Planet 9 Search Turning Up Wealth Of New Objects

Artist's impression of the the possible Planet 9 at the edge of the Solar System. Credit: Robin Dienel/Carnegie Science

In 2014, Scott Sheppard of the Carnegie Institution for Science and Chadwick Trujillo of Northern Arizona University proposed an interesting idea. Noting the similarities in the orbits of distant Trans-Neptunian Objects (TNOs), they postulated that a massive object was likely influencing them. This was followed in 2016 by Konstantin Batygin and Michael E. Brown of Caltech suggesting that an undiscovered planet was the culprit.

Since that time, the hunt has been on for the infamous “Planet 9” in our Solar System. And while no direct evidence has been produced, astronomers believe they are getting closer to discerning its location. In a paper that was recently accepted by The Astronomical Journal, Sheppard and Trujillo present their latest discoveries, which they claim are further constraining the location of Planet 9.

For the sake of their study, Sheppard and Trujillo relied on information obtained by the Dark Energy Camera on the Victor Blanco 4-meter telescope in Chile and the Japanese Hyper Suprime-Camera on the 8-meter Subaru Telescope in Hawaii. With the help of David Tholen from the University of Hawaii, they have been conducting the largest deep-sky survey for objects beyond Neptune and the Kuiper Belt.

This survey is intended to find more objects that show the same clustering in their orbits, thus offering greater evidence that a massive planet exists in the outer Solar System. As Sheppard explained in a recent Carnegie press release:

“Objects found far beyond Neptune hold the key to unlocking our Solar System’s origins and evolution. Though we believe there are thousands of these small objects, we haven’t found very many of them yet, because they are so far away. The smaller objects can lead us to the much bigger planet we think exists out there. The more we discover, the better we will be able to understand what is going on in the outer Solar System.”

Their most recent discovery was a small collection of more extreme objects who’s peculiar orbits differ from the extreme and inner Oort cloud objects, in terms of both their eccentricities and semi-major axes. As with discoveries made using other instruments, these appear to indicate the presence of something massive effecting their orbits.

All of these objects have been submitted to the International Astronomical Union’s (IAU) Minor Planet Center for designation. They include 2014 SR349, an extreme TNO that has similar orbital characteristics as the previously-discovered extreme bodies that led Sheppard and Trujillo to infer the existence of a massive object in the region.

Another is 2014 FE72, an object who’s orbit is so extreme that it reaches about 3000 AUs from the Sun in a massively-elongated ellipse – something which can only be explained by the influence of a strong gravitational force beyond our Solar System. And in addition to being the first object observed at such a large distance, it is also the first distant Oort Cloud object found to orbit entirely beyond Neptune.

And then there’s  2013 FT28, which is similar but also different from the other extreme objects. For instance, 2013 FT28 shows similar clustering in terms of its semi-major axis, eccentricity, inclination, and argument of perihelion angle, but is different when it comes to its longitude of perihelion. This would seem to indicates that this particular clustering trend is less strong among the extreme TNOs.

Beyond the work of Sheppard and Trujillo, nearly 10 percent of the sky has now been explored by astronomers. Relying on the most advanced telescopes, they have revealed that there are several never-before-seen objects that orbit the Sun at extreme distances.

And as more distant objects with unexplained orbital parameters emerge, their interactions seem to fit with the idea of a massive distant planet that could pay a key role in the mechanics of the outer Solar System. However, as Sheppard has indicated, there really isn’t enough evidence yet to draw any conclusions.

“Right now we are dealing with very low-number statistics, so we don’t really understand what is happening in the outer Solar System,” he said. “Greater numbers of extreme trans-Neptunian objects must be found to fully determine the structure of our outer Solar System.”

Alas, we don’t yet know if Planet 9 is out there, and it will probably be many more years before confirmation can be made. But by looking to the visible objects that present a possible sign of its path, we are slowly getting closer to it. With all the news in exoplanet hunting of late, it is interesting to see that we can still go hunting in our own backyard!

Further Reading: The Astrophysical Journal Letters

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Thanks, Comet Pluto. Solar System Nomenclature Needs A Major Rethink

Four images from New Horizons’ Long Range Reconnaissance Imager (LORRI) were combined with color data from the Ralph instrument to create this global view of Pluto. Credits: NASA/JHUAPL/SwRI

Pluto can’t seem to catch a break lately. After being reclassified in 2006 by the International Astronomical Union, it seemed that what had been the 9th planet of the Solar System was now relegated to the status of “dwarf planet” with the likes of Ceres, Eris, Haumea, and Makemake. Then came the recent announcements that the title of “Planet 9” may belong to an object ten times the mass of Earth located 700 AU from our Sun.

And now, new research has been produced that indicates that Pluto may need to be reclassified again. Using data provided by the New Horizons mission, researchers have shown that Pluto’s interaction with the Sun’s solar wind is unlike anything observed in the Solar System thus far. As a result, it would seem that the debate over how to classify Pluto, and indeed all astronomical bodies, is not yet over.

In a study that appeared in the Journal of Geophysical Research, a team of researchers from the Southwest Research Institute – with support from the Johns Hopkins University Applied Physics Laboratory, the Laboratory of Atmospheric and Space Physics at University of Colorado and other institutions – examined data obtained by the New Horizon mission’s Solar Wind Around Pluto (SWAP) instrument.

Basically, solar wind effects every body in the Solar System. Consisting of electrons, hydrogen ions and alpha particles, this stream of plasma flows from our Sun to the edge of the Solar System at speeds of up to 160 million kilometers per hour. When it comes into contact with a comet, there is a discernible region behind the comet where the wind speed slows discernibly.

Meanwhile, where solar wind encounters a planet, the result is an abrupt diversion in its path. The region where this occurs around a planet is known as a “bow shock”, owing to the distinctive shape it forms. The very reason the New Horizons mission was equipped with the SWAP instrument was so that it could gather solar wind data from the edge of the Solar System and allow astronomers to create more accurate models of the environment.

But when the Southwestern Research Institute team examined the SWAP data, which was obtained during the New Horizons’ July 2015 flyby of Pluto, what they found was surprising. Previously, most researchers thought that Pluto was characterized more like a comet, which has a large region of gentle slowing of the solar wind, as opposed to the abrupt diversion solar wind encounters at a planet like Mars or Venus.

What they found instead was that the dwarf planet’s interaction with solar wind was something the fell between that of a comet and a planet. As Dr. David J. McComas – the Assistant Vice President of the Space Science and Engineering Division at the Southwest Research Institute – said during a NASA news release about the study: “This is a type of interaction we’ve never seen before anywhere in our solar system. The results are astonishing.”

Examining both the lighter hydrogen ions that are thrown off by the Sun, and the heavier methane ions that are produced by Pluto, they found that the former showed a 20% rate of deceleration behind Pluto. This, and the bow shock Pluto produces, were both consistent with that of a comet. At the same time, they found that Pluto’s gravity was strong enough that it is able to retain the heavier methane ions, which is consistent with a planet.

Between these two readings, it seems that Pluto is something of an anomaly, behaving as something of a hybrid. Yet another surprise from a celestial body that has been full of them lately. And under the circumstances, it may lead to another round of “classification debates”, as astronomers attempt to find a new class for bodies that behave like both comets and planets.

As Alan Stern of the Southwestern Research Institute, and the principal investigator of the New Horizon’s mission, explained, “These results speak to the power of exploration. Once again we’ve gone to a new kind of place and found ourselves discovering entirely new kinds of expressions in nature.”

Further Reading: Journal of Geophysical Research

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