The study, which used a thermal evolution model for Pluto updated with data from New Horizons, found that if Pluto's ocean had frozen into oblivion millions or billions of years ago, it would have caused the entire planet to shrink. But there are no signs of a global contraction to be found on Pluto's surface. On the contrary, New Horizons showed signs that Pluto has been expanding

The pictures New Horizons sent back from its close encounter with the Kuiper Belt's most famous denizen showed that Pluto was much more than a simple snowball in space. It has an exotic surface made from different types of ices—water, nitrogen and methane. It has mountains hundreds of meters high and a vast heart-shaped plain. It also has giant tectonic features—sinuous faults hundreds of kilometers long as deep as 4 kilometers. It was those tectonic features that got scientists thinking that a subsurface ocean was a real possibility for Pluto.

"What New Horizons showed was that there are extensional tectonic features, which indicate that Pluto underwent a period of global expansion," Hammond said. "A subsurface ocean that was slowly freezing over would cause this kind of expansion."

Scientists think that there may have been enough heat-producing radioactive elements within Pluto's rocky core to melt part of the planet's ice shell. Over time in the frigid Kuiper belt, that melted portion would eventually start to refreeze. Ice is less dense than water, so when it freezes, it expands. If Pluto had on ocean that was frozen or in the process of freezing, extensional tectonics on the surface would result, and that's what New Horizons saw.

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There aren't many other ways on Pluto to get such features. One way might have been through a gravitational tug of war with its moon, Charon. But the active gravitational dynamics between the two have long since wound down, and some of the tectonics look fairly fresh (on a geologic timescale). So, many scientists believe that an ocean is the strongest scenario.

That's where the thermal evolution model run by Hammond and his colleagues comes in. The model includes updated data from New Horizons on Pluto's diameter and density, key parameters in understanding the dynamics in Pluto's interior. The model showed that because of the low temperatures and high pressure within Pluto, an ocean that had completely frozen over would quickly convert from the normal ice we all know to a different phase called ice II. Ice II has a more compact crystalline structure than standard ice, so an ocean frozen to ice II would occupy a smaller volume and lead to a global contraction on Pluto, rather than an expansion.

"We don't see the things on the surface we'd expect if there had been a global contraction," Hammond said. "So we conclude that ice II has not formed, and therefore that the ocean hasn't completely frozen."

There are a few caveats, the researchers point out. The formation of ice II is dependent on the thickness of Pluto's ice shell. Ice II only forms if the shell is 260 kilometers thick or more. If the shell is thinner than that, the ocean could have frozen without forming ice II. And if that were the case the ocean could have frozen completely without causing contraction. However, the researchers say there's good reason to believe that the ice shell is more than 260 kilometers. Their updated model suggests that Pluto's ice shell is actually closer to 300 or more kilometers thick. In addition, the nitrogen and methane ices that New Horizons found on the surface bolster the case for a thick ice shell.

Swift gamma-ray bursts—a 3D step toward standard candles

A new way to use the most powerful explosions in the Universe to calibrate its expansion has been developed by a team of researchers (Sergey Postnikov, Xavier Hernandez from Institute of Astronomy , UNAM, and Michal Ostrowski .

Newborn giant planet grazes its star

A morsel of never-before-seen alien rock has been dug up in a limestone quarry in Sweden, where it had lain deeply buried for about 470 million years, scientists said Tuesday.

Life's first handshake: Chiral molecule detected in interstellar space

Hazes and clouds high up in the atmospheres of exoplanets may make them appear bigger than they really are, according to new research by astronomers at the Space Research Institute (IWF) of the Austrian Academy of Sciences.

Kepler-1647b: New planet is largest discovered that orbits two suns

New data compare, contrast Pluto's icy moons A newly downlinked spectral observation of Pluto's moon Nix from NASA's New Horizons spacecraft provides compelling evidence that its surface is covered in water ice, similar to what the New Horizons team discovered recently ...US space firm Blue Origin conducted a successful fourth test Sunday of its reusable New Shepard rocket, which dropped back to Earth for a flawless upright landing seen on a live webcast.

