WHAT IS A ROGUE PLANET?
A rogue planet is a planetary-mass object
that travels through space without being
gravitationally bound to a star.
Unlike Earth, Jupiter or Neptune, it does
not follow a normal orbit around a host star.
Some may have formed around stars and later
been ejected from their planetary systems.
HOW DO THEY BECOME ROGUE?
Young planetary systems can be chaotic.
When several massive planets interact
gravitationally, one planet can receive
enough energy to be thrown completely out
of the system.
After that, it can continue travelling
through interstellar space for millions
or billions of years.
CAN THEY FORM ALONE?
Scientists are investigating whether
some planetary-mass objects could form
directly from collapsing clouds of gas,
without ever orbiting a star.
The distinction between a very small
brown dwarf and a rogue planet can
therefore be complicated.
COULD THEY HAVE MOONS?
A rogue planet could potentially retain
moons after leaving its original system.
However, detecting such moons would be
extremely difficult because both objects
would be drifting through the darkness
of interstellar space.
THE MYSTERY OF ROGUE PLANETS
NO SUNRISE
A rogue planet would not experience
a normal sunrise or sunset because
there is no nearby star illuminating
its surface.
EXTREME COLD
Without stellar heating, the surface
could become incredibly cold, although
internal heat may remain for a long time.
HARD TO FIND
They emit very little visible light,
making direct observation extremely
difficult.
MICROLENSING
Astronomers can sometimes detect
planetary-mass objects when their gravity
briefly magnifies the light of a distant star.
ANCIENT WORLDS
Some rogue planets could have travelled
through the Milky Way for billions of years.
UNKNOWN POPULATION
Astronomers are still determining how
many rogue planets exist in our galaxy.
DID YOU KNOW?
A rogue planet could be travelling through
the Milky Way with no star nearby to light
its surface — a planetary world wandering
alone through interstellar darkness.
HOW CAN A PLANET BECOME ROGUE?
Some rogue planets may form in planetary systems and later be ejected through gravitational interactions with other planets or stars. Others may form more directly from collapsing material without ever orbiting a star, depending on how such objects are defined and classified.
Because rogue planets do not have a nearby host star illuminating them, they are difficult to find. Astronomers can search for them using techniques such as gravitational microlensing and infrared observations of sufficiently warm nearby objects.
Brown Dwarfs · Stars