Science & Technology

Isotope analysis reveals the underlying reason why Mars does not have liquid water on its surface today


An expression by an artist on Mars using surface water like the earth.Credits: Image Source: NASA Earth Observatory / Joshua Stevens; NOAA National Environmental Satellite, Data, and Information Service; NASA / JPL-Caltech / USGS; Graphic Design by Sean Garcia / Washington University

Water is essential to life on Earth and other planets, and scientists say it is Mars‘Early history. However, there is no liquid water on the surface of Mars today. A new study from Washington University in St. Louis suggests a fundamental reason: Mars may be too small to hold large amounts of water.

Remote sensing research and analysis of Martian meteorites dating back to the 1980s shows that Mars was once richer in water than Earth. NASAThe Viking Orbiter spacecraft—and more recently the curiosity and patience rover on the ground—returned dramatic images of the Martian landscape characterized by river valleys and flood canals.

Despite this evidence, no liquid water remains on the surface. Researchers have proposed many possible explanations, including weakening the magnetic field on Mars, which can lead to the loss of a thick atmosphere.

However, one study was in the week of September 20, 2021. Minutes of the National Academy of Sciences It suggests a more fundamental reason why Mars today looks so dramatically different from Earth’s “blue marble.”

“The fate of Mars was fixed from the beginning,” said Khun Wan, the lead author of the study, an assistant professor of earth and planetary sciences in the University of Washington’s arts and sciences. “There is probably a threshold for the size requirements of rocky planets to hold enough water to allow habitability and plate tectonics at masses above Mars.”

In a new study, Wang and his collaborators used stable isotopes of the potassium (K) element to estimate the presence, distribution, and abundance of volatile elements on various planetary bodies.

Potassium is a moderately volatile element, but scientists have decided to use it as a tracer for more volatile elements and compounds, such as water. This is a relatively new method that differs from previous attempts to use the ratio of potassium to thorium (Th) collected by remote sensing and chemical analysis to determine the amount of volatiles that Mars once had. ..In previous studies, members of the study group used the potassium tracer method. Study the formation of the moon..

Wang and his team measured the potassium isotope composition of 20 previously confirmed Martian meteorites, selected to represent the bulk silicate composition of the Red Planet.

Using this approach, researchers say that Mars lost more potassium and other volatiles than Earth during its formation, but retained more of these volatiles than the Moon and Asteroid 4-Vesta. Decided.

Researchers have found a clear correlation between body size and potassium isotope composition.

Catalina Rodders, a research professor of earth and planetary sciences at the University of Washington, co-author of the study, said: “The discovery of the correlation between K isotope composition and planetary gravity is a new discovery with important quantitative implications for when and how differentiated planets received and lost volatiles.”

“The Martian meteorite is the only sample we can use to study the chemical composition of Martian bulk,” Wang said. “These Martian meteorites are of varying ages, from hundreds of millions to four billion years, recording the history of Martian erratic evolution. Measuring isotopes of moderately volatile elements such as potassium. By doing so, it is possible to estimate the degree of depletion of volatile substances on bulk planets and compare different small solar system bodies.

“It is arguable that there used to be liquid water on the surface of Mars, but the total amount of water that once existed on Mars is difficult to quantify by remote sensing and rover studies alone,” Wang said. Stated. “There are many models of Mars’ bulk moisture. In some of them, early Mars was damp than Earth. I don’t think it was.”

Jen Tian, ​​a graduate student in Wang’s lab and a scholar at the McDonnell International Academy, is the first author of this treatise. Postdoctoral fellow Piers Koefoed and Hannah Bloom, who graduated from the University of Washington in 2020, are co-authors. Wang and Lodders are faculty fellows at the University’s McDonnell Space Science Center.

Researchers have pointed out that the findings will affect the search for life on planets other than Mars.

Being too close to the Sun (or too close to a star for exoplanets) can affect the amount of volatiles that the planet can hold. Distance measurements from this star are often included in the index of the “habitable zone” around the star.

“This study emphasizes that there is a very limited size range for having enough water but not too much water for the planet to develop a habitable surface environment,” said space habitability. Klaus Megger of the Sex Center said. University of Bern, Switzerland, co-author of the study. “These results will guide astronomers in finding exoplanets that can live in other solar systems.”

Wang now believes that for planets within the habitable zone, the size of the planet needs to be emphasized and considered on a daily basis. Exoplanet You can support your life.

“The size of an exoplanet is one of the easiest parameters to determine,” Wang said. “Based on size and mass, size is the primary determinant of volatility retention, so we know if exoplanets are candidates for life.”

Reference: “Martian potassium isotope composition reveals the mechanism of planetary volatility retention” September 20, 2021 Minutes of the National Academy of Sciences..
DOI: 10.1073 / pnas.2101155118

Isotope analysis reveals the underlying reason why Mars does not have liquid water on its surface today Isotope analysis reveals the underlying reason why Mars does not have liquid water on its surface today

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