planet Study

Blue planet: Study proposes new origin theory for Earth’s abundant water – The Times of Israel

AFP — Water covers 70 percent of the Earth’s surface and is crucial to life as we know it, but how it got here has been a longstanding scientific debate.

The puzzle was a step closer to being solved Thursday after a French team reported in the journal Science they had identified which space rocks were responsible, and suggested our planet has been wet ever since it formed.

Cosmo-chemist Laurette Piani, who led the research, told AFP the findings contradicted the prevalent theory that water was brought to an initially dry Earth by far-reaching comets or asteroids.

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Asteroids are rocky celestial objects that orbit the sun; comets are made of ice and dust, and also orbit the sun; and meteoroids are much smaller objects, mostly fragments of asteroids and comets.

According to early models for how the Solar System came to be, the large disks of gas and dust that swirled around the Sun and eventually formed the inner planets were too hot to sustain ice.

This would explain the barren conditions on Mercury, Venus and Mars — but not our blue planet, with its vast oceans, humid atmosphere and well-hydrated geology.

Scientists therefore theorized that the water came along after, and the prime suspects were meteorites known as carbonaceous chondrites that are rich in hydrous minerals.

But the problem was that their chemical composition doesn’t closely match our planet’s rocks.

The carbonaceous chondrites also formed in the outer Solar System, making it less likely they could have pelted the early Earth.

Stars move in the night sky during the Perseid meteor shower in the Pineios Lake near the village of Velanidi, Peloponnese, Greece, August 13, 2020. (AP Photo/Petros Giannakouris)

Planetary building blocks

Another group of meteorites, called enstatite chondrites, are a much closer chemical match, containing similar isotopes, or types, of oxygen, titanium and calcium.

This indicates they were Earth’s and the other inner planets’ building blocks.

However, because these rocks formed close to the Sun, they had been assumed to be too dry to account for Earth’s rich reservoirs of water.

To test whether this was really true, Piani and her colleagues at Centre de Recherches Petrographiques et Geochimiques (CRPG, CNRS/Universite de Lorraine) used a technique called mass spectrometry to measure the hydrogen content in 13 enstatite chondrites.

The rocks are now quite rare, making up only about two percent of known meteorites in collections, and it is hard to find them in pristine, uncontaminated condition.

The team found that the rocks contained enough hydrogen in them to provide Earth with at least three times the water mass of its oceans — and possibly much more.

They also measured two isotopes of hydrogen, because the relative proportion of these is very different from one celestial object to another.

“We found the hydrogen isotopic composition of enstatite chondrites to be similar to the one of the water stored in the terrestrial mantle,” said Piani, comparing it to a DNA match.

The isotopic composition of the oceans was found to be consistent with a mixture containing 95 percent of water from the enstatite chondrites — more proof these were responsible for the bulk of Earth’s water.

The authors further found that the nitrogen isotopes from the enstatite chondrites are similar to Earth’s — and proposed these rocks could also be the source of the most abundant component of our atmosphere.

Piani added that research doesn’t exclude later addition of water by other sources like comets, but indicates that enstatite chondrites contributed significantly to Earth’s water budget at the time the planet formed.

The work “brings a crucial and elegant element to this puzzle” wrote Anne Peslier, a planetary scientist for NASA, in an accompanying editorial.

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Dwarf planet

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

(CNN)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, according to new research.

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’s 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’s 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,” said Carol Raymond, Dawn’s principal investigator at NASA’s Jet Propulsion Laboratory in California, in a statement.
“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’s the first time they’ve been spotted on a dwarf planet.

An unusual 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 don’t 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: Europa Clipper and JUICE, or JUpiter ICy moons Explorer.
“Dawn accomplished far more than we hoped when it embarked on its extraordinary extraterrestrial expedition,” said Marc Rayman, Dawn’s mission director at JPL, in a statement. “These exciting new discoveries from the end of its long and productive mission are a wonderful tribute to this remarkable interplanetary explorer.”

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Ceres planet

Planet Ceres is an ‘ocean world’ with sea water beneath surface, mission finds – The Guardian

The dwarf planet Ceres long believed to be a barren space rock is an ocean world with reservoirs of sea water beneath its surface, the results of a major exploration mission showed on Monday.
Ceres …
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planet reserves

Planet reserves rideshare slots on SpaceX Starlink launches – Spaceflight Now

Two SkySat satellites receive their supply of “green” propellant before a launch on a Vega rocket from French Guiana in 2016. Credit: ESA/CNES/Arianespace – Photo Optique Video du CSG – P. Baudon

Three of Planet’s commercial SkySat Earth-imaging spacecraft will ride to space on top of a stack of SpaceX Starlink satellites next month aboard a Falcon 9 rocket, and three more will hitch a ride on another SpaceX mission later this summer.

