

Its nickname? “Farout.”

The far-out object — which is also known by its more official but less colorful designation, 2018 VG18 — was detected with Japan’s 8-meter Subaru Telescope in Hawaii during a campaign to look for extremely distant solar system objects, including a hypothetical Planet X or Planet Nine.

Further observations to confirm Farout’s distance and determine its brightness and color were made with the 6.5-meter Magellan Telescopes at the Carnegie Institution for Science’s Las Campanas Observatory in Chile. The observations were reported today in a circular distributed by the International Astronomical Union’s Minor Planet Center.

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Dawn probe falls silent, ending mission to Ceres

Dawn's view of Ceres
This photo of Ceres and the bright regions in Occator Crater was one of the last views NASA’s Dawn spacecraft transmitted before it completed its mission. This view, which faces south, was captured on Sept. 1 from an altitude of 2,340 miles as the spacecraft was ascending in its elliptical orbit. (NASA / JPL-Caltech / UCLA / MPS / DLR / IDA Photo)

Dawn is dead, but Dawn is not gone: Today NASA said that the Dawn spacecraft has fallen out of contact with Earth, presumably because it’s run out of the thruster fuel that was used to keep its antennas oriented toward Earth and its power-generating solar panels oriented toward the sun.

After Dawn missed out on communications sessions on Wednesday and today, NASA declared an end to the mission.

During its 11 years in space, Dawn sent back unprecedented closeups of the asteroid Vesta as well as Ceres, which is the largest known asteroid and the smallest confirmed dwarf planet.

Dawn will continue circling Ceres for decades to come in the main asteroid belt, 257 million miles out from the sun.

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Planet search turns up a dwarf called ‘The Goblin’

Subaru Telescope
The International Space Station leaves a streak above the Subaru Telescope in a long-exposure image. Observations using the Subaru Telescope led to the discovery of the mini-world known as The Goblin. (Subaru Telescope / NAOJ Photo / Hideaki Fujiwara)

While searching for a hypothetical Planet Nine, astronomers found a distant mini-world that’s been given a spooky nickname: “The Goblin.”

The icy object was found at a distance of about 80 astronomical units from the sun, which translates to 7.4 billion miles. (One astronomical unit, or AU, equals 93 million miles, which is the distance between Earth and the sun.) That’s more than twice as far away as dwarf planet Pluto.

A research team led by Scott Sheppard of the Carnegie Institution of Science first spotted The Goblin just before Halloween in 2015. That timing, plus the fact that it was given the numerical designation 2015 TG387, gave rise to the trick-or-treat nickname. (T.G. … Get it?)

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Historical study revisits debate over Pluto

Pluto and Charon
A composite image from NASA’s New Horizons spacecraft shows enhanced-color views of Pluto at lower right and Charon, its largest moon, at upper left. (NASA / JHUAPL / SwRI Photo)

Twelve years after the International Astronomical Union voted in a definition of planethood that reclassified Pluto, the debate goes on.

A newly published study uses the historical record to take aim at the definition’s most controversial clause: the idea that a planet in the solar system has to “clear the neighborhood of its orbit,” so that no other worlds are at a similar orbital distance.

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Pluto’s champions tell the tale of an epic mission

Image: Pluto stamp
The 1991 stamp that served as the rallying cry for the New Horizons Mission to Pluto is “updated” by members of the New Horizons science team on July 14, 2015, the day the spacecraft flew past Pluto. Principal investigator Alan Stern is at far left. (Credit: Bill Ingalls / NASA)

It took nine years for NASA’s New Horizons spacecraft to get to Pluto, and laying the groundwork for that history-making space mission here on Earth took nearly twice as long.

The drama and intrigue surrounding New Horizons during those decades, as chronicled in a new book titled “Chasing New Horizons: Inside the First Mission to Pluto,” might be enough for any planetary scientist. But Alan Stern — the book’s co-author, the mission’s principal investigator and arguably Pluto’s most ardent defender — is ready to do it all again.

Stern doesn’t expect his campaign to send an orbiter to Pluto to face quite as many challenges, now that the world knows so much more about the dwarf planet with a giant heart.

“I hope it’s a more straightforward process,” Stern told GeekWire. “First of all, there are now a lot more people who are interested in going back to Pluto. … Now that we’ve done the flyby, there isn’t a planetary scientist in the world that isn’t impressed.”

