ISF Logo   IS Forum
Forum Index Register Members List Events Mark Forums Read Help

Go Back   International Skeptics Forum » General Topics » Science, Mathematics, Medicine, and Technology
 


Welcome to the International Skeptics Forum, where we discuss skepticism, critical thinking, the paranormal and science in a friendly but lively way. You are currently viewing the forum as a guest, which means you are missing out on discussing matters that are of interest to you. Please consider registering so you can gain full use of the forum features and interact with other Members. Registration is simple, fast and free! Click here to register today.
Reply
Old 13th February 2020, 03:57 PM   #1
William Parcher
Show me the monkey!
 
William Parcher's Avatar
 
Join Date: Jul 2005
Posts: 24,256
Planets Form Gently

New Horizons spacecraft 'alters theory of planet formation'

Originally Posted by BBC News
Scientists say they have "decisively" overturned the prevailing theory for how planets in our Solar System formed.

The established view is that material violently crashed together to form ever larger clumps until they became worlds. New results suggest the process was less catastrophic - with matter gently clumping together instead.

The study appears in Science journal and has been presented at the American Association for the Advancement of Science meeting in Seattle. The study's lead researcher, Dr Alan Stern, said that the discovery was of "stupendous magnitude".

"There was the prevailing theory from the late 1960s of violent collisions and a more recent emerging theory of gentle accumulation. One is dust and the other is the only one standing. This rarely happens in planetary science, but today we have settled the matter," he told BBC News.

The claim arises from detailed study of an object in the outer reaches of the Solar System. Named Arrokoth, the object is more than six billion km from the Sun in a region called the Kuiper belt. It is a pristine remnant of planet formation in action as the Solar System formed 4.6 billion years ago, with two bodies combining to form a larger one.

Scientists obtained high-resolution pictures of Arrokoth when Nasa's New Horizons spacecraft flew close to it just over a year ago. It gave scientists their first opportunity to test which of the two competing theories was correct: did its components crash together or was there gentle contact? The analysis by Dr Stern and his team could find no evidence of violent impact. The researchers found no stress fractures, nor was there any flattening, indicating that the objects were squashed together gently.

"This is completely decisive," said Dr Stern. "In one fell swoop, the flyby of Arrokoth was able to decide between the two theories."...
https://www.bbc.com/news/science-environment-51295365
Attached Images
File Type: jpg 0.jpg (29.2 KB, 9 views)
__________________
Bigfoot believers and Bigfoot skeptics are both plumb crazy. Each spends more than one minute per year thinking about Bigfoot.
William Parcher is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Old 13th February 2020, 04:01 PM   #2
theprestige
Penultimate Amazing
 
Join Date: Aug 2007
Posts: 42,106
That's weird. I always assumed it was soft accretion. Never even knew that hard impact was the prevailing hypothesis. Don't see why it would even make sense.
theprestige is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Old 13th February 2020, 04:15 PM   #3
sphenisc
Philosopher
 
sphenisc's Avatar
 
Join Date: Jul 2004
Posts: 5,094
Sure...now tell me how the moon was formed again.
__________________
"The cure for everything is salt water - tears, sweat or the sea." Isak Dinesen
sphenisc is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Old 13th February 2020, 06:13 PM   #4
Myriad
Hyperthetical
 
Myriad's Avatar
 
Join Date: Nov 2006
Location: Betwixt
Posts: 15,936
It's almost as though condensed objects with escape velocities in the fractions of meters per second range will tend to accrete more gently than ones with escape velocities in the thousands or tens of thousands of meters per second.

How "gently" did Shoemaker-Levy 9 accrete with Jupiter?
__________________
A zømbie once bit my sister...
Myriad is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Old 13th February 2020, 06:56 PM   #5
Puppycow
Penultimate Amazing
 
Puppycow's Avatar
 
Join Date: Jan 2003
Posts: 24,680
Why can't it be both?

Some formed gently but there were also some violent collisions?
__________________
A fool thinks himself to be wise, but a wise man knows himself to be a fool.
William Shakespeare
Puppycow is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Old 13th February 2020, 10:06 PM   #6
arthwollipot
Observer of Phenomena
Pronouns: he/him
 
arthwollipot's Avatar
 
Join Date: Feb 2005
Location: Location, Location
Posts: 65,739
Originally Posted by Myriad View Post
It's almost as though condensed objects with escape velocities in the fractions of meters per second range will tend to accrete more gently than ones with escape velocities in the thousands or tens of thousands of meters per second.

