New Dwarf Planet is Most Distant Object Yet Observed in our Solar System

It has been estimated that there may be hundreds of dwarf planets in the Kuiper belt and Oort Cloud of the outer Solar System. So far we’ve found – and actually seen – just a few. This past week, one more dwarf planet was added to the list and comes in at the most distant object ever seen in the Solar System.

This newly found world, initially named V774104, is about 15.4 billion kilometers from the Sun. At 103 AU, it is three times further from the Sun than Pluto, and is more distant than the previous record holder, Eris, which lies at 97 AU.

The discovery of V774104 was announced by one of the astronomers who found the object, Scott Sheppard, from the Carnegie Institution for Science, at the American Astronomical Society’s Division for Planetary Sciences fall meeting last week. Sheppard, along with Chad Trujillo and David Tholen used Japan’s 8-meter Subaru Telescope in Hawaii to make the find.

Astronomers say this newly spotted dwarf planet shows the depths of our Solar System.

“The discovery of V774104 is more proof that the Solar System is bigger than we thought,” said astronomer Joseph Burns from Cornell University, who was not associated with the discovery. “We need a little more time to pin down the orbit and determine the object’s exact size, but it must be big to see it at this distance.”

The size of V774104 is currently estimated to be between 500 and 1000 kilometers in diameter, which is less than half Pluto’s size.

While the size of the object is of some interest to astronomers who are searching for KBOs, even more interesting is pinning down its orbit. With its recent discovery, the orbit of V774104 has yet to be tracked for long periods of time.

If the orbit of V774104 comes closer to the Sun, such as between 30 to 50 AU, then it would be considered an icy Kuiper Belt objects which are more common among bodies like this found so far. Their orbits are more elongated because they fall under the gravitational influence of Neptune.

Of even more interest are what Sheppard called “inner Oort Cloud objects,” (also called “sednoids”). Theses bodies exist in a part of the Solar System that astronomers used to think was fairy empty. Of the two previously observed objects in this class — Sedna and 2012 VP113. — their orbits never come closer to the Sun than 50 AU, and they have a semi-major axis greater than 150 AU. The eccentric orbits of these objects have yet to be explained.

Colin Johnston from the Armagh Planetarium clarifies:

This means at their closest to the Sun they are still beyond the Kuiper Belt which lies 30-50 au from the Sun. Only two other objects in this category are known: 90377 Sedna and 2012 VP113.

They intrigue astronomers as they inhabit what was expected to be a largely empty region between the Kuiper Belt and the Oort Cloud, the Solar System’s yet to observed reservoir of comets. As well, the current highly elliptical orbits of Sednoids cannot be their original orbits, the chance of smaller bodies in such eccentric paths accreting into objects hundreds of kilometres across is fantastically low. Sednoids must have originally formed in relatively circular orbits, possibly in the Oort Cloud.

“Non-eccentric orbits seem to be the anomaly here,” Burns told Universe Today.

So, this likely means that something other than the Sun is responsible for influencing the erratic orbits of such small objects like V774104. One theory is that there might be a large planet at the outer reaches of the Solar System influencing the orbits of these distant objects.

Of course, among some crowds that brings up the hypothetical Planet X. But Burns was quick to dismiss that idea.

“While we certainly don’t understand well these objects, we may want to scatter off an object like Planet X,” he said via email.

At the AAS meeting last week, Sheppard said the likely alternative is that the orbits of these objects might reflect the primordial conditions of the Solar System, which formed more than 4.5 billion years ago. This makes them even more enticing for study, and Sheppard and his team will be keeping a close eye on V774104 to try and learn more. Nature News reported that the team plans to look for it again this week using the Magellan Telescopes in Chile, and then again in a year, to calculate its orbit and determine whether if it is an inner Oort cloud resident or an icy Kuiper Belt object.

Further reading: Nature, Armagh Planetarium,Centauri Dreams, Science.

Stealing Sedna

Turns out, our seemly placid star had a criminal youth of cosmic proportions.

A recent study out from Leiden Observatory and Cornell University may shed light on the curious case of one of the solar system’s more exotic objects: 90377 Sedna.

