Caltech Researchers Find Evidence of a Real Ninth Planet

Caltech press release

Caltech researchers have found evidence of a giant planet tracing a bizarre, highly elongated orbit in the outer solar system. The object, which the researchers have nicknamed Planet Nine, has a mass about 10 times that of Earth and orbits about 20 times farther from the sun on average than does Neptune (which orbits the sun at an average distance of 2.8 billion miles). In fact, it would take this new planet between 10,000 and 20,000 years to make just one full orbit around the sun.

Planet 9 Artist's Concept
This artistic rendering shows the distant view from Planet Nine back towards the sun. The planet is thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side. Credit: Caltech/R. Hurt (IPAC)
The researchers, Konstantin Batygin and Mike Brown, discovered the planet’s existence through mathematical modeling and computer simulations but have not yet observed the object directly.

“This would be a real ninth planet,” says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy. “There have only been two true planets discovered since ancient times, and this would be a third. It’s a pretty substantial chunk of our solar system that’s still out there to be found, which is pretty exciting.”

Brown notes that the putative ninth planet—at 5,000 times the mass of Pluto—is sufficiently large that there should be no debate about whether it is a true planet. Unlike the class of smaller objects now known as dwarf planets, Planet Nine gravitationally dominates its neighborhood of the solar system. In fact, it dominates a region larger than any of the other known planets—a fact that Brown says makes it “the most planet-y of the planets in the whole solar system.”

Batygin and Brown describe their work in the current issue of the Astronomical Journal and show how Planet Nine helps explain a number of mysterious features of the field of icy objects and debris beyond Neptune known as the Kuiper Belt.

“Although we were initially quite skeptical that this planet could exist, as we continued to investigate its orbit and what it would mean for the outer solar system, we become increasingly convinced that it is out there,” says Batygin, an assistant professor of planetary science. “For the first time in over 150 years, there is solid evidence that the solar system’s planetary census is incomplete.”

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Walk through the Solar System

A scale model of the solar system, laid out along Mamalahoa Highway through the center of Waimea. That is what we create every year for the Waimea Solar System Walk.

Starting on the lawn of Keck Observatory headquarters you can walk from the Sun to the outer solar system at the Canada France Hawai’i Telescope headquarters. Four and a half billion kilometers reduced to one kilometer (2.8 billion miles to about 1/2 mile). At this scale the Earth becomes a the size of a small bead and Jupiter a marble. Walking a model like this give a whole new appreciation for the scale of our solar system, driving home the idea that space is really, really big.

Dozens of kids and parents took advantage of the event to learn a bit about space and astronomy. Starting at the Sun they could wander from the inner solar system to the outer solar system. Passports handed out at Keck HQ were stamped at each planet along the way as the tour and each planet was manned by volunteers to answer questions.

Against the odds, it was a pretty nice day in Waimea. The characteristic strong winds and blowing drizzle was absent. We had sunny skies and when the wind died away in the afternoon, it became somewhat hot. This allowed for great views through the solar telescopes and nice conditions to stroll the length of the main street.

The experience was aided by volunteers who came in from organizations across the island, each bringing some educational fun to the planet walk. Nancy Tashima from the Onizuka Center covered Mercury, using some great material from the MESSENGER mission including 3D photos and glasses.

Gary Fujihara brought a splendid collection of meteorites. Using the asteroid belt as his home base to educate folks about the many minor bodies in the solar system and the material that falls to Earth.

Keck and CFHT staff put everything together and manned most of the booths. Members of the West Hawai’i Astronomy club helped out at registration and brought solar telescopes to view our Sun. Given clear skies in Waimea the view was fantastic. There were several good sunspots and wonderful prominences to be seen. It was great to see all those who volunteered their Saturday to help out.

A lot of smiling faces to be seen as kids and parents explored our solar system and learned. Always nice when you can slip a little knowledge in with the fun.

Zodiacal Light

A strange glow visible long after sunset, or well before dawn, along the path of the Sun in the sky. Called the “False Dawn” by Muhammad in Islamic texts and by other classical sources, this glow is often confused with the light of dawn, or simply overlooked by many.

Zodiacal Light
False dawn, actually zodiacal light, rising over Mauna Kea
Once thought to be the extended atmosphere of the Sun, the zodiacal light was recognized as something interesting by early scientists. The real reason for the glow was not understood until described by Nicolas Fatio de Duillier in 1684.

The answer is simply dust.

Space is not only very big and mostly empty, it can also be dirty. Dust from comets, dust from asteroid collisions, dust floating in orbit about the Sun, reflecting sunlight and glowing across the sky. Because this dust lies in the plane of the solar system the glow is visible as a band along the ecliptic and through the constellations of the zodiac. The dust is thickest, and the glow brightest nearer the Sun, thus the glowing dust is best seen when the Sun is just out of sight, after dusk, or before dawn. The light is simply reflected light. Looking at the spectrum of the zodiacal light shows it to be sunlight, with the same spectral features.

The zodiacal light can be quite bright, clearly visible to any who look in the hour after dusk, or before dawn. It can be bright enough to be a nuisance to amateur astronomers attempting to view through their telescopes. At the same time it is a sign of clear dark skies, as it is otherwise hidden by the glow of artificial light. The slightest amount of moonlight or light pollution and this glow disappears from sight.

The effect can be seen completely across the sky, along the ecliptic, as a very faint glowing band when viewed from the darkest of places. Directly opposite the Sun in the sky is a brighter spot in the glow, the gegenschein or counterglow. A form of glory, the dust reflects sunlight back in the direction it came.

The zodiacal band and the gegenschein are both visible from Mauna Kea on a dark night. From this dark place the most subtle of astronomical spectacles can be appreciated.