Wednesday, May 22, 2019

Remnants of Ancient Ice Sheets Found Buried on Mars


A view of Mars showing the planet’s northern polar ice cap. A new study led by The University of Texas at Austin has found remnants of ancient ice caps buried in the north polar region.

Credit ISRO / ISSDC / Emily Lakdawalla.

Scientists have discovered remnants of ancient ice sheets buried in sand a mile beneath Mars’s north pole, they report in a new study. The findings show conclusive evidence of the waxing and waning of polar ice on the red planet due to changes in its orbit and tilt, according to the study’s authors.

Researchers at the University of Texas at Austin and the University of Arizona made the discovery using measurements gathered by the Shallow Radar (SHARAD) instrument on NASA’s Mars Reconnaissance Orbiter. SHARAD emits radar waves that can penetrate up to a mile and a half beneath Mars’s surface.

The new findings, published today in AGU’s journal Geophysical Research Letters, are important because the layers of ice are a record of past climate on Mars in much the same way that tree rings are a record of past climate on Earth, according to the researchers. Studying the geometry and composition of these layers could tell scientists whether climate conditions were previously favorable for life.

The team found layers of sand and ice that were as much as 90 percent water in some places. If melted, the newly discovered ice would be equivalent to a global layer of water around Mars at least 1.5 meters (5 feet) deep, which could be one of the largest water reservoirs on the planet, according to the researchers.

A vertically exaggerated view of Mars’ north polar cap. Researchers estimate that if melted, the massive ice deposits discovered in this region would cover the planet in 1.5 meters (5 feet) of water.

Credit: SA/DLR/FU Berlin; NASA MGS MOLA Science Team.

“We didn’t expect to find this much water ice here,” said Stefano Nerozzi, a graduate research assistant at the University of Texas Institute for Geophysics (UTIG) and lead author of the new study. “That likely makes it the third largest water reservoir on Mars after the polar ice caps.”

The findings were corroborated by an independent study using gravity data instead of radar, led by researchers at Johns Hopkins University and also published today in Geophysical Research Letters, of which Nerozzi is a co-author.

Layers of sand and ice

The authors suspect the layers formed when ice accumulated at the poles during past ice ages on Mars. Each time the planet warmed, a remnant of the ice caps became covered by sand, which protected the ice from solar radiation and prevented it from dissipating into the atmosphere.

Scientists have long known about glacial events on Mars, which are driven by variations in the planet’s orbit and tilt. Over periods of about 50,000 years, Mars leans toward the sun before gradually returning to an upright position, like a wobbling spinning top. When the planet spins upright, the equator faces the sun, allowing the polar ice caps to grow. As the planet tilts, the ice caps retreat, perhaps vanishing entirely.

Until now, scientists thought the ancient ice caps were lost. The new findings show that in fact significant ice sheet remnants have survived under the planet’s surface, trapped in alternating bands of ice and sand, like layers on a cake.

A composite image showing alternating layers of ice and sand in an area where they are exposed on the surface of Mars. The photograph, taken with the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter, was adjusted to show water ice as light-colored layers and sand as darker layers of blue. The tiny bright white flecks are thin patches of frost.

Credit: NASA/JPL/University of Arizona.

Jack Holt, a professor at the Lunar and Planetary Laboratory of the University of Arizona and co-author of the new study, said the research provides new, important insights into the exchange of water ice between the poles and the midlatitudes, where his research group previously confirmed the presence of widespread glaciers, also using the SHARAD instrument.

“Surprisingly, the total volume of water locked up in these buried polar deposits is roughly the same as all the water ice known to exist in glaciers and buried ice layers at lower latitudes on Mars, and they are approximately the same age,” he said.

Sudying this record of past polar glaciation could help determine whether Mars was ever habitable, according to Nerozzi.

“Understanding how much water was available globally versus what’s trapped in the poles is important if you’re going to have liquid water on Mars,” Nerozzi said. “You can have all the right conditions for life, but if most of the water is locked up at the poles, then it becomes difficult to have sufficient amounts of liquid water near the equator.”

