Two New Moons for Jupiter

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Advances in technology have lead to the discovery of new planets outside of our Solar System, and now even new moons in our own backyard.

Last September, two satellites – the smallest ever discovered – were found orbiting Jupiter.

That brings the number of Jovian moons to a whopping 66.  The moons – each about 1 km in size – are very distant from Jupiter. It takes the tiny satellites 580 and 726 days to orbit the gas giant.

The discovery could lead us one step closer to understanding the formation and evolution of our solar system. At least that’s the hope of Scott Sheppard, who works at the the Department of Terrestrial Magnetism at the Carnegie Institution of Science in Washington, D.C. It was Sheppard who, with the help of the massive Magellan telescope at Las Campanas, Chile, initially observed the moons.

“The new satellites are part of the outer retrograde swarm of objects around Jupiter. It is likely there are about 100 satellites of this size around Jupiter,” Sheppard said, explaining that Magellan has made it easier to detect objects further away from Earth. “Up until the last decade, the technology wasn’t there to discover these things because they are very small and very faint.”

The two tiny, irregular moons are called S/2011 J1 and S/2011 J2. Thankfully, those names aren’t expected to stick. Once officially confirmed (Sheppard expects it to happen this year), he will have the opportunity to name each. But, Sheppard can’t pick just any moniker. The names, according to the International Astronomical Union, must be related to Jupiter or Zeus, the Roman and Greek mythological figures who served as king of the gods.

Credit: NASA/ESA/E. Karkoschka (U. Arizona)

Maybe that’s why Sheppard hasn’t yet thought of any names for the soon-to-be members of the Jovian moon list. Are there any names that haven’t already been chosen? Europa, Thebe, Io, Callisto, Sinope, Ganymede …

Naming requirements will definitely need to change because, as Sheppard explains, there are a lot more moons to discover around some of our other gas – and ice – giants.

“There are a similar amount of objects orbiting Saturn and Neptune, which are more distant from the Sun,” Sheppard said, citing a survey of the sky conducted by the Carnegie Institution of Washington in the early 2000s. “If larger telescopes are built in the future, we’ll be able to discover more of these objects and find out what the objects are like,” Sheppard said.

And finding more of these smaller, distant, irregular satellites is a key to understanding our past.

Here’s why: Irregular satellites are believed to have been captured by their respective planets because the moons typically orbit in the opposite direction of the planet’s rotation, and, they also have eccentric and highly inclined orbits.

Those types of moons differ from regular satellites, which are believed to have formed from the same materials that comprise the planet. That’s because the moons tend to have nearly circular orbits, and, they orbit their respective planets in the same direction that the planet rotates.

A planet can temporarily capture an object, i.e. Shoemaker-Levy 9, but in the present time, “a planet has no known efficient mechanism to permanently capture satellites. Thus, outer satellite capture must have occurred near the time of planet formation when the Solar System was not as organized as it is now,” Sheppard said.

“The orbital history of a satellite can be very complex … but understanding where a satellite came from can tell us about the formation and evolution of our Solar System.”

Click here to learn more about the Carnegie Institution’s Department of Terrestrial Magnetism. For more information about Jovian moons, go to Scott Sheppard’s Jupiter Satellite Page.

AVIATR: An Airplane Mission for Titan

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It has been said that the atmosphere on Titan is so dense that a person could strap a pair of wings on their back and soar through its skies.

It’s a pretty fascinating thought. And Titan – Saturn’s largest moon – is a pretty fascinating place. After all, it’s the only other body in our solar system (besides Earth, of course) that has that type of atmosphere and evidence of liquid on its surface.

“As far as its scientific interest, Titan is the most interesting target in the Solar System,” Dr. Jason W. Barnes of the University of Idaho told Universe Today.

That’s why Barnes and a team of 30 scientists and engineers created an unmanned mission concept to explore Titan called AVIATR (Aerial Vehicle for In-situ and Airborne Titan Reconnaissance). The plan, which primarily consists of a 120 kg plane soaring through the natural satellite’s atmosphere, was published online late last month.

The goal of the plane concept – which according to Barnes can serve as a standalone mission or as part of a larger Titan-focused exploration program – is to study the moon’s geography (its mountains, dunes, lakes and seas), as well as its atmosphere (the wind, haze, clouds and rain. Did you know that Titan is the only other place is our solar system where it rains?)

AVIATR is composed of three vehicles: one for space travel, one for entry and descent into Titan, and a plane to fly through the atmosphere. AVIATR, estimated to cost $715 million, would not prevent other missions from occurring on Titan, Barnes said. Instead, it would supplement the science being done by other projects.

“The science that AVIATR could do complements the science that can be accomplished from both orbiting and landed platforms,” the article stated.

Unfortunately, it seems like the plane concept won’t be happening anytime soon.

That’s because Titan didn’t make the National Research Council’s “Decadal Survey” – a prioritization of future planetary missions. (Read more about the survey in this Universe Today post.)

“Titan was deferred to another decade,” Barnes said.

But, he hopes to continue to build support for AVIATR so that it can get onto the next decadal survey in 2020. “We certainly had a lot of interest from people. We are breaking the paradigm that a balloon was the right way to go to Titan,” Barnes said.

So, why send an unmanned plane to study Titan’s atmosphere?

“Titan is the best place to fly an airplane in the whole solar system. We can go when and where we want,” Barnes said, adding that when compared to Earth, there’s four times more air and seven times less gravity on Titan. “A balloon is stuck in the wind.”

According to the article:

“A balloon entrained in primarily zonal winds near the equator would have no mechanism by which to travel to the polar regions to observe lakes and shoreline processes. Even if it were possible to get there, it is not clear that it would be desirable to send a balloon to the poles where Titan’s most violent meteorological activity takes place. AVIATR is both able to fly to the poles and is sufficiently robust to survive there.”

Mission poster for AVIATR. Credit: Mike Malaska

There’s also this issue: A shortage of plutonium-238.

“The radioactive decay of plutonium-238 provides the heat that powers RTGs, which can power spacecraft where there is insufficient sunlight for solar panels to operate. NASA is presently investing in a new type of RTG, called the ASRG,” the article stated. “A traditional hot-air balloon will not work on Titan with an ASRG owing to its lower heat production. In contrast, the AVIATR mission is specifically enabled by the use of ASRGs. The power density (in Watts per kilogram) and longevity of the ASRG allow an electrically-powered aircraft to fly on Titan.”

A plane could also find potential landing spots for future exploration. And, “since we are flying, we fly west the whole time so we can stay on the day side of Titan,” Barnes said.

That daylight would also help AVIATR collect photographic data during its travels and, according to Barnes, when it’s time to downlink that information, the plane would conserve energy by gliding through the air.

“And in doing so, we can also sample of bunch of altitude ranges,” Barnes said. “We are sampling the whole time.”

The plan seems interesting enough, but it’ll be quite a while before any data from the prospective mission would be coming back to Earth. If the plan is accepted (the earliest being 2020), the project would still have to be built, then once completed it would take 7 1/2 years to reach Titan. Once there, the mission would take about a nominal Earth year to study.

“I now realize that it’s a career-long project,” Barnes said to Universe Today. “The plan at this point is to keep this in the forefront of people’s minds and take whatever new ideas that people suggest and try to improve its prospect for selection.

To view the complete proposal, published in Experimental Astronomy, go here.