Tag Archives: water in space

An artist’s view of the TRAPPIST-1 system. The TRAPPIST-1 star is home to the largest batch of roughly Earth-size planets ever found outside our solar system. An international study involving researchers from the Universities of Bern, Geneva and Zurich now shows that the exoplanets have remarkably similar densities, which provides clues about their composition (NASA/JPL-Caltech)

The Trappist-1 exoplanets could be worlds of water or rust

The star system of Trappist-1 is home to the largest group of Earth-like planets ever discovered elsewhere in the Universe by astronomers. This means that investigating these seven rocky worlds gives us a good idea of how common exoplanets with similar compositions to our own are in the Milky Way and the wider cosmos.

New research has revealed that these planets, which orbit the Trappist-1 star 40 light-years away from Earth, all have remarkably similar compositions and densities. Yet, all are less dense than Earth.

The results could indicate these are worlds with much more water than is found on earth, or possibly even that these planets are composed almost entirely of rust.

An artist’s view of the TRAPPIST-1 system. The TRAPPIST-1 star is home to the largest batch of roughly Earth-size planets ever found outside our solar system. An international study involving researchers from the Universities of Bern, Geneva and Zurich now shows that the exoplanets have remarkably similar densities, which provides clues about their composition (NASA/JPL-Caltech)
An artist’s view of the TRAPPIST-1 system. The TRAPPIST-1 star is home to the largest batch of roughly Earth-size planets ever found outside our solar system. An international study involving researchers from the Universities of Bern, Geneva and Zurich now shows that the exoplanets have remarkably similar densities, which provides clues about their composition (NASA/JPL-Caltech)


This similarity between the exoplanets makes the Trappist-1 system significantly different from our own solar system which consists of planets with radically compositions and densities. Trappist-1’s worlds are dense, meaning they are like the rocky planets in our solar system, Earth, Mars, Venus, and Mercury. The system seems to be lacking larger gas dominated planets like Jupiter, Saturn, Uranus and Neptune.

The finding, documented in a paper published in the Planetary science Journal shows how the system, first discovered in 2016, offers insight into the wide variety of planetary systems that could fill the Universe.

This chart shows, on the top row, artist concepts of the seven planets of TRAPPIST-1 with their orbital periods, distances from their star, radii, masses, densities and surface gravity as compared to those of Earth. On the bottom row, the same numbers are displayed for the bodies of our inner solar system: Mercury, Venus, Earth and Mars. (NASA/ JPL - Caltech)
This chart shows, on the top row, artist concepts of the seven planets of TRAPPIST-1 with their orbital periods, distances from their star, radii, masses, densities and surface gravity as compared to those of Earth. On the bottom row, the same numbers are displayed for the bodies of our inner solar system: Mercury, Venus, Earth and Mars. (NASA/ JPL – Caltech)

“The new observations allowed us to use transit data from a much longer time span than was available to us for the 2018 calculations,” explains Simon Grimm of the University of Bern, who as well as being involved in the current study, was part of a 2018 team that provided the most accurate calculation of the masses of the seven planets thus far. “With the new data, we were able to refine the mass and density determinations of all seven planets.

“It turned out that the derived densities of the planets are even more similar than we had previously expected.”

Seven Exoplanets with Similar Densities

The similarity in densities observed in the Trappist-1 exoplanets seen by the astronomers hailing from the Universities of Bern, Geneva and Zurich, indicates that there is a good chance they are composed of the same materials at similar ratios.

These are the same materials that we believe form most terrestrial planets, iron, oxygen, magnesium, and silicon. But there is a significant difference between our terrestrial world and the Trappist-1 exoplanets.

Comparison of TRAPPIST-1 to the Solar System: A planet's density is determined by its composition, but also by its size: Gravity compresses the material a planet is made of, increasing the planet's density. Uncompressed density adjusts for the effect of gravity, and can reveal how the composition of various planets compare. (NASA/JPL-Caltech 4)
Comparison of TRAPPIST-1 to the Solar System: A planet’s density is determined by its composition, but also by its size: Gravity compresses the material a planet is made of, increasing the planet’s density. Uncompressed density adjusts for the effect of gravity, and can reveal how the composition of various planets compare. (NASA/JPL-Caltech )

The planets in the Trappist-1 system appear to be about 8% less dense than the Earth. This suggests that the materials that comprise them exist in different ratios than they do throughout our home planet.

