# Why is the heliosphere oval shaped? **URL:** \ **Category:** Factual Questions\ **Created:** [December 11, 2018, 8:21am UTC](https://boards.straightdope.com/t/why-is-the-heliosphere-oval-shaped/825931 "2018-12-11T08:21:19Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Measure\_for\_Measure](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/measure_for_measure/32/557_2.png) [@Measure\_for\_Measure](https://boards.straightdope.com/u/Measure_for_Measure)\ **Post date:** [December 11, 2018, 8:21am UTC](https://boards.straightdope.com/t/why-is-the-heliosphere-oval-shaped/825931/1 "2018-12-11T08:21:19Z")
As I understand it: The [heliosphere](https://en.wikipedia.org/wiki/Heliosphere) is a region around the sun formed by the solar wind. Beyond it the sun’s solar wind is stopped by the interstellar medium. The heliosphere has a leading edge on one side and a comet-like trail on the other. Why? Perhaps the solar system is rotating around the galactic center, moving through the [interstellar medium](https://en.wikipedia.org/wiki/Interstellar_medium) (IM), whatever that is. But shouldn’t IM be rotating around the galactic core as well? Why would solar system matter be traveling faster than IM matter? Or is interstellar wind just a function of the relative placement of nearby stars? So: explain to me the solar wind/interstellar medium interaction. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [December 11, 2018, 9:33am UTC](https://boards.straightdope.com/t/why-is-the-heliosphere-oval-shaped/825931/2 "2018-12-11T09:33:34Z")
The ISM is observed to be fairly [turbulent](https://en.wikipedia.org/wiki/Interstellar_medium#Structures), so locally may be moving against the direction our solar system is heading in. Specifically, the flow in our[local neighbourhood](https://en.wikipedia.org/wiki/Local_Interstellar_Cloud) is coming from our nearest neighbour stellar association and is [perpendicular to our own trajectory.](https://en.wikipedia.org/wiki/Local_Interstellar_Cloud#/media/File:The_Local_Interstellar_Cloud_and_neighboring_G-cloud_complex.gif) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 11, 2018, 9:06pm UTC](https://boards.straightdope.com/t/why-is-the-heliosphere-oval-shaped/825931/3 "2018-12-11T21:06:23Z")
Each star’s motion, and for that matter the motion of each molecule of the ISM, is independent. On average, they have a certain circulatory motion around the Galaxy, but individual stars vary. ---
**Author:** ![DSYoungEsq](https://avatars.discourse-cdn.com/v4/letter/d/c6cbf5/32.png) [@DSYoungEsq](https://boards.straightdope.com/u/DSYoungEsq)\ **Post date:** [December 11, 2018, 9:54pm UTC](https://boards.straightdope.com/t/why-is-the-heliosphere-oval-shaped/825931/4 "2018-12-11T21:54:11Z")
> [@MrDibble](#): > > The ISM is observed to be fairly [turbulent](https://en.wikipedia.org/wiki/Interstellar_medium#Structures), so locally may be moving against the direction our solar system is heading in. Specifically, the flow in our[local neighbourhood](https://en.wikipedia.org/wiki/Local_Interstellar_Cloud) is coming from our nearest neighbour stellar association and is [perpendicular to our own trajectory.](https://en.wikipedia.org/wiki/Local_Interstellar_Cloud#/media/File:The_Local_Interstellar_Cloud_and_neighboring_G-cloud_complex.gif) > [@Chronos](#): > > Each star’s motion, and for that matter the motion of each molecule of the ISM, is independent. On average, they have a certain circulatory motion around the Galaxy, but individual stars vary. Eddies. Eddie’s in the [time] current. 😃 ---
**Author:** ![snfaulkner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snfaulkner/32/433_2.png) [@snfaulkner](https://boards.straightdope.com/u/snfaulkner)\ **Post date:** [December 11, 2018, 9:59pm UTC](https://boards.straightdope.com/t/why-is-the-heliosphere-oval-shaped/825931/5 "2018-12-11T21:59:45Z")
> [@DSYoungEsq](#): > > Eddies. Eddie’s in the [time] current. 😃 [Eddie’s somewhere in time?](https://en.wikipedia.org/wiki/File%3AIron_Maiden_-_Somewhere_in_Time.jpg?wprov=sfla1) ---
**Author:** ![Measure\_for\_Measure](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/measure_for_measure/32/557_2.png) [@Measure\_for\_Measure](https://boards.straightdope.com/u/Measure_for_Measure)\ **Post date:** [December 12, 2018, 4:07am UTC](https://boards.straightdope.com/t/why-is-the-heliosphere-oval-shaped/825931/6 "2018-12-12T04:07:43Z")
Asked and answered. > [@Chronos](#): > > Each star’s motion, and for that matter the motion of each molecule of the ISM, is independent. On average, they have a certain circulatory motion around the Galaxy, but individual stars vary. Didn’t know that. So where is the Earth going? Quora has a nice article detailing the earth’s speed relative to various locations: [In what direction does Earth travel faster in universe? Around Sun, with Sun in Milky-way or with our own Galaxy in local group?](https://www.quora.com/In-what-direction-does-Earth-travel-faster-in-universe-Around-Sun-with-Sun-in-Milky-way-or-with-our-own-Galaxy-in-local-group/answer/Valentin-Ghincolov) [This site](http://ryanmarciniak.com/archives/1509) contains an image of the sun moving around the galactic center, while oscillating above and below the galactic plane. It is moving towards its galactic height, and will reach the peak in 14 million years, not a long time is astronomical terms. (Age of universe: 13,772 million years). ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [December 12, 2018, 7:05am UTC](https://boards.straightdope.com/t/why-is-the-heliosphere-oval-shaped/825931/7 "2018-12-12T07:05:48Z")
