Earth is our Solar System’s bluest planet, and yet no one really knows where all our water came from.
The dust of a nearby asteroid has now revealed a potentially overlooked source: the Sun.
Some water on our planet, it seems, might have been created by a river of charged particles, blown from the upper atmosphere of the Sun billions of years ago.
When solar wind interacts with the tiny dust particles found on certain asteroids, it can create a small amount of water, and this could explain some of the liquid we find here on our planet.
Most modern models suggest the majority of H20 on Earth originally came from an extraterrestrial source, possibly from C-type asteroids in the Jupiter-Saturn region and beyond.
These far-away asteroids are thought to be the parent bodies of carbonaceous chondrite meteorites that regularly crash into Earth, and this particular type of meteorite is known to contain a significant amount of water-containing minerals.
But carbonaceous chondrites probably aren’t the only way water was initially delivered to Earth. Other types of water-rich meteorites could have also done the same, especially since carbonaceous chondrites can’t account for Earth’s entire water budget.
There are other types of chondrite asteroids that could have also held particles of water, albeit to a lesser extent. The near-Earth asteroid, Itokawa, for instance, is an ordinary chondrite asteroid, and an analysis of samples taken from this silicate-rich rock in 2010 found signs of water, and the source could very well be the Sun.
Solar wind irradiation has been proposed in the past as a possible way to form water on silicate-rich materials floating in space.
In the lab, volatile hydrogen ions have been shown to react with silicate minerals, resulting in water as a byproduct, and electron microscopy and electron spectroscopy studies have found direct evidence of H20 within extraterrestrial dust particles in the past.
Theoretically, if water becomes trapped in these dust particles, the element will be protected from space weathering and can then be delivered via meteorites to other bodies in space.
“This phenomenon could explain why the regoliths of airless worlds such as the Moon, which were once thought to be anhydrous, contain several percent H20,” the authors of the new study explain.
To explore this hypothesis further and in a slightly different way, researchers turned to the S-type asteroid, Itokawa, to see if this object contains a ‘volatile reservoir’ of isotypes similar to that of solar wind.
While most water isotypes on Earth match carbonaceous chondrites, a small percentage don’t, and the Sun or the solar nebula have been proposed as possible sources.
In a nearby stellar nursery called the Orion Nebula, young, massive stars are blasting far-ultraviolet light at the cloud of dust and gas from which they were born.
This intense flood of radiation is violently disrupting the cloud by breaking apart molecules, ionizing atoms and molecules by stripping their electrons, and heating the gas and dust.
“The fact that massive stars shape the structure of galaxies through their explosions as supernovas has been known for a long time. But what people have discovered more recently is that massive stars also influence their environments not only as supernovas, but through their winds and radiation during their lives,” said one of the team’s principal investigators, Olivier Berné, a research scientist at the French National Centre for Scientific Research in Toulouse.
While it might sound like a Friday-night watering hole, the Orion Bar is actually a ridge-like feature of gas and dust within the spectacular Orion Nebula. A little more than 1,300 light-years away, this nebula is the nearest region of massive star formation to the Sun. The Orion Bar is sculpted by the intense radiation from nearby, hot, young stars, and at first glance appears to be shaped like a bar. It is a “photodissociation region,” or PDR, where ultraviolet light from young, massive stars creates a mostly neutral, but warm, area of gas and dust between the fully ionized gas surrounding the massive stars and the clouds in which they are born. This ultraviolet radiation strongly influences the gas chemistry of these regions and acts as the most important source of heat.
PDRs occur where interstellar gas is dense and cold enough to remain neutral, but not dense enough to prevent the penetration of far-ultraviolet light from massive stars. Emissions from these regions provide a unique tool to study the physical and chemical processes that are important for most of the mass between and around stars. The processes of radiation and cloud disruption drive the evolution of interstellar matter in our galaxy and throughout the universe from the early era of vigorous star formation to the present day.
“The Orion Bar is probably the prototype of a PDR,” explained Els Peeters, another of the team’s principal investigators. Peeters is a professor at the University of Western Ontario and a member of the SETI Institute. “It’s been studied extensively, so it’s well characterized. It’s very close by, and it’s really seen edge on. That means you can probe the different transition regions. And since it’s close by, this transition from one region to another is spatially distinct if you have a telescope with high spatial resolution.”
