I have a scientific research vessel that is exploring an alien galaxy.

I would like this vessel to detect and then explore a planet that was not previously known about, which means it (or potentially its entire solar system) was never seen or detected by scans from Earth (or another colonized planet).

When the ship crashes on the alien planet, they will be nearly impossible to rescue because they seemed to vanish into space.

Could this phenomenon be caused by anything natural? If there are multiple causes, what is something that is unlikely to be anticipated by people searching for the missing vessel? I really don't want them to ever be found.

Some details that might matter:

  • The planet must be potentially habitable.
  • The ship must be able to travel to it without any specialized equipment to resist the environment.
  • The ship does not necessarily have a tracking beacon that must be interfered with, as it can be damaged another way.
  • The planet / solar system can be anywhere relative to Earth or other colonized planets.
  • $\begingroup$ If you don't mind keeping it unexplained and a little mystical, you could have a Bermuda Triangle-esque space cloud that ships mysteriously disappear in. The real triangle has an explanation, but no one knows what it is. $\endgroup$
    – Starpilot
    Commented Jul 26, 2018 at 17:39
  • $\begingroup$ @Starpilot Good idea. I think that is what I'll resort to if I can't find a more scientific explanation. $\endgroup$
    – Anthony
    Commented Jul 26, 2018 at 17:48
  • 3
    $\begingroup$ If its an 'alien galaxy', meaning not our own, then the individual system isn't likely to be perceivable from Earth unless its star is massive. $\endgroup$ Commented Jul 26, 2018 at 18:04
  • 1
    $\begingroup$ You need your ship to lose contact with Earth way before the crash, otherwise they will report the location of the planet. $\endgroup$
    – user3106
    Commented Jul 26, 2018 at 20:51

11 Answers 11


For the whole star system to be undetected, we need to handwave away some science. Unless the star is far away form the space observed by a civilization and it hides behind very bright or impenetrable object like galactic core, it will certainly be visible, at least in some wavelength, and catalogued.

The planets are another matter. Currently we can detect planets only under very good conditions. Assuming this spacefaring civilization does not make significant advances in detecting planets in other systems, there will be little known about them until the system is visited by an expedition.

In your particular scenario, a ship may be traveling in a different galaxy without communication. Nobody back home knows for sure which stars it may visit. So while the star itself can be known, there will be no way to single it out because there will be thousands and millions of them.

  • $\begingroup$ If someone is tooling around the galaxy, they'll be technologically capable of trivially detecting planets long before anyone has to head over in that direction. The only reason why it's not easy now is that it's expensive to get stuff up to space in order to look for it. If you can easily and cheaply get stuff into space, with current tech you can directly detect an Earth-size planet at 1 AU from its star at a distance of 50 parsecs with a 12 meter telescope at 600 nm wavelength. $\endgroup$ Commented Jul 26, 2018 at 18:52

The solar system could be passing through a dense dust cloud. The solar wind would clear out some of the dust as it entered the cloud. You would not be able to see the star easily unless you were looking at it from the direction it went into the cloud.


First you need a very dim star, brown dwarf stars are extremely dim in the visible spectrum they're almost impossible to spot except by specialised infrared surveys. Such a star does theoretically, have a habitable zone where an earthlike world might support life for some millions of years, not native life though, there isn't enough time for evolution.

A world around such a star will be in a very tight orbit making a small rocky world like Earth hard to spot in an occlusion based survey like that used by the Kepler so the presence of a world at that location could go undiscovered almost indefinitely. If the planet orbits it's star with an elliptic at right angles to Earth as observation point you can't spot it using modern planet hunting methods at all.

To disappear a ship with a communication system, and presumably the knowledge base to build a new one if the original gets trashed you need a world where getting a signal out is really hard. This can be accomplished through any or a combination of a powerful magnetosphere, which a world that close to a star will probably need anyway to be habitable and/or a highly charged ionosphere. Either of which will block a wide range of signal mediums.

With a star that's almost impossible to spot at long range, a world you can't see even if you know where to look, and effective signal jamming, your ship will vanish without a trace. If ship has been a half a degree off course for the last hundred light years of travel it will probably be impossibly lost since no-one's looking along it's actual course but it's plotted course which is not the same thing at all. That's assuming modern technology and techniques but given routine space travel, odds are a society that advanced is going to be more aware of what's out there than we can imagine.


Your planet is a Rogue Planet - a planet, which does not have its own star, but "orbits a galactic center directly".

According to Wikipedia, rogue planets are able to sustain life:

In an Earth-sized object that has a kilobar atmospheric pressure of hydrogen and a convective gas adiabat, the geothermal energy from residual core radioisotope decay could maintain a surface temperature above the melting point of water, allowing liquid-water oceans to exist. These planets are likely to remain geologically active for long periods. If they have geodynamo-created protective magnetospheres and sea floor volcanism, hydrothermal vents could provide energy for life. Thus, humans could live on such a star-less planet, although food sources would be limited.


