16 | SCIENCE ILLUSTRATED
ASTRONOMY The GJ 3512 object is around 31
light years from Earth, and astronomers used to
think it was a double star system, with two stars
orbiting one another. But analyses made by
astronomers from the Autonomous University in
Spain have revealed something quite different:
a huge gas planet closely orbiting a small star
known as a red dwarf. The combination is so
unusual that it challenges astronomers’ ideas
about how gas giants such as Jupiter are formed.
The newly-discovered gas giant has been named
GJ 3512 b. It has a mass of at least 46% that of
Jupiter, whereas the red dwarf star has a mass only
12% of that of the Sun. So the two objects are much
closer in size than the Sun is to its biggest planet.
The distance between the two objects is also
closer. The gas giant orbits the red dwarf at a
distance shorter than the distance between the Sun
and Mercury, the Solar System’s innermost planet.Both the distance and the relative sizes have
come as major surprises to scientists. Until now
astronomers have thought that gas giants such as
Jupiter formed in a two-step process. From a disc of
gas and dust around a star, a core of ice and small
rock fragments first collect until they gain a weight
at least 10 times that of Earth. The core’s gravity is
then so intense that the planet can subsequently
collect and maintain a thick atmosphere of
hydrogen and helium. But the Spanish astronomers’
computer simulations show that GJ 3512 b cannot
have formed in this way: it would have taken too
long, and the core would only have been completed
after the gases had long disappeared from the disc.
Instead, scientists think that the gas giant formed
in a faster process where the disc of gas and dust
collapsed, forming the core all at once. If so, gas
giants orbiting red dwarfs might be far more
common than astronomers used to think.Red dwarf’s gas giant conundrum
The discovery of a Jupiter-like planet orbiting close to a red dwarf star
forces astronomers to adjust their theories about solar system formation.The gas planet in the alien
solar system has a diameter
70% of the star it is orbiting.The diameter of Jupiter,
which is a little bigger
than GJ 3512 b, is only about
one-tenth of the Sun's.GJ 3512 b is almost
as big as its starJupiter is tiny
compared to the SunGJ 3512 B'S DIAMETER:
136,311kmJUPITER'S
DIAM142,984kmETER:RED DWGJ 3512'S ARF
DIAM194,730km ETER:DIAMTHE SUN'S ETER:
1,392,000kmGas giant is surprisingly close to its star
If the gas planet of GJ 3512 b belonged to our Solar System, it would be the innermost planet, even closer
to the Sun than Mercury. The planet’s size is also much closer to that of its star than Jupiter’s is to the Sun.EARTHMERCURYTHE SUNVENUSGJ 3512 bTHE GJ 3512 B
GAS GIANT
PLACED IN
OUR SOLAR
SYSTEMMERCURY
IS ORBITING
CLOSEST
TO THE SUN
IN OUR SOLAR
SYSTEMSCIENCE UPDATE