The Orion Bar is representative of what scientists think were the harsh physical conditions of PDRs in the universe billions of years ago. “We believe that at this time, you had ‘Orion Nebulas’ everywhere in the universe, in many galaxies,” said Berné. “We think that it can be representative of the physical conditions in terms of the ultraviolet radiation field in what are called ‘starburst galaxies,’ which dominate the era of star formation, when the universe was about half its current age.”
The formation of planetary systems in interstellar regions irradiated by massive young stars remains an open question. Detailed observations would allow astronomers to understand the impact of the ultraviolet radiation on the mass and composition of newly formed stars and planets.
In particular, studies of meteorites suggest that the solar system formed in a region similar to the Orion Nebula. Observing the Orion Bar is a way to understand our past. It serves as a model to learn about the very early stages of the formation of the solar system.
NASA’s Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) mission is targeted to launch in 2024. SPHEREx will help astronomers understand both how our universe evolved and how common are the ingredients for life in our galaxy’s planetary systems. Credits: Caltech
NASA has selected Space Exploration Technologies (SpaceX) of Hawthorne, California, to provide launch services for the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) mission.
SPHEREx is a planned two-year astrophysics mission to survey the sky in the near-infrared light, which, though not visible to the human eye, serves as a powerful tool for answering cosmic questions involving the birth of the universe, and the subsequent development of galaxies.
It also will search for water and organic molecules – essentials for life as we know it – in regions where stars are born from gas and dust, known as stellar nurseries, as well as disks around stars where new planets could be forming. Astronomers will use the mission to gather data on more than 300 million galaxies, as well as more than 100 million stars in our own Milky Way galaxy.
The total cost for NASA to launch SPHEREx is approximately $98.8 million, which includes the launch service and other mission related costs.
The SPHEREx mission currently is targeted to launch as early as June 2024 on a Falcon 9 rocket from Space Launch Complex-4E at Vandenberg Air Force Base in California.
NASA’s Launch Services Program at the agency’s Kennedy Space Center in Florida will manage the SpaceX launch service. The mission, which is funded by the Astrophysics Division of NASA’s Science Mission Directorate at the agency’s headquarters in Washington, is led by the Explorer’s Program at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. NASA’s Jet Propulsion Laboratory in Southern California is responsible for the mission’s overall project management, systems engineering, integration, and testing and mission operations.
This illustration shows NASA’s Cassini spacecraft flying through plumes on Enceladus in October 2015. Credit: NASA/JPL-Caltech
Several years ago, planetary scientist Lynnae Quick began to wonder whether any of the more than 4,000 known exoplanets, or planets beyond our solar system, might resemble some of the watery moons around Jupiter and Saturn. Though some of these moons don’t have atmospheres and are covered in ice, they are still among the top targets in NASA’s search for life beyond Earth. Saturn’s moon Enceladus and Jupiter’s moon Europa, which scientists classify as “ocean worlds,” are good examples.
“Plumes of water erupt from Europa and Enceladus, so we can tell that these bodies have subsurface oceans beneath their ice shells, and they have energy that drives the plumes, which are two requirements for life as we know it,” says Quick, a NASA planetary scientist who specializes in volcanism and ocean worlds. “So if we’re thinking about these places as being possibly habitable, maybe bigger versions of them in other planetary systems are habitable too.”
Quick, of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, decided to explore whether—hypothetically—there are planets similar to Europa and Enceladus in the Milky Way galaxy. And, could they, too, be geologically active enough to shoot plumes through their surfaces that could one day be detected by telescopes.
Through a mathematical analysis of several dozen exoplanets, including planets in the nearby TRAPPIST-1 system, Quick and her colleagues learned something significant: More than a quarter of the exoplanets they studied could be ocean worlds, with a majority possibly harboring oceans beneath layers of surface ice, similar to Europa and Enceladus. Additionally, many of these planets could be releasing more energy than Europa and Enceladus.
Scientists may one day be able to test Quick’s predictions by measuring the heat emitted from an exoplanet or by detecting volcanic or cryovolcanic (liquid or vapor instead of molten rock) eruptions in the wavelengths of light emitted by molecules in a planet’s atmosphere. For now, scientists cannot see many exoplanets in any detail. Alas, they are too far away and too drowned out by the light of their stars. But by considering the only information available—exoplanet sizes, masses and distances from their stars—scientists like Quick and her colleagues can tap mathematical models and our understanding of the solar system to try to imagine the conditions that could be shaping exoplanets into livable worlds or not.
