<p>The surface of Pluto is not just young, but <em>very</em> young, and also differentiated. The 'heart', Sputnik Planum, may be currently active, with flowing glaciers, and nitrogen snow. This area may have be resurfaced during Pluto's perihelion. Your theory cannot account for the very young age of the surface. </p>

<p>Next capture of a rogue planet is not easy. It would need Pluto to interact with the outer planets, to slow it down to enter solar orbit (otherwise a rogue planet would just pass through the solar system and come out the other side) A captured rogue would be unlikely to have the relatively low eccentricty of pluto. </p>

<p>Finally, while we don't know how common rogue planets are, they are probably not common, and given the massive distances between stars, the chances of any rogue just happening to have passed anywhere near the solar system in the last billion years in the right direction to be captured to Pluto's orbit is very low.</p>

<p>Conclusion. Pluto formed around the sun. A capture theory does not explain the observed young surface of Pluto, and modelling suggests a capture would be very unusual.</p>

CC BY-SA 3.0
2015-10-05T18:12:12.360Z
Pluto was at perihelion in 1989. Is Sputnik Planum only 26 years old? :-D I agree that capture seems unlikely, unless there are raining Pluto's out there. And wherever it was formed, it probably was in a proto-planetary disk with heavy cratering anyway. But recent resurfacing is also a mystery. A closer look at some other Kuiper Belt objects might be helpful, but unfortunately there's only one of each planet. I bet the New Horizons data already holds a good explanation to be understood and published in a few years.
LocalFluff
CC BY-SA 3.0
2015-10-06T10:15:40.300Z
Rogue planets are estimated to be upwards of *exceedingly numerous*.  The ratio rogue planets:stars has estimates ranging from ~2 to ~100,000.  A very large range, so quite consistent with your statement that we don't know how common they are, but by sheer numbers they appear to be no more rare than stars themselves.  Encountering them may still be quite rare, though.  Space is extremely vast, after all.
zibadawa timmy
CC BY-SA 3.0
2015-10-05T17:30:37.373Z
2015-10-05T17:30:37.373Z
James K
<p>(Edit, I think my original conclusion here was wrong, having read up about it).</p>
<p>While it seems probable that Pluto and Charon were formed by collision, I gather it's unlikely that this collision was so recent as to explain their lack of craters and young surface.   The Collision, by most articles I've read, happened when the solar system was young, not in the last 100 million years.</p>
<p>Now, it's possible that none of this is certain, but I retract that part of my original post.</p>
<p>But, the creation of Charon by giant collision remains likely  <a href="http://www.space.com/23136-pluto-moons-orbits-giant-impact.html" rel="nofollow noreferrer">See here</a>, and <a href="http://www.researchgate.net/publication/7281381_A_giant_impact_origin_for_Pluto%27s_small_moons_and_satellite_multiplicity_in_the_Kuiper_belt" rel="nofollow noreferrer">here.</a>   That would suggest formation within our solar-system, not from outside.</p>
<p>Pluto/Charon are also among a fairly common orbital region called <a href="https://en.wikipedia.org/wiki/Trans-Neptunian_object" rel="nofollow noreferrer">Trans-Neptunian objects</a>.</p>
<p>According to <a href="https://en.wikipedia.org/wiki/Charon_%28moon%29#Orbit" rel="nofollow noreferrer">Wikipedia</a> they suggest the collision that formed Charon happened 4.5 billion years ago.</p>
<p>Sedna (love the story, by the way), has a very elongated and distant orbit which seems more likely with capture of an object.   I agree with everything James Kilfinger said.   Rogue planet/Rogue object capture may happen from time to time, but the rogue object would need to get quite close (close is a relative term here) to our solar system for a sizable body that orbits the sun to orbit the rogue object's orbit.</p>
<p>Highly elongated orbits would seem likely for solar-system orbital capture.  Pluto is somewhat elongated but I think, not a good candidate.   Binary star systems probably have significantly higher numbers of captures, which I think, is neither here nor there to your question.</p>
<p>The Sun and the 4 large outer planets should be able to capture rogue objects (credit to as @paulgarrett ), provided the rogue object's approach is just right.   It needs to be both, not to fast relative to a stable orbit and it needs to pass close to one of the planets.  This would make a capture possible.   Perhaps Planet-Nine could capture rogue objects, if it exists, but capture would be rare.  Most objects would just fly past with too much velocity for capture.</p>

