This Week in Space

Blue Moon

Early Friday morning saw a celestial event that occurs, well, once in a blue moon.

At about 3:23 a.m. PST, the second full moon in one month, known as a blue moon, illuminated the night sky, with the first occurring on July 2. This was the first blue moon, by this definition, experienced since 2012, and the last until 2018.

How did we end up with an extra full moon? It is a contrast between the calendar month and the lunar month—lunar (or synodic) months average about 29.5 days, making them shorter than calendar months, which have 30 or 31 (except February with 28 or 29). The extra half-day to one-and-a-half days add up over the months, eventually causing some years to have 13 full moons rather than 12.

Historically, however, a blue moon was considered the third full moon in a season with four full moons. Typically, the time between each equinox and solstice only hosts three. By this reasoning, 2015 has no blue moon, but we will experience one on May 21, 2016 (with other full moons occurring on March 23, April 21, and June 20 that spring). The modern definition stemmed from the March 1946 issue of Sky and Telescope magazine, when James Hugh Pruett incorrectly referenced the 1937 Maine Farmer’s Almanac, writing, “This second [full moon] in a month, so I interpret it, was called Blue Moon.” The simpler definition caught on and was popularized on radio, in print, and even the Trivial Pursuit board game.

The moon itself, however, will not appear blue in color. While the origin of the name is uncertain, one rumor is that the Farmer’s Almanac, many, many decades ago, would denote these pesky extra full moons in blue ink. Certain Earth-based atmospheric events, like volcanic eruptions or fires, have been known to given the blue a blue-ish quality. In September 1950, for example, heavy wildfires across the US and Canada caused a thick haze with particles just the right size to scatter blue light. However, the moon was a waxing gibbous at the time, not full.

To keep track of the moon and other happenings in the night sky, check out the Morrison Planetarium’s quarterly sky guides, planet watch, and seasonal notes or download our annual pocket almanac. –Elise Ricard

Atmospheric activity on the Dwarf Planets

As NASA’s New Horizons probe zoomed past the dwarf planet Pluto on July 14, it turned around and took a departing image of Pluto’s tenuous atmosphere backlit by the light of the Sun, looking almost like the solar corona visible during a total eclipse. Coupled with the spacecraft’s detection of a long “tail” of ionized nitrogen extending tens of thousands of miles away from the Sun, this observation has led scientists to conclude that Pluto’s atmosphere is being lost to space, gradually being stripped away by the solar wind. As Principal Investigator Alan Stern pointed out at a July 17 press conference, this process is known to have occurred in the past on other planets but is taking place on Pluto on a scale not seen on any other major body orbiting the Sun. Co-investigator Fran Bagenal suggested the rate of atmospheric loss could be as much as 500 tons per hour, compared to only 1 ton per hour on Mars.

Although New Horizons’ Pluto encounter has ended, the spacecraft now continues into the Kuiper Belt, to encounter a different object in two or three years’ time.

Meanwhile, New Horizons’ counterpart in the asteroid belt, NASA’s Dawn spacecraft, is circling another dwarf planet—Ceres, named after the Roman goddess of the harvest and the only dwarf planet in the inner solar system. Having arrived in early March, Dawn has been gradually maneuvering to lower orbits for more detailed looks at the surface. In mid-July, it left its Survey Orbit of 2,700 miles (4,400 kilometers) and is currently in the five-week long process of spiraling to a lower, 910-mile (1,470-kilometer) High Altitude Mapping Orbit. When it completes the maneuver around mid-August, it will observe for approximately two-and-a-half months, adding to its already-impressive list of discoveries, including a solitary, conical mountain towering three miles (five kilometers) above the heavily-cratered landscape around it, signs of relatively-recent resurfacing in some areas, and, most curiously, bright spots peppering the surface. The most closely-watched of these is called “Spot 5,” comprised of a tight cluster of perhaps a dozen smaller spots, located inside the 57-mile (92-kilometer) wide crater. The crater has been named Occator, after a mythological helper of Ceres. The nature of the spots has still not been firmly established, but it’s certain that they are reflective surfaces glinting in sunlight rather than light sources. Plausible theories to explain them have included reflective ice, salt deposits, geysers, or volcanoes.

Recent observations have revealed what appears to be a haze around this cluster, appearing to fill about half of Occator but never extending beyond the crater’s rim. This suggests a cloud of vapor hanging relatively low to the ground, contained by the crater walls, and some media outlets took to calling it a “mini-atmosphere.” Although at least eight other bright spots have been identified dotting Ceres, no similar hazes have so far been associated with them. Dawn will undoubtedly get a better look from its High Altitude Mapping Orbit next month. Then, when it descends to its final Low Altitude Mapping Orbit in December, it will spend the next six months viewing the surface from only 230 miles (375 kilometers) away, providing our best view yet. –Bing Quock

Brown Dwarfs: Acting like Planets, Forming like Stars

Pluto isn’t the only object in the galaxy with an identity crisis. Another type of celestial body, brown dwarfs, also prove difficult to classify. These cool, dim objects are difficult to detect (with the first one only confirmed in 1994), and while they possess some planet-like characteristics, they are too massive to be planets. However, they also lack sufficient mass to fuse hydrogen in their cores, a defining characteristic of stars. As a result, they are often referred to as “failed stars.”

In the last week and a half, two separate studies utilizing radio observations from the Karl G. Jansky Very Large Array (VLA) found brown dwarfs to be both more planet-like in their auroral displays, and more star-like in their formation.

One big question surrounding brown dwarfs is how they form. Is it like star formation, when a giant cloud of gas and dust collapses, accumulating mass and ejecting jets of material outward from the disk’s poles—or is it more like planet formation, when material from the disk orbiting a young star eventually coalesces into rocky, icy, or gaseous worlds?

In a press release last week from National Radio Astronomy Observatory, a team of astronomers observing brown dwarfs still forming in a star-forming region over 450 light-years away announced the first direct evidence of the former—they found four brown dwarfs with jets matching those emitted during star formation. While this was suspected, the new evidence provides confirmation.

“We conclude that the formation of brown dwarfs is a scaled-down version of the process that forms larger stars,” said Oscar Morata, of the Academia Sinica.

While their formation may be star like, other characteristics are less so. Specifically in terms magnetic activity, brown dwarfs have now been found to act like giant planets, generating hugely powerful auroras near magnetic poles.

The findings, reported in this week’s Nature, were the first time auroras have been detected outside the solar system, let alone around on a brown dwarf.

How the lights are being generated is a bit of a mystery still, since there is not a nearby star to generate the charged particles that normally interact with an atmosphere to create aurorae. It may be possible that a nearby, yet undetected, planet or moon is throwing off material, similar to how some of Jupiter's auroras are produced by charged particles emitted from volcanoes on its moon Io.

For Dr. Stuart Littlefair of University of Sheffield, his team’s discovery is enough to sway the brown dwarf debate towards “large planet.” "We already known from observations of brown dwarfs that they have clouds in the atmosphere. Now we know they also show auroras, it is yet more reason to consider brown dwarfs as scaled-up versions of planets rather than scaled-down version of stars.” –Elise Ricard

Image Credit: Matthias Kabel / Wikimedia Commons