While the assumptions that go into these mathematical models are educated guesses, they can help scientists narrow the list of promising exoplanets to search for conditions favorable to life so that NASA’s upcoming James Webb Space Telescope or other space missions can follow up.
“Future missions to look for signs of life beyond the solar system are focused on planets like ours that have a global biosphere that’s so abundant it’s changing the chemistry of the whole atmosphere,” says Aki Roberge, a NASA Goddard astrophysicist who collaborated with Quick on this analysis. “But in the solar system, icy moons with oceans, which are far from the heat of the Sun, still have shown that they have the features we think are required for life.”
To look for possible ocean worlds, Quick’s team selected 53 exoplanets with sizes most similar to Earth, though they could have up to eight times more mass. Scientists assume planets of this size are more solid than gaseous and, thus, more likely to support liquid water on or below their surfaces. At least 30 more planets that fit these parameters have been discovered since Quick and her colleagues began their study in 2017, but they were not included in the analysis, which was published on June 18 in the journal Publications of the Astronomical Society of the Pacific.
With their Earth-size planets identified, Quick and her team sought to determine how much energy each one could be generating and releasing as heat. The team considered two primary sources of heat. The first, radiogenic heat, is generated over billions of years by the slow decay of radioactive materials in a planet’s mantle and crust. That rate of decay depends on a planet’s age and the mass of its mantle. Other scientists already had determined these relationships for Earth-size planets. So, Quick and her team applied the decay rate to their list of 53 planets, assuming each one is the same age as its star and that its mantle takes up the same proportion of the planet’s volume as Earth’s mantle does.
This animated graph shows levels of predicted geologic activity among exoplanets, with and without oceans, compared to known geologic activity among solar system bodies, with and without oceans. Credit: Lynnae Quick & James Tralie/NASA’s Goddard Space Flight Center
Next, the researchers calculated heat produced by something else: tidal force, which is energy generated from the gravitational tugging when one object orbits another. Planets in stretched out, or elliptical, orbits shift the distance between themselves and their stars as they circle them. This leads to changes in the gravitational force between the two objects and causes the planet to stretch, thereby generating heat. Eventually, the heat is lost to space through the surface.
One exit route for the heat is through volcanoes or cryovolcanoes. Another route is through tectonics, which is a geological process responsible for the movement of the outermost rocky or icy layer of a planet or moon. Whichever way the heat is discharged, knowing how much of it a planet pushes out is important because it could make or break habitability.
For instance, too much volcanic activity can turn a livable world into a molten nightmare. But too little activity can shut down the release of gases that make up an atmosphere, leaving a cold, barren surface. Just the right amount supports a livable, wet planet like Earth, or a possibly livable moon like Europa.
In the next decade, NASA’s Europa Clipper will explore the surface and subsurface of Europa and provide insights about the environment beneath the surface. The more scientists can learn about Europa and other potentially habitable moons of our solar system, the better they’ll be able to understand similar worlds around other stars—which may be plentiful, according to today’s findings.
“Forthcoming missions will give us a chance to see whether ocean moons in our solar system could support life,” says Quick, who is a science team member on both the Clipper mission and the Dragonfly mission to Saturn’s moon Titan. “If we find chemical signatures of life, we can try to look for similar signs at interstellar distances.”
When Webb launches, scientists will try to detect chemical signatures in the atmospheres of some of the planets in the TRAPPIST-1 system, which is 39 light years away in the constellation Aquarius. In 2017, astronomers announced that this system has seven Earth-size planets. Some have suggested that some of these planets could be watery, and Quick’s estimates support this idea. According to her team’s calculations, TRAPPIST-1 e, f, g and h could be ocean worlds, which would put them among the 14 ocean worlds the scientists identified in this study.
The researchers predicted that these exoplanets have oceans by considering the surface temperatures of each one. This information is revealed by the amount of stellar radiation each planet reflects into space. Quick’s team also took into account each planet’s density and the estimated amount of internal heating it generates compared to Earth.
“If we see that a planet’s density is lower than Earth’s, that’s an indication that there might be more water there and not as much rock and iron,” Quick says. And if the planet’s temperature allows for liquid water, you’ve got an ocean world.
“But if a planet’s surface temperature is less than 32 degrees Fahrenheit (0 degrees Celsius), where water is frozen,” Quick says, “then we have an icy ocean world, and the densities for those planets are even lower.”
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