Dwarf Planet Ceres is an ocean world with salty water under the surface, NASA mission finds

Ceres is a dwarf planet and the largest known object in the asteroid belt between Mars and Jupiter. And now we know it may be an ocean world with intriguing geologic activity taking place on and just below its surface. While this global ocean beneath the planet’s surface likely froze over time, remnants of it may still be present beneath a large impact crater on Ceres.

The presence of salts may have preserved the liquid as a brine, despite cold temperatures. The suite of seven studies published Monday in the journals Nature Astronomy, Nature Geoscience, and Nature Communications. Between 2011 and 2018, NASA’s Dawn mission embarked on a 4.3 billion-mile journey to two of the largest objects in our solar system’s main asteroid belt.

Ceres is about 592 miles across, 14 times smaller than Pluto. Dawn visited Vesta and Ceres, becoming the first spacecraft to orbit two deep-space destinations. This new research is based on observations made during Dawn’s orbit of Ceres between 2015 and 2018, including close passes it made of the dwarf planet just 22 miles above the surface toward the end of the mission.

During that time, Dawn was focused on the 57-mile-wide Occator Crater, a 22-million-year-old feature that appeared to showcase bright spots.

These eye-catching characteristics were discovered to be sodium carbonate, or a compound including oxygen, carbon, and sodium. But it was unclear how those bright spots came to be in the crater. Data from the end of Dawn’s mission revealed an extensive and slushy reservoir of brine, or salty liquid, beneath the crater. It is 25 miles deep and extends out for hundreds of miles.

When the impact that created the crater struck Ceres, it may have allowed the reservoir to deposit bright salts visible in the crater by fracturing the planet’s crust. As the fractures reached the salty reservoirs, the brine was able to reach the surface of the crater floor. As the water evaporated, a bright, salty crust remained behind. And brines may still be rising to the surface today, which suggests the activity on Ceres is not due to melting that may have occurred when the planet was impacted.

In fact, Dawn’s data also indicated the presence of hydrated chloride salts at the center of the largest bright area at the crater’s center, called Cerealia Facula. This hydrohalite compound is common in marine ice on Earth, but it is the first time hydrohalite has been found outside of our planet. The salts appear to dehydrate fairly quickly on the surface, at least, astronomically speaking.

This dehydration occurs over hundreds of years.

But the measurements taken by Dawn showed water was still present. This suggests that brine may still be rising to the surface of the crater and that salty liquid could still exist inside of Ceres. For the large deposit at Cerealia Facula, the bulk of the salts were supplied from a slushy area just beneath the surface that was melted by the heat of the impact that formed the crater about 20 million years ago.

The impact heat subsided after a few million years. However, the impact also created large fractures that could reach the deep, long-lived reservoir, allowing brine to continue percolating to the surface. There are also mounds and hills visible in the crater likely created when flows of water froze in place, suggesting geologic activity on Ceres. These conical hills are similar to pingos on Earth, or small mountains made of ice found in the polar regions.

Although features like this have also been found on Mars, it is the first time they have been spotted on a dwarf planet. The pingo-like structures and the water that pushes up through fractures in the crater revealed that Ceres actually experienced cryovolcanic activity, or ice volcanoes, beginning around 9 million years ago. The process is likely ongoing.

This kind of cryovolcanic activity has been witnessed on icy moons in the outer solar system, with plumes of material ejecting into space.

But it was never expected to occur on dwarf planets or asteroids in the asteroid belt, which are thought to be waterless and inactive. Ceres changes that theory because it has proven to be water-rich and definitely active. A survivor from the earliest days of the solar system as it formed 4.5 billion years ago, Ceres was more of an “embryonic planet”. Essentially, it started to form, but never finished.

Jupiter, the largest planet in our solar system, and the force of its gravity likely stunted Ceres’ growth. So around 4 billion years ago, Ceres found its home in the asteroid belt along with all of the other leftovers from the formation of the solar system. The idea that liquid water can remain preserved on dwarf planets and asteroids is an intriguing one for scientists.

