<p>That is a very good timing for this question.</p>

<p>There is a comet with the name <strong>C/2017 U1 (PANSTARRS)</strong>, that was just discovered a few days ago (on 18th October) which has an orbital <strong>eccentricity of <code>1.18</code></strong>, which is by far highest eccentricity recorded so far.</p>

<p>The eccentricity describes how strongly "elliptical" an orbit is and refers to the variable <code>e</code> in the formula of <a href="https://en.wikipedia.org/wiki/Kepler_orbit" rel="nofollow noreferrer">Kepler's orbit</a>. <code>1.18</code> makes the orbit a <strong>hyperbolic</strong> one, meaning it is not an actual orbit, but has higher velocity than the required escape velocity and is basically just passing by in our solar system. And it's the first recorded comet so far that has an hyperbolic orbit.</p>

<p>This comet is the first candidate for an interstellar comet ever in recorded history. It is already pretty certain that it originated from interstellar space, but not official yet.</p>

<p>Quote from <a href="http://www.minorplanetcenter.net/mpec/K17/K17UI1.html" rel="nofollow noreferrer">minorplanetscenter.net</a>:</p>

<blockquote>
  <p>Further observations of this object are very much desired.  Unless there
  are serious problems with much of the astrometry listed below, strongly
  hyperbolic orbits are the only viable solutions.  Although it is probably
  not too sensible to compute meaningful original and future barycentric orbits,
  given the very short arc of observations, the orbit below has e ~ 1.2 for
  both values.  If further observations confirm the unusual nature of this
  orbit, this object may be the first clear case of an interstellar comet.</p>
</blockquote>

<p><strong>Sources:</strong></p>

<ul>
 <li><a href="http://www.minorplanetcenter.net/mpec/K17/K17UI1.html" rel="nofollow noreferrer">http://www.minorplanetcenter.net/mpec/K17/K17UI1.html</a></li>
 <li><a href="https://en.wikipedia.org/wiki/C/2017_U1_(PANSTARRS)" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/C/2017_U1_(PANSTARRS)</a> </li>
 <li><a href="https://i.sstatic.net/ImGUR.jpg" rel="nofollow noreferrer">https://i.sstatic.net/ImGUR.jpg</a></li>
</ul>

