A recent study, run jointly by researchers at the Technion in Haifa as well as at the University of Bordeaux, has shed new light on the shady origins of Earth’s moon. For decades, scientists have found consensus on what formed it, but not exactly where it came from.
The Giant Impact Theory posits that some large object slammed into the Earth, tearing both the primordial Earth and the impactor apart in a gigantic firework that lit up the early Solar System. After mere hours, all the heavy elements like iron and nickel re-coagulated into the formation of a metallic core, around which much of the debris coalesced to form the "modern" Earth, according to the theory. The leftovers orbited the Earth as a ring for possibly as little as a year.
“There is this latent assumption that all impactors are the same. What we tried to explore was the possibility that they are not,” Hagai Perets of the Technion told Arutz Sheva. Perets authored the study along with Alessandra Mastrobuono-Battisti of Technion and Sean Raymond of Bordeaux.
The Technion has a thriving Physics Department with several notable studies on astronomy. Perets is also the co-author of several other studies on supernovae, planetary instability and another study called Effects of Intermediate Mass Black Holes on Nuclear Star Clusters.
“The mere fact it impacted Earth meant they were highly likely to crash in the first place, were in same environment and would have had a similar composition of material based on where they formed in the solar system.”
Theories abound as to where the impactor came in from. Beyond hitting Earth at an angle, there had been debate in the past as to whether or not it was a large asteroid, an earlier moon, or another planet. That theoretical planet is known as Theia by astronomers.
“We don't just look at the other planets but also the impactors. We look at the composition and compare to the composition of planet impacted,” says Perets. “We found that a large portion of all the impactors were very similar to the planet it impacted. This was a completely different story from what we were used to hearing.”
“We found two main things: 1) the planet and the impactor could have a very similar composition and 2) different planets in the same [solar] system have different composition.”
“Both the Earth and Theia formed at the same time and collected material in the same regions [of the Solar System]," Perets asserted.
What does it have to do with the theory of alien life?
There is a theory in planetary science that there are ‘habitable zones’ around stars where planets supporting life might exist. That zone is called the Goldilocks Zone - as in the region is not too hot, nor too cold; it’s ‘just right.’
Expanding on the understanding of locality relative to a star, does this also lend evidence that planets close by will have a high chance of developing life? Will they always develop an atmosphere; have liquid water; or moderate temperatures at some point in their histories?
“I don't think that's a major outcome of this research. All you need is enough heavy material - carbon and oxygen overall - it's not new implication on that issue - consistent result relevant for any type of system.
Perets also said that using this study as a predictor for the possibility of collections of habitable planets in other solar systems is somewhat problematic because we do not have a lot of concrete evidence about the composition of “exoplanets” – planets which orbit other stars outside (exo-) our own star system.
“It is very difficult to check this against other solar systems because we haven't found any exo-moons just yet. What we do have in our own Solar System the chance to check the Martian moons and check them relative to Mars.”
“As it relates to habitability, there's a wide range for this Goldilocks region. Actually, if you look at the formal definition, Venus and Mars both sit in it.”
That opens up the possibility, in conjunction with Earth’s obvious habitability and the theoretical similarity with Thea, the chance that all four of these planets were at one point (if not at the same time) suitable to host life.
“But if Venus once had much nicer temperatures as opposed to what it has now with the greenhouse effect or if Mars once had a stronger atmosphere and warmer temperatures, they would also have been habitable. This is also true for other habitable zone – Goldilocks – planets.”
“It goes in both directions. We could see [potentially] habitable planets with the right temperature, even an earth-like planet, but other physical properties which are tough to take into account could limit that, like the composition of the atmosphere.”
“Then again, a very thick atmosphere might help even in a region where it is too cold.”
Perets alerts the reader to consider the moons around the Solar System’s gas giants Jupiter and Saturn, which themselves might either be covered in water of have a strong atmosphere. Without the heat provided by the sun, the strong gravity at work in those moons’ respective orbits around their host planets could churn the cores of the moons and cause volcanic activity, plate tectonics and other seismic activity that could also influence the habitability of the atmosphere.
“There is so much more to determining the temperature of the planet. We'll have access to information from exo-solar planets in the next few years,” says Perets, potentially “finding some evidence for bacteria or organisms.”
When asked what else he was working on, Perets said that a related study would try to figure out if Earth’s moon was truly the planet’s first.
“Our current moon might not be the first one. We might see new moons forming and colliding, or being ejected from the system.”