THE SOUTHWORTH PLANETARIUM
207-780-4249      www.usm.maine.edu/planet
70 Falmouth Street     Portland, Maine 04103
43.6667° N                   70.2667° W
Founded January 1970
Julian date:  2457762.16

                 “Tomorrow belongs to those who can hear it coming."

                                         -David Bowie

THE DAILY ASTRONOMER

Tuesday, January 10, 2017

More Than One Wham?

About four billion years ago,or thereabouts, a small, spherical body, still warm from the fierce heat of formation, was wandering through the infant solar system.   Though significantly smaller than most of the major bodies that had just congealed out of the primordial nebula, this rock ball was nevertheless physically formidable.    It was also rather content with its isolation, being naturally inclined toward solitude rather than companionship.   Suddenly, as it meandered through the inner solar system, it came upon Earth. It was not the verdant,blue-green world with which we are familiar. It was a harsh, toxic world suffocated by noxious gases pressing down on a paper-thin crust that was still often lacerated by exposing veins of molten rock.           The interloping body saw Earth.      Earth saw the interloping body.     The immediate attraction drew them closer together.  Though their initial mutual approach was rather tentative, as their separation distance decreased,their approach speeds accelerated.     Faster and faster, through the impulse of mutual attraction, they approached even close and,embracing destiny, the two bodies collided with a world-shattering bang!

Or, more technically, a WHAM!

The impact energy annihilated the small interloper and gouged out a big portion of the infant Earth.  Vaporized material from both bodies scattered into space.     It then quickly solidified and congealed to form the moon.

This introduction,   including the romantic insinuation, summarizes the Wham Theory:  the notion that a violent collision between Earth and an errant body formed the moon. This theory arose after analysis of the Apollo moon samples showed that the moon was both chemically similar and dissimilar to Earth. Had the moon merely been a captured body, as once believed, it would have been wholly dissimilar to Earth. Had the moon been a piece of Earth that had detached, also as once believed, it would have been similar to Earth.  

The Wham Theory seemed to explain the chemically similarities and the chemical differences between Earth and the moon. However, recently  researchers have developed computer simulations that replicated the conditions that prevailed during the epoch of the early solar system      These simulations suggest that the moon didn't form after just a single impact.  Instead, multiple impacts may have formed an array of "mini moons."   These little bodies would have then coalesced into the larger moon we see in our skies now.

​The moon might have formed out of an agglomeration of smaller "mini-moons,"

as opposed to having formed after a single impact between the infant Earth and a Mars-sized body. 

This new, "mini-moon amalgamation" theory assumes that the early solar system was such a violent place where collisions were common.      Any significant impact would have displaced matter from the largely molten Earth.  This material would have then formed  a small moon.   The small moons created by these minor impacts would then eventually collide to produce larger bodies. Ultimately, these series of collisions would have created the single moon.

So, it is possible that the moon contains even more Earth material than once assumed. Moreover, that serene orb that silvers our forests and casts luster onto snow fields might have been born out of an unimaginably violent series of devastating impacts.