Space Sunday: Tabby’s Star, NASA’s plans and the Moon’s atmosphere

Is a circumstellar dust ring responsible for the irregular dimming of Tabby’s Star? Credit: NASA/JPL

Yet another study has appeared in an attempt to shed light (pun intended) on the mysterious behaviour of Tabby’s Star.

Regular readers of my Space Sunday columns will recognise this name as belonging to the more formally titled KIC 8462852, an F-type main-sequence star located in the constellation Cygnus approximately 1,480 light years from Earth (and which is also called Boyajian’s Star). This star experiences odd periods of dramatic dimming in its light output every so often (with the Kepler Space Observatory recording a loss of up to 22%), with the fluctuations lasting several solar days before it suddenly resumes its normal luminosity as observed from our solar system.

Many theories have been put forward for what is happening – most of which I’ve covered in these pages. They range from theories about vast alien mega-structures – such as a Dyson sphere, to theories of the star itself suffering what is called “avalanche” activity within itself, to ideas involving huge cometary clouds and giant ringed planets,  or just a single giant ringed planet being responsible.

In the most recent study, Extinction and the Dimming of KIC 8462852, a US / Belgian team of scientists suggest that “none of the above” might actually be the correct answer on why the star goes through its irregular dimming cycle. Instead, they argue tit is the result of a huge but thin and uneven dust ring rotating slowly around the star.  What makes this theory particularly compelling is that it draws on three independently gathered sets of data in order to form the hypothesis.

The first of these data sources is NASA’s Spitzer Space Telescope, used to gather data on Tabby’s Star in the infra-red wave band during December 2016. The second is the Swift Gamma-Ray Burst mission, which gathered data on the star in the ultraviolet band during the same period of observation; also at the same time, the Belgian AstroLAB IRIS Observatory’s 68-cm (27-in) reflecting telescope gathered data in the visible light spectrum.

Artist’s concept of KIC 8462852, which has experienced unusual changes in luminosity over the past few years. Credit: NASA/JPL

What the team found, essentially, was that Tabby’s Star experienced less dimming in the infra-red band than in the ultraviolet – a strong indication that there was a mass of materials, each particle just a few micrometres in diameter, passing between the star and the observatories. While it had been previously suggested the dimming could be the result of an interstellar dust cloud lying somewhere in space between Earth and Tabby’s star, the team discounted this as a possible culprit.

Instead the team took their findings and charted known periods of dimming witnessed with Tabby’s Star and determined a circumstellar dust ring surrounding the star, and rotating around it one every 700 days would actually account for the majority of dimming periods observed from Earth. However, two types of even still do now fit the model.

The first of these is some very short-term “spurts” of dimming which have been noted during 2017. The second is the really large dips in luminosity seen by the Kepler Space Observatory. One potential explanation for the “spurts” of dimming, confirmed through multiple independent observations, is that they might be the result of a cometary cloud orbiting the star and coming between it and Earth. This was actually one of the earliest theories put forward to account for all of Tabby’s Star’s odd behaviour, but it fits the “spurts” of dimming a lot better.

The really big dimming periods, when the star appeared to lose up to 22% of its brightness pose their own problem. They were only observed by Kepler, and have yet to be seen to the same magnitude during any other period of observation, making quantifying them hard. Kepler itself is now studying stars in another portion of the galaxy, so cannot be used to further observe Tabby’s Star to see if such huge dips can again be seen.

Thus, there may yet be another mystery to Tabby’s Star waiting to be solved – or other theories on the fluctuating brightness which may yet be put forward. But for now, the circumstellar dust ring seems to be the most fitting explanation for much of the star’s odd behaviour.

The Moon’s Ancient Atmosphere

That’s the startling conclusion of a new study, supported by NASA’s Solar System Exploration Research Virtual Institute, and recently published in Earth and Planetary Science Letters.

Map of basaltic lavas that emitted gases on the lunar nearside. Credit: Debra Needham
Map of basaltic lavas that emitted gases on the lunar near side. Credit: Debra Needham

That the Moon was subject to intense volcanic activity in its early history is evidenced by the massive  volcanic basalt maria (“seas”) on its surface. From Earth, these form the dark patches and patterns we can see with the naked eye. They were created three to four billion years ago, when the interior of the Moon was still hot and generating magmatic plumes. In places, these broke through the lunar crust, flowing outwards for hundreds of kilometres. Analysis of rock sample returned to Earth by the Apollo astronauts has long revealed these lava flows carried with them gases like carbon monoxide and the ingredients for water, sulphur, and other volatile elements.