Like Alexander pointed out in the comments the last sentence is highly doubtable. In the original article it is stated that

We have shown that an Earth-like rogue planet drifting through interstellar space could harbor a subglacial liquid ocean despite its low emission temperature, and so might be considered habitable.

The high pressure atmosphere required for on-surface oceans would render human life surviving without technical aid (after all, humans in your universe have developed interstellar travel - so, who knows?) improbable.

This may be solved (Thanks to Jarred Allen) by the rogue planet having a moon, that, heated by tidal heating and radioactive decay (not too much - we don't want radiation sickness), may be able to support human life, in some weird ecological niche.


The next paragraph states also, that

[these] bodies would be difficult to detect because of their weak thermal microwave radiation emissions, although reflected solar radiation and far-infrared thermal emissions may be detectable from an object that is less than 1000 astronomical units from Earth.

Bonus Part:

They are as common as sand in the desert - while scientists don't seem to be too sure about how many of them there are, more than ~25 billion in the milky way alone seems to be reasonable [Source: Again, Wikipedia. Taken the estimation of Przemek Mróz for the amount of Jupiter-Sized rogue planets in relation to the number of stars in the milky way].

Some scientists even say this value is a little bit larger: by a factor of roughly 400 000 [Estimation of the "Kavli Institute for Particle Astrophysics and Cosmology"]

  • $\begingroup$ Hmm, I highly doubt that humans can live on a planet with "kilobar atmospheric pressure of hydrogen". $\endgroup$
    – Alexander
    Commented Jul 27, 2018 at 0:01
  • $\begingroup$ @Alexander give the rogue jupiter a rocky or icy moon. Problem solved. $\endgroup$ Commented Jul 27, 2018 at 1:54
  • $\begingroup$ @JarredAllen and Alexander: Thanks for the feedback, I edited the answer $\endgroup$ Commented Jul 27, 2018 at 5:04
  • $\begingroup$ @Jarred Allen Icy. It's going to be very, very icy. $\endgroup$
    – Alexander
    Commented Jul 27, 2018 at 5:53

An alien galaxy. Ships travel must faster than light or you don't have a story. If it takes a ship to do communication faster than light, then it's easy to be lost.

If you want to send for help, you need a message capsule that is a miniature spaceship. If you have used up your message capsules then they won't hear from you.

It's a galaxy with somewhere between a hundred million to a hundred trillion stars. It is being explored. If you need to land on a random planet and you don't get a message out, they won't find you any time soon. If they search a million stars a year, and check whether you are on any habitable planets, they will find you within 100 to 100 million years.

Kind of like the old sailing ships. If you got shipwrecked on an undiscovered island, you didn't get rescued until somebody else discovered the island.

To get a potentially habitable planet -- maybe a few billion years ago, somebody created terraforming nanos that spread everywhere. If one of them found a planet that could be terraformed it created algae etc to get a life cycle going, and also made many billions of nanos, and created a nano-launcher which launched trillions of other nanos that might find other habitable planets. Earth was found by one of those billions of years ago, and as of 2018 our scientists have not noticed the nano launchers which are sending a thousand tiny projectiles a year and will send a trillion of them in the next billion years. Whoever spread them in our galaxy also spread them in the one being explored.

So there are lots of habitable planets, because that's one kind of planet the nanos make. Everything alive has DNA a lot like yours, and mostly the same amino acids, they mostly don't make amino acids that poison you, etc.

It isn't that big a deal that you found a habitable planet, there are lots of them -- except habitable planet! -- but it's worth checking out if you have to stop there for other reasons.


I'm no astronomer, but from what I know of spatial observation :

First, you want your planet to be impossible to see. If you have a finite number of observation points, the system could be conveniently hidden behind another sun from each of these points. You could also have an atmosphere that absorb light (means it always appear dark from the outside) and the planet in an orbit plan that never passes between an observation point and its sun.

It's pretty important that it be the only planet in the system, otherwise one might speculate its position from the way its gravity field impacts other astral bodies.

It could also simply be too far. We simply don't observe all stars, especially the farthest ones.

Last, If your ship moves at FTL speed, it could land on a system whose light won't reach your other colonies until hundreds of years.


You could have something really bright, like a recent supernova, between Earth and the star system in question that simply overwhelms sensors on Earth. It is like trying to read a glow-in-the-dark watch with a spotlight shining in your face. There is nothing wrong with the watch itself, but you can't see it because it is far too dim compared to the spotlight.


Distance is always useful for hiding an astronomical body.

