Category: Space Sunday

Around the world on August 17th, 2017, some 70 telescopes and observatories – including the Laser Interferometer Gravitational-Wave Observatory (LIGO), responsible for confirming the existence of gravitational waves (see here and here for more) – quietly turned their attention on the same spot in the constellation Hydra.

“I don’t think it’s out of the question that this is the most observed astronomical event ever. It’s a thrilling notion, and a little overwhelming,” said LIGO spokesperson David Shoemaker. “We’ve got somewhere between a quarter and a third of all the world’s astronomers working with us.”

The reason? Hours earlier, an observatory in Chile had detected gravitational waves followed by a burst of gamma radiation – potentially the signature of two neutron stars colliding far beyond our galaxy. If so, the detection would be the first time gravitational waves have been observed originating from something other than the merger of two black holes. Hence, an alert was issued to observatories around the globe, resulting in the massed focusing on instruments on that single point in space.

Over the coming days, the data revealed that a collision between two neutron stars in what is referred two as a “kilonova”  – which sits between a star going nova and a super-massive star going supernova.  It marks the first confirmation that neutron star mergers can cause gamma ray bursts. However, there is much more to the event.

Neutron stars are the dense remnants of massive stars that long ago exploded as supernovae. The two stars in question are located in galaxy NGC 4993, 130 million light years from Earth. Originally, these stars were each around 10-20 times the mass of our sun; after each went supernova, they collapsed down to bodies around 16 km (10 mi) in diameter, comprised entirely of neutrons so densely packed, that despite their small size, each still had a mass perhaps twice that of our own Sun.

These two neutron stars, located close together, were gradually drawn together over the course of perhaps 11 billion years by their mutual gravities until they collided, venting huge amounts of energy across the spectrum and space-time in what astronomers call a “multi-messenger event”. It was the arrival of the light waves and gravitational waves here on Earth, 130 million years later, that astronomers from around the world were keen to observe, marking the first time a cosmological event of this nature has been observed in both gravitational waves and light, producing a huge amount of data for researchers to study.

Thanks to the alert sent out by the Chilean observatory, over 3,500 astronomers and more than 100 instruments  – including LIGO and a the Hubble Space Telescope responded, making the event the first to be observed through the detection of visible light and gravitational waves. Their findings are now being made public, and include some remarkable facts.

These include the first confirmation that neutron star mergers can cause gamma ray bursts – although there is some questions over what this might in fact mean. It also marks the first measurement of the universe’s expansion using gravitational waves.In addition, as the collision was recorded in wavelengths right across the electromagnetic spectrum, from radio to gamma rays, it is the first time a cosmological event of this nature has been observed in both gravitational waves and light. A further result of the observations is that astronomers have witnessed heavy elements being formed from the aftermath of the event.

“People have long suspected that heavy elements were made in neutron star mergers, but this is really the first time we’ve nailed that down,” Andrew Levan, an astronomer at the University of Warwick in the UK. “This merger made something like the mass of the Earth in gold, along with other heavy elements such as platinum, lead and uranium.”

It was actually the discovery that heavy elements were being formed in the material resulting from the collision which confirmed the event was an actual collision of two neutron stars. The elements would only be formed if neutrons were being ejected from the two stars to collide with lighter atoms in the surrounding space. Material would only be ejected if the objects in collision each had a surface, something black holes don’t have – they only have an event horizon.

This in turn indicated the event was far closer that the previous five detections of gravitational waves which have occurred since 2015. These have been the result of pairs of black holes merging, none of which have been closer than 1.3 billion light years away. That the gravitational waves were observed alongside of light waves also gave further confirmation of another of Einstein’s general relativity predictions: that light and gravitational waves travel and more-or-less the same speed.

Observations and data gathering continued after the initial explosion was detected, although the light from the collision faded over the 6-8 days following the event, and astronomers are keen to discover what has been left behind. Currently, the region of NGC 4993 where the kilonova occurred is obscured behind a cloud of matter and heavy elements, leading to questions on whether or not the two stars may have merged to form an even larger neutron star, or whether they collapsed into a black hole. Some of those studying the data gathered believe the gamma ray burst recorded after the initial detection of gravitational waves might be indicative of the latter, the result of matter left over from the event and collapse being drawn into the event horizon.

Summing up the significance of the event, astronomer Tony Piro from the Harvard–Smithsonian Centre for Astrophysics said, “The ability to study the same event with both gravitational waves and light is a real revolution in astronomy. We can now study the universe with completely different probes, which teaches things we could never know with only one or the other.”

Continue reading “Space Sunday: when neutron stars collide” →

I’ve written several times about the risk radiation poses to dee space missions; particularly Galactic Cosmic Rays (GCRs), the so-called “background radiation” left over from the big bang. As I’ve noted, while solar radiation – up to and including Solar Particle Events (SPEs or “solar storms”) can be reasonably well dealt with, on account of the particles being relatively low-energy – 13 centimetres (5 inches) of water or similar liquid – is pretty good protection against the primary radiation threat of SPEs, for example – GCRs are far harder to deal with.