CC BY-SA 3.0
2017-10-25T15:57:43.550Z
Wow, that's great news, and yes, quite a coincidence. OK maybe in a week or two as more astrometry can be collected the uncertainty in the orbital elements will settle down and more certain values will be available. Thanks!
uhoh
CC BY-SA 3.0
2017-10-25T15:58:39.683Z
"It is already pretty certain that it originated from outer space, but not official yet." I think you mean *outside of the solar system*, not just *outer space*?
uhoh
CC BY-SA 3.0
2017-10-25T16:03:38.450Z
yeah sorry, typo correcting it :)
RononDex
CC BY-SA 3.0
2017-10-25T16:11:56.447Z
The aliens are coming. Just wait until the sensationalist press get hold of this. :D
Mick
CC BY-SA 3.0
2017-10-25T17:27:43.270Z
@Mick wait until the conspiracy theories arrive xD
RononDex
CC BY-SA 3.0
2017-10-25T17:36:20.560Z
How far out is it? I've no idea how to interpret orbital elements. A rendezvous mission would be brilliant.
Mick
CC BY-SA 3.0
2017-10-25T17:39:47.820Z
@Mick a rendezvous is not going to happen, its only observable for a few days because it is passing through our solar system very quickly. You would have to launch a mission immediately in order to have any chance of catching it before it leaves our solar system again for good.
And for the distance: It changes very fast, check its orbit here: https://upload.wikimedia.org/wikipedia/commons/0/03/C2017U1still.gif
RononDex
CC BY-SA 3.0
2017-10-26T19:21:40.683Z
@RononDex I've just noticed the recent question [What speed did the (interstellar) comet C/2017 U1 PANSTARRS have at perihelion?](https://space.stackexchange.com/q/23500/12102) and the [comment](https://space.stackexchange.com/questions/23500/#comment67098_23500) which links to the SwRI astronpysicist Simon Porter's tweet PSA: [If you drop the single worst observation for Comet C/2017 U1 (PANSTARRS), the eccentricity drops to 0.93](https://twitter.com/AscendingNode/status/923223634386206720) and an extended discussion there. Looks like a few more weeks of observations is called for.
uhoh
CC BY-SA 3.0
2017-10-27T08:28:57.297Z
It has also be reclassified as an asteroid. A/2017 U1
James K
CC BY-SA 3.0
2017-10-27T09:12:07.797Z
Damn, looks like bad measurement data then. Well who knows wether that "worst" point is a good one or not, we can't know
RononDex
CC BY-SA 3.0
2017-10-29T11:13:04.047Z
Best fit from MPC has e = 1.2 https://twitter.com/cosmos4u/status/923697091322429441 http://www.minorplanetcenter.net/mpec/K17/K17UI5.html This confirms a strongly hyperbolic orbit
James K
CC BY-SA 3.0
2017-11-17T14:33:34.930Z
The asteroid seems to have been given a name. I'm not sure if it's 100% official yet. http://bbc.com/news/science-environment-42019778 Linked there is this, apparently submitted to ApJ letters ($e=1.197$)
uhoh
CC BY-SA 3.0
2017-10-25T14:42:35.207Z
2017-10-25T16:03:48.300Z
2017-10-25T16:03:48.300Z
RononDex
<p>After reading <a href="https://astronomy.stackexchange.com/a/6388/7982">this answer</a> I wondered if there have been document comets with orbits on non-return, hyperbolic trajectories as they approached the Sun.</p>

<p>This means that they would not be gravitationally bound to the sun, so either they came from outside the solar system, or they managed to gain energy through a collision, or close pass with a large planet like Jupiter.</p>

<p>The quickest way to find the comet with the "highest" orbit is to ask for the one with the largest <a href="https://en.wikipedia.org/wiki/Specific_orbital_energy" rel="nofollow noreferrer">specific orbital energy</a>, the total energy (kinetic + potential) divided by the mass, (Joules/kg). For a bound orbit the value would be negative, for an unbound, non-returning orbit it would be positive.</p>

<p><strong>Question:</strong> What documented comet has/had the highest specific orbital energy? It should be an identified object with a known or measured orbit, not just a generic, nameless "edge-of-the-<a href="https://en.wikipedia.org/wiki/Oort_cloud" rel="nofollow noreferrer">Oort Cloud</a> placeholder." </p>

<orbit><comets>
What documented comet has/had the highest specific orbital energy?
uhoh
# What documented comet has/had the highest specific orbital energy?

(Asked by: username_0 on 2017-10-24)

After reading [this answer](https://astronomy.stackexchange.com/a/6388/7982) I wondered if there have been document comets with orbits on non-return, hyperbolic trajectories as they approached the Sun.

This means that they would not be gravitationally bound to the sun, so either they came from outside the solar system, or they managed to gain energy through a collision, or close pass with a large planet like Jupiter.

The quickest way to find the comet with the "highest" orbit is to ask for the one with the largest [specific orbital energy](https://en.wikipedia.org/wiki/Specific_orbital_energy), the total energy (kinetic + potential) divided by the mass, (Joules/kg). For a bound orbit the value would be negative, for an unbound, non-returning orbit it would be positive.

**Question:** What documented comet has/had the highest specific orbital energy? It should be an identified object with a known or measured orbit, not just a generic, nameless "edge-of-the-[Oort Cloud](https://en.wikipedia.org/wiki/Oort_cloud) placeholder."

**Tags:** orbit, comets

---

## 1 answers

### Answer by username_1 on 2017-10-25. Score: 5 | Accepted answer

That is a very good timing for this question.

