The newfound honeycomb fractures are the "most
compelling evidence to date" that Mars was tilted more extremely than it
is today.
A network of polygon-shaped cracks were detected dozens of meters below on Mars (Credit: NASA/JPL-Caltech/University of Arizona) |
Each crevasse spans 70 meters (230 feet) — about half a
football field — and is bordered by 30-meter-wide (98-feet-wide) slurries of
ice and mud. It's likely, scientists say, that this material is somewhere
between 2 billion and 3.5 billion years old. The patterns were spotted in the
data sent home by China's now-incommunicado Zhurong
rover which explored an expansive, bumpy region north of Mars' equator
named Utopia Planitia.
Zhruong rolled just a little over one kilometer (0.6 miles)
toward Mars'
southern region in that one year, but even during such a short trip, its radar
had sensed a continuous pattern of 15 buried polygons — suggesting there may be
more waiting to be found, study lead author Lei Zhang of the Chinese Academy of
Sciences told Space.com in an email.
On Earth,
similar patterns are known to form only in Greenland, Iceland and Antarctica
when drastic temperature dips caused by seasonal changes contract and fracture
the ground. Ice and mud that sometimes fill these cracks stops them from ever
healing, causing the surface to eventually split further. A similar process on
Mars, some 2 billion to 3.5 billion years ago, would have caused the newly
detected crevasses, which are tens of meters larger than any found on our
planet. "These polygons are huge," said Zhang.
This discovery, in short, provides fresh evidence that the
Red Planet once hosted water and a friendly climate to life as we know it.
Puzzlingly, the pattern also suggests tropical regions on
Mars were cold enough to cause cracks similar to those seen near Earth's icy
pole. The mystery could be answered by an existing (but unproven) theory that
suggests Mars was once a lot more tilted on its axis than it is today — up to
forty degrees or more — approximately 5 million years ago. "Such an
extremely tilted scenario muddies the waters between thinking of polar regions
as cold and low-latitudes as warm," Zhang said.
William Rapin, a scientist at the Institut de Recherche en
Astrophysique et Planétologie in Paris, who was not affiliated with the new
research, says the newfound buried polygon pattern is "an interesting
find" and would help understand the inner workings of a critical period on
Mars which may have been hospitable toward life. Rapin was part of a team
that recently found similarly shaped, centimeter-sized mud
cracks on the Martian surface near the Gale crater presently being explored
by NASA'sCuriosity rover.
NASA's Curiosity Rover (Credit: NASA/JPL-Caltech/MSSS) |
Accessing areas from a similarly ancient period on Earth is
difficult because our planet routinely recycles its surface. But on Mars,
"we have all those strata in very good condition," Rapin said.
"So we can investigate an era that was maybe favorable for the origin of
life itself."
Mars' tilt or obliquity has shifted over the past 3.5
billion years. If it weren't tilted at all, its equator would be the
warmest due to receiving the most direct sunlight, and temperature would dip
toward the poles. But computer models show the wobbly planet was excessively
tipped a few million years ago, meaning that where sunlight landed changed
throughout the year. For half of its orbit around the sun, about six months,
Mars in this epoch experienced nights that "reached" as far as its
equator, Rapin said.
Mars' tilt has been known to vary more than Earth's does,
having shifted by more than ten degrees over 100,000 years. In fact, that
change is what scientists believe caused such dramatic changes to its climate,
turning it from a once-blue oasis to the arid red land we presently see. But
the newly detected polygon pattern could help scientists narrow down
exactly when those drastic climate changes occurred, said
Zhang.
The fact that the pattern was detected 35 meters (115 feet)
below the surface "means the polygons formed, developed over some time,
but then stopped suddenly," he explained. Martian soil in the recent past
must not have experienced the same temperature swings, causing it to layer on
top of those crevices. "The time that the polygons stopped might be a time
that the climate changed — suddenly shifting from a quite cold to a quite nice,
temperate climate."
The Zhurong rover went silent late
last year after it failed to wake up from its scheduled hibernation, and
scientists presume it succumbed to Mars' heavy dust storms. Meanwhile, NASA's
Curiosity rover, which notched 4,000 days on Mars last month, will reach a
terrain next year pockmarked with fractures large enough to be seen from orbit.
Rapin hypothesizes those may represent the occurrence of an ancient, extreme
drought and hopes to compare them to the newfound polygons at Utopia Planitia.
"They are pretty far," said Rapin. "It's kind
of a dream that we reach them."
This research is described in a paper published last month in the journal Nature
Astronomy.
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