Last month, Stern and other New Horizons scientists signed onto a white papercalling for NASA to fund an in-depth study of potential Pluto orbiter missions. That grass-roots approach mirrors how the “Pluto Underground” campaign for New Horizons got started around a restaurant table in Baltimore,  back in 1989.

“Chasing New Horizons,” written by Stern and astrobiologist David Grinspoon, traces the twists and turns that led from there to the piano-sized spacecraft’s launch in 2006 and its Pluto flyby in 2015.

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Water, water everywhere on dwarf planet Ceres

Hydrogen on Ceres
NASA’s Dawn spacecraft determined the hydrogen content of the upper yard, or meter, of Ceres’ surface. Blue indicates where hydrogen content is higher, near the poles, while red indicates lower content at lower latitudes. (NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / PSI Photo)

Readings from instruments aboard NASA’s Dawn orbiter support the view that a treasure trove of frozen water lies just beneath the surface of the dwarf planet Ceres.

Researchers reported those findings today at the American Geophysical Union’s fall meeting San Francisco, as well as in two papers published by Nature Astronomy and Science.

The findings are based on hydrogen readings from Dawn’s gamma ray and neutron detector, or GRaND, as well as from the spacecraft’s cameras and infrared mapping spectrometer.

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Dawn probe points to ice volcano on Ceres

Image: Ceres' Ahuna Mons
Ceres’ lonely mountain, Ahuna Mons, is seen in this simulated perspective view. The elevation has been exaggerated by a factor of two. The view was made using enhanced-color images from NASA’s Dawn mission. (Credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / PSI)

Scientists say a mysterious mountain on the dwarf planet Ceres was apparently once an ice volcano, spewing salty water and mud instead of lava.

They also say Ceres has patches of water ice that can be seen on or near the surface, and might have an off-and-on atmosphere that contains water vapor.

The scientists say all this and more in six research papers published in this week’s issue of the journal Science. The studies are based on more than a year’s worth of orbital observations from NASA’s Dawn spacecraft. Dawn is still circling 590-mile-wide Ceres, which is the solar system’s smallest dwarf planet as well as its biggest main-belt asteroid.

The mysterious mountain is Ahuna Mons, a 3-mile-high peak that looks like a bright space pyramid. Scientists took note of the peak’s concave top, its elliptical base, cracks at the summit, steep slopes and other features that pointed to previous volcanic activity.

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Hunt for Planet Nine leads to mini-worlds

Image: Planet X
An artist’s conception shows Planet X, a.k.a. Planet Nine. (Credit: Robin Dienel / Carnegie Inst.)

The hypothetical world known as Planet X or Planet Nine hasn’t yet been found, but thanks to the search, astronomers have discovered smaller worlds on the solar system’s edge.

Mapping such objects could lead to the big discovery: a planet that’s thought to be at least several times bigger than Earth, lurking at least 200 times farther away from the sun. Or it could lead to a different explanation for the puzzling, highly elongated orbits of some of the objects that lie far beyond Pluto.

Planet Nine’s existence was proposed last year as the most elegant way to account for the orbits of worlds such as Sedna and 2012 VP113 (which has been nicknamed “Biden” in honor of the veep). Ever since then, astronomers have been surveying the skies in hopes of tracking it down.

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One year later, New Horizons revisits Pluto flyby

160714-pluto6
Composite image shows enhanced-color views of Charon and Pluto. (Credit: NASA / JHUAPL / SwRI)

One year ago today, NASA’s New Horizons probe whizzed past Pluto and opened up a new frontier for planetary science – and to mark the occasion, the mission team is looking back at its greatest hits and looking ahead to a landing.

“It’s strange to think that only a year ago, we still had no real idea of what the Pluto system was like,” project scientist Hal Weaver, who’s based at the Johns Hopkins University Applied Physics Laboratory, said in a news release celebrating the anniversary. “But it didn’t take long for us to realize Pluto was something special, and like nothing we ever could have expected.”

After more than nine years of cruising through interplanetary space, the piano-sized New Horizons spacecraft flew by Pluto and its moons at a speed of more than 30,000 mph on July 14, 2015, capturing readings as it went. Since then, the probe has been transmitting gigabytes’ worth of data back to Earth at a slow but steady rate.

The pictures have been unprecedented, providing the first close look at icy worlds that whirl more than 3 billion miles from the sun, in a region known as the Kuiper Belt. They’ve even inspired a set of postage stamps.

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