This difference in density could be the result of several different factors.

One of the possibilities being investigated by the team is that the surfaces of the Trappist-1 exoplanets could be covered with water, reducing their overall density. Combining the planetary interior models with the planetary atmosphere models, the team was able to evaluate the water content of the seven TRAPPIST-1 planets with what Martin Turbet, an astrophysicist at the University of Geneva and co-author of the study describes as “a precision literally unprecedented for this category of planets.”

For the Trappist-1 system’s four outermost planets, should water account for the difference in density, the team has estimated that water would account for 5% of their overall masses. This is considerably more than the 0.1% of Earth’s total mass made up of water.

Rust Nevers Sleeps for the Trappist-1 Planets

Another possibility that could explain why the Trappist-1 exoplanets have lower densities than Earth is the fact that they could be composed of less iron than our planet is–21% rather than the 32% found in the Earth.

It’s also possible that the iron within the seven exoplanets could be bonded with oxygen forming iron oxides–commonly known as rust. This additional oxygen would reduce the planet’s densities.

Shown here are three possible interiors of the TRAPPIST-1 exoplanets. The more precisely scientists know the density of a planet, the more they can narrow down the range of possible interiors for that planet. All seven planets have very similar densities, so they likely have a similar compositions (NASA/ JPL - Caltech)
Shown here are three possible interiors of the TRAPPIST-1 exoplanets. The more precisely scientists know the density of a planet, the more they can narrow down the range of possible interiors for that planet. All seven planets have very similar densities, so they likely have a similar composition (NASA/ JPL – Caltech)

Iron oxides give Mars its rust-red colour, but they are pretty much confined to its surface. Its core is comprised of non-oxidized iron like the solar system’s other terrestrial planets. If iron-oxide accounts for the seven exoplanet’s lower densities it implies that these worlds are rusty throughout and lacking solid non-oxidized iron cores.

“The lower density might be caused by a combination of the two scenarios – less iron overall than and some oxidized iron,” explains Eric Angol, an astrophysicist at the University of Washington and lead author of the new study. “They might contain less iron than Earth and some oxidized iron like Mars.”

Angol also points out that the Trappist-1 planets are likely to have a low-water content, an idea supported by previous research. “Our internal and atmospheric structure models show that the three inner planets of the TRAPPIST-1 system are likely to be waterless and that the four outer planets have no more than a few per cent water, possibly in liquid form, on their surfaces,” says Turbet.

This seems to favour the theory that the lower density of the Trappist-1 planets is a result of one or both of the iron scenarios suggested by the researchers.

There’s Still a Lot to Learn from Trappist-1


Since its discovery in 2o16, the Trappist system has been the subject of a wealth of observations made by both space and ground-based telescopes alike. Before it was decommissioned at the start of January 2020 the team used the Spitzer Space Telescope to collect their data. This telescope, operated by NASA’s Jet Propulsion Laboratory, alone has clocked in more than 1,000 hours of targeted observations of the exoplanets.

This new study demonstrated the importance of studying systems such as Trappist-1 for extended periods of time.

Caroline Dorn, an astrophysicist at the University of Zurich also highlights the fact that studying systems like this could answer questions about the habitability of exoplanets and the possibility of life elsewhere in the Universe.

“The TRAPPIST-1 system is fascinating because around this one star we can learn about the diversity of rocky planets within a single system,” concludes Dorn. “And we can actually learn more about an individual planet by studying its neighbours as well, so this system is perfect for that.”

“The night sky is full of planets, and it’s only been within the last 30 years that we’ve been able to start unravelling their mysteries, also for determining the habitability of these planets.”

Original Research

Agol. E., Dorn. C., Grimm. S. L., et al, ‘Refining the transit timing and photometric analysis of TRAPPIST-1: Masses, radii, densities, dynamics, and ephemerides,’ Planetary Science Journal, [https://arxiv.org/abs/2010.01074]

Mars then and Now. The Red Planet has been stripped of water for billions of years, but the main mechanism of water loss is different now than it was a billion years ago (NASA)

Water stripped from Mars’ upper atmosphere may explain how it became a barren Red Planet

A new study has revealed the detection of water in the upper atmosphere of Mars for the first time. The discovery gives scientists a good idea of the mechanism that is currently stripping the Red Planet of its water. 

