Ti paternity test fingers Earth Moon's parent

Wolfram-Alpha

Steve Koppes
UChicagoNews

A new chemical analysis of lunar material collected by Apollo astronauts in the 1970s conflicts with the widely held theory that a giant collision between Earth and a Mars-sized object gave birth to the moon 4.5 billion years ago.

In the giant-collision scenario, computer simulations suggest that the moon had two parents: Earth and a hypothetical planetary body that scientists call “Theia.” But a comparative analysis of titanium from the moon, Earth and meteorites, published by Junjun Zhang, graduate student in geophysical sciences at the University of Chicago, and four co-authors indicates the moon’s material came from Earth alone.

If two objects had given rise to the moon, “Just like in humans, the moon would have inherited some of the material from the Earth and some of the material from the impactor, approximately half and half,” said Nicolas Dauphas, associate professor in geophysical sciences at UChicago, and co-author of the study, which appears in the March 25 edition of Nature Geoscience.

“What we found is that the child does not look any different compared to the Earth,” Dauphas said. “It’s a child with only one parent, as far as we can tell.”

The research team based their analysis on titanium isotopes — forms of titanium that contain only slight subatomic variations. The researchers selected titanium for their study because the element is highly refractory. This means that titanium tends to remain in a solid or molten state rather than becoming a gas when exposed to tremendous heat. The resistance of titanium isotopes to vaporization makes it less likely that they would become incorporated by the Earth and the developing moon in equal amounts.

Titanium also contains different isotopic signatures forged in countless stellar explosions that occurred before the sun’s birth. These explosions flung subtly different titanium isotopes into interstellar space. Different objects in the newly forming solar system gobbled up those isotopes in different ways through collisions, leaving clues that let scientists infer where the solar materials including the moon came from.
Planetary DNA

“When we look at different bodies, different asteroids, there are different isotopic signatures. It’s like their different DNAs,” Dauphas said. Meteorites, which are pieces of asteroids that have fallen to Earth, contain large variations in titanium isotopes. Measurements of terrestrial and lunar samples show that “the moon has a strictly identical isotopic composition to the Earth,” he said.

“We thought that the moon had two parents, but when we look at the composition of the moon, it looks like it has only one parent,” Zhang said.

Zhang initially found variations in the titanium isotopic composition between the lunar and terrestrial samples. She then corrected the results for the effects of cosmic rays, which could have changed the titanium isotopic composition of the lunar samples.

The Earth and the moon are constantly bombarded by cosmic rays from the sun and from more distant sources in the galaxy. Earth’s atmosphere and magnetic field prevents most of these rays from reaching its surface, but the moon has no such protection.

“We compared the titanium isotopic composition with samarium and gadolinium since those two systems are very sensitive to the cosmic-ray effect,” Zhang said. The only compositional differences the scientists expected to see in samarium and gandolinium between Earth and moon would be the result of cosmic rays. “We found a very nice linear correlation between titanium and samarium or gadolinium,” she said.

Zhang’s titanium analyses greatly reinforce previous work by other researchers who came to the same conclusion after comparing terrestrial and lunar oxygen isotopes, which are less refractory and thus more likely to gasify during a giant impact than titanium.
Lunar Conundrum

Solving the conundrum of the moon’s origin probably will prove challenging because all of the alternative scenarios for the moon’s formation have drawbacks.

For example, it is possible that even though titanium is refractory, it might still have gasified in the giant impact and then became incorporated into the disk of Earth-orbiting material that developed into the moon. This might have erased the signature of the titanium from Theia, which could explain the UChicago team’s observations. The problem with this scenario is that the disk may have fallen back to Earth if too much material was exchanged between the two bodies.

An old idea, long abandoned, is that the moon arose via fission from a molten, rapidly rotating Earth following a giant impact. This idea explains the similarity between Earth and moon, but how such a large, concentrated mass could spin fast enough to split in two remains problematical.

According to a third scenario, Earth collided with an icy body lacking entirely in titanium. There are no bodies made purely of ice in the solar system, however. “They would always have a significant fraction of solid material, so you would still expect the object to deliver some titanium,” Dauphas said.

It’s also possible that Theia had the same composition as Earth. This is unlikely, however, because of the widely accepted view that the Earth incorporated material over tens of millions of years in collisions with smaller bodies that flew in from different regions of the developing solar system.

“We thought we knew what the moon was made of and how it formed, but even 40 years after Apollo, there is still a lot of science to do with those samples that are in curatorial facilities at NASA,” Dauphas said.

Did the Moon come from Earth?

During the 1970's, scientists proposed that an object the size of Mars could have collided with Earth and thrown enough matter into orbit to create the Moon [Don Davis / The New Solar System].

Kelly Beatty
Sky & Telescope

"New findings show that Earth and the Moon have identical isotopic ratios of tungsten — and that's a problem for the widely accepted "big splat" hypothesis."