Unlike other icy ocean worlds in our solar system, such as Saturn’s moon Enceladus and Jupiter’s moon Europa, asteroids and dwarf planets do not experience internal heating. Enceladus and Europa benefit from internal heating that occurs when they interact gravitationally with the massive planets they orbit. The Dawn mission ended in 2018 when the spacecraft ran out of fuel and could no longer communicate with NASA.

It was placed into long-term orbit around Ceres that will prevent impact, protecting its organic materials and subsurface liquid.

The findings made possible by the Dawn mission have scientists eager to explore the dwarf planet and its potential for life in greater detail in the future. While there is not currently another mission planned for exploring Ceres, two upcoming missions will explore Jupiter and its icy moons Ganymede, Callisto, and Europa. Dawn accomplished far more than scientists hoped when it embarked on its extraordinary extraterrestrial expedition.

These exciting new discoveries from the end of its long and productive mission are a wonderful tribute to this remarkable interplanetary explorer. The asteroid Ceres, once thought to be just a large rock orbiting between Mars and Jupiter, has slushy volcanoes and liquid saltwater beneath its surface that may have formed an underground ocean in the past, new research suggests. The research is part of seven studies of Ceres using data from NASA’s Dawn robot spacecraft, published in the journals Nature Astronomy, Nature Geoscience, and Nature Communications.

Two of the studies indicate that a bright spot in the large Occator crater of Ceres is caused by saltwater seeping from fractures in the rocky crust. That suggests Ceres has buried reservoirs of saltwater and may still have an underground ocean. Ongoing activity in Occator brings additional and independent evidence for a deep brine layer, and upgrades Ceres to the realm of ocean worlds.

Although Saturn’s moon Enceladus and Jupiter’s moon Europa are thought to have subsurface oceans, they are both much warmer than the nearly-frozen reservoirs of saltwater on Ceres.

But the frozen dwarf planet Pluto may also have had subsurface oceans, and the new studies of Ceres could have implications for future investigations of icy worlds. Ceres, currently about 200 million miles from Earth, is the largest object in our solar system’s main asteroid belt. It is almost 600 miles across, with gravity strong enough to pull it into a rough sphere.

Under the rules of the International Astronomical Union, that makes asteroid Ceres a dwarf planet, perhaps the only dwarf planet closer than Pluto. NASA’s Dawn probe was launched in 2007 and spent years traveling to the asteroid belt with its slow but extremely efficient ion engine. From 2011 until 2012, NASA’s Dawn probe orbited the asteroid Vesta, the second-largest object in the asteroid belt at 320 miles across.

NASA’s Dawn probe arrived at Ceres in 2015 and studied it until 2018, orbiting to within 25 miles of the asteroid’s surface before it finally ran out of fuel. Early studies of Ceres using Dawn mission data suggested it had a residual saltwater layer, and the latest studies have strengthened that idea. The more data the scientists got, it became very clear that there was geologic activity.

There were fluids arriving at the surface fairly recently.

Another study led by planetary scientist Maria Cristina De Sanctis of Italy’s National Institute of Astrophysics (INAF) in Rome determined the bright spot at Occator crater contains a form of sodium chloride chemically bound to molecules of water. That chemical form rapidly dries out, which leads scientists to conclude it is extremely recent in geological time. It could be 100,000 years ago, or a thousand years ago, or even last week.

Another study interprets some other bright spots on Ceres as evidence of “cryovolcanoes” that allow icy saltwater from reservoirs in the crust to seep on to the surface. Taken together, the studies suggest Ceres is an active world, although it is very cold, with temperatures of around minus 100 degrees Fahrenheit in the sunlight. The buried reservoirs, more than eight times saltier than oceans on Earth, are thought to start about 25 miles below the crust and have a temperature of about minus 31 degrees Fahrenheit, warm enough to have the consistency of slushy mud, but much too cold for life to evolve.

Yet Ceres is much more interesting that anyone expected, and scientists are pushing for a second probe to follow Dawn to the asteroid. The idea that Ceres ever had a buried saltwater layer is controversial however, and some scientists think the latest studies are not conclusive. There is no solid evidence for a past ocean on Ceres based on the papers.

The presence of hydrated silicates and local salts at the surface suggests water-rock interaction in Ceres’ history, but not necessarily an ocean.