The surface of Mars is cold and dry —bereft of liquid water — but this wasn’t always the case. Studies of the Martian surface have discovered the tell-tale tracks of long dry ancient rivers and sedimentary deposits that indicate lake beds into which water once flowed. This poses the question of how the Red Planet lost its liquid water?

A study published in the journal Science suggests a new mechanism that could have driven Mars’ water loss. A team of astronomers has used data collected from Mars’ atmosphere by NASA’s Neutral Gas and Ion Mass Spectrometer on the Mars Atmosphere and Volatile Evolution spacecraft (MAVEN) to discover water in the planet’s upper atmosphere. 

“For the first time, we have seen water in the upper atmosphere of Mars, at around 150 km above the surface. Other scientists have previously observed water in the middle atmosphere,” Shane Wesley Stone, a PhD. Candidate in Planetary Sciences at the Lunar and Planetary Laboratory, University of Arizona, and one of the paper’s authors tells ZME Science. “Water in the upper atmosphere is quickly destroyed and can escape to space, which is why our observations of water in the upper atmosphere are significant.”

Mars then and Now. The Red Planet has been stripped of water for billions of years, but the main mechanism of water loss is different now than it was a billion years ago (NASA)
Mars then and Now. The Red Planet has been stripped of water for billions of years, but the main mechanism of water loss is different now than it was a billion years ago (NASA)

Water transported to the upper atmosphere of Mars is converted to atomic hydrogen, which is then so-light that it is lost to space. This process could have been driving Mars’ water loss for billions of years. Water had previously been detected in the lower atmosphere, where scientists believed it was confined, but this is the first detection of water in the upper atmosphere, which caught the team by surprise. 

“We did not know that water makes it all the way to the upper atmosphere, so we did not know how important this upward transport of water is to the escape of hydrogen to space and thus to water lost from Mars,” Stone says, explaining that water higher in the atmosphere would be broken down much more rapidly than happens closer to the martian surface. “Water which makes it to the upper atmosphere is destroyed in about 4 hours. This destruction of water would be ten times slower in the middle atmosphere, where most of the products of this destruction would be transported downward back toward the surface.”

Rising Damp: How Does Water Make its Way to Mars’ Upper Atmosphere?

Stone explains that the team is not yet certain what processes are lifting water to Mars’ upper atmosphere, but their study has yielded some good clues as to what may be the major players in this phenomenon. 

“We see a seasonal trend in the upper atmospheric water abundance,” says the planetary chemist. “During summer in the southern hemisphere, the water abundance in the upper atmosphere is largest. During summer in the northern hemisphere, the water abundance in the upper atmosphere is smallest but is still significant.”

Stone explains that this seasonal trend is caused by two things. Firstly, during southern summer, Mars is closer to the Sun than it is during the rest of the Martian year. Secondly, this is also the season of dust storms on Mars. He adds: “Relatively close proximity to the Sun and dust storms both lead to heating in the atmosphere, which leads to greater transport of water to the upper atmosphere.”

The researcher points to a massive Martian dust storm that occurred in 2018 as being a major contributing factor to water in the upper atmosphere. The storm was first spotted by NASA’s Mars Reconnaissance Orbiter (MRO) on May 30th 2018 and by June of that year, it had grown to a planet encompassing event. 

Rotating globes from May 28 and July 1 show a global dust storm completely obscuring the surface of Mars. (NASA)

“Dust storms lead to a sudden splash of water into the upper atmosphere: during the global dust storm of 2018, the water abundance in the upper atmosphere increases by 20x relative to the nominal seasonal abundance,” Stone says. “Smaller surges of water are observed during regional dust storms that occur every Mars year of 687 days. Global storms occur about once every 10 Earth years.”