CC BY-SA 4.0
2024-07-23T15:53:16.120Z
As in @JamesK's answer, it's not an issue of the strength of the gravity of the star, since that's not the way "capture" works. Years ago, this did surprise me. That is, if something is moving fast through interstellar space, the star's gravity actually speeds the thing up at first, as it goes (approximately, not exactly) toward the star, and that extra moment allows the thing to escape, "slowing down" to its original velocity. The only way to have "loss" is quirky interactions with giant planets, etc., along the way.
paul garrett
CC BY-SA 4.0
2024-08-10T05:01:54.333Z
@paulgarrett you're absolutely right, and re-reading my last paragraph, I worded it poorly.    I've since edited.   Thanks for the correction.
userLTK
CC BY-SA 4.0
2024-08-14T06:11:38.257Z
To clarify, and I've made this comment on the OP, Pluto and Charon have an expected amount of cratering for bodies at the edge of the Kuiper Belt that are several billion years old.  Impact speeds are much slower there, so craters are smaller from the same-sized impactor in the inner solar system, and their gravitational cross-section is much smaller than other, larger bodies on which you'd see more impact craters.
Stuart Robbins
CC BY-SA 4.0
2015-10-05T04:50:12.907Z
2024-08-10T05:01:37.153Z
2024-08-10T05:01:37.153Z
userLTK
<p>Pluto and Charon seem to have surprisingly young surfaces, considering that resurfacing events were expected to be rare for them.</p>

<p>Could the explanation be that they actually <em>are</em> young? Formed later than the Solar system at some other star and then ejected and captured? Or that they are ancient but have extra-Solar origin and have little cratering because they have spent billions of years as a vagabond planet system in empty interstellar space? <a href="http://www.universetoday.com/121637/stealing-sedna/">Sedna</a> is believed to be <a href="http://arxiv.org/abs/1506.03105">captured</a>.</p>

CC BY-SA 4.0
2024-08-14T06:11:36.040Z
Pluto and Charon have an expected amount of cratering for bodies at the edge of the Kuiper Belt that are several billion years old.  Impact speeds are much slower there, so craters are smaller from the same-sized impactor in the inner solar system, and their gravitational cross-section is much smaller than other, larger bodies on which you'd see more impact craters.
Stuart Robbins
<pluto><surface><rogue-planet><charon>
Could Pluto and Charon have extra-Solar origin?
LocalFluff
# Could Pluto and Charon have extra-Solar origin?

(Asked by: username_0 on 2015-10-04)

Pluto and Charon seem to have surprisingly young surfaces, considering that resurfacing events were expected to be rare for them.

Could the explanation be that they actually *are* young? Formed later than the Solar system at some other star and then ejected and captured? Or that they are ancient but have extra-Solar origin and have little cratering because they have spent billions of years as a vagabond planet system in empty interstellar space? [Sedna](http://www.universetoday.com/121637/stealing-sedna/) is believed to be [captured](http://arxiv.org/abs/1506.03105).

**Tags:** pluto, surface, rogue-planet, charon

> **Comments:**
> **username_1**: Pluto and Charon have an expected amount of cratering for bodies at the edge of the Kuiper Belt that are several billion years old.  Impact speeds are much slower there, so craters are smaller from the same-sized impactor in the inner solar system, and their gravitational cross-section is much smaller than other, larger bodies on which you'd see more impact craters.  

---

## 2 answers

### Answer by username_2 on 2015-10-05. Score: 6

The surface of Pluto is not just young, but *very* young, and also differentiated. The 'heart', Sputnik Planum, may be currently active, with flowing glaciers, and nitrogen snow. This area may have be resurfaced during Pluto's perihelion. Your theory cannot account for the very young age of the surface.

Next capture of a rogue planet is not easy. It would need Pluto to interact with the outer planets, to slow it down to enter solar orbit (otherwise a rogue planet would just pass through the solar system and come out the other side) A captured rogue would be unlikely to have the relatively low eccentricty of pluto.