Even if an ocean existed, it should be stripped away very early in the history of Ceres. But other scientists are warmer to the idea. These papers constrain the compositions of the liquids and the order in which they were emplaced on the surface is a stunningly detailed timeline of brine-driven cryovolcanism on Ceres. Earlier this year, nevertheless, another group of scientists announced the first use of a radio telescope to detect an exoplanet.

Painstaking and cautious analysis of the data revealed that the star was not taking a trip in a perfectly straight line, but was taking a trip more of a snaking course. The periodicity and amplitude of the wiggle revealed a planet on a 221-day orbit, and between 38 and 46 percent of the mass of Jupiter, a little bigger than Saturn, which is around 30 percent of the mass of Jupiter. Giant worlds, like Jupiter and Saturn, are expected to be uncommon around little stars like this one, and the astrometric technique is best at finding Jupiter-like worlds in broad orbits, so the astronomers were surprised to discover a lower mass, Saturn-like world in a reasonably compact orbit.

Astronomers expected to find a bigger world, comparable to Jupiter, in a wider orbit. The astrometric method is more frequently utilized to study binary stars, whose gravitational effect on each other is a lot more pronounced than the effect of a planet on a star. The astrometric strategy has been utilized to discover an exoplanet, although it has been utilized to study already-known exoplanets, and never before with a radio telescope.

It was not through astrometry, however by discovering the circular polarization of radio waves created by a world’s movement through a red electromagnetic field.

Although the detection was rather challenging, the astronomers’ success verifies the guarantee of both radio telescopes and the astrometric strategy in discovering planets that other methods miss out on. The Gaia telescope is presently surveying the Milky Way, developing the most in-depth and accurate astrometric map of the galaxy yet. It is anticipated that this information will blow astrometric exoplanet detection broad open, with an estimated 10s of countless exoplanet discoveries to come.

The research study has been published in The Astronomical Journal. The freshly found exoplanet, with a mass equivalent to that of Saturn, is located about 35 light-years away. However, it is not simply the planet, nor the star, that is so innovative here. What is particularly unique in this discovery is how astronomers used a radio telescope to track the movement of the star through the Milky Way, and identify the snaking wiggle because motion as the star is gravitationally impacted by an orbiting exoplanet.

This extremely tricky achievement is called the astrometric method, and it is the very first time it has been successfully deployed utilizing a radio telescope. Using an orbital wobble to spot an exoplanet is not a new idea. The orbital centre of a planetary system is not in the middle of the star. Rather, all bodies in the system orbit a mutual centre of gravity, called the barycentre.

The barycentre of the Solar System, for example, is just outside the surface area of the Sun, generally due to the gravitational influence of planets Jupiter and Saturn.

When we are looking at other stars with enormous, carefully orbiting exoplanets, this result can be detected in the way light wavelengths are extended or compressed as the star moves around. This detection method is called Doppler spectroscopy, or the radial speed technique, and it is one of the more typical methods for discovering exoplanets. The hunt for exoplanets in our galaxy is a deeply important endeavor.

The more exoplanets we discover, the better we can comprehend our own Solar System, and how life emerges in the Universe. To date, over 4,000 exoplanets have been verified, but a new discovery might expand the search, helping us to find exoplanets that formerly have shown too difficult to discover. The astrometric technique is a little bit different. The Milky Way’s stars are not repaired in space.

They move the galaxy, and the study of this movement is called astrometry. Rather than utilizing modifications in wavelengths, the astrometric strategy looks for variances from a straight line of motion. This technique can be utilized to discover exoplanets that Doppler spectroscopy can not, such as exoplanets circling in larger orbits around their stars.

The astronomers’ method matches the radial speed method, which is more sensitive to worlds orbiting in close orbits, while the astronomers’ method is more conscious massive worlds in orbits even farther from the star.

Indeed, these other techniques have discovered just a few planets with characteristics such as world mass, orbital size, and host star mass, comparable to the planet the astronomers discovered. The VLBA, and the astrometry method in general, could reveal lots of more comparable planets. The VLBA is the Very Long Baseline Array, a network of 10 radio antennas widely dispersed throughout the United States.

For 18 months starting in June 2018, the research group tracked a small star called TVLM 513-46546 across space for a year and a half.

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