How "gently" did Shoemaker-Levy 9 accrete with Jupiter?
Pretty gently. Those bits left wakes, but that normalised quickly. More like a pebble in a pond than a smash.
__________________
Self-described nerd.

My mom told me she tries never to make fun of people for not knowing something.
- Randall Munroe
arthwollipot is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Old 13th February 2020, 11:44 PM   #7
a_unique_person
Director of Hatcheries and Conditioning
 
a_unique_person's Avatar
 
Join Date: Jul 2002
Location: Waiting for the pod bay door to open.
Posts: 41,806
What is their sample size?
__________________
Continually pushing the boundaries of mediocrity.
Everything is possible, but not everything is probable.
“Perception is real, but the truth is not.” - Imelda Marcos
a_unique_person is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Old 14th February 2020, 12:18 AM   #8
Roboramma
Penultimate Amazing
 
Roboramma's Avatar
 
Join Date: Feb 2005
Location: Shanghai
Posts: 13,505
Originally Posted by Puppycow View Post
Why can't it be both?

Some formed gently but there were also some violent collisions?
What Myriad said makes sense to me. If you have two small bodies in a violent collision I don't see how they end up accreting.

When you get to larger bodies you can have more high energy collisions that end up with a single body afterward.

Maybe the question is, within the range of relative velocities within the escape velocity of the larger of the two bodies (or perhaps the escape velocity of the two combined in a similarly dense sphere), what is the typical distribution of relative velocities before collision? I'd expect something like the a normal distribution, but that's just a guess.
__________________
"... when people thought the Earth was flat, they were wrong. When people thought the Earth was spherical they were wrong. But if you think that thinking the Earth is spherical is just as wrong as thinking the Earth is flat, then your view is wronger than both of them put together."
Isaac Asimov
Roboramma is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Old 14th February 2020, 10:22 AM   #9
lomiller
Penultimate Amazing
 
lomiller's Avatar
 
Join Date: Jul 2007
Posts: 10,343
Originally Posted by Roboramma View Post
What Myriad said makes sense to me. If you have two small bodies in a violent collision I don't see how they end up accreting.
He’s missing the point IMO. Shoemaker-Levy 9 was already orbiting Jupiter, so Jupiter’s own gravity played a big role in making the impact as large as it was. So yes it makes sense that larger object will experience lager impacts, but it’s not quite what the article is discussing. It's not saying the collisions that form planets in the initial stages, it's explain why these collisions are not violent.


I think what this article is saying is that in the early stages of formation proto-planets accretion is in the form of material that is already tied together gravitationally so the collisions taking place are not with objects on different orbits around the sun. Rather it’s dust and debris that is already tied together by gravity and is already sharing a common orbit around the Sun. This explains why these collisions grow the object instead of blowing it apart.
__________________
"Anything's possible, but only a few things actually happen"

Last edited by lomiller; 14th February 2020 at 10:25 AM.
lomiller is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Old 14th February 2020, 10:41 AM   #10
theprestige
Penultimate Amazing
 
Join Date: Aug 2007
Posts: 42,106
First, dust is orbiting the sun every which way. But there's some slight irregularity in the overall angular momentum of the dust cloud. Slightly more dust is on one orbital plane than the others. This irregularity, over time, tends to force the rest of the dust cloud into that plane, and that orbital direction. As more dust accretes into that disk, it starts to clump together as more irregularities manifest. Over time, the planets form, all orbiting on more or less the same plane, in the same direction.

Obviously the process isn't finished yet; Pluto and other outer bodies are still doing quite a bit of "every which way" dust cloud stuff. And even in the inner system, large lumps of accreted stuff still bump into each other from time to time. But those violent impacts happen after the initial planetary formation from the accretion disk. They're not a primary mechanism for formation in the first place.
theprestige is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Reply

International Skeptics Forum » General Topics » Science, Mathematics, Medicine, and Technology

Bookmarks

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -7. The time now is 08:12 PM.
Powered by vBulletin. Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.

This forum began as part of the James Randi Education Foundation (JREF). However, the forum now exists as
an independent entity with no affiliation with or endorsement by the JREF, including the section in reference to "JREF" topics.

Disclaimer: Messages posted in the Forum are solely the opinion of their authors.