Does it take an Orpheus impact to make a big moon?

[ehkzu]

Orpheus hit Earth, made the Moon outside the Roche limit, mainly from Earth's crust. Impact blows off excess water, makes dry continents possible. Moon stabilizes Earth's axial tilt, makes us possible. My question: is there any other plausible way for an Earthlike planet orbiting in its star's life zone to get a relatively big moon? <br /><br />I understand a capture is extremely unlikely--the planetoid would most likely just roll on by, its inertia overwhelming mutual gravitational attraction. Moreover, even if its relative velocity was so low as to make capture possible we'd still wind up with a water planet punctuated by just a few islands. Right? <br /><br />Second question: what would be a plausible range of sizes for a moon formed the way ours was? <br /><br />That is, how much bigger could it be before it caused such a tectonic ruckus on Earth as to make advanced life difficult?

 

[terra_firma]

I've just joined this forum, indeed, this website. I know little of astronomy. My question relates to a satellite tv program about the Moon that I saw a few nights ago: talked about was a collision between Earth and Orpheus, which in turn created the Moon and what the repercussions are. Is this really a theory or merely a hypothesis? Did it really happen?

 

[vogon13]

Seems quite likey as it explains many details about earth moon system.<br /><br />It's possible something similar may have happened to Pluto. <br /><br />Additionally, some explanations for the equatorial ridge feature of Iapetus imply a large oblique impacting body long ago.<br /><br />Would expect some asteroids to show signs of same occurence. Existence of Dactyl may be explained this way.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[rhodan]

Terra_Firma,<br /><br />This is a nice website on the subject, briefly discussing the different theories about the Moon's origin, but supportive of the Orpheus thesis: The Origin of the Moon.

 

[CalliArcale]

Welcome aboard, Terra_Firma!<br /><br />The Orpheus impact is a hypothesis at best. It might be more accurate to call it a model. It's a guess of how the Moon could have formed. It does a surprisingly good job of fitting the available evidence, but at present there really isn't a way to test it. It's quite possible that it happened. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[nexium]

The Orpheus impact is surely main stream, but I agree, Hypothesis rather than theory. Astronomy is often hypothesis rather than theory. Much of astronomy will likely be replace by new hypothesis is less than a century. I think the hypothesis that the moon formed the same time as the earth in about the present location, has lost followers because the moon has about 1/2 the average density of Earth, and surface isotope ratios are quite different. A foot below the surface; the moon isotopes may be less different, so there is a chance the formed the same time hypothesis will be revieved. Neil