Three International Space Station astronauts land in Kazakhstan

An unprecedented view from the Gemini South telescope in Chile probes a swarm of young and forming stars that appear to have been shocked into existence. The group, known as N159W, is located some 158,000 light years away

Astrophysicists release new study of one of the first stars

Astronomers explain mystery of magnetically powered jets produced by supermassive black holes A simulation of the powerful jets generated by supermassive black holes at the centers of the largest galaxies explains why some burst forth as bright beacons visible across the universe, while others fall apart and never ....

Astronomers detect glitch in a millisecond pulsar

Unexpected excess of giant planets in star cluster An international team of astronomers have found that there are far more planets of the hot Jupiter type than expected in a cluster of stars called Messier 67. This surprising result was obtained using a number of telescopes ...

Relax, it'll be 1,500 years before aliens contact us

How black hole jets punch out of their galaxies A simulation of the powerful jets generated by supermassive black holes at the centers of the largest galaxies explains why some burst forth as bright beacons visible across the universe, while others fall apart and never ..

NASA spacecraft barreling toward Jupiter for July 4 meetup

Scientists detect most distant signs of oxygen in the universe Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) detected a clear signal from oxygen in a galaxy located 13.1 billion light-years away from us. This is the most distant oxygen ever detected. Oxygen ...

Black holes and measuring gravitational waves

Desert telescope stakes out supermassive black hole First postulated more than 230 years ago, black holes have been extensively researched, frequently depicted, even featured in sci-fi films.

Northwestern University astrophysicists have predicted history. In a new study, the scientists show their theoretical predictions last year were correct: The historic merger of two massive black holes detected Sept. 14, 2015, could easily have been formed through dynamic interactions in the star-dense core of an old globular cluster.

Colliding black holes do not emit light; however, they do release a phenomenal amount of energy as gravitational waves. The first detection of these waves occurred Sept. 14, and the second—announced to the world this morning—occurred three months later. These events have launched a new era in astronomy: using gravitational waves to learn about the universe.


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  • "Thanks to LIGO, we're not just theorists speculating anymore—now we have data," said Frederic A. Rasio, a theoretical astrophysicist at Northwestern and senior author of the study. "A relatively simple and well understood process seems to work. Simple freshman physics—Newton's first law of motion—explains the gravitational dynamics of the first black holes detected by LIGO."

    Rasio will detail how the first LIGO detection fits into his team's theory at a media briefing at 2:15 p.m. Pacific Daylight Time today (June 15) at the summer meeting of the American Astronomical Society (AAS) in San Diego.

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  • At a separate media briefing earlier today, the LIGO Scientific Collaboration announced its second detection—on Boxing Day in the U.K. and Christmas Day 2015 in the U.S.—of gravitational waves and merging black holes. This growing population of black holes will help astrophysicists learn more about the universe..

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  • "We were ecstatic by the news announced earlier this year by LIGO about its first detection of colliding black holes," said Carl L. Rodriguez, lead author of the study and a Ph.D. student in Rasio's research group. "The findings are pretty much where we thought they would be. We look forward to working with the data from new detections."

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    "Simple physical processes make the heavy black holes go to the center of the cluster," Rasio said. "These pairs eventually merge and are detected by LIGO." He is the Joseph Cummings Professor in the department of physics and astronomy in Northwestern's Weinberg College of Arts and Sciences.

Rodriguez and colleagues used 52 detailed computer models to demonstrate how a globular cluster acts as a dominant source of binary black holes, producing hundreds of black hole mergers over a cluster's 12-billion-year lifetime. By comparing the models to recent observations of clusters in the Milky Way galaxy and beyond, the results show that Advanced LIGO (Laser Interferometer Gravitational-Wave Observatory) could eventually see more than 100 binary black hole mergers per year.

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