September 5 () –
The Hubble Space Telescope has joined NASA’s MAVEN mission to unravel the mystery of the escape into space of much of the water that Mars contained billions of years ago.
“There are only two places that water can go. It can freeze into the ground, or the water molecule can break into atoms, and the atoms can escape from the top of the atmosphere into space,” he explained. in a statement study leader John Clarke of the Center for Space Physics at Boston University in Massachusetts. “To understand how much water there was and what happened to it, we need to understand how atoms escape into space.”
Clarke and his team combined data from Hubble and MAVEN (Mars Atmosphere and Volatile Evolution) to measure the amount and current rate of hydrogen atoms escaping into space. This information allowed them to extrapolate the escape rate back in time to understand the history of water on the Red Planet.
Sunlight breaks down water molecules in the Martian atmosphere into hydrogen and oxygen atoms. Specifically, the team measured hydrogen and deuterium, which is a hydrogen atom with a neutron in its nucleus. This neutron gives deuterium twice the mass of hydrogen. Because of its greater mass, deuterium escapes into space much more slowly than normal hydrogen.
Over time, as more hydrogen than deuterium was lost, the ratio of deuterium to hydrogen built up in the atmosphere. Measuring the ratio today gives scientists a clue as to how much water there was during the warm, wet period on Mars.By studying how these atoms are currently escaping, they can understand the processes that determined the escape rates over the past four billion years and thus extrapolate back in time.
Although most of the data in the study comes from the MAVEN spacecraft, it is not sensitive enough to see the emission of deuterium at all times of the Martian yearUnlike Earth, Mars moves far from the Sun in its elliptical orbit during the long Martian winter, and deuterium emissions become weak. Clarke and his team needed the Hubble data to “fill in the blanks” and complete an annual cycle of three Martian years (each of which is 687 Earth days). Hubble also provided additional data dating back to 1991, prior to MAVEN’s arrival at Mars in 2014.
The combination of data from these missions provided the first holistic view of hydrogen atoms escaping from Mars into space.
“In recent years, scientists have discovered that Mars has an annual cycle that is much more dynamic than expected 10 or 15 years ago,” Clarke explained. “The entire atmosphere is very turbulent, heating and cooling on short time scales, even hours. The atmosphere expands and contracts as the Sun shines on Mars.” varies by 40 percent over the course of a Martian year“.
The team found that the escape rates of hydrogen and deuterium change rapidly when Mars is close to the Sun. In the classic picture scientists previously had, these atoms were thought to slowly diffuse upward through the atmosphere. to a height where they could escape.
But that picture no longer accurately reflects the whole story, because scientists now know that atmospheric conditions change very quickly. When Mars is close to the Sun, water molecules, which are the source of hydrogen and deuterium, They rise through the atmosphere very quickly releasing atoms at high altitudes.
The second finding is that the changes in hydrogen and deuterium are so rapid that atomic escape requires additional energy to account for them. At the temperature of the upper atmosphere, only a small fraction of the atoms have enough speed to escape Mars’ gravity.
Faster (superthermal) atoms occur when something gives the atom an extra energy boost. These events include collisions of protons from the solar wind entering the atmosphere or sunlight. which drives chemical reactions in the upper atmosphere.
Studying the history of water on Mars is critical not only to understanding the planets in our own solar system, but also the evolution of Earth-sized planets around other stars. Astronomers are finding more and more of these planets, but they are difficult to study in detail, according to NASA.
Mars, Earth, and Venus are in or near our solar system’s habitable zone, the region around a star where liquid water could accumulate on a rocky planet; However, the three planets have radically different current conditions. Together with its sister planets, Mars can help scientists understand the nature of distant worlds throughout our galaxy.
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