Distant Sedna (circled) moving against the starry background). Image credit: NASA/Hubble
Distant Sedna (circled) moving against the starry background). Image credit: NASA/Hubble

A team led by astronomer Mike Brown discovered 90377 Sedna in late 2003. Provisionally named 2003 VB12, the object later received the name Sedna from the International Astronomical Union, after the Inuit goddess of the sea.

From the start, Sedna was an odd-ball. Its 11,400 year orbit takes it from a perihelion of 76 astronomical units (for context, Neptune is an average of 30 AUs from the Sun) to an amazing 936 AUs from the Sun. (A thousand AUs is 1.6% of a light year, and 0.4% of the way to Proxima Centauri, the closest star to our solar system). Currently at a distance of 86 AU and headed towards perihelion in 2076, we’re lucky we caught Sedna as it ‘neared’ (we use the term ‘near’ loosely in this case!) the Sun.

But this strange path makes you wonder what else is out there, and how Sedna wound up in such an eccentric orbit.

Zooming out; the inner solar system (upper left), the outer solar system (upper right), the orbit of Sedna (lower right) and the inner edge of the Oort cloud (lower left).  Image credit: NASA
Zooming out; the inner solar system (upper left), the outer solar system (upper right), the orbit of Sedna (lower right) and the inner edge of the Oort cloud (lower left). Image credit: NASA

The study, entitled How Sedna and family were captured in a close encounter with a solar sibling  looks at the possibility that Sedna may have been snatched from another star early on in our Sun’s career (of interstellar crime, perhaps?)  The team used supercomputer simulations modeling 10,000 encounters to discover which types of near stellar passages might result in an ice dwarf world in a Sedna-like orbit.

“We constrained the parent star of Sedna to have between one and two times the mass of the Sun and its closest approach to be 200-400 AUs,” Dr. Lucie Jilkova of Leiden Observatory told Universe Today. “Such a close encounter probably happened while the Sun was still a member of its birth star cluster — a family of about 1,000 stars, so called solar siblings, born at the same time relatively close together — which was about 4 billion years ago.”

Image credit:
The orbit of Sedna. (Note Neptune and Pluto towards the center) Image credit: NASA/JPL

The best fit for what we see today in the outer solar system in the case of Sedna, is a close (340 AU) passage from the Sun — that’s over 11 times Neptune’s distance — of a 1.8 solar mass star  inclined at an angle of 17-34 degrees to the ecliptic. Sedna’s current orbital inclination is 12 degrees.

Rise of the Sednitos

The paper assigns the term ‘Sednitos’ (also sometimes referred to as ‘Sednoids’) for these Edgeworth-Kuiper Belt intruders with similar characteristics to Sedna. In 2012, 2012 VP113, dubbed the ‘twin of Sedna,’ was discovered by astronomers at the Cerro Tololo Inter-American Observatory in a similar looping orbit. The ‘VP’ designation earned the as yet unnamed  remote world the brief nickname ‘Biden’ after U.S. Vice President Joe Biden… hey, it was an election year.

There’s good reason to believe something(s?) out there shepherding these Senitos into a similar orbit with a comparable argument of perihelion. Researchers have suggested the existence of one or several planetary mass objects loitering out in the 200-250 AU range of the outer solar system… note that this is

a separate scientific-based discussion versus any would-be Nibiru related non-sense, don’t even get

us started…

If researchers in the study are correct, Sedna may have lots of company, with perhaps 930 planetesimals predicted in the ‘Sednito region’ of the solar system from 50 to 1,000 AUs and 430 more additional planetesimals littering the inner Oort cloud from the same early event.

“We focused on a particular example of a stellar encounter with characteristics from the ranges mentioned,” Dr. Jilkova said. “For this example, we estimated that there would be about 430 bodies similar to Sedna in the outer solar system (beyond 75 AU).”

Fun fact: One possible controversial candidate for the birth cluster of Sol and our solar system is the open cluster M67 in Cancer.  It’s an intriguing notion to try and track down the star we stole Sedna from 4 billion years ago using spectral analysis, though researchers in the study point out that the other more massive star is probably an aging white dwarf by now.