The team believe that water is moving upward past what planetary scientists call the hygropause — a cold layer in the atmosphere at which water condenses from vapour to liquid, forming clouds. “This because, as we and other scientists have found, the Martian hygropause is not as efficient at trapping water close to the surface as the hygropause on Earth,” Stone says. “The hygropause on Mars is not as efficient because it is too warm: when Mars is closest to the Sun and when dust storms occur, heating caused by these processes warms the hygropause, allowing water to move upward.”

The mechanism their finding reveals is currently the main way that Mars loses water, but Stone points out that this likely wasn’t always the case.

The Changing Picture of Water Loss on Mars

Water transported to Mars’ upper atmosphere by seasonal effects and dust storms where it is broken down to hydrogen and then lost to space is currently the predominant mechanism of water loss on Mars, but the team says this is only because of the Red Planet’s current environment. The water loss mechanisms that have proceeded for billions of years were likely different in the past in terms of both dominance and the speed at which they proceed.

“This process we describe is an important factor in Martian water loss today. However, this water could only be transported to the upper atmosphere relatively recently, over the last billion years or so,” Stone says. “Much of Mars’ atmosphere was lost to space before this time, leading to the weak hygropause which allows water into the upper atmosphere. All escape processes we observe today were likely faster in the past.”

NASA scientists have determined that a primitive ocean on Mars held more water than Earth's Arctic Ocean and that the Red Planet has lost 87 percent of that water to space. Credits: NASA/GSFC
NASA scientists have determined that a primitive ocean on Mars held more water than Earth’s Arctic Ocean and that the Red Planet has lost 87 per cent of that water to space. Credits: NASA/GSFC

The team reached this conclusion due to the fact that when all the water loss rates of the present-day escape processes are summed, their current escape rate is too slow to explain all the water loss that scientists know must have occurred over the last few billion years. 

“We know that over 4 billion years, Mars lost about 66% of its atmosphere to space,” Stone explains. “If we talk about water specifically, Mars has lost 10s to 100s of meters of a ‘global equivalent layer’ of water — equivalent to spreading all of the water lost by Mars over its surface to form an even layer and then reporting how deep this layer would be.”

The process the team describe is responsible for the loss of 44 cm of H2O over the last billion years, and global dust storms are responsible for the loss of an additional 17 cm on top of this over the last billion years.

“In the present epoch, during most of the Martian year, this process we describe is just as important as the ‘classical process’ — the basic process scientists thought responsible for the transport of hydrogen to the upper atmosphere since the first work on this topic in the early 1970s,” Stone says. “During global storms, this water which makes it to the upper atmosphere produces 10x more escaping hydrogen than does the classical process.”

Big Surprises and Future Investigations

Stone describes that the next steps for this research involve figuring out exactly how important this new water loss mechanism has been throughout the history of Mars. 

“Extrapolating back over billions of years is extremely difficult and doing it correctly takes time. We still need to understand better the specific transport processes responsible for delivering this water to the upper atmosphere,” he says, adding that the team’s findings came as something as a shock even to them. “The entire project was a huge surprise to us: we were surprised to see water this high in the atmosphere, we were surprised to see the seasonal trend in the water abundance, and we were surprised by just how big an effect the global dust storm has on the upper atmospheric water abundance.” 

Comparing the atmospheres of earth and Mars could help scientists determine the chances of liquid water existing on exxoplanets. (ESA)

Researching water loss from Mars is likely to be an important step in understanding how abundant water is throughout the Universe, as Dimitra Atri, a researcher from the Space Science at NYU Abu Dhabi (NYUAD), recently told ZME Science: “Since it is extremely difficult to observe the escape process in exoplanets, we are planning to study this phenomenon in great detail on Mars with the UAE’s Hope mission.”

Thus, this type of study could tell us how unique Earth is in terms of the possession of liquid water in the Universe. Something that could, in turn, tell us about the chances of life on exoplanets. 

“Mars used to look like Earth: warmer and wetter with a thick atmosphere and abundant liquid water on its surface,” Stone concludes. “But over the history of the solar system, Mars’ water was lost to space, leaving behind the cold, dry, red planet we see today. Regardless, Mars will be the next planet on which humans step foot.”

S.W. Stone; R.V. Yelle; D.Y. Lo, et al, [2020], ‘Hydrogen escape from Mars is driven by seasonal and dust storm transport of water,Science.