Scientists said on Tuesday that these cryovolcanoes
— numbering perhaps 10 or more — stand anywhere from six-tenths of a mile (1
km) to 4-1/2 miles (7 km) tall. Unlike Earth volcanoes that spew gases and
molten rock, this dwarf planet's cryovolcanoes extrude large amounts of ice —
apparently frozen water rather than some other frozen material — that may have
the consistency of toothpaste, they said.
Features on the asteroid belt dwarf planet
Ceres, Saturn's moons Enceladus and Titan, Jupiter's moon Europa and Neptune's
moon Triton also have been pegged as cryovolcanoes. But those all differ from
Pluto's, the researchers said, owing to different surface conditions such as
temperature and atmospheric pressure, as well as different mixes of icy
materials.
"Finding these features does indicate
that Pluto is more active, or geologically alive, than we previously thought it
would be," said planetary scientist Kelsi Singer of the Southwest Research
Institute in Boulder, Colorado, lead author of the study published in the
journal Nature Communications.
"The combination of these features
being geologically recent, covering a vast area and most likely being made of
water ice is surprising because it requires more internal heat than we thought
Pluto would have at this stage of its history," Singer added.
Pluto, which is smaller than Earth's moon
and has a diameter of about 1,400 miles (2,380 km), orbits about 3.6 billion
miles (5.8 billion km) away from the sun, roughly 40 times farther than Earth's
orbit. Its surface features plains, mountains, craters and valleys.
Images and data analysed in the new study,
obtained in 2015 by New Horizons, validated previous hypotheses about
cryovolcanism on Pluto.
The study found not only extensive evidence
for cryovolcanism but also that it has been long-lived, not a single episode,
said Southwest Research Institute planetary scientist Alan Stern, the New
Horizons principal investigator and study co-author.
"What's most fascinating about Pluto
is that it's so complex - as complex as the Earth or Mars despite its smaller
size and high distance from the sun," Stern said. "This was a real
surprise from the New Horizons flyby, and the new result about cryovolcanism
re-emphasizes this in a dramatic way."
The researchers analyzed an area southwest
of Sputnik Planitia, Pluto's large heart-shaped basin filled with nitrogen ice.
They found large domes 18-60 miles (30-100 km) across, sometimes combining to
form more complexly shaped structures.
An elevation called Wright Mons, one of the
tallest, may have formed from several volcanic domes merging, yielding a shape
unlike any Earth volcanoes. Although shaped differently, it is similar in size
to Hawaii's large volcano Mauna Loa.
Like Earth and our solar system's other
planets, Pluto formed about 4.5 billion years ago. Based on an absence of
impact craters that normally would accumulate over time, it appears its
cryovolcanoes are relatively recent — formed in the past few hundred million
years.
"That is young on a geologic
timescale. Because there are almost no impact craters, it is possible these
processes are ongoing even in the present day," Singer said.
Pluto has lots of active geology, including
flowing nitrogen ice glaciers and a cycle in which nitrogen ice vaporizes
during the day and condenses back to ice at night — a process constantly
changing the planetary surface.
"Pluto is a geological
wonderland," Singer said. "Many areas of Pluto are completely
different from each other. If you just had a few pieces of a puzzle of Pluto
you would have no idea what the other areas looked like." © Reuters
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