New evidence in support of the Planet Nine hypothesis

Will another planet be added to the list of Mercury,
Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune in our
Solar System? Credit: NASA

Last year, astronomers announced the existence of an unknown
planet in our solar system. However, this hypothesis was
subsequently called into question as biases in the
observational data were detected. Now, Spanish astronomers
have used a novel technique to analyse the orbits of the
so-called extreme trans-Neptunian objects and, once again,
they report that there is something perturbing them—a planet
located at a distance between 300 to 400 times the Earth-sun

At the beginning of 2016, researchers from the California
Institute of Technology (Caltech, USA) announced that they had
evidence of the existence of this object, located at an average
of 700 AU and with a mass 10 times that
of the Earth. Their calculations were motivated by the peculiar
distribution of the orbits found for the trans-Neptunian
objects (TNO) in the Kuiper belt, which suggested the presence
of a Planet Nine within the solar system.

However, scientists from the Canadian-French-Hawaiian project
OSSOS detected biases in their own observations of the orbits
of the TNOs, which had been systematically directed towards the
same regions of the sky, and considered that other groups,
including the Caltech group, may be experiencing the same
issues. According to these scientists, it is not necessary to
propose the existence of a massive perturber to explain these
observations, as they are compatible with a random distribution
of orbits.

Now, however, two astronomers from the Complutense University
of Madrid have applied a new technique less exposed to
observational bias to study the so-called “extreme
trans-Neptunian objects” (ETNOs)—located at average distances
greater than 150 AU, and which never cross Neptune’s orbit. For
the first time, the distances from their to the sun have been analysed, and the
results, published in the journal MNRAS, once again
indicate a planet beyond Pluto.

The nodes are the two points at which the orbit of an ETNO, or
any other celestial body, crosses the plane of the solar
system. These are the precise points where the probability of
interacting with other objects is the highest, and therefore,
at these points, the ETNOs may experience a drastic change in
their orbits or even a collision.

Like the comets that interact with Jupiter

“If there is nothing to perturb them, the nodes of these
extreme trans-Neptunian objects should be uniformly
distributed, as there is nothing for them to avoid, but if
there are one or more perturbers, two situations may arise,”
explains Carlos de la Fuente Marcos, one of the authors, to
SINC. “One possibility is that the ETNOs are stable, and in
this case, they would tend to have their nodes away from the
path of possible perturbers. But if they are unstable, they
would behave as the comets that interact with Jupiter do,
tending to have one of the nodes close to the orbit of the
hypothetical perturber.”

Using calculations and data mining, the Spanish astronomers
have found that the nodes of the 28 ETNOs analysed (and the 24
extreme Centaurs with average distances from the sun of more
than 150 AU) are clustered in certain ranges of distances from
the sun; furthermore, they have found a correlation where none
should exist between the positions of the nodes and the
inclination, one of the parameters which defines the
orientation of the orbits of these icy objects in space.

“Assuming that the ETNOs are dynamically similar to the comets
that interact with Jupiter, we interpret these results as signs
of the presence of a planet that is actively interacting with
them in a range of distances from 300 to 400 AU,” says De la
Fuente Marcos. “We believe that what we are seeing here cannot
be attributed to the presence of observational bias.”

Until now, studies that challenged the existence of Planet Nine
using the data available for these trans-Neptunian objects
argued that there had been systematic errors linked to the
orientations of the orbits (defined by three angles) due to the
way the observations had been made. Nevertheless, the nodal
distances mainly depend on the size and shape of the orbit,
parameters which are relatively free of observational bias.

“It is the first time that the nodes have been used to try to
understand the dynamics of the ETNOs”, De la Fuente Marcos
says, adding that discovering more ETNOs (at the moment, only
28 are known) would permit the proposed scenario to be
confirmed and subsequently constrain the orbit of the unknown
planet via the analysis of the distribution of the nodes.

The authors note that their study supports the existence of a
planetary object within the range of parameters considered both
in the Planet Nine hypothesis of Mike Brown and Konstantin
Batygin from Caltech, and in the original one proposed in 2014
by Scott Sheppard from the Carnegie Institute and Chadwick
Trujillo from the University of North Arizona; it also
corresponds with their own earlier studies, which suggested
that there is more than one unknown planet in our solar system.

Is there also a Planet Ten?

De la Fuente Marcos explains that the hypothetical Planet Nine
suggested in this study has nothing to do with another possible
planet or planetoid situated much closer to us, and hinted at
by other recent findings. Also applying to the orbits of the TNOs of the
Kuiper Belt, astronomers Kathryn Volk and Renu Malhotra from
the University of Arizona (USA) have found that the plane on
which these objects the sun is slightly warped, a
fact that could be explained if there is a perturber of the
size of Mars at 60 AU from the sun.

“Given the current definition of a planet, this other
mysterious may not be a true planet, even if it
has a size similar to that of the Earth, as it could be
surrounded by huge asteroids or dwarf ,” explains the Spanish astronomer. “In
any case, we are convinced that Volk and Malhotra’s work has
found solid evidence of the presence of a massive body beyond
the so-called Kuiper Cliff, the furthest point of the
trans-Neptunian belt, at some 50 AU from the sun, and we hope
to be able to present soon a new work which also supports its

Explore further:

Extreme trans-Neptunian objects lead the way to Planet Nine

More information: C. de la Fuente Marcos, R. de la
Fuente Marcos. “Evidence for a possible bimodal distribution of
the nodal distances of the extreme trans-Neptunian objects:
avoiding a trans-Plutonian planet or just plain
bias?”. Monthly Notices of the Royal Astronomical
: Letters, July 2017. DOI:

Journal reference:
Monthly Notices of the Royal Astronomical Society

Provided by:
Spanish Foundation for Science and Technology (FECYT)