I'm an Astronomy noob, but I'm interested in learning how stars and planets work. Everything started with the Trappist-1. I read about it, and it's fascinating. However, it's impossible for me to localize it with my current state of knowledge. Therefore, I would like to ask some general questions here.

First of all, during high school, I have learned that we are in the solar system and there are some planets orbiting the sun. Easy to remember and imagine, but there are stars, planets, constellations, etc. which I can't manage to relate to this basic system that I learned about.

And what confused me a lot are these two pictures:

enter image description here


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And this definition of an exoplanet:

An exoplanet or extrasolar planet[...]

From the pictures, I can see that Trappist is in fact in the solar system. Is this right? And if this is right, why in the world did it take us so many years to find it? We have one Voyager that is almost out from the solar system. Couldn't it find it before? And is it possible to find more planets in our solar system? Is it because Voyager went only in the x-y direction, and not "perpendicular" to the orbits?

I'm sorry for asking these stupid questions, but I simply can't build new knowledge on my current low-level understanding of the solar system. This is my current knowledge: enter image description here

Can you please help me to answer the above questions?

  • 5
    $\begingroup$ I really liked this question, even if you consider it of a low level. What matters is the approach to something one doesn't know, admitting it and looking /asking for answers. My compliments for your attitude. I thought seeing so many ignorant in astronomy was a big pain for me. You made me understand that what causes me pain is their attitude towards it and science in general. Thanks. $\endgroup$ Mar 15, 2017 at 17:54
  • $\begingroup$ Thank you! I know what you mean. There was already a person who called my question stupid :-) He deleted the comment, I guess. $\endgroup$
    – Physther
    Mar 16, 2017 at 11:08
  • 2
    $\begingroup$ The top response here is very accurate so I will add nothing by re-explaining it. I will however, say that whoever called it a stupid question was wrong and I'll not insult them to make my point but stupidity or the spectrum to which it exists: intelligence, has nothing to do your level of knowledge. Endeavouring to understand more about the way things work is the opposite of stupid. Knowledge is a powerful tool for the intelligent but it is not a measure as such. Keep learning, do not be intimidated and remember: I know what color my eyes are and you don't.... does that make you stupid? or ma $\endgroup$
    – Dylan
    Sep 20, 2017 at 17:18
  • $\begingroup$ don't know something? ask a question. Now you know that something. $\endgroup$ Sep 25, 2017 at 15:36

3 Answers 3


During high school, I have learned that we are in the solar system and there are some planets orbiting the Sun.

Yes that is correct. According to current definitions of what counts as a planet, there are 8 planets orbiting our Sun $-$ Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. There are also a collection of smaller "Dwarf Planets" which include (in no particular order): Pluto, Ceres, Eris, and Makemake. There's also a lot of other minor solar system bodies out there like asteroids, comets, etc.

but there are stars, planets, constellations

Yes, there are many other stars out there besides our own (as you can see by simply looking up at the night sky). Each of those stars has the potential for having its own planets, much like ours does. Any planet outside our own solar system is referred to as an exoplanet (exo- meaning outside or external). Within the past 20 or so years we've developed the technology to find exoplanets around other stars and this TRAPPIST-1 discovery was simply the latest and most sensational discovery. To date we've discovered ~3500 exoplanets.

What confused me a lot are these two pictures. [...] And this definition of an exoplanet.

Those pictures, while seeming to show the the TRAPPIST-1 planets in our solar system, are not indicating that those planets actually reside in our solar system. Instead, what they're trying to do is compare the new TRAPPIST-1 system to our own so you can see the relative sizes. In your first image, you see Jupiter along with the orbits and distances of a few of its Moons. Next to it, you see the TRAPPIST-1 system with the seven planets we know of around it. Next to that is the Sun where you can just begin to see the orbit of Mercury (with the other planets beyond the bounds of the image. The point here is just to compare sizes of orbits. Clearly this TRAPPIST-1 system is much smaller than our own since all 7 planets orbit closer to the main star that even Mercury does for us. However, it is still bigger than Jupiter and its moons. They're not trying to make the point that these systems reside in the same place, just putting them together for comparison.

As for the second image you have, what they're trying to show here (I assume) is the habitability zone. Around every star, depending on the star's size and temperature, there will be a good distance to be from the star that is optimal for life to exist. You don't want your planet to be too hot (by being too close) or too cold (by being too far). This image appears to be showing you the regions where a planet can be at a good distance from TRAPPIST-1 and still be at a good temperature. There is the Inner B line which I take to be the Inner Boundary of this zone. In other words, if a planet is any closer than this, it will be too hot. There's also the Outer B (or Outer Boundary) where beyond that, any planet would be too cold for life. Finally they have the Earth B. I can't be certain but I believe this point is actually the distance for the "optimal" temperature that we have here on Earth. In other words, the best chance a planet has of being at a good temperature for life is to orbit between Inner B and Outer B and ideally be at the distance of Earth B. This image also shows that the orbit of the planet TRAPPIST-1e is close to Earth B and still inside Outer B, meaning it is likely to be at a hospitable temperature for life (which is good news for us!). I won't go into what an AU (aside from mentioning it is a unit of distance) or the frost line, since they're not pertinent to the point of the image. Feel free to ask other questions for that.

Lastly, the definition of an exoplanet you found describes it an "extrasolar planet". That just means it is beyond our solar system $-$ "extra-" meaning "outside" or "beyond" and "solar" referring to our own Sun.

  • $\begingroup$ Boy, Zephyr… are you patient! $\endgroup$ Sep 12, 2022 at 19:30

From the pictures, I can see that Trappist is in fact in the solar system. Is this right?

The intent of those pictures is to give an idea of the small size of the TRAPPIST-1 star system.

TRAPPIST-1 is not in the solar system. It is instead a star system (a very small star system) that is about 40 light years from our own solar system. By comparison, the distance between the Sun and Proxima Centauri, the nearest star other than the Sun, is about 4.22 light years, and the distance between the Sun and Voyager 1 is currently about 0.0022 light years.


You're not stupid for asking this. I'll give you what i think will help you. You that all of these stars are part of the milky way galaxy, that means that they are all a collection of planets, stars, and other objects that are in a cluster by gravity.

So, the TRAPPIST-1 system is around forty light years away, which means if we were traveling at the speed of light, it would take 40 years to get there.

Basically, in order for the TRAPPIST-! system to be part of our own system, it needs to be orbiting the sun, or the star in the TRAPPIST-1 system needs to be orbiting our sun.

When two stars orbit each other, it is called a binary system. There have been some planets found in binary systems.

So if the TRAPPIST-1 system was part of the solar system, its planets and its star would most likely be orbiting us. But the distance from the sun makes the planets orbit TRAPPIST-1 (their star), and not out star (the Sun).

  • $\begingroup$ Do you need me to explain anything more? $\endgroup$ Mar 16, 2017 at 14:36

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