Read the full article HERE.

Ina of the Meniscus Hollows

Joel Raupe
Lunar Pioneer

Before my daughter left for college I tried to pass along a little advice Kurt Vonnegut once tried to impress upon me. I paraphrase: "warn your little Grade A students whom they shall inevitably meet on campus, no matter how gifted they may be. His name is Wolfgang Amadeus Mozart."

Such was the case yesterday only a few hours after posting "Whale of a hollow," which became an excuse to post a perspective shot of an extrusion dome on the geologically interesting southwestern edge of Mare Serenitatis.

The hollows perched on this isolated, but otherwise typical, mare extrusion dome resemble similar features discovered early in the Messenger survey of Mercury. We had a lot of images left over after a thorough study of this one site on the Moon from five months ago. And after simply stumbling on the "whale" structure, while we were examining a newly-released LROC Narrow Angle Camera (NAC) frame showing the Ranger 6 impact, we jumped on an excuse to discuss the Aratus-Serenitatis dome in that context; with the Ina structure and its distant cousin that also happens to resemble a cave dweller's rendition of a whale, or perhaps something one might see from the air flying over the plains of Nazca.

One of the better images of the Aratus-Serenitatis extrusion dome (24.77°N, 7.98°E), before LRO, is this 1971 Mapping Camera view (AS15-M-0410) from the Apollo 15 Service Module, 104 kilometers overhead. For a 21st century look at this dome, and in relief, an animated image demonstrating changes in the landscape during the long lunar day can be seen HERE [NASA/GSFC/Arizona State University].

Which brings us to "Mozart," who manifested almost immediately, first in the form of Phil Stooke, of Western Ontario University, a selenographer well-known for startlingly accurate maps of the Apollo landing sites before these were photographed for the first time in four decades from LRO. He also shares our interest in using the new and deep reservoir of LROC imagery to document the artifacts of human activity on the Moon, and he Emailed us after presenting a fairly comprehensive paper on the topic of lunar "meniscular hollows" at the 43rd Lunar and Planetary Science Conference underway in The Woodlands, Texas. Stooke gently recommended his paper, presented that very evening,

LUNAR MENISCUS HOLLOWS. P. J. Stooke, Department of Geography and Centre for Planetary Science and Exploration, University of Western Ontario, London, Ontario, Canada; 43rd Lunar and Planetary Science Conference (2012), #1011.

My first impression was how ridiculous the context view shown in yesterday's post appeared, one showing the location in Mare Tranquillitatis of the "whale" structure in its "serendipitous" relation to a nearby crater created by the 1964 impact of Ranger 6. That part of the floor of western Tranquillitatis, around the Ross and Arago crater and dome groupings, is crowded with these out-gas-formed "hollows." It will require some revision, to say the least. 

Figure 1. from LUNAR MENISCUS HOLLOWS, P.J. Stooke, U. Western Ontario, #1011, 43rd Lunar and Planetary Science Conference (2012), "Twenty Lunar Meniscus Hollows. Scales vary, image widths are between 300 and 1000 m, approximately." View a full-sized version of the plate HERE [Phil Stooke].

Of course, that's what's being said of all the lunar maps and textbooks these days, and that's a good thing.

The second question is an unfair one. Are there any such "blow-outs" on the Moon's farside? Even the Lunar Reconnaissance Orbiter Camera hasn't photographed the entire Moon in high-resolution, but it's close.

While examining his impressive catalog of 27 nearside hollows, as we prepared to show it off beyond the narrow confines required by the conference, YouTube videographer jayem4646 , who's work has appeared in these pages before, followed up on Stooke's note by calling attention to perhaps the best attempt so far to digest what's been so recently learned about the Ina structure, the "D caldera," and most famous of the lunar meniscus hollows.

It's seen in the embedded video above, way ahead of the Scientific Visualization Studio (SVS) at Goddard, and definitely in their class. 

We missed attending the LPSC this year, but it's warmed more than one heart knowing someone attending that grand meeting found the website useful, or at least amusing!

LSA2 - March 15, 16, 2012

The second annual Lunar Superconductor Applications Workshop (and other cold temperature technologies and science opportunities for the lunar polar regions) will be held March 15 and 16, 2012, at the Woodlands Waterway Marriot Convention Center (the same hotel as the LPSC) in Houston. Topics include high temperature superconductivity, low temperature power and electronics, cryogenic engineering and lunar science. Formal presentations are interspersed with informal design challenge discussions throughout the meeting. See more details on the website www.lsa2012.com

The single most important discovery in Lunar science is the confirmation of icy volatiles at the Lunar poles. This not only makes the Moon an exciting destination in its own right, but the Lunar poles are a Rosetta Stone for cryogenic chemistry and physics throughout the solar system and beyond.