Planet announced the rideshare launch agreement with SpaceX on Wednesday, confirming plans to launch six satellites on two previously-scheduled Falcon 9 missions carrying more of SpaceX’s Starlink broadband satellites into orbit.

The first three SkySat satellites will fly into orbit on SpaceX’s dedicated ninth Starlink mission planned for launch from Cape Canaveral some time in June, Planet said. Three more SkySat spacecraft will launch on a Starlink mission later this summer.

Mike Safyan, vice president of launch for San Francisco-based Planet, said the SkySat satellites will be mounted at the very top of the stack of Starlink payloads inside the fairing on each Falcon 9 flight. The SkySats will attach to the Starlink stack using a custom adapter.

Built by Maxar, each of the SkySat satellites weighs around 242 pounds (110 kilograms) at launch. The SkySats are about the side of a mini-refrigerator, and their optical instruments produce images of Earth with a resolution of less than 2.4 feet, or about 72 centimeters, according to Planet.

A view of 60 Starlink satellites stacked before a previous Falcon 9 launch. Credit: SpaceX

With somewhere between 100 and 150 Earth-imaging spacecraft in its fleet, Planet operates the world’s second-largest constellation of commercial satellites after SpaceX’s Starlink Internet network. Planet’s fleet includes Dove CubeSats designed for quick-response imaging, and 15 SkySats to capture sharper views of Earth.

The first 15 SkySat satellites launched into polar sun-synchronous orbits and fly in in north-south paths around Earth. Sun-synchronous orbits are popular for remote sensing and environmental satellites because they allow regular imaging of the Earth’s surface with the sun at the same angle.

“About half of the SkySats currently pass overhead in a morning crossing plane, while the other half moves in an afternoon crossing plane, so together they provide twice-daily coverage of select areas on a global scale,” Safyan wrote on Planet’s website. “SkySats 16-21 will operate at a ‘mid-inclination’ orbit of 53 degrees, complementing the sun-synchronous fleet, and will offer more targeted coverage and raw image capacity in key geographic regions.”

Starlink satellites fly in the same type of orbit at an inclination of 53 degrees. Safyan told Spaceflight Now the SkySats will use their own propulsion to maneuver from the Starlink injection orbit to an operating altitude of around 250 miles (400 kilometers).

The first 15 SkySats have launched on a range of rockets, riding a Ukrainian-Russian Dnepr booster in 2013, a Russian Soyuz launcher in 2014, an Indian PSLV and a European Vega rocket in 2016, Northrop Grumman’s Minotaur-C rocket in 2017, and a Falcon 9 mission in 2018.

SpaceX is selling capacity on Starlink launches to other companies who want to book rides for small satellites, offering an online booking system for prospective customers. SpaceX says launch prices for a rideshare payload of up to 440 pounds, or 200 kilograms, start at $1 million.

In addition to selling excess room on Starlink missions, SpaceX is planning as many as three dedicated Falcon 9 rideshare launches per year to sun-synchronous orbit. The first of the company’s dedicated rideshare missions is scheduled for December from Vandenberg Air Force Base in California.

One of Planet’s SkySat Earth-viewing satellites captured this angled, “off-nadir” view of Shanghai in 2018. Credit: Planet

The rideshare launches are similar to a sun-synchronous orbit multi-satellite launch from Vandenberg on a Falcon 9 rocket in December 2018. But that mission was managed by Spaceflight, a rideshare launch broker based in Seattle, which purchased the entire capacity of a Falcon 9 rocket and sold slots to commercial and government customers.

Now SpaceX itself is putting together rideshare launches, selling slots directly to satellite operators and brokers that then distribute mass and volume allotments to their customers.

The majority of SpaceX’s launches this year will add satellites to the Starlink fleet, which is designed to beam broadband Internet service to consumers around the world. The first phase of the Starlink network will include 1,584 satellites in low Earth orbit, but SpaceX eventually plans to launch thousands more on dozens of Falcon 9 missions.

The flat-panel Starlink satellites launch in a stack inside the Falcon 9 rocket’s payload fairing. Each Starlink craft weighs more than a quarter ton, and a load of 60 of the satellites weighs more than 34,000 pounds (15.6 metric tons).

Gwynne Shotwell, SpaceX’s president and chief operating officer, said in December that she hopes to book rideshare payloads on all of the company’s Starlink launches. If necessary, SpaceX could reduce the number of Starlink satellites on a particular launch to accommodate a secondary payload.

“You can take a satellite off, or if it’s super tiny, you can just put it on the top,” Shotwell said.

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Follow Stephen Clark on Twitter: @StephenClark1.

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