Note the now outdated comet like tail shape is based on the belief that we are orbiting the galactic center but that view has been superseded by modern evidence. > [@](#): > > “The main difference is the new model’s lack of a trailing, comet-like tail on one side of the heliosphere. This tail is shown in the old model in light blue.” > **[NASA’s Cassini, Voyager Missions Suggest New Picture of Sun’s Interaction...](https://www.nasa.gov/missions/cassini/nasas-cassini-voyager-missions-suggest-new-picture-of-suns-interaction-with-galaxy/)** > > New data from NASA’s Cassini mission, combined with measurements from the two Voyager spacecraft and NASA’s Interstellar Boundary Explorer, or IBEX, suggests Mapping our suns neighbors is still something that is going on today, and the closest neighbors were only located in 2013 and 2014. With the Gaia mission data this is getting more complete but the assumption that we are simply orbiting around the galactic center turns out to be a bit simplistic. There is some research that is just hitting the pre-print world that should produce some interesting papers over the next couple of years. Astrophysicist Jackie Faherty specifically is one person who has been doing a lot of work around brown dwarfs and co-moving groups. The bigger question is _when_ is Wikipedia and other non-technical resources going to update their data to discard the comet like shape claims and move to the more correct rounded heliosphere representations. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [December 12, 2018, 7:24am UTC](https://boards.straightdope.com/t/why-is-the-heliosphere-oval-shaped/825931/8 "2018-12-12T07:24:31Z")
Ah apparently the debate is still ongoing, with some classical theory adherents questioning the observational data from Cassini and IBEX. But I am going to root for the [“croissant” shape](https://arxiv.org/abs/1808.05997) not out of merit but just because the thought makes me laugh. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [December 12, 2018, 8:40am UTC](https://boards.straightdope.com/t/why-is-the-heliosphere-oval-shaped/825931/9 "2018-12-12T08:40:01Z")
> [@rat\_avatar](#): > > Mapping our suns neighbors is still something that is going on today, and the closest neighbors were only located in 2013 and 2014. I assume this is a reference to Luhman 16 and WISE 0855-0714. Those are not the Sun’s closest neighbors. Alpha Centauri is still the closest and Barnard’s Star is the next. Those two recent discoveries are the third and fourth closest, respectively. > [@](#): > > With the Gaia mission data this is getting more complete but the assumption that we are simply orbiting around the galactic center turns out to be a bit simplistic. Orbits only follow simple ellipses when the two masses can be approximated to point masses. The galaxy is nowhere close to being a point mass, so it should have been obvious all along that the sun doesn’t follow one. And the fact that the Sun’s path bobs up and down in relation to the plane of the galaxy has been known for quite a while, although I don’t know when it was discovered. As for discovering new nearby stars, it’s unlikely Gaia will find anything really close, that is within 10 ly or so. Any unknown stars that close are probably too dim for Gaia to see. The two recent discoveries are brown dwarfs and were discovered by an orbiting infrared observatory (WISE). There may be more close brown dwarfs found in the WISE data, though. In fact, you can even look for them online, if you want: [Backyard Worlds](https://www.zooniverse.org/projects/marckuchner/backyard-worlds-planet-9/classify). You may also find Planet 9 in that data. ---
**Author:** ![K.Sharon](https://avatars.discourse-cdn.com/v4/letter/k/46a35a/32.png) [@K.Sharon](https://boards.straightdope.com/u/K.Sharon)\ **Post date:** [December 12, 2018, 10:32am UTC](https://boards.straightdope.com/t/why-is-the-heliosphere-oval-shaped/825931/10 "2018-12-12T10:32:41Z")
It was at first speculated that the heliosphere was reached out into a tear shape by its involvement with the ISM. The U.S. space tests Voyager 1 and 2 crossed the end daze at a partition of 94 and 84 AU from the Sun in 2004 and 2007, independently. Since the two Voyagers are leaving the nearby planetary framework in different ways, this gathered the heliosphere has an uneven shape. Regardless, coming about view of particles in the heliosheath by the Cassini rocket orbiting Saturn and the Interstellar Boundary Explorer revolving around Earth showed the heliosphere was extremely a circle. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [December 12, 2018, 6:22pm UTC](https://boards.straightdope.com/t/why-is-the-heliosphere-oval-shaped/825931/11 "2018-12-12T18:22:24Z")