There is a comet with the name **C/2017 U1 (PANSTARRS)**, that was just discovered a few days ago (on 18th October) which has an orbital **eccentricity of `1.18`**, which is by far highest eccentricity recorded so far.

The eccentricity describes how strongly "elliptical" an orbit is and refers to the variable `e` in the formula of [Kepler's orbit](https://en.wikipedia.org/wiki/Kepler_orbit). `1.18` makes the orbit a **hyperbolic** one, meaning it is not an actual orbit, but has higher velocity than the required escape velocity and is basically just passing by in our solar system. And it's the first recorded comet so far that has an hyperbolic orbit.

This comet is the first candidate for an interstellar comet ever in recorded history. It is already pretty certain that it originated from interstellar space, but not official yet.

Quote from [minorplanetscenter.net](http://www.minorplanetcenter.net/mpec/K17/K17UI1.html):

> Further observations of this object are very much desired. Unless there
> are serious problems with much of the astrometry listed below, strongly
> hyperbolic orbits are the only viable solutions. Although it is probably
> not too sensible to compute meaningful original and future barycentric orbits,
> given the very short arc of observations, the orbit below has e ~ 1.2 for
> both values. If further observations confirm the unusual nature of this
> orbit, this object may be the first clear case of an interstellar comet.

**Sources:**

* <http://www.minorplanetcenter.net/mpec/K17/K17UI1.html>
* <https://en.wikipedia.org/wiki/C/2017_U1_(PANSTARRS)>
* <https://i.sstatic.net/ImGUR.jpg>

> **Comments:**
> **username_0**: Wow, that's great news, and yes, quite a coincidence. OK maybe in a week or two as more astrometry can be collected the uncertainty in the orbital elements will settle down and more certain values will be available. Thanks!  
> **username_0**: "It is already pretty certain that it originated from outer space, but not official yet." I think you mean *outside of the solar system*, not just *outer space*?  
> **username_1**: yeah sorry, typo correcting it :)  
> **username_2**: The aliens are coming. Just wait until the sensationalist press get hold of this. :D  
> **username_1**: @Mick wait until the conspiracy theories arrive xD  
> **username_2**: How far out is it? I've no idea how to interpret orbital elements. A rendezvous mission would be brilliant.  
> **username_1**: @Mick a rendezvous is not going to happen, its only observable for a few days because it is passing through our solar system very quickly. You would have to launch a mission immediately in order to have any chance of catching it before it leaves our solar system again for good. And for the distance: It changes very fast, check its orbit here: https://upload.wikimedia.org/wikipedia/commons/0/03/C2017U1still.gif  
> **username_0**: @RononDex I've just noticed the recent question [What speed did the (interstellar) comet C/2017 U1 PANSTARRS have at perihelion?](https://space.stackexchange.com/q/23500/12102) and the [comment](https://space.stackexchange.com/questions/23500/#comment67098_23500) which links to the SwRI astronpysicist Simon Porter's tweet PSA: [If you drop the single worst observation for Comet C/2017 U1 (PANSTARRS), the eccentricity drops to 0.93](https://twitter.com/AscendingNode/status/923223634386206720) and an extended discussion there. Looks like a few more weeks of observations is called for.  
> **username_3**: It has also be reclassified as an asteroid. A/2017 U1  
> **username_1**: Damn, looks like bad measurement data then. Well who knows wether that "worst" point is a good one or not, we can't know  
> **username_3**: Best fit from MPC has e = 1.2 https://twitter.com/cosmos4u/status/923697091322429441 http://www.minorplanetcenter.net/mpec/K17/K17UI5.html This confirms a strongly hyperbolic orbit  
> **username_0**: The asteroid seems to have been given a name. I'm not sure if it's 100% official yet. http://bbc.com/news/science-environment-42019778 Linked there is this, apparently submitted to ApJ letters ($e=1.197$)  

---