Finally, while we don't know how common rogue planets are, they are probably not common, and given the massive distances between stars, the chances of any rogue just happening to have passed anywhere near the solar system in the last billion years in the right direction to be captured to Pluto's orbit is very low.

Conclusion. Pluto formed around the sun. A capture theory does not explain the observed young surface of Pluto, and modelling suggests a capture would be very unusual.

> **Comments:**
> **username_0**: Pluto was at perihelion in 1989. Is Sputnik Planum only 26 years old? :-D I agree that capture seems unlikely, unless there are raining Pluto's out there. And wherever it was formed, it probably was in a proto-planetary disk with heavy cratering anyway. But recent resurfacing is also a mystery. A closer look at some other Kuiper Belt objects might be helpful, but unfortunately there's only one of each planet. I bet the New Horizons data already holds a good explanation to be understood and published in a few years.  
> **username_3**: Rogue planets are estimated to be upwards of *exceedingly numerous*.  The ratio rogue planets:stars has estimates ranging from ~2 to ~100,000.  A very large range, so quite consistent with your statement that we don't know how common they are, but by sheer numbers they appear to be no more rare than stars themselves.  Encountering them may still be quite rare, though.  Space is extremely vast, after all.  

---

### Answer by username_4 on 2015-10-05. Score: 1

(Edit, I think my original conclusion here was wrong, having read up about it).

While it seems probable that Pluto and Charon were formed by collision, I gather it's unlikely that this collision was so recent as to explain their lack of craters and young surface. The Collision, by most articles I've read, happened when the solar system was young, not in the last 100 million years.

Now, it's possible that none of this is certain, but I retract that part of my original post.

But, the creation of Charon by giant collision remains likely [See here](http://www.space.com/23136-pluto-moons-orbits-giant-impact.html), and [here.](http://www.researchgate.net/publication/7281381_A_giant_impact_origin_for_Pluto%27s_small_moons_and_satellite_multiplicity_in_the_Kuiper_belt) That would suggest formation within our solar-system, not from outside.

Pluto/Charon are also among a fairly common orbital region called [Trans-Neptunian objects](https://en.wikipedia.org/wiki/Trans-Neptunian_object).

According to [Wikipedia](https://en.wikipedia.org/wiki/Charon_%28moon%29#Orbit) they suggest the collision that formed Charon happened 4.5 billion years ago.

Sedna (love the story, by the way), has a very elongated and distant orbit which seems more likely with capture of an object. I agree with everything username_2ilfinger said. Rogue planet/Rogue object capture may happen from time to time, but the rogue object would need to get quite close (close is a relative term here) to our solar system for a sizable body that orbits the sun to orbit the rogue object's orbit.

Highly elongated orbits would seem likely for solar-system orbital capture. Pluto is somewhat elongated but I think, not a good candidate. Binary star systems probably have significantly higher numbers of captures, which I think, is neither here nor there to your question.

The Sun and the 4 large outer planets should be able to capture rogue objects (credit to as @paulgarrett ), provided the rogue object's approach is just right. It needs to be both, not to fast relative to a stable orbit and it needs to pass close to one of the planets. This would make a capture possible. Perhaps Planet-Nine could capture rogue objects, if it exists, but capture would be rare. Most objects would just fly past with too much velocity for capture.

> **Comments:**
> **username_5**: As in @JamesK's answer, it's not an issue of the strength of the gravity of the star, since that's not the way "capture" works. Years ago, this did surprise me. That is, if something is moving fast through interstellar space, the star's gravity actually speeds the thing up at first, as it goes (approximately, not exactly) toward the star, and that extra moment allows the thing to escape, "slowing down" to its original velocity. The only way to have "loss" is quirky interactions with giant planets, etc., along the way.  
> **username_4**: @paulgarrett you're absolutely right, and re-reading my last paragraph, I worded it poorly.    I've since edited.   Thanks for the correction.  
> **username_1**: To clarify, and I've made this comment on the OP, Pluto and Charon have an expected amount of cratering for bodies at the edge of the Kuiper Belt that are several billion years old.  Impact speeds are much slower there, so craters are smaller from the same-sized impactor in the inner solar system, and their gravitational cross-section is much smaller than other, larger bodies on which you'd see more impact craters.  

---