If your ships uses some type of hyperspace or subspace jumps to instantly move from one place to another, and if travel between solar systems and even other galaxies is common, some sort of accident or miscalculation during a jump through space could make it much longer than the normal jump through space.

Suppose that exploring spaceships normally jump to stars that are between 50 and 100 light years from Earth. Suppose this exploring starship wants to jump from the star system it just explored to the system next on his list, only 5.042 light years away, and for some reason which never happened before, the starship jumps ten million times as far, or 50,420,000 light years. Suppose that the spaceship only has enough fuel lief for a few short jumps, enough to find a nearby star system with a habitable planet and reach that. Suppose that the starship's only method of communication is to return to headquarters with their reports, and now they can't do that.

At the time of the story humans are exploring space 50 to 100 light years from Earth. And now an unprecedented and previously unimaginable accident has sent the spaceship 500,000 to 1,000,000 times as far as the zone of exploration.

Since the zone of space that includes the lost spaceship has about 125,000,000,000,000,000 to 1,000,000,000,000,000,000 times the volume of the present limits of human exploration, the time it takes human explorers to explore space as far out as the distance to the lost spaceship may be approximately 125,000,000,000,000,000 to 1,000,000,000,000,000,000 times as long as the time it took to explore out to 50 to 100 light years from Earth.

This is just a crude calculation, but it gives the general idea that a spaceship that jumps through space a great enough distance and can't get back might not be discovered by other explorers from Earth for many, many millions or billions of years, which would seem like "never" by human time standards.

If there is no form of faster than light radiation in your fictional universe, their astronomers, and the navigators on their ships, will have to use electromagnetic radiation, as our astronomers do, to study the universe.

The expansion of the universe can exceed the speed of light at great enough distances, because it is the space between objects that is expanding, and the objects are not technically moving.

So since distant parts of the the universe could have been expanding at many times the speed of light, and since light from those objects can only reach us aat the speed of light, and since the universe is only 13,000,000,000 or so light years old, there could be galaxies far beyond the most distant light that astronomers can detect, galaxies whose light might not reach Earth until billions or trillions of years.

Since the universe has expanded since the oldest light reaching Earth was emitted 13,000,000,000 years ago, the most distant objects we can see are now about 45,700,000,000 light years away. Thus we cannot now see or chart any astronomical object beyond about 45,700,000,000 light years away.

And that will have changed only minutely 10,000 years in the future, for example, when Earthlings might be exploring 1,000 light years from Earth. if some event causes a starship to make an unplanned jump 150,000,000,000 light years, and it is for some reason impossible to program a reverse duplicate jump, the crew will be lost.

If the radius that they can detect astronomical objects is 45,700,000,000 light years from their current position, and they have records of astronomical bodies within a radius of 45,700,000,000 light years from Earth, there will be a gap of 58,600,000,000 light years between the two sets of observations and they can never identify a known object to show the way back to Earth. And at that distance it could be trillions of years before explorers from Earth reach their region of space - which is the same as never by human standards of time.

Suppose that the starship is a colony ship taking many tens or hundreds of thousands of colonists and their equipment to a planet to be colonized, and the "accidental" distant jump far into space is actually caused by a dissident group among the colonists, who want to go to a distant world and found their own independent society, for the other colonists to do things their way. The dissidents could make certain that it was impossible for the other colonists to ever find their way back to Earth space.


One way is for the the ship to cross the event horizon of a massive rotating black hole. The planet is inside as well. They'll never get out and eventually be pulled apart as they get nearer the singularity.

The question then becomes, why did they go into this massive black hole? Were they surveying it and accidentally crossed the event horizon?

As an aside, the gravitational forces of a massive black hole are low enough that you can survive close to and even within the event horizon.


The planet might be inside a dyson sphere. For a far enough observer, the whole star system would look like a black hole for all practical purposes.

Alternatively, the planet's system might be behind a wormhole. For practical purposes, looking straight into a wormhole would show you something from a far away region in space, hiding whatever is on the other side (around, not through) of the wormhole.


I'm not sure if this answer will work or not:

Central body: A large black hole.

Orbiting it close: A brown dwarf or perhaps a star.

Orbiting it far: An ordinary planet.

Your hidden planet: In the L4 or L5 position relative to the brown dwarf.

These two bodies are positioned just outside the Roche limit of the black hole and are suffering severe effects. The solid body is merely tidally locked and stretched but the gaseous one is bleeding off mass. The result is a torus of gas around the black hole, the hidden planet is within this. The planet isn't truly invisible, but the presence of the gas torus makes it very hard to spot compared to an ordinary planet and thus it was missed.

For an examination of this, look at The Integral Trees by Larry Niven. (There's also The Smoke Ring but it doesn't really add much about the environment.) Note that his ring is a smaller system and there is no hidden planet.


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