However, there are materials which can block them. Again, I’ve written about Hydrogenated boron nitride nanotubes (BNNTs). These are something being developed by NASA’s Langley Flight Centre in Virginia; extremely flexible, they can be used in the construction of key elements of space vehicles – walls, floors, ceilings, for example – and can even be woven into a material used as a lining in space suits to protect astronauts.  Similarly, borated polyethylene – already used for radiation shielding in nuclear reactors aboard US naval vessels, medical vaults and linear accelerators, among other applications – offers a means to provide primary radiation protection within the structure of space vehicles.

However, these are only effective in stopping primary radiation damage – that is, damage cause by the direct impact of radiation on living cells. A far, far greater risk people in deep space will face is from so-called secondary radiation,  particularly in the case of GCRs.  simply put, when a GCR particle collides with another, it sends energetic neutrons, protons and other particles in all directions, which can collide with others. It’s like a bullet striking something and scattering shrapnel, potentially doing damage to a lot of cells if they strike a living body. The problem here is that the more material used to block the effects of primary radiation damage, the more the risk of secondary radiation damage is increased.

This means that there is unlikely to be a single solution to the issue of radiation exposure on deep space missions such as to Mars. Which is why scientists aren’t looking for one. NASA, for example has been conducting research into technologies such as BNNTs and magnetic shielding for space vehicles for over a decade. The latter, if possible, would use a magnetic field around a space vehicle to protect the crew, much as Earth’s magnetic field protects us. The problem here is that such systems currently require huge amounts of electrical power and can add a significant amount of mass to a space vehicle.

Another avenue of research being investigated is the use of pharmaceuticals as possible radiation inhibitors. Drugs such as potassium iodide, diethylenetriamine pentaacietic acid (DTPA) and the dye known as “Prussian blue” have for decades been used to treat radiation sickness. The theory is now that they could be used as part of a preventative regime of preventative treatment for astronauts on deep space missions.

The whole subject of radiation protection has become a focus in light of NASA’s “new” directive to return humans to the Moon and also because of Elon Musk’s determination to send humans to Mars, possibly as early as the mid-2020s. Because of this, NASA has been highlighting its research into radiation exposure management of late, which also includes solar weather forecasting (to help warn crews in deep space about the risk of SPEs, etc.), and in looking at 20+ years of orbital operations aboard the shuttle ISS and Russia’s MIr space station. All of this is leaving some at NASA feeling very positive about efforts to send humans beyond Earth orbit, as Pat Troutman, the NASA Human Exploration Strategic Analysis Lead, stated in a NASA press statement on the matter:

Some people think that radiation will keep NASA from sending people to Mars, but that’s not the current situation. When we add the various mitigation techniques up, we are optimistic it will lead to a successful Mars mission with a healthy crew that will live a very long and productive life after they return to Earth.

Whether progress on all fronts will be sufficiently advanced to encompass something like Elon Musk’s aggressive approach to human missions to Mars remains to be seen. However, with the “new” directive for NASA to return humans to the Moon, there’s a good chance we’ll see some of the current initiatives in radiation protection bearing fruit in the next few years.

The Risk Posed by Tiangong 1

Tiangong 1 (“Heavenly Palace 1”), the first Chinese orbital facility has been creating some sensationalist headlines of late.  Launched in 2011, the facility saw two crews spend time aboard it, prior to it being run on an automated basis from 2013. On March 21st, 2016 the Chinese Manned Space Engineering Office announced that they had disabled the facility’s data service in preparation for shifting their focus to the (then) upcoming Tiangong 2 facility and in allowing Tiangong 1’s orbit to decay so it would burn-up re-entering the upper atmosphere.

The time-frame from re-entry was predicted to be late 2017 / early 2018. However, around the time Tiangong 2 was launched the Chinese space agency admitted they’d lost attitude control of the laboratory, so they could no longer orient it as it orbits the Earth. As a result, the facility has been under scrutiny from Earth by individuals and groups monitoring the rate of its orbital decay.

One of these observers is astrophysicist Jonathan McDowell of Harvard university. In early October he released a statement indicating that as a loss of attitude control coupled with increased atmospheric friction has resulted in a sharp decline in Tiangong 1’s altitude to the point where it could see the vehicle re-enter the Earth’s atmosphere in the next few months. He also noted – accurately – that some elements of the 8.5 tonne vehicle could survive re-entry and reach the surface of the Earth (something the Chinese have always noted).

Unfortunately, his report led to some sensationalist responses from portions of the media. For example, one UK media tabloid blasted: “Out-of-control space station to smash into Earth THIS MONTH…and it could hit ANYWHERE. … A MASSIVE space station is hurtling towards Earth!” (block capital their own, not mine); other newspapers also highlighted the upper-end of the risk posed by the vehicle’s re-entry.

Needless to say such reports wildly over-egg the situation. The reality is that Tiangong’s orbit carries it over vast swathes of ocean and large areas of sparsely populated land. As such, while there is a risk of parts of the station reaching the ground, the chances of them hitting a populated area are remote. In this, Tiangong reflects the US Skylab mission in 1979 and the Russian Salyut 7 / Cosmos 1686 combination of 1991. Both of these where much larger than Tiangong 1 (77 tonnes and 40 tonnes respectively), both made an uncontrolled re-entry, and in both cases, wreckage did not cause loss of life.

Continue reading “Space Sunday: radiation, rings and pollution” →

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 it 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.

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.

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.

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?

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?

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!