Contacts and sources:
Lauren Lipuma, American Geophysical Union
Stefano Nerozzi, University of Texas at Austin
Jack Holt, University of Arizona


Citation: “Buried ice and sand caps at the north pole of Mars: Revealing a record of climate change in the cavi unit with SHARAD” Stefano Nerozzi and Jack W. Holt
https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2019GL082114  This paper is freely available through June 30.

Bonobo Mothers Help Their Sons Have More Offspring

Mothers’ presence influences the reproductive success of their adult sons among bonobos.

In many social animal species individuals share child-rearing duties, but new research from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, finds that bonobo mothers go the extra step and actually take action to ensure their sons will become fathers. This way bonobo mothers increase their sons’ chance of fatherhood three-fold.

Adult bonobo male in the Kokolopori Bonobo Reserve, D.R. Congo.

Credit: © Martin Surbeck, Kokolopori Bonobo Research

"This is the first time that we can show the impact of the mother’s presence on a very important male fitness trait, which is their fertility," says Martin Surbeck, a primatologist at the Max Planck Institute for Evolutionary Anthropology. "We were surprised to see that the mothers have such a strong, direct influence on the number of grandchildren they get."

Surbeck and his colleagues observed wild populations of bonobos in the Democratic Republic of Congo, as well as wild populations of chimpanzees in Côte d'Ivoire, Tanzania, and Uganda. They found that while both bonobo and chimpanzee mothers would advocate for their sons in male-on-male conflicts, bonobo moms went the extra mile to aid their sons’ copulation efforts. This involved protecting their sons’ mating attempts from other males and intervening in other male’s mating attempts.

The bonobo mothers were also able to use their rank in the bonobo’s matriarchal society to give their sons access to popular spots within social groups in the community and help them achieve higher male status - and therefore, better mating opportunities. The authors note that these interactions were rare in chimpanzee societies and did not have an effect on male fertility; in chimpanzees males hold dominant positions over females, making the actions of chimp mothers less influential than those of bonobo mothers.
No help for daughters

Interestingly, bonobo moms did not extend similar help to their daughters, nor were there any observations of daughters receiving assistance in rearing their offspring. "In bonobo social systems, the daughters disperse from the native community and the sons stay," Surbeck says. "And for the few daughters that stay in the community, which we don’t have many examples of, we don’t see them receiving much help from their mothers."

Moving forward, Surbeck and his team would like to better understand the benefits these behaviors confer on bonobo mothers. Currently, they think that it allows for an indirect continuation of their genes. "These females have found a way to increase their reproductive success without having more offspring themselves," he says, noting that the prolongation of the post-reproductive human female lifespan, as well as the early-age at which human women can no longer bare children, may have evolved from this indirect method of continuing their genetic line.

Surbeck acknowledges that gathering data on post-reproductive lifespans of females in chimp and bonobo communities will require a long-term, collaborative study, similar to this one. "Without the help and participation from all of the field sites where data was collected, these important interactions could have been overlooked," he says. "Now as the director of a bonobo field site, I’m looking forward to further exploring this topic."




Contacts and sources:
Dr. Martin Surbeck, Sandra Jacob
Max Planck Institute for Evolutionary Anthropology

Citation: Males with a mother living in their group have higher paternity success in bonobos but not chimpanzees.
Martin Surbeck, Christophe Boesch, Catherine Crockford, Melissa Emery Thompson, Takeshi Furuichi, Barbara Fruth, Gottfried Hohmann, Shintaro Ishizuka, Zarin Machanda, Martin N. Muller, Anne Pusey, Tetsuya Sakamaki, Nahoko Tokuyama, Kara Walker, Richard Wrangham, Emily Wroblewski, Klaus Zuberbühler, Linda Vigilant, Kevin Langergraber. Current Biology, 2019; 29 (10): R354 DOI: 10.1016/j.cub.2019.03.040