It’s been 11 years since Pluto was demoted to dwarf planet status. Since then astronomers have focused their eyes and telescopes in the space beyond Pluto, searching for additional planets.
In 2014, astronomers Chad Trujillo and Scott S. Sheppard inferred the possible existence of a very large trans-Neptunian planet, which came to be known as Planet Nine.
In a new paper, scientists Kat Volk and Renu Malhotra of the University of Arizona's Lunar and Planetary Laboratory (LPL), present compelling evidence of a new planetary body in the Kuiper belt with a mass somewhere between that of Mars and Earth.
Planet Nine
Planet Nine is a hypothesized large planet in an orbit far beyond Pluto, the gravitational effects of which would explain the improbable orbital configuration of a group of trans-Neptunian objects (TNOs) that orbit mostly beyond the Kuiper belt.
In a 2014 letter to the journal Nature, astronomers Chad Trujillo and Scott S. Sheppard inferred the possible existence of a massive trans-Neptunian planet from similarities in the orbits of the distant trans-Neptunian objects Sedna and 2012 VP113. On 20 January 2016, researchers Konstantin Batygin and Michael E. Brown at Caltech explained how a massive outer planet would be the likeliest explanation for the similarities in orbits of six distant objects. See table below for the estimated size and orbital parameters of the proposed object.
Batygin and Brown used simulations to show that the hypothesized planet with the proposed parameters results in clustered orbits for the observed TNOs.
Batygin and Brown suggest that it may be a primordial giant planet core that was ejected from its original orbit during the early phases of the Solar System's evolution. Others have proposed that it was captured from another star, or that it formed on a very distant circular orbit and was perturbed onto its current eccentric orbit during a distant encounter with another star. en.wikipedia.org/…
The Recent Case Against Planet 9
A new study weakens the case for Planet Nine; the authors state that the clustering of the observed TNOs may be a result of sampling bias; they accounted for the fact that certain bodies are preferentially spotted in certain parts of the sky at certain times of year and removing this bias eliminates the claimed clustering.
The authors used data from the Outer Solar System Origins Survey (OSSOS), a large program that ran on the Canada-France-Hawaii Telescope from 2013–2017, discovering more than 800 new TNOs. The authors conclude that the orbital distribution of the OSSOS sample is consistent with being detected from a uniform underlying angular distribution, meaning no clustering.
Even though the new study weakens the basis of the proposed Planet Nine, it does not explain the observed clustering or prove that Planet Nine does not exist.
Renu Malhotra, an astronomer at the University of Arizona in Tucson, states that the OSSOS team has not proved that these biases actually enhance the appearance of clustering among distant Kuiper belt objects, so its paper does little to change the debate.
Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington DC and part of the team that first suggested the presence of an unseen planet, agrees. Even with the new data, the best explanation for the odd grouping of Kuiper belt objects is a planet, he says.
Konstantin Batygin, an astronomer at the California Institute of Technology in Pasadena and a member of the other team that proposed the existence of Planet Nine, states that clustering is only one line of evidence for Planet Nine; discoveries of Kuiper belt objects that aren’t tethered to Neptune, and others with orbits nearly perpendicular to those of most Solar System objects, are most easily explained by the presence of a large planet in the outer Solar System.
www.scientificamerican.com/...
“Planet” 10
In their paper, Kat Volk and Renu Malhotra of the University of Arizona's Lunar and Planetary Laboratory, present evidence of a possible planetary body with a mass somewhere between that of Mars and Earth. They observed that the average orbital plane of 600 icy distant Kuiper Belt's objects (KBO) is tilted away from the invariable (mean) plane by an unexpected eight degrees.
"The most likely explanation for our results is that there is some unseen mass," says Volk, a postdoctoral fellow at LPL and the lead author of the study. "According to our calculations, something as massive as Mars would be needed to cause the warp that we measured."
The new planetary body is hypothesized to lie close to the Kuiper belt at a distance of around 55-60 AU. By comparison, Planet Nine is estimated to swing out to 1,200 AU.
Because a planet, by its new definition, has to have cleared its orbit of minor planets such as KBOs (that’s why Pluto lost its planethood), the authors refer to the hypothetical object as a planetary mass object. The data also do not rule out the possibility that the tilt could result from more than one planetary mass object.
Key parameters for Planet Nine and “Planet” Ten.
Parameter |
Planet Nine |
Planet Ten |
Mass |
10x Earth |
Between that of Mars and Earth |
Diameter |
2-4x Earth |
|
Orbital period |
10-20 thousand years |
Probably similar to Pluto’s period of 248 years |
Average distance from Sun |
700 AU
Sun-Earth distance = 1 AU
Sun-Neptune distance = 35 AU
|
55-60 AU
(7.6-8.3 light-hours)
|
Closest approach to Sun (perihelion) |
200 AU
|
|
Farthest distance from Sun (aphelion) |
1,200 AU
(6.9 light-days)
|
|
Orbital inclination |
30o relative to the ecliptic (Earth’s orbital plane) |
7o relative to the invariable (mean) plane |
The Kuiper Belt
The Kuiper belt is an area extending from the orbit of Neptune (at 30 AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times as wide and 20 to 200 times as massive. Like the asteroid belt, it consists mainly of small bodies, or remnants from the Solar System's formation. Most Kuiper belt objects are composed largely of frozen volatiles (termed "ices"), such as methane, ammonia and water. The total mass is estimated to range between 1/25 and 1/10 the mass of the Earth, although some estimates are as high as 30 Earth masses.
The Oort Cloud
The Oort cloud is a theoretical cloud of predominantly icy planetesimals believed to surround the Sun to as far as somewhere between 50,000 and 200,000 AU. It is divided into two regions: a disc-shaped inner Oort cloud (or Hills cloud), between 2,000 and 20,000 AUs and a spherical outer Oort cloud between 20,000 and 200,000 AUs. The Kuiper belt is less than one thousandth as far from the Sun as the Oort cloud.
Although no confirmed direct observations of the Oort cloud have been made, it may be the source of all long-period and Halley-type comets entering the inner Solar System, and many of the centaurs and Jupiter-family comets as well.
The outer Oort cloud may have trillions of objects larger than 1 km, billions larger than 20 km. Its total mass is is estimated at five times that of Earth. The mass of the inner Oort cloud has not been characterized.
Future Observations
Detecting small planetary objects at such distances is beyond the capabilities of current telescopes. The Large Synoptic Survey Telescope, scheduled for first light in 2020, will take unprecedented, real-time surveys of the sky and help detect many more KBOs and possibly planet 9 and 10.
The Large Synoptic Survey Telescope (LSST), with an 8.4-meter primary mirror, will photograph the entire available sky every few nights. The telescope uses a novel 3-mirror design which delivers sharp images over a very wide 3.5-degree diameter field of view, feeding a 3.2-gigapixel CCD imaging camera, the largest digital camera ever constructed.
The telescope will be located on the El Peñón peak of Cerro Pachón, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile.
References
- Unseen 'planetary mass object' signalled by warped Kuiper Belt — phys.org/…
- The Curiously Warped Mean Plane of the Kuiper Belt — arxiv.org/…
- Goodbye, Planet Nine! New And Better Data Disfavors A Giant World Beyond Neptune — www.forbes.com/…
- OSSOS VI. Striking Biases in the Detection of Large Semimajor Axis Trans-Neptunian Objects — arxiv.org/…
- Planet Nine — en.wikipedia.org/…
- Pluto - Planet or Dwarf Planet? — www.dailykos.com/…
- www.ossos-survey.org/…