Mark Showalter and his research team at the SETI Institute in Mountain View, California, are on a roll. They’ve shown us yet again how much we have to learn about our closest planetary neighbors.

In 2011 and 2012, Showalter’s team discovered two additional moons orbiting Pluto. (The International Astronomical Union recently decided on the names Kerberos and Styx for these moons, despite an overwhelming public vote to name one of them Vulcan.) Using the Hubble Space Telescope, the same researchers recently discovered a new moon orbiting Neptune.

“I got nice pictures of the arcs [segments of the planet’s rings], which was my main purpose, but I also got this little extra dot that I was not expecting to see,” says Showalter.

At 65,400 miles from Neptune, the speedy, newly-discovered moon completes an orbit every 23 hours. This moon is hard to track, but more than 150 archived images from Hubble between 2004 and 2009 enabled Showalter to track down the orbit of the new moon.

“The moons and arcs orbit very quickly, so we had to devise a way to follow their motion in order to bring out the details of the system,” he says. “It’s the same reason a sports photographer tracks a running athlete—the athlete stays in focus, but the background blurs.” (Showalter compares capturing the new moon to Eadweard James Muybridge’s famous racehorse photographs in a blog post earlier this week.)

This 12-mile wide moon is the smallest of the Neptunian system (which currently includes 14 moons), and revolves around Neptune between the orbits of Larissa and Proteus. For now the tiny dot is called S/2004 N 1. The official name may not be put to vote this time (but Star Trek fans can get cracking on ideas).

S/2004 N 1’s discovery brings up additional questions besides its new name. A mini moon like this should have had trouble forming in the neighborhood of much larger moons.

“How you can have a 20-kilometre object around Neptune is a little bit of a puzzle,” says Showalter. “It’s far enough away that its orbit is stable. Once you put it there it will stay there. The question is, how did it get there?”

Triton is Neptune’s biggest moon, orbiting in the direction opposite Neptune’s spin. Astronomers originally thought that a moon of this type would have to be captured by Neptune’s gravity, destroying all smaller moons in the process.

Stay tuned to learn S/2004 N 1’s new name, and perhaps new theories about how it originated in the first place!

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Image: NASA, ESA, M. Showalter

Recent research makes it seem like astronomers can’t look up without finding exoplanets. Data illustrate scores of super earths, planets in their habitable zones, and multiple-planet systems… But a specific type of planet has proven elusive: a planet orbiting at a considerable distance from its parent star.

Gemini Observatory’s Planet-Finding Campaign recently completed the most extensive direct imaging survey to date, but the results were mostly devoid of large planets—especially gas giants—at significant distances from their parent stars. This may seem counter-intuitive… After all, we think of our own solar system as ordinary or average, and it includes giant planets such as Uranus and Neptune, which orbit quite far away from our sun.

Michael Liu, leader of the Gemini Planet-Finding Campaign, sums up the situation this way: “We’ve known for nearly 20 years that gas-giant planets exist around other stars, at least orbiting close-in. Thanks to leaps in direct imaging methods, we can now learn how far away planets can typically reside. The answer is that they usually avoid significant areas of real estate around their host stars. The early findings, like HR 8799, probably skewed our perceptions.”

Exoplanet discoveries are usually based on data taken from the parent star, but HR 8799 was one of the first star systems observed directly from Earth. Using the Gemini telescope, researchers could see gas-giants at large orbital distances from their sun. At the time of discovery in 2008, they did not have enough background knowledge to realize that HR 8799 was very, very unusual.

But gas giants aren’t missing; they just tend to cling to their parent stars in a close orbit. And this lack of distant gas giant planets is apparent across all sizes and types of stars.

Difficulty finding planets at distant orbits has a silver lining, because absent planets can actually tell us more about planet formation. Astronomers are developing an explanation for the strange holes in dust disks surrounding young stars. “It makes sense that where you see debris cleared away that a planet would be responsible, but we did not know what types of planets might be causing this. It appears that instead of massive planets, smaller planets that we can’t detect directly could be responsible,” said Zahed Wahhaj of the European Southern Observatory.

Even though the missing planets have taught us something, the search for planets with orbits similar to that of Uranus and Neptune continues. And we thought we lived in an average solar system…

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Image credit: NASA/ESA/C.Carreau

Previous studies have noted that a “dynamical instability” (which is to say, a complex interaction of gravitational effects of different planets on one another) affected the orbits of giant planets when the solar system was a mere 600 million years old. As a result, the giant planets and smaller bodies scattered away from each other… A little bit of self-segregation.

Some small bodies migrated into the Kuiper Belt and others traveled farther inward, producing impacts on the terrestrial planets and the Moon. The giant planets shifted around as well. Jupiter, for example, scattered most small bodies outward and moved inward.

Jupiter played one of the biggest roles in the solar system’s youth. Scientists believe it protected smaller planets, like our own, from colliding with each other. Scientists explain the giant world’s protective status through the “jumping Jupiter” theory. “They proposed that Jupiter’s orbit quickly changed when Jupiter scattered off of Uranus or Neptune during the dynamical instability in the outer solar system,” says David Nesvorny of the Southwest Research Institute.

But when Nesvorny ran computer simulations of this “jumping Jupiter” theory, he ran into a problem. While Jupiter did in fact jump through interactions with Uranus or Neptune, the simulations also showed that Uranus or Neptune got knocked out of the solar system.

So Nesvorny wondered whether the early solar system could have had five giant planets instead of four. By running the simulations with an additional giant planet with mass similar to that of Uranus or Neptune, things suddenly fell in place.

Nesvorny believes that jumping Jupiter ejected one planet from the solar system, leaving the four gas giant planets we know and love behind. Thankfully, Jupiter jumped, leaving the terrestrial planets (including Earth) undisturbed.

“The possibility that the solar system had more than four giant planets initially, and ejected some, appears to be conceivable in view of the recent discovery of a large number of free-floating planets in interstellar space, indicating the planet ejection process could be a common occurrence,” says Nesvorny.

This research appears in a recent edition of the Astrophysical Journal Letters.

Image: Southwest Research Institute