A Mini-Pluto at the Edge of Our Solar System

Astronomers have better measurements now of what is turning out to be a smaller version of Pluto located so far away that it may take 1,100 years to orbit the Sun. Nicknamed D.D. (or DeeDee) for Distant Dwarf, this remarkable small world appears to be about 400 miles in diameter -- only about 1/4 the size of Pluto, but possibly still big enough to be round like a planet.

D.D. was found in the fall of 2016 by a team of astronomers led by David Gerdes of the University of Michigan. As so often happens in astronomy, they were looking for something completely different, but found D.D. as part of their work. Now they have used an array of radio telescopes, called ALMA, to measure D.D.'s size and also to estimate its temperature. Ninety-two times as far from the Sun as the Earth is, D.D. is thought to be at minus 405 degrees Fahrenheit (minus 243 degrees Celsius; or only 30 degrees above nature's limit, absolute zero.)

D.D. is part of a whole zone of icy objects out beyond Neptune (astronomers call them Trans-Neptunian Objects or TNO's,) About 2,000 TNOs are now known, but most of them are too small and irregular (knotty potato-shaped) to be called dwarf planets. Pluto, the first TNO dwarf planet, was discovered in 1930, but in the last decade of the 20th century and the first decade of the 21st century, others were found, including Eris, Makemake, and Haumea. (If the names sound unusual, it's because we are trying now to name these outer worlds after mythological beings from many cultures, not just the ancient Greeks or Romans!)

We need more observations of D.D. before we are ready to call it a dwarf planet. If you thought that Pluto was being insulted when we called it a dwarf planet, perhaps it will help you to know that Pluto is the "first" of a whole new category of worlds. Five dwarf planets are now officially recognized by the International Astronomical Union, and at least six other worlds out beyond Neptune may eventually be included in the group. It may be years before we know if D.D. will join them.

But it's wonderful to see the Sun's family growing in this way, with our new instruments and surveys able to find worlds that literally are "far out!"

There is a Possible Super Earth in the Outer Solar System

Out there, way beyond the Sun's family, astronomers have discovered thousands of planets orbiting other stars. Among these alien planets, we have discovered a significant number of "Super Earths" -- planets more massive than our Earth but less massive than the smallest giants in our solar system, Uranus and Neptune. Our solar system has no such Super Earths, but many other systems do; they may be quite common.

Now, Michael Brown and Konstantin Batygin at Caltech, propose that we might just have a Super Earth in our solar system, but so far from the Sun, it takes between 10,000 and 20,000 years to make one orbit! (Pluto, for comparison, takes about 250 years.)

Brown and Batygin have been examining the orbits of icy chunks way beyond Pluto, in the region we call the Kuiper Belt. There are several chunks out there, including one Brown discovered in 2003, called Sedna, that move in an oddly aligned way. After testing many computer models to explain their odd orbit, their best model indicates there could be a planet 10 times the mass of our own Earth, whose stronger gravity is affecting the motions of many objects out where it orbits. Just a few of the affected chunks have been discovered so far and the planet itself has NOT be seen.

So this is a somewhat daring hypothesis, which the two astronomers explain in this brief video: https://www.youtube.com/watch?v=6poHQ2h00ZA

Please note that our image is a painting that Caltech commissioned. No one knows what this Planet Nine looks like.

Now here is the human side of the story. Michael Brown led the team that discovered Eris, the dwarf planet that is the same size as Pluto, in 2005. When he discovered it, he told his wife that he had just discovered a tenth planet and she had made a good decision in marrying him. Alas, instead of being acknowledged as the 10th planet, Eris caused astronomers to rethink the status of Pluto, and remove it from being the 9th planet. Brown was gracious about it, but you can imagine how disappointing it all was for him.

So now Brown may have "discovered" (or at least predicted) a real new planet. He is already nicknaming it "Planet Nine" and it's so big, no one will be able to call it a dwarf! If it is confirmed one day, he can go back to his wife and tell her, "Well, maybe I only discovered a dwarf planet before, but now I have discovered a real planet at last." Not a bad thing to discuss over dinner!

You can see a video where Brown discusses his role in the Pluto and Eris story at: https://www.youtube.com/watch?v=7pbj_llmiMg

Brown and Batygin