Liquid Water on Pluto?

Prior to 2015, scientists knew little about Pluto, mainly because it is dim and small from Earth’s perspective, not to mention 4.67 billion miles away.

When NASA’s New Horizons space probe flew by the far-away dwarf planet, imaging it in unprecedented detail, the historic mission raised more questions than answers. For one, the probe’s findings raised suspicions that some of Pluto’s mountains were formed on a bedrock of water ice.

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According to a new study, computer simulations provide have provided compelling evidence that an insulating layer near the surface is keeping a subsurface ocean from freezing beneath Pluto’s ice. In other words, there could be a liquid ocean on the planet.

A team of Japanese scientists published the study, proposing that such an otherworldly idea is possible because a thin layer of ice containing trapped gas molecules, known as gas hydrates, at the bottom of the ice shell could be insulating the ocean.  By calculating Pluto’s temperature and the thickness of the ice shell, the scientists concluded that the gas hydrates would be enough to maintain a subsurface ocean.

Understanding how a subsurface ocean can exist on Pluto will provide scientists with invaluable information to better understand how similar bodies of water can exist on other planets, too. Liquid water oceans are thought to exist inside icy satellites of gas giants such as Europa and Enceladus. Understanding the survival of subsurface oceans is of fundamental importance not only to planetary science but also to astrobiology.

Scientists have been repeatedly surprised and bewildered by the data New Horizons collected and processed from its flyby in 2015. Even the initial photos showed unexpected complexity of the dwarf planet.

The study is published in in the journal Nature Geoscience.

Moonquakes Too

In 2010, an analysis of images from NASA’s Lunar Reconnaissance Orbiter (LRO) found that the Moon shriveled like a raisin as its interior cooled, leaving behind thousands of cliffs called thrust faults on the lunar surface. A new analysis of archival data from seismometers deployed during the Apollo missions gives the first evidence that these thrust faults are still active and likely producing moonquakes today as the Moon continues to gradually cool and shrink.

Researchers found that a number of the quakes recorded in the Apollo data happened very close to the faults seen in the LRO imagery. The LRO images also show physical evidence of geologically recent fault movement, such as landslides and tumbled boulders.

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Astronauts placed five seismometers on the Moon’s surface during the Apollo 11, 12, 14, 15, and 16 missions. The Apollo 11 seismometer operated only for three weeks, but the four remaining instruments recorded 28 shallow moonquakes from 1969 to 1977. On Earth, the quakes would have ranged in magnitude from about 2 to 5.

Using the revised location estimates from their new algorithm, scientists found that the epicenters of eight of the 28 shallow quakes were within 19 miles of faults visible in the LRO images. This was close enough for the team to conclude that the faults likely caused the quakes.

The researchers also found that six of the eight quakes happened when the Moon was at or near its apogee, the point in the Moon’s orbit when it is farthest from Earth. This is where additional tidal stress from Earth’s gravity causes a peak in the total stress on the Moon’s crust, making slippage along the thrust faults more likely.

The LRO imaged more than 3,500 fault scarps on the Moon. Some of these images show landslides or boulders at the bottom of relatively bright patches on the slopes of fault scarps or nearby terrain. Brighter areas indicate regions that are freshly exposed by an event such as a moonquake.

Other LRO fault images show fresh tracks from boulder falls, suggesting that quakes sent these boulders rolling down their cliff slopes. Such tracks would be erased relatively quickly, in terms of geologic time, by the constant rain of micrometeoroid impacts on the Moon.

The study appears in the journal Nature Geoscience.

Moonshots

Last month, NASA’s Mars Odyssey orbiter captured a new thermal image of Phobos, the larger of Mars’ two moons. Each color in the full-moon image represents a temperature range detected by Odyssey’s Thermal Emission Imaging System (THEMIS) camera. Each observation is done from a slightly different angle or time of day, providing new kinds of data.

The new, full-moon view is better for studying material composition, whereas earlier half-moon views are better for looking at surface textures. With the half-moon views, scientists could see how rough or smooth the surface is and how it’s layered. With the new full-moon views, scientists can gather data on what minerals are in it, including metals.

These three views of the Martian moon Phobos were taken by NASA’s Mars Odyssey orbiter using its THEMIS camera. Each color represents a different temperature range. The upper image was taken in a full-moon phase, which is better for studying material composition. The two views below were taken while Phobos was in a half-moon phase, which is better for studying surface textures. Image credit: NASA / JPL-Caltech / ASU / SSI.

Iron and nickel are two such metals. Depending on how abundant the metals are, and how they’re mixed with other minerals, researchers might be able to determine whether Phobos is a captured asteroid or a pile of Mars fragments blasted into space by a giant impact long ago.

Human exploration of Phobos has been discussed in the space community as a distant, future possibility, and a Japanese sample-return mission to the tiny moon is scheduled for launch in the 2020s. These and future observations could help future missions identify hazards and find safe areas to land of the surface.

Hubble Finds More Interesting Stuff

New data from the Spitzer and Hubble space telescopes show that in particular wavelengths of infrared light, some of the first galaxies to form in the Universe (less than 1 billion years after the Big Bang) were considerably brighter than astronomers anticipated.

No one yet knows for sure when the first stars in our Universe burst to life. Evidence suggests that between 100 million and 200 million years after the Big Bang, the Universe was filled mostly with neutral hydrogen gas that had perhaps just begun to coalesce into stars, which then began to form the first galaxies.

By about 1 billion years after the Big Bang, the Universe had become a sparkling firmament. Something else had changed, too: electrons of the omnipresent neutral hydrogen gas had been stripped away in a process known as ionization.

The Epoch of Reionization, the changeover from the Universe full of neutral hydrogen to one filled with ionized hydrogen, is well documented.

Before this Universe-wide transformation, long-wavelength forms of light, such as radio waves and visible light, traversed the Universe more or less unencumbered. But shorter wavelengths, including ultraviolet light, X-rays and gamma rays, were stopped short by neutral hydrogen atoms. These collisions would strip the neutral hydrogen atoms of their electrons, ionizing them.

But what could have produced enough ionizing radiation to affect all the hydrogen in the Universe? Was it individual stars? Giant galaxies?

If either were the culprit, those early cosmic colonizers would have been different than most modern stars and galaxies, which typically don’t release high amounts of ionizing radiation. Then again, perhaps something else entirely caused the event, such as quasars.

Researchers found that early galaxies were particularly bright in two specific wavelengths of infrared light produced by ionizing radiation interacting with hydrogen and oxygen gases within the galaxies. This implies that the galaxies were dominated by young, massive stars composed mostly of hydrogen and helium. They contain very small amounts of heavy elements, like nitrogen, carbon and oxygen, compared to stars found in modern galaxies.

These stars were not the first stars to form in the Universe (those would have been composed of hydrogen and helium only) but were still members of very early generations of stars.

The Epoch of Reionization wasn’t an instantaneous event, so while the new results are not enough to close the book on this cosmic event, they do provide new details about how the Universe evolved during this time and how the transition played out.

The findings are published in the Monthly Notices of the Royal Astronomical Society.