> [@dtilque](#): > > I assume this is a reference to Luhman 16 and WISE 0855-0714. Those are not the Sun’s closest neighbors. Alpha Centauri is still the closest and Barnard’s Star is the next. Those two recent discoveries are the third and fourth closest, respectively. > > Orbits only follow simple ellipses when the two masses can be approximated to point masses. The galaxy is nowhere close to being a point mass, so it should have been obvious all along that the sun doesn’t follow one. And the fact that the Sun’s path bobs up and down in relation to the plane of the galaxy has been known for quite a while, although I don’t know when it was discovered. > > As for discovering new nearby stars, it’s unlikely Gaia will find anything really close, that is within 10 ly or so. Any unknown stars that close are probably too dim for Gaia to see. The two recent discoveries are brown dwarfs and were discovered by an orbiting infrared observatory (WISE). There may be more close brown dwarfs found in the WISE data, though. In fact, you can even look for them online, if you want: [Backyard Worlds](https://www.zooniverse.org/projects/marckuchner/backyard-worlds-planet-9/classify). You may also find Planet 9 in that data. My computer is actually crunching through the Gaia dr2 for another problem but I could replicate the animation here: [![](https://img.youtube.com/vi/LOJ1XmbSKhM/maxresdefault.jpg "The Milky Way as You’ve Never Seen It Before – AMNH SciCafe") ](https://www.youtube.com/watch?v=LOJ1XmbSKhM&t=908) But yes Gaia isn’t perfect for dwarfs, but it is in combination with the co-moving collections of stars and the implications for formation I was talking about. As the particular ideas I was talking about are in peer review I don’t want to link to that data right now as it may be a dead end. While Gaia isn’t great for brown dwarfs it is filling in a lot of gaps on knowledge about how groups of objects are formed and move and I expect some papers will be out in the next two years. _Note I am just a hobbyist, and I am using Gaia data related to the galaxy rotation problem and my misconceptions as motivation for self stud. While I have spent way too much of my personal funds building a machine for this goal I am being obtuse because these ideas were run across due to programming needs and not direct study. But the excitement from that areas researchers is quite palpable._ ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [December 12, 2018, 7:18pm UTC](https://boards.straightdope.com/t/why-is-the-heliosphere-oval-shaped/825931/12 "2018-12-12T19:18:42Z")
Speaking of which: [https://www.scientificamerican.com/article/voyager-2-spacecraft-enters-interstellar-space/](https://www.scientificamerican.com/article/voyager-2-spacecraft-enters-interstellar-space/) ---
**Author:** ![Measure\_for\_Measure](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/measure_for_measure/32/557_2.png) [@Measure\_for\_Measure](https://boards.straightdope.com/u/Measure_for_Measure)\ **Post date:** [December 14, 2018, 5:39pm UTC](https://boards.straightdope.com/t/why-is-the-heliosphere-oval-shaped/825931/13 "2018-12-14T17:39:55Z")
This thread has been helpful. I’ll try to summarize for the benefit of those who, like myself, have little familiarity with astro-physics. The sun rotates around the galaxy once every 230 million years. Within a human lifespan, the sky doesn’t change at all and maps of more than a dozen stars don’t need to be edited as time goes by. I understand though that the sky seen 100,000 years ago was a little different. So move the picture frame out to a hundred or more light years and shorten the time frame to a human lifespan and things are pretty static. That said, the sun is moving 20 km/sec (12 miles/sec) towards the star Vegas. Which is incredibly fast in terrestrial terms. > [@Chronos](#): > > Each star’s motion, and for that matter the motion of each molecule of the ISM, is independent. On average, they have a certain circulatory motion around the Galaxy, but individual stars vary. I typically don’t like videos, but rat avatar linked to an amazing depiction of the movement of 10,000 stars over many millions of years. He even was kind enough to jump in at 15:19 where the action begins: [https://www.youtube.com/watch?v=LOJ1XmbSKhM&feature=youtu.be&t=908](https://www.youtube.com/watch?v=LOJ1XmbSKhM&feature=youtu.be&t=908) According to my eyes, while stars in the field move in all directions, they tend to move in clumps and some directions are much more likely than others. Again though, within human time scales it would be a static picture. Oh yeah, and the shape of the heliopause is a matter of scientific debate.