Makemake is a dwarf planet about 1,400 kilometers in diameter (or about 2/3 the size of Pluto). It is about 45 AU from the Sun, making it part of the Kuiper belt. We now know it also has at least one moon. 

The moon, known as MK 2, is about 160 kilometers in diameter. While Makemake is the second brightest Kuiper belt object (after Pluto), its moon is quite dark. This is similar to Pluto’s moon Charon, which is also much darker than its planet. It’s possible that MK 2 simply lacks the mass necessary to keep a gravitational hold on icy volatiles as they are warmed by the Sun.

One big advantage of this new discovery is that it will allow us to better understand the composition of Makemake. By watching the moon’s orbit we can accurately determine the mass of both MK 2 and Makemake. This will give us a good measure of their densities, which will allow us to determine if they are more rocky or icy.

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The Kuiper belt is a region of objects beyond the orbit of Neptune. You can think of it as an outer asteroid belt, where the bodies are icy rather than rocky. The dwarf planets Pluto, Haumea and Makemake are part of the belt, as well as about 100,000 other bodies. It’s generally thought that the Kuiper belt likely formed during the great migration, when Jupiter moved farther out from the Sun due to interactions with other outer planets. One of the questions, then, is whether other planetary systems would also have a Kuiper belt. Recently, observations from the Gemini South Telescope in Chile have found a similar belt around a young star.

The team observed a ring around a 10-20 million year old star that’s about 50% more massive than our Sun. The belt lies in a range of 37 – 55 AU from the star, which is a similar range to that of our own Kuiper belt. It’s brightness also indicates a similar composition to the Kuiper belt. What’s particularly striking about the ring is that it isn’t centered on the star, but is offset slightly. This could be explained by gravitational interactions with large planets, similar to the way Jupiter affected the formation of the Kuiper belt.

Paper: Thayne Currie, et al. Direct Imaging and Spectroscopy of a Young Extrasolar Kuiper Belt in the Nearest OB Association. arXiv:1505.06734 [astro-ph.EP] (2015)

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The New Horizons spacecraft is on its way to Pluto. It will fly-by the dwarf planet in July 2015. The spacecraft will have far too much speed to stay near Pluto, so after its visit the craft will continue its journey away from the Sun. Given that Pluto marks the inner edge of the Kuiper belt, it would be nice if New Horizons could explore other Kuiper belt objects.  

This is the goal of a recent search by the Hubble telescope. From now through August, Hubble will scan the skies in the region of Pluto in an effort to find Kuiper belt objects. So far, Hubble has found two such objects, seen above. If one is found within range, the trajectory of New Horizons can be adjusted to visit the world after Pluto, likely reaching the new object a few years later.

Hopefully after Pluto we’ll be able to explore newer horizons.

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Whenever I talk about the planets of the solar system, someone usually asks “what about Pluto?”  Many people have an emotional attachment to the planet, and feel somewhat offended that the mean astronomers have declared the tiny world to be not a planet.  So what about Pluto?  Well, it turns out we now know a great deal more about the planet than we did when you were little, and we’ll soon know even more.

When Pluto was first discovered in 1930, it was seen only as a faint point of light that moved relative to background stars.  It was only due to photographic observations that it was discovered at all.  Because of its distance it was difficult to determine the characteristics of Pluto.  We had no way to determine its mass, and estimating its size could only be done by guessing its albedo (how much light it reflects).  If it was a bright world it could be rather small, but if it was a dark world it would be rather big.

Left: first image of Pluto with moon Charon.
Right: more modern Hubble image.

Then in 1977 a magnified photographic image of pluto showed a slight bulge.  Analysis of other images showed the bulge appeared with a period of about 6 days.  Pluto’s moon Charon had been discovered.  With the discovery of a moon it was then possible to determine the mass of Pluto.  It was found that Pluto’s mass was quite small, less than a fifth of our own Moon.  Later we determined its diameter is only about 70% that of the Moon.

Pluto is clearly part of the Kuiper family. Credit: Scott Sheppard

That alone is enough to question the idea that Pluto should be considered a planet, but then we began to find more objects with similar distances and orbits as Pluto.  They form the Kuiper belt, which is an icy version of the asteroid belt beyond the orbit of Neptune.  Pluto is the largest Kuiper belt object (KBO), but we now know of more than a thousand KBOs larger than 100 km.  Pluto is very clearly part of a family of objects.  Which is one of the reasons it was demoted from being a planet.

The planet Pluto everyone loved was a dim speck of light.  The last planet at the edge of our solar system.  The dwarf planet Pluto of today is the largest member of an icy belt that marks the beginning of the outer solar system.  It is also the first such object we will explore.  In 2015 the New Horizons spacecraft will make a flyby of Pluto, giving us the first detailed images of a KBO.

So don’t mourn Pluto the dim dot of a planet.  Celebrate Pluto, the king of the Kuiper belt, and guardian of the great beyond.

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There’s a newly discovered dwarf planet in our solar system, which was recently announced in Nature. The term dwarf planet should be used lightly here, since this new planet hasn’t been added to the official IAU list of dwarf planets.  It doesn’t even have a name beyond its designation of 2012 VP113, though it has been nicknamed Biden (after the U.S. Vice President) by its discoverers.

In some ways this new dwarf planet is similar to Sedna.  Both bodies have orbits beyond the region of Pluto and the Kuiper belt, and there are similarities to their orbits in terms of eccentricity and orientation.  Comparison of their orbits to dynamical models seem to indicate that both Sedna and “Biden” are inner bodies of the Oort cloud, which we know exists from the studies of comets but haven’t observed directly.  This likely means there are more objects with similar orbits yet to be discovered.

The motion of VP113 over several hours is seen in red, green, and blue. Credit: Scott S. Sheppard.

One of the more interesting aspects of this discovery is that the orbits of Sedna and VP113 seem to imply the existence of a much larger object even further out.  Given the orbital similarity of the two dwarf planets, it is possible that they have a resonance with a large distant planet.  When the team ran simulations to test the validity of this idea, they found the best solution was an object of about 10 Earth masses with a circular orbit of radius 250 AU.

The authors clearly point out that this result is tentative, and there are other simulation results that work almost as well.  But the possibility of a large outer body is interesting.  Pluto and the other dwarf planets (official and unofficial) so far discovered are small.  None of them are larger than the Moon.  This is part of the reason there is such a clear line between planet and dwarf planet.  But if there is an object of 10 Earth masses out there, it blurs the line a bit.  On the one hand, it would clearly be of planet size, and in a fairly circular orbit.  On the other hand it could be part of a larger system of Oort cloud bodies.

But all that is hypothetical at this point.  For now, we have another candidate dwarf planet, and it seems clear that more are out there waiting to be discovered.

Paper: Chadwick A. Trujillo & Scott S. Sheppard, A Sedna-like body with a perihelion of 80 astronomical units. Nature 507, 471–474  (2014) doi:10.1038/nature13156

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