The origin of the Moon is usually explained by a Mars-sized body striking the Earth, making a debris ring that eventually collected into a single natural satellite, the Moon, but there are a number of variations on this giant-impact hypothesis, as well as alternate explanations, and research into how the Moon came to be continues.[1][2] Other proposed scenarios include captured body, fission, formed together (condensation theory, Synestia), planetesimal collisions (formed from asteroid-like bodies), and collision theories.[3]
The standard giant-impact hypothesis suggests the Mars-sized body, called Theia, impacted Earth, creating a large debris ring around Earth, which then accreted to form the Moon. This collision also resulted in the 23.5° tilted axis of the earth, thus causing the seasons.[1] The Moon’s oxygen isotopic ratios seem to be essentially identical to Earth’s.[4] Oxygen isotopic ratios, which may be measured very precisely, yield a unique and distinct signature for each solar system body.[5] If Theia had been a separate protoplanet, it probably would have had a different oxygen isotopic signature from Earth, as would the ejected mixed material.[6] Also, the Moon’s titanium isotope ratio (50Ti/47Ti) appears so close to the Earth’s (within 4 ppm) that little if any of the colliding body’s mass could likely have been part of the Moon.[7]
When and How Did the Moon Form?
New studies offer contrasting scenarios for making the Moon. One argues for a one big splat early in solar-system history; a second envisions a score of lesser blows that built up the Moon over time; and a third suggests water was involved.
Given the trove of lunar samples in hand and the power of modern laboratory analyses, you’d think that by now geochemists should have completely nailed exactly how the Moon formed. But not so — in fact, there’s still lots of debate on how Earth formed.
Artwork of a Mars-sized object colliding into the Earth early in solar system history. Many planetary scientists believe that an impact such as this threw off the debris which eventually formed the Moon.
Lynette Cook / Getty ImagesHere’s the basic problem: about 30 years ago, dynamicists showed that a body roughly the mass of Mars could have struck Earth a glancing blow and ejected enough debris into orbit to collect into a Moon-size object. In virtually all of those simulations, most of what ends up in the Moon came from the impactor rather than from Earth.
Throwing Water on the Problem
As if the How and When of the Moon’s formation weren’t complicated enough, a third new analysis argues that — despite its extreme dryness today — the Moon likely contained a lotof water when it formed. In the same issue of Nature Geoscience, Yanhao Lin (Vrije Universiteit Amsterdam) and three others describe their experimental attempts to mimic how the Moon’s magma ocean solidified. Lower density minerals would have floated to the top, forming a crust.
They find that the suite of minerals found in the lunar crust today — combined with its thickness — argue that water was part of the mix at a concentration of 270 to 1,650 ppm. This might not seem like much — but if proven true there’d be significant implications.
“A wet start of the Moon, coupled with the strong similarities between the composition of the Moon and the composition of the silicate Earth,” Lin’s team concludes, “suggests that equally high concentrations of water were present in the Earth at the time of the Moon-forming event.”
Richard Rohr Meditation: We Are Already One
Believe it or not, a Roman Catholic priest first proposed the Big Bang theory of the origin of the universe. In 1927, Georges Lemaître, a Belgian priest, astronomer, and physics professor, suggested that the expanding universe might be traced back to a single point of origin, a singularity. As Ilia Delio describes, “[It] appeared like a little quantum size blip on the screen [creatio ex nihilo] and inflated rapidly like a balloon and since that time, it has been expanding.” [2] I’ll let Delio, a scientist, explain the implications for this cosmology—our story of the universe:
Every human person desires to love and to be loved, to belong to another, because we come from another. We are born social and relational. We yearn to belong, to be part of a larger whole that includes not only friends and family but neighbors, community, trees, flowers, sun, Earth, stars. We are born of nature and are part of nature; that is, we are born into a web of life and are part of a web of life. We cannot know what this means, however, without seeing ourselves within the story of the Big Bang universe. Human life must be traced back to the time when life was deeply one, a Singularity, whereby the intensity of mass-energy exploded into consciousness. Deep in our DNA we belong to the stars, the trees, and the galaxies.
Deep within we long for unity because, at the most fundamental level, we are already one. We belong to one another because we have the same source of love; the love that flows through the trees is the same love that flows through my being
Why is the discovery of merging neutron stars important?
Reasons why this is important:
- It is the first simultaneous detection of a gravitational wave and electromagnetic signal (and the strongest GW signal yet). It spectacularly corroborates the reality of the GW detection technology and analysis. The progenitor has been unambiguously located in a (relatively) nearby galaxy, allowing a host of other telescopes to obtain detailed measurements.
- It shows that GWs travel at the speed of light, a further verification of Einstein’s General Relativity.
- It shows that most of the very heavy elements such as gold, platinum, osmium etc. are plausibly produced by merging neutron stars and constrains the rate of such mergers in the local universe.
- It shows that short gamma ray bursts – some of the most energetic explosions in the universe – can be caused by neutron star mergers.
- It is the closest detected short gamma ray burst (with a known distance). That the progenitor has also been characterised allows a closer investigation of the interesting physics underlying the ejection and jet mechanisms thought to be responsible for the gamma rays.
- It provides observational constraints on how matter behaves at extremely high densities, testing our understanding of fundamental physics to its limits – for example, the details of the gravitational wave signal moments before merger are diagnostic of the interior conditions of neutron stars at densities of ∼1018∼1018 kg/m33.
- It provides an independent way of measuring the expansion of the universe, because the distance to the GW source pops out of the analysis and can be compared with the redshift of the identified host galaxy. The result agrees with measurements made using the cosmic microwave background and the distance-redshift relation calibrated by other means, verifying our estimation of distances, at least in the local universe.