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The Moon might be older than scientists previously thought — a new study shines light on its history
2024-12-20 - 2024-12
The Moon might be older than scientists previously thought — a new study shines light on its history
A physicist, a chemist and a mathematician walk into a bar. It sounds like the start of a bad joke, but in my case, it was the start of an idea that could reshape how scientists think about the history of the Moon.
The three of us were all interested in the Moon, but from different perspectives: As a geophysicist, I thought about its interior; Thorsten Kleine studied its chemistry; and Alessandro Morbidelli wanted to know what the Moon’s formation could tell us about how the planets were assembled 4.5 billion years ago.
When we got together to discuss how old the Moon really was, having those multiple perspectives turned out to be crucial.
How did the Moon form?
At a conference in Hawaii in the late 1980s, a group of scientists solved the problem of how the Moon formed. Their research suggested that a Mars-size object crashed into the early Earth, jettisoning molten material into space. That glowing material coalesced into the body now called the Moon.
This story explained many things. For one, the Moon has very little material that evaporates easily, such as water, because it began life molten. It has only a tiny iron core, because it was mostly formed from the outer part of the Earth, which has very little iron. And it has a buoyant, white-colored crust made from minerals that floated to the surface as the molten Moon solidified.
The glowing, newly formed Moon was initially very close to the Earth, at roughly the distance that TV satellites orbit. The early Moon would have raised gigantic tides on the early Earth, which itself was mostly molten and spinning rapidly.
These tides took energy from the Earth’s spin and transferred some to the Moon’s orbit, slowly pushing the Moon away from the Earth and slowing the Earth’s spin as they did so. This motion continues today – the Moon still recedes from the Earth about 2 inches per year.
As the Moon moved away, it passed through particular points where its orbit temporarily became disturbed. These orbital disturbances were an important component of its history and are a key part of our hypothesis.
Ancient Mars' thick crust could have supported hidden water reservoirs and rare magmas, new research suggests
2024-12-19 - 2024-12
The study, led by Rice University's Cin-Ty Lee, demonstrates that the southern highlands' thick crust—up to 80 kilometers in some areas—was hot enough during the Noachian and early Hesperian periods (3–4 billion years ago) to undergo partial melting in the lower crust. This process, driven by radioactive heating, could have produced significant amounts of silicic magmas such as granites and supported subsurface aquifers beneath a frozen surface layer.
"Our findings indicate that Mars' crustal processes were far more dynamic than previously thought," said Lee, the Harry Carothers Wiess Professor of Geology and professor of Earth, environmental and planetary sciences.
"Not only could thick crust in the southern highlands have generated granitic magmas without plate tectonics, but it also created the thermal conditions for stable groundwater aquifers—reservoirs of liquid water—on a planet we've often considered dry and frozen."
The research team—including Rice professors Rajdeep Dasgupta and Kirsten Siebach, postdoctoral research associate Duncan Keller, graduate students Jackson Borchardt and Julin Zhang and Patrick McGovern of the Lunar and Planetary Institute—employed advanced thermal modeling to reconstruct the thermal state of Mars' crust during the Noachian andearly Hesperian periods. By considering factors such as crustal thickness, radioactive heat generation and mantle heat flow, the researchers simulated how heat affected the potential for crustal melting and groundwater stability.
Intl. congress on nanoscience, nanotechnology slated for January
2024-12-20 - 2024-12
2 populations of dark comets in the solar system could tell researchers where the Earth got its oceans
Published: December 20, 2024 1.16pm GMT
The water that makes up the oceans acted as a key ingredient for the development of life on Earth. However, scientists still do not know where the water here on Earth came from in the first place.
One leading idea is that space rocks such as comets and asteroids delivered water to the Earth through impacts. As a planetary scientist, I’m curious about the kinds of space objects that could have led to the formation of the oceans. For the past few years, I’ve been studying a type of object that I called a dark comet – which could be just the culprit. In a new study my colleagues and I published in December 2024, we discovered two classes of these elusive dark comets
What is a comet?
The solar system is teaming with small bodies such as comets and asteroids. These space rocks were fundamental building blocks of planets in the early solar system, while the remaining leftovers are the comets and asteroids seen today.
These objects are also avenues by which material can be transported throughout the solar system. These small worlds can contain things such as rubble, ice and organic material as they fly through space. That’s why researchers see them as good potential candidates for delivering ices such as water and carbon dioxide to the Earth while it was forming.
Traditionally, the difference between comets and asteroids is that comets have beautiful cometary tails. These tails form because comets have ice in them, while asteroids supposedly do not.
When a comet gets close to the Sun, these ices heat up and sublimate, which means they turn from ice into gas. The gas heats up because of the sunlight and is then blown off the comet’s surface in a process called outgassing. This outgassing brings with it rubble and small dust grains, which reflect sunlight.
Asteroids, on the other hand, do not have cometary tails. Presumably, they are more like classic rocks – without ice on their surfaces.
What is a nongravitational acceleration?
The outgassing material from the surface of a comet produces a cometary tail and a rocketlike recoil. The fast moving gas pushes on the surface of the comet, and this causes it to accelerate. This process drives comets’ motion through space on top of the motion set by the gravitational pull of the Sun.
So, when comets outgas, they have what planetary scientists call nongravitational acceleration – motion that isn’t caused by the gravity of objects in the solar system. Planetary scientists typically measure the nongravitational accelerations of comets after detecting their cometary tails.
What are dark comets?
Our team identified a class of small bodies in the solar system that take some of the properties of both comets and asteroids. We called them dark comets.
These dark comets have nongravitational accelerations like comets, so they experience a rocketlike recoil from co