Astronomy from the surface of Sedna is mind-bending to contemplate. Currently 86 AU from the Sun and headed towards perihelion in 2076, Sol would appear only 20” across from the surface of Sedna, but would still shine at magnitude -17 to -18 near perihelion, about 40 to 100 times brighter than a Full Moon. Fast forward about 5,500 years towards aphelion, however, and the Sun would dim to a paltry magnitude -12, a full magnitude (2.5 times) dimmer than the Full Moon.

The view from Sedna looking towards the inner solar system in 2015. Image credit: Starry Night Education Software.
The view from Sedna looking towards the inner solar system in 2015. Note the five degree red field of view marker. Image credit: Starry Night Education Software.

Shining at magnitude +21 in the constellation Taurus, astronomers know little else about Sedna. Based on brightness estimates, Sedna measures about 1,000 km in diameter. It does appear to be the reddest object in the solar system, and may turn out to be the ‘red twin of Pluto’ as recently revealed by NASA’s New Horizons spacecraft, complete with a surface rich in tholins.

And a new generation of observatories may uncover a treasure trove of Sednitos. The European Space Agency’s Gaia astrometry mission should uncover lots of new asteroids, comets, exoplanets and distant Kuiper Belt objects as a spin-off to its primary mission. Then there’s the Large Synoptic Survey Telescope, set to see first light in 2019.

“The key piece of the puzzle is to actually observe more Sedna-like objects.” Dr Jilkova said. “Currently, we know only of two such bodies. More discoveries are expected in the following years and they will shed light on the origin of Sedna and its family and the ‘criminal record’ of the Sun.”

It’s a fascinating story of interstellar whodunit for sure, as our Sun’s early days of wanton juvenile delinquency unravel before the eyes of modern day astronomical detectives.

Discovery! Possible Dwarf Planet Found Far Beyond Pluto’s Orbit

What is a dwarf planet? Some astronomers have been asking that question after Pluto was demoted from planethood almost a decade ago, partly due to discoveries of other worlds of similar proportions.

Today, astronomers announced the discovery of 2012 VP113, a world that, assuming its reflectivity is moderate, is 280 miles (450 kilometers) in size and orbiting even further away from the sun than Pluto or even the more distant Sedna (announced in 2004). If 2012 VP113 is made up mostly of ice, this would make it large (and round) enough to be a dwarf planet, the astronomers said.

Peering further into 2012 VP113’s discovery, however, brings up several questions. What are the boundaries of the Oort Cloud, the region of icy bodies where the co-discoverers say it resides? Was it placed there due to a sort of Planet X? And what is the definition of a dwarf planet anyway?

First, a bit about 2012 VP113. Its closest approach to the Sun is about 80 astronomical units, making it 80 times further from the Sun than Earth is. This puts the object in a region of space previously known only to contain Sedna (76 AU away). It’s also far away from the Kuiper Belt, a region of rocky and icy bodies between 30 and 50 AU that includes Pluto.

The discovery images of 2012 VP113. Each one was taken about two hours apart on Nov. 5, 2012. Behind the object, you can see background stars and galaxies that remained still (from Earth's perspective) in the picture frame. Credit: Scott S. Sheppard: Carnegie Institution for Science
The discovery images of 2012 VP113. Each one was taken about two hours apart on Nov. 5, 2012. Behind the object, you can see background stars and galaxies that remained still (from Earth’s perspective) in the picture frame. Credit: Scott S. Sheppard: Carnegie Institution for Science

“The detection of 2012 VP113 confirms that Sedna is not an isolated object; instead, both bodies may be members of the inner Oort Cloud, whose objects could outnumber all other dynamically stable populations in the Solar System,” the authors wrote in their discovery paper, published today in Nature.

The Oort cloud (named after the Dutch astronomer Jan Oort, who first proposed it) is thought to contain a vast number of smallish, icy bodies. This NASA web page defines its boundaries as between 5,000 and 100,000 AUs, so 2012 VP113 obviously falls short of this measure.

The astronomers hypothesize that 2012 VP113 is part of a collection of “inner Oort cloud objects” that make their closest approach at a distance of more than 50 AU, a boundary that is thought to avoid any “significant” interference from Neptune. Orbits of these objects would range no further than 1,500 AU, a location hypothesized as part of the “outer Oort cloud” — the spot where “galactic tides start to become important in the formation process,” the team wrote.