In the study, work, Dr. Debra H. Needham, Research Scientist of NASA Marshall Space Flight Centre, and Dr. David A. Kring, Senior Staff Scientist, at the Lunar and Planetary Institute (LPI), used the amounts of trace gases and volatiles in the Apollo samples as a baseline for calculating the probable amount of gases released during those ancient lunar eruptions. Their findings suggest that the gases were released is sufficient quantities over a long enough period of time, reaching its peak around 3.5 billion years ago, to form a transient  lunar atmosphere. It then persisted for about 70 million years after the volcanic activity ended, before the bulk of the gases were lost to space.

Distribution of the volcanic “seas” of the Moon (in blue) – sites of ancient eruptions. Credit: Nasa

The two largest pulses of gases were produced when lava seas filled the Serenitatis and Imbrium basins about 3.8 and 3.5 billion years ago, respectively. The margins of those lava seas were explored by astronauts of the Apollo 15 and 17 missions, who collected the samples that provided the ages of the eruptions.

This new picture of the Moon has important implications for future exploration. The analysis of Needham and Kring quantifies a source of volatiles that may have been trapped from the atmosphere in the cold, permanently shadowed regions near the lunar poles and may well provide a source of ice suitable for a sustained lunar exploration programme. Volatiles trapped in these icy deposits might be used  provide air and fuel for astronauts conducting lunar surface operations.

“We Chose To Go to the Moon, Because That’s What We Were Doing Anyway”

The re-invoked US National Space Council (NSC) held its inaugural meeting n Thursday, October 5th, 2017 at the Smithsonian National Air and Space Museum’s (NASM) Steven F. Udvar-Hazy Centre.

Chaired by the Vice President, the Council was originally  established in 1989 by then-President George H.W. Bush to serve the same purpose as the National Aeronautics and Space Council, which oversaw US space policy between 1958 and 1973. That NSC was disbanded in 1993 by the Clinton administration.

In this first meeting, the NSC sought to overturn NASA’s “Journey to Mars” endeavour in favour of a more focused plan to return to the Moon – or did they?

The inaugural meeting of the re-formed NSC, October 5th, 2017. Credit:  NASA / Joel Kowsky

But how new and bold is this directive?

The reality is, what Pence announced on behalf of the NSC on October 5th and despite all the hurrahs, is pretty much what NASA was already doing anyway, and had been doing since President Obama signed the NASA Authorisation Act of 2010. That is: build the Orion Multi-Purpose Crew Vehicle and the Space Launch System, establish the Deep Space Gateway in cis-lunar space as an “enabler” for lunar missions and missions to Mars, and develop a presence on the Moon while deferring Mars to some nebulous 2030s time frame. The only significant difference is the instruction for NASA to actually flesh-out the lunar outpost element.

On the one hand, this is good, as it means no mass overturning of the apple cart (a favourite past time of incoming administrations)  and a scramble to sort the apples out again. On the other, it still leaves NASA pursuing goals of questionable need – such as the Deep Space Gateway itself. Which, despite all the hype surrounding it, isn’t actually required for either for getting to the Moon or Mars. Rather, it is an objective that’s become fixed in the NASA mindset, and is now being rationalised on the basis that it is part of the mindset, rather than it offering a means to achieve things that cannot be better (and more cost-effectively) achieved through other methods.

What’s in a Name?

Making it safe to reference the “BFR” – the Big “Falcon” Rocket! Credit: SpaceX

At the 68th International Astronautical Congress (IAC) at the end of September, Elon Musk unveiled more of his thinking around sending humans to Mars.

The linchpin of his aspirations is the massive Interstellar Transport System (ITS) rocket SpaceX is developing. This has caused not a few parents some headaches when explaining things to their children, or created a dilemma when explaining the concept in polite company.

It’s not that explaining the ITS concept in complicated. Far from it. Rather, it’s the fact that Musk has chosen to present the ITS launch system using the acronym he originally defined for it: BFR. This, as just about everyone interested in space exploration knows, stands for “big f***ing rocket”. Descriptive yes, given the size of the beast (see right). But suitable for sensitive or young ears? Er, no, possibly not.

So, how does one deal with explaining what “BFR” means to said sensitive / young ears? SpaceX President Gwynne Shotwell recently offered a solution.

While addressing the National Space Council on October 5th, Shotwell – quite probably with a twinkle of humour in his eye –  played on the company’s use of “Falcon” in naming their rockets (the Falcon 9 and Falcon Heavy) to get around the BFR acronym.

“Last week,” he said. “Elon announced — or, basically, gave an update on,” he then paused a bit, before continuing, “the Big Falcon Rocket programme. The Big Falcon Rocket and Big Falcon Spaceship.”

So there you have it, a non-offensive and semi-accurate way to explain “BFR” to the kids!



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