Sessions: Thursday, March 15, 2012 • Cold Temperature Power Systems and Components • Cold Temperature Electronics • Design Challenge: LunarCubes for Deep Cryo  Friday, March 16, 2012 • Cold Temperature Science of and on the Lunar Surface • Engineering Systems and Instruments for Operating in and Gathering Measurements from Cold Temperature Environments • Design Challenge: TEGA vs. RESOLVE • Keynote Lunch Speaker: David Gump, President of Astrobotic Technology Inc.

Further evidence of recent lunar geologic activity

Close-up of the "Virtanen graben" field, near the 18.29°N, 180.79°E, on the central meridian of the lunar far side. From LROC Narrow Angle Camera observation M136355592RE (LRO orbit 5228, August 13, 2010; resolution 0.66 meters from 59.85 km). This LROC NAC frame, along with M136362376, were used by Mark Robinson and colleagues at Arizona State University to create a Digital Terrain Model of the Virtanen graben in November 2010. That DTM can be explored HERE.

Images and elevation models from NASA's Lunar Reconnaissance Orbiter (LRO) appear to show the Moon's crust is being stretched, forming miniature valleys in a few small places on the lunar surface. A team of investigators will present their findings at the upcoming Lunar and Planetary Science Conference as evidence that this geologic activity occurred less than 50 million years ago, a very recent time in relation to the Moon's estimated age of roughly 4.575 billion years.

Researchers analyzing high-resolution images obtained by the Lunar Reconnaissance Orbiter Camera (LROC) have shown many small, narrow trenches typically much longer than they are wide, indicating the lunar crust is being pulled apart at these locations. These linear valleys, known as graben, form when the moon's crust stretches, breaks and drops down along two bounding faults. A handful of these graben systems have already been identified across the lunar surface and are cited as evidence the Moon may be shrinking.

"We think the moon is in a general state of global contraction because of cooling of a still hot interior," said Thomas Watters of the Center for Earth and Planetary Studies at the Smithsonian's National Air and Space Museum, lead author of a paper on this research appearing in the March issue of the journal Nature Geoscience.

"The graben tell us forces acting to shrink the moon were overcome in places by forces acting to pull it apart. This means the contractional forces shrinking the moon cannot be large, or the small graben might never form."

Full width (about 5 km wide) of LROC NAC DTM"Virtanen
graben 1;" the small rectangle is the field of view seen in the
image above [NASA/GSFC/Arizona State University].

The weak contraction suggests that the moon, unlike terrestrial planets, did not completely melt in the very early stages of its evolution. Rather, observations support an alternative view that only the moon's exterior initially melted forming an ocean of molten rock.

In August 2010, the team used LROC images to identify physical signs of contraction on the lunar surface, in the form of lobe-shaped cliffs known as lobate scarps.

The scarps are evidence the moon shrank globally in the geologically recent past and might still be shrinking today. The team saw these scarps widely distributed across the moon and concluded it was shrinking as the interior slowly cooled.

Based on the size of the scarps, it is estimated that the distance between the moon's center and its surface shrank by approximately 300 feet. The graben were an unexpected discovery and the images provide contradictory evidence that the regions of the lunar crust are also being pulled apart.

"This pulling apart tells us the moon is still active," said Richard Vondrak, LRO Project Scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "LRO gives us a detailed look at that process."

As the LRO mission progresses and coverage increases, scientists will have a better picture of how common these young graben are and what other types of tectonic features are nearby. The graben systems the team finds may help scientists refine the state of stress in the lunar crust.

"It was a big surprise when I spotted graben in the far side highlands," said co-author Mark Robinson of the School of Earth and Space Exploration at Arizona State University, principal investigator of LROC. "I immediately targeted the area for high-resolution stereo images so we could create a three-dimensional view of the graben.  It's exciting when you discover something totally unexpected and only about half the lunar surface has been imaged in high resolution.  There is much more of the moon to be explored."

DERIVATION OF ABSOLUTE MODEL AGES FOR LUNAR LOBATE SCARPS
van der Bogert, Hiesinger, Banks, Watters and Robinson, LPSC #1847

Lobate Scarp or Fluidized Ejecta (November 10, 2011)

LROC: Lunar Landslides! (October 15, 2011)

LROC: Tectonics at the edge of Procellarum (October 13, 2011)

Scarps in Schrödinger (September 28, 2011)

LROC: lobate scarp in Xenophanes (September 14, 2011)

Wrinkled Planet (May 3, 2011)

Too brief an expedition to a lobate scarp (August 24, 2010)

Moon geologically active, cooling and shrinking (August 19, 2010)

Updated map of lunar graben, lobate scarps and further more recent topographic features broadly hinting Earth's Moon is not "dead," as once assumed, but geologically active [NASA/GSFC/DLR/Smithsonian CEPS/Arizona State University].