“Some of these inner Oort cloud objects could rival the size of Mars or even Earth. This is because many of the inner Oort cloud objects are so distant that even very large ones would be too faint to detect with current technology,” stated Scott Sheppard, co-author of the paper and a solar system researcher at the Carnegie Institution for Science. (The lead author is the Gemini Observatory’s Chadwick Trujillo, who co-discovered several dwarf planets with the California Institute of Technology’s Mike Brown.)

The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA
The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA

One large question is how 2012 VP113 and Sedna came to be. And of course, with only two objects, it’s hard to draw any definitive conclusions. Theory 1 supposes that the gas giant planets beyond Earth ejected a “rogue” planet (or planets) that in turn threw objects from the Kuiper Belt to the more distant inner Oort Cloud. “These planet-sized objects could either remain (unseen) in the Solar System or have been ejected from the Solar System during the creation of the inner Oort Cloud,” the researchers wrote.

(Planet X hopers: Note that NASA just released results from its Wide-Field Infrared Survey Explorer that found nothing Saturn’s size (or bigger) as far as 10,000 AU, and nothing bigger than Jupiter at 26,000 AU.)

Theory 2 postulates that a passing star moved objects closer to the Sun into the inner Oort cloud. The last, “less-explored” theory is that these objects are “extrasolar planetesimals” — small worlds from other stars — that happened to be close to the Sun when it was born in a field of stars.

However these objects came to be, the astronomers estimate there are 900 objects with orbits similar to Sedna and 2012 VP113 that have diameters larger than 620 miles (1,000 kilometers). How do we know which are dwarf planets, however, given their distance and small size?

Artist's impression of Makemake, a dwarf planet about two-thirds Pluto's size. Credit: ESO/L. Calçada/Nick Risinger (skysurvey.org)
Artist’s impression of Makemake, a dwarf planet about two-thirds Pluto’s size. Credit: ESO/L. Calçada/Nick Risinger (skysurvey.org)

The International Astronomical Union’s definition of a dwarf planet doesn’t mention how big an object has to be to qualify as a dwarf planet. It reads: “A dwarf planet is an object in orbit around the Sun that is large enough (massive enough) to have its own gravity pull itself into a round (or nearly round) shape. Generally, a dwarf planet is smaller than Mercury. A dwarf planet may also orbit in a zone that has many other objects in it. For example, an orbit within the asteroid belt is in a zone with lots of other objects.”

That same page mentions there are only five recognized dwarf planets: Ceres, Pluto, Eris, Makemake and Haumea. Brown led the discovery of the last three dwarf planets in this list, and calls himself “the man who killed Pluto” because his finds helped demote Pluto from planethood to dwarf planet status.

It’s hard for official bodies to keep up with the pace of discovery, however. Brown’s webpage lists 46 “likely” dwarf planets, which under this definition would give him 15 discoveries.

“Reality … does not pay much attention to official lists kept by the IAU or by anyone else,” he wrote on that page. “A more interesting question to ask is: how many round objects are there in the solar system that are not planets? These are, by the definition, dwarf planets, whether or not they ever make it to any offiicially sanctioned list. If the category of dwarf planet is important, then it is the reality that is important, not the official list.”

Artist's impression of the dwarf planet Haumea and its moons, Hi'aka and Namaka. Credit: NASA
Artist’s impression of the dwarf planet Haumea and its moons, Hi’aka and Namaka. Credit: NASA

His analysis (which focuses on Kuiper Belt objects) notes that most objects are too faint for us to notice if they are round or not, but you can get a sense of how round an object is by its size and composition. The asteroid belt’s Ceres (at 560 miles or 900 km) is the only known round, rocky object.

For icier objects, he suggested looking to icy moons to understand how small an object can be and still be round. Saturn’s moon Mimas is round at 250 miles (400 km), which he classifies as a “reasonable lower limit” (since observed satellites of 125 miles/200 km are not round).

Discovery of 2012 VP113 came courtesy of the new Dark Energy Camera (DECam) at the National Optical Astronomy Observatory’s 4-meter telescope in Chile. The orbit was determined with the Magellan 6.5-meter telescope at Carnegie’s Las Campanas Observatory, also in Chile.

The paper, called “A Sedna-like body with a perihelion of 80 astronomical units”